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Susitna-Watana Hydroelectric Project Document
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Title:
Fluvial geomorphology modeling below Watana Dam study, Study plan
Section 6.6 : Initial study report
SuWa 207
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Prepared by Tetra Tech, Watershed GeoDynamics
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Draft initial study report
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Susitna-Watana Hydroelectric Project document number 207
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[Anchorage : Alaska Energy Authority, 2014]
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February 2014
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Alaska Energy Authority
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Study plan Section 6.6
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Draft
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269 p. in various pagings
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The following parts of Section 6.6 appear in separate files: Main report ; Figures ; Appendices A-E
with attachment.
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Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Fluvial Geomorphology Modeling
below Watana Dam Study
Study Plan Section 6.6
Initial Study Report
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
Watershed GeoDynamics
February 2014 Draft
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page i February 2014 Draft
TABLE OF CONTENTS
Executive Summary ...................................................................................................................... x
1. Introduction ....................................................................................................................... 1
2. Study Objectives................................................................................................................ 3
3. Study Area ......................................................................................................................... 4
3.1. Downstream Study Limit ...................................................................................5
3.2. Focus Areas ........................................................................................................6
4. Methods and Variances in 2013 ....................................................................................... 7
4.1. Study Component: Bed Evolution Model Development, Coordination, and
Calibration..........................................................................................................7
4.1.1. Existing Information and Need for Additional Information ...................... 7
4.1.2. Methods .................................................................................................... 10
4.1.3. Variances from Study Plan ....................................................................... 47
4.2. Study Component: Model Existing and with-Project Conditions....................48
4.2.1. Existing Information and Need for Additional Information .................... 48
4.2.2. Methods .................................................................................................... 48
4.2.3. Variances from Study Plan ....................................................................... 51
4.3. Study Component: Coordination and Interpretation of Model Results ...........51
4.3.1. Existing Information and Need for Additional Information .................... 51
4.3.2. Methods .................................................................................................... 51
4.3.3. Variances from Study Plan ....................................................................... 57
5. Results .............................................................................................................................. 58
5.1. Study Component: Bed Evolution Model Development, Coordination, and
Calibration........................................................................................................58
5.1.1. Development of Bed Evolution Model Approach and Model Selection . 58
5.1.2. Coordination with other Studies ............................................................... 62
5.1.3. Model Resolution and Mesh Size Considerations.................................... 63
5.1.4. Focus Area Selection ................................................................................ 64
5.1.5. Model Calibration and Validation ............................................................ 64
5.1.6. Tributary Delta Modeling......................................................................... 65
5.1.7. Large Woody Debris Modeling................................................................ 67
5.1.8. Wintertime Modeling and Load-Following Operations ........................... 67
5.1.9. Field Data Collection Efforts ................................................................... 67
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page ii February 2014 Draft
5.1.10. Electronic Data ......................................................................................... 73
5.2. File Name: Study Component: Model Existing and with-Project Conditions .74
5.2.1. Existing Conditions – Base Case Modeling ............................................. 75
5.2.2. Future Conditions – with-Project Scenarios............................................. 76
5.2.3. Uncertainty ............................................................................................... 76
5.2.4. Synthesis of Reach-Scale and Local-Scale Analyses ............................... 76
5.2.5. Electronic Data ......................................................................................... 76
5.3. Study Component: Coordination and Interpretation of Model Results ...........76
5.3.1. Integration of Geomorphology and Fluvial Geomorphology Modeling
Study ............................................................................................. 77
5.3.2. Coordination of Results with Other Resource Studies ............................. 77
5.3.3. Electronic Data ......................................................................................... 78
6. Discussion......................................................................................................................... 78
6.1. Study Component: Bed Evolution Model Development, Coordination, and
Calibration........................................................................................................78
6.1.1. Development of Bed Evolution Model Approach and Model Selection . 78
6.1.2. Coordination with other Studies ............................................................... 79
6.1.3. Model Resolution and Mesh Size Considerations.................................... 80
6.1.4. Focus Area Selection ................................................................................ 80
6.1.5. Model Calibration and Validation ............................................................ 80
6.1.6. Tributary Delta Modeling......................................................................... 81
6.1.7. Large Woody Debris Modeling................................................................ 81
6.1.8. Wintertime Modeling and Load-Following Operations ........................... 81
6.1.9. Field Data Collection Efforts ................................................................... 81
6.2. Study Component: Model Existing and with-Project Conditions....................89
6.2.1. Existing Conditions – Base Case Modeling ............................................. 89
6.2.2. Future Conditions – with-Project Scenarios............................................. 89
6.2.3. Uncertainty ............................................................................................... 89
6.2.4. Synthesis of Reach-Scale and Local-Scale Analyses ............................... 90
6.3. Study Component: Coordination and Interpretation of Model Results ...........90
6.3.1. Integration of Geomorphology and Fluvial Geomorphology Modeling
Study ............................................................................................. 90
6.3.2. Coordination of Results with Other Resource Studies ............................. 91
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iii February 2014 Draft
7. Completing the Study ..................................................................................................... 91
8. Literature Cited .............................................................................................................. 91
9. Tables ............................................................................................................................... 98
10. Figures ............................................................................................................................ 122
APPENDICES
Appendix A: Bed-material Samples
Appendix B: Bed-material Sample Locations in Focus Areas
Appendix C: Bank-material Samples
Appendix D: Water Surface Measurements
Appendix E: Evaluation of 50-Year Simulation Period, Pacific Decadal Oscillation, and
Selection of Representative Annual Hydrographs
ATTACHMENTS
Attachment A: Field Report, Field Assessment of Underwater Camera Pilot Test for Sediment
Grain Size Distribution
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iv February 2014 Draft
LIST OF TABLES
Table 3.1-1. Schedule for the downstream study limit determination process for the
Fluvial Geomorphology Modeling below Watana Dam Study. ........................................... 98
Table 4.1-2. Average Annual Sediment Loading at USGS Gaging Stations (R&M
Consultants, Inc. 1982b). ...................................................................................................... 98
Table 4.1-2. Average Annual Sediment Loading at USGS Gaging Stations and Watana
Dam (Harza-Ebasco 1984). ................................................................................................... 98
Table 4.1-3 Model input and results interactions among various Studies and study
components. .......................................................................................................................... 99
Table 4.1-4. Summary of model parameter precedencies for water resources models to
be applied in the Susitna-Watana licensing effort. ............................................................. 100
Table 4.1-5. Calibration Datasets for 1-D and 2-D Bed Evolution Models. .............................. 101
Table 4.1-6. Sieve bulk sample area dimensions. ....................................................................... 101
Table 4.1-7. 2013 Susitna-Watana airborne LiDAR data specifications. ................................... 102
Table 4.1-8. Comparison of NMAS/NSSDA Vertical Accuracy (ASPRS 2004). .................... 102
Table 4.3-1: Primary output variables for which values are taken directly from the 1-D
and 2-D Bed Evolution models and relevance to other studies. ......................................... 103
Table 4.3-2: Key variables needed for the impact assessments for which results are
obtained through additional analysis of predictions taken directly from the 1-D and
2-D Bed Evolution models. ................................................................................................. 104
Table 5.1-1 Potential 1-D Bed Evolution Models. ..................................................................... 106
Table 5.1-2 Potential 2-D Bed Evolution Models Selected for Final Evaluation. ...................... 107
Table 5.1-3 Tributary Modeling. ................................................................................................ 108
Table 5.1-4 Initial Manning’s Roughness Coefficients for 1-D and 2-D Bed Evolution
Models. ................................................................................................................................ 109
Table 5.1-5. Sources and Types of Data Used to Develop the 2-D Models. .............................. 110
Table 5.1-6: Focus Areas in the Middle Susitna River Segment. ............................................... 110
Table 5.1-7: Upstream and Downstream PRM boundaries for Geomorphic Assessment
Areas. .................................................................................................................................. 110
Table 5.1-8 Tributary Modeling Results. .................................................................................... 111
Table 5.1-9. Summary of the number of bank observations along the Susitna River and
tributaries in 2013. .............................................................................................................. 112
Table 5.1-10. Summary of the number of sediment samples collected along the Susitna
River and tributaries in 2013. .............................................................................................. 112
Table 5.1-11. Sediment sampling conducted at the Tributary Delta study sites. ........................ 113
Table 5.1-12. Cross Sections Surveyed through 2013 Field Season. ......................................... 114
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page v February 2014 Draft
Table 5.1-13. Water-Surface Elevation (WSE) measurements collected during the Focus
Area topographic surveys by Fish and Aquatics Instream Flow (ISR Section 8.5)............ 115
Table 5.1-14. Water surface elevations measurements collected for model calibration as
part of the ADCP survey by Fish and Aquatics Instream Flow (ISR Section 8.5). ............ 115
Table 5.1-15. Summary of 2012-2013 data collected at ESS stationsa. ...................................... 116
Table 5.1-16. Priority Area 01 South vertical accuracy tests results for 2013 LiDAR. ............. 117
Table 5.1-17. Priority Area 02 South, 03 and 04 vertical accuracy tests results for 2013
LiDAR. ................................................................................................................................ 117
Table 5.1-18. 2011 Matanuska-Susitna LiDAR vertical accuracy verification results. ............. 118
Table 5.1-19. 2011 Matanuska-Susitna LiDAR comparison to obtain average elevation
difference. ........................................................................................................................... 118
Table 5.1-20. 2011 Matanuska-Susitna LiDAR vertical accuracy verification results after
indexing. .............................................................................................................................. 119
Table 6.1-1. Lower Susitna River Bed-material Samples Collected in 1984 (R&M
Consultants 1985). .............................................................................................................. 119
Table 6.1-2. Middle Susitna River Bed-material Samples Collected in 1983 (Harza-
Ebasco 1984). ...................................................................................................................... 120
Table 6.1-3. Candidate Cross Sections Surveys for the Next Study Season. ............................. 120
Table 6.1-4. Flow thresholds for evaluating coupled measurements of flow and WSE. ............ 121
Table 6.1-5. ADCP Discharge Measurements Collected at the Focus Areas in 2013. ............... 121
LIST OF FIGURES
[See separate file for figures]
Figure 3.1-1. Current limits of the Fluvial Geomorphology Modeling Study and large-
scale river segments.
Figure 3.2-1. Location of Focus Areas in the Middle Susitna River Segment with
geomorphic reaches shown.
Figure 4.1-1. Sketch of transect locations (identified as L, C and R) for surface sampling
at sample location PRM 113.5 (left) and photograph of sample location, view
downstream (right).
Figure 4.1-2. Example of completed field data form for coarse-grained surface samples.
Figure 4.1-3. Three functions to calculate minimum sampling depth (dsample in ft) from
the Dmax particle size (Modified from Figure 4.18 from Bunte and Abt, 2001).
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page vi February 2014 Draft
Figure 4.1-4. Minimum sample weight for sediment with different Dmax sizes (Dmax =
0.1% of the sample weight for Dmax < 32mm, Dmax = 1% of the sample weight for
Dmax < 128mm and Dmax = 5% of the sample weight for Dmax > 128mm
(Modified from Figure 4.20 from Bunte and Abt, 2001)
Figure 4.1-5: Example of complete field data form for subsurface samples.
Figure 4.1-6: Example of front and back of 2013 bank observation data sheets.
Figure 4.1-7. 2011 Matanuska-Susitna Borough LiDAR collections and 2013 ground
survey point locations.
Figure 4.1-8. Example ground survey points displayed over aerial photography
Figure 4.1-9. Example ground survey points displayed over TIN derived from LiDAR
point cloud.
Figure 4.2-1 Fluvial Geomorphology Model Interdependencies.
Figure 5.1-1. Cross Section Locations for Reach Scale 1-D Sediment-Transport Model
Figure 5.1-2. Cross Section Locations for Reach Scale 1-D Sediment-Transport Model
Figure 5.1-3. Cross Section Locations for Reach Scale 1-D Sediment-Transport Model
Figure 5.1-4. Cross Section Locations for Reach Scale 1-D Sediment-Transport Model
Figure 5.1-5. Cross Section Locations for Reach Scale 1-D Sediment-Transport Model
Figure 5.1-6. Cross Section Locations for Reach Scale 1-D Sediment-Transport Model
Figure 5.1-7. Cross Section Locations for Reach Scale 1-D Sediment-Transport Model
Figure 5.1-8. Cross Section Locations for Reach Scale 1-D Sediment-Transport Model.
Figure 5.1-9. Merged Hydrographic Survey and LiDAR Survey at PRM 117.9.
Figure 5.1-10. Triangular Irregular Network (TIN) Developed to Represent the Channel
and Portions of the Overbanks at FA-104.
Figure 5.1-11. One-foot Interval Contour Mapping of FA-104 Developed from the TIN
(Figure 5.1-10).
Figure 5.1-12. Two-foot Interval Contour Mapping Developed from the 2013 LiDAR
Survey of FA-104.
Figure 5.1-13. Extents of the SRH-2D Habitat Mesh
Figure 5.1-14. Geomorphic surface mapping of FA-104 Whiskers Slough.
Figure 5.1-15. Example of Habitat Areas at FA-104 Selected to Have a Fine Mesh Size
(6.5 feet, 2 m). The Habitat Areas Were Identified by the Aquatic Habitat Team.
Figure 5.1-16. Example of SRH-2D Mesh in Habitat Area at the Mouth of Whiskers
Creek (in FA-104) Selected to Have a Fine Mesh Size (2 meters).
Figure 5.1-17. SRH-2D Bed Evolution Mesh. The Mesh Contains Approximately 10,000
Elements.
Figure 5.1-18: Locations of Middle Susitna River Segment Focus Areas.
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page vii February 2014 Draft
Figure 5.1-19. Predicted Depth Distribution at FA-104 for 24,000 cfs.
Figure 5.1-20. Predicted Velocity Distribution at FA-104 for 24,000 cfs.
Figure 5.1-21. Predicted Depth Distribution at FA-104 for 100,000 cfs.
Figure 5.1-22. Predicted Velocity Distribution at FA-104 for 100,000 cfs.
Figure 5.1-23. Lower Susitna River Segment Tributary Locations Relative to
Geomorphic Reaches.
Figure 5.1-24. Middle Susitna River Segment Tributary Locations Relative to
Geomorphic Reaches and Focus Areas.
Figure 5.1-25: Sediment samples and bank observations collected at FA-104 (Whiskers
Slough).
Figure 5.1-26. GoPro image from Whiskers Slough with lights, lasers, and scale in video
mode.
Figure 5.1-27. GoPro image from ESS40 with lasers and the Brinkman Q-Beam Starfire
II underwater fishing light.
Figure 5.1-28. GoPro image from ESS40 with lasers and without lights
Figure 5.1-29. 2013 LiDAR priority areas and collection.
Figure 6.1-1. Lower Susitna River Segment Bed Material Comparison.
Figure 6.1-2. Middle Susitna River Segment Bed Material Comparison.
Figure 6.1-3. Lower Susitna River Segment Screening of Coupled WSE and Flow
Measurements.
Figure 6.1-4. Middle Susitna River Segment Screening of Coupled WSE and Flow
Measurements.
Figure 6.1-5. ADCP Flow Measurement Locations at Whiskers Slough (FA-104).
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page viii February 2014 Draft
LIST OF ACRONYMS, ABBREVIATIONS, AND DEFINITIONS
Abbreviation Definition
1-D one-dimensional
2-D two-dimensional
AEA Alaska Energy Authority
ADCP Acoustic Doppler Current Profiler
AGL Above Ground Level
ASPRS American Society for Photogrammetry and Remote Sensing
BEI Bank Energy Index
cfs Cubic feet per second
CIRWG Cook Inlet Region Working Group
CVA Consolidated Vertical Accuracy
DEM Digital elevation model
EFDC Environmental Fluid Dynamics Code
FA Focus Area
FERC Federal Energy Regulatory Commission
FVA Fundamental Vertical Accuracy
FGM Fluvial Geomorphology Modeling below Watana Dam Study
GAA Geomorphic Assessment Area
GIS Geographic Information System
HEC Hydraulic Engineering Center
HEC-RAS Hydraulic Engineering Centers River Analysis System
IFIM Instream Flow Incremental Methodology
IFS Instream Flow Study
ILP Integrated Licensing Process
IMU Inertial Measurement Unit
ISR Initial Study Report
LED light-emitting diode
LiDAR Light Detection and Ranging
LR Lower River
LWD large woody debris
m meters
Mat-Su Matanuska-Susitna
MC main channel
MR Middle River
NDEP National Digital Elevation Program
NMFS National Marine Fisheries Service
OS Operating Scenario
PDO Pacific Decadal Oscillation
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page ix February 2014 Draft
Abbreviation Definition
Project Susitna-Watana Hydroelectric Project
PRM Project River Mile
RIFS Riparian Instream Flow Study
RM River Mile
RMSEz Root Mean Square Error in the Z axis (vertical)
RSP Revised Study Plan
SC side channel
SPD Study Plan Determination
SRH-2D Sedimentation and River Hydraulics – Two-Dimensional
SuWa Susitna Watana
SVA Supplemental Vertical Accuracy
TIN Triangulated Irregular Network
TM Technical Memorandum
TWG Technical Wrokgroup
USACE United States Army Corps of Engineers
USBR United States Bureau of Reclamation
USGS U.S. Department of the Interior, Geological Survey
USR Updated Study Report
WSE Water Surface Elevation
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page x February 2014 Draft
EXECUTIVE SUMMARY
Fluvial Geomorphology Modeling below Watana Dam Study 6.6
Purpose The overall goal of this study is to model the potential effects of the proposed
Project on the fluvial geomorphology of the Susitna River and to assist in
predicting the magnitude of geomorphic response. Data collected include (1)
bed and bank material samples; (2) observations of channel, bank, island, and
floodplain surfaces including erosional, depositional, and other features; (3)
various types of surveys of channel bathymetry and floodplain geometry; and
(4) measurements of discharge, velocity, and water surface elevations. These
data were collected along the Susitna River, lateral channels and features,
major tributaries, and smaller tributaries. The models in the Fluvial
Geomorphology Modeling below Watana Dam Study include hydraulic and
sediment transport models of (1) sediment processes at selected tributaries to
evaluate sediment supplies and tributary delta effects, (2) reach-scale
processes of the Susitna River system below Watana Dam including major
tributaries, and (3) local-scale processes at selected Focus Areas in the
Middle Susitna River.
Status The data listed above were collected throughout the Susitna River between
PRM 29.9 and PRM 146.1 in 2013 to supplement data collected in 2012.
These data also include approximately 10 miles of the Chulitna River, 4 miles
of the Talkeetna River, and 11 smaller tributaries. Detailed data were
collected at 7 Focus Areas. Additional data will be collected in the next
study season. Models have been developed in 2013 of the 11 smaller
tributaries. The data are currently being used to develop the 1-D reach-scale
model of the Susitna River below Watana Dam and 2-D local-scale models of
7 Focus Areas in the Middle Susitna River. Initial 2-D Bed Evolution models
have been developed for 2 Focus Areas and these models are currently being
calibrated.
Study
Components
1) Bed Evolution Model Development, Coordination, and Calibration
includes coordination with other Project studies and stakeholders, data
collection, and development of numerical models to accurately simulate
river and floodplain fluvial geomorphic processes below Watana Dam.
2) Model Existing and with-Project Conditions applies the numerical
models to simulate existing conditions and with-Project scenarios.
3) Coordination and Interpretation of Model Results integrates the
Fluvial Geomorphology Modeling below Watana Dam Study with the
Geomorphology Study and other studies to understand key processes,
provide needed information, and make valid comparisons of model
results.
2013 Variances There were no variances to the 2013 Study Plan. While land access was not
available for portions of the river and tributaries adjacent to Cook Inlet
Regional Working Group (CIRWG) lands, this was not considered a variance
because this study was designed to collect data over multiple years.
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page xi February 2014 Draft
Fluvial Geomorphology Modeling below Watana Dam Study 6.6
Steps to
Complete the
Study
As explained in the cover letter to this draft ISR, AEA’s plan for completing
this study will be included in the final ISR filed with FERC on June 3, 2014.
Highlighted
Results and
Achievements
The data that have been collected are sufficient to develop, calibrate, and
validate the 1-D reach-scale and 2-D local-scale models for the three study
components listed above. The models will provide necessary results to
identify additional data needs for the next year of study. The results will also
be used for a proof-of-concept demonstration of integration with the Fish and
Aquatics Instream Flow Study (Study 8.5). The proof-of-concept
demonstration will provide for additional refinement of modeling approaches
and study integration.
The following data have been collected and are currently being analyzed:
• 11 Smaller Tributaries
o 4 to 10 cross-sections surveyed per tributary
o 1 to 8 bed-material samples per tributary
• Susitna, Chulitna, and Talkeetna rivers
o 91 cross-sections surveyed in 2013 (88 surveyed in 2012)
o 1 to 3 water surface elevations measurements per surveyed cross-
section
o Bed-material samples at approximate 2-mile intervals in Middle
Susitna, Chulitna and Talkeetna rivers, and at approximate 3-mile
intervals in Lower Susitna River
o Approximately 60 bank material samples in Middle Susitna River
• Focus Areas (7 in 2013)
o Detailed bathymetric survey
o Approximately 20 bed-material samples per Focus Area
o Approximately 8 bank-material samples per Focus Area
o Approximately 600 water surface elevation measurements per Focus
Area collected during bathymetric survey
o ADCP velocity and discharge measurements at approximately 7
transects at two different flows (dates)
o Approximately 25 water surface elevation measurements collected
during ADCP data collection per Focus Area
The following models have been developed or are in process:
• Hydraulic/sediment transport models of 11 smaller tributaries
• 1-D reach-scale hydraulic/sediment transport model of Susitna River
below Watana Dam including the lower 10 miles of the Chulitna River
and lower 4 miles of the Talkeetna River
• 2-D Hydraulic Models of 7 Focus Areas (2 are initially calibrated)
• 2-D Sediment Transport Models of 7 Focus Areas (2 include initial model
networks)
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page xii February 2014 Draft
Fluvial Geomorphology Modeling below Watana Dam Study 6.6
The 1-D and 2-D Bed Evolution Models have been narrowed to two
candidates each that are being tested to determine which model is best suited
for simulating processes on the Susitna River system. Preliminary results of
one 2-D Hydraulic Model have been provided to the Fish and Aquatics
Instream Flow Study (Study 8.5) to develop tools to integrate the studies.
Significant coordination has occurred between this study (Study 6.6),
Geomorphology (Study 6.5), Fish and Aquatics Instream Flow (Study 8.5),
Riparian Instream Flow (Study 8.6), Ice Processes in the Susitna River (Study
7.6), Water Quality (Study 5.6), and Groundwater (Study 7.5) studies to
develop understanding of the physical processes that form and maintain
channel and floodplain features and habitats.
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 1 February 2014 Draft
1. INTRODUCTION
On December 14, 2012, Alaska Energy Authority (AEA) filed its Revised Study Plan (RSP) with
the Federal Energy Regulatory Commission (FERC or Commission) for the Susitna-Watana
Hydroelectric Project (FERC Project No. 14241), which included 58 individual study plans
(AEA 2012). Included within the RSP was the Fluvial Geomorphology Modeling below Watana
Dam Study, Study 6.6. RSP Study 6.6 focuses on the modeling planned for assessing the effects
of the proposed Project and its operations on water quality in the Susitna River basin.
On February 1, 2013, FERC staff issued its study determination (February 1 SPD) for 44 of the
58 studies, approving 31 studies as filed and 13 with modifications. On April 1, 2013 FERC
issued its study determination (April 1 SPD) for the remaining 14 studies, approving 1 study as
filed and 13 with modifications. RSP Section 6.6 was one of the 13 approved with
modifications. In its April 1 SPD, FERC recommended the following:
Modeling in Focus Areas
- We recommend that AEA file by June 30, 2013, the proposed technical memorandum
related to the selection and application of the one- and two-dimensional models
(proposed for development in the second quarter of 2013). We also recommend that
the technical memorandum include the following information:
1) specification of the one- and two-dimensional models to be used in the fluvial
geomorphology modeling pursuant to this study as well as the aquatic habitat models
pursuant to Study 8.5 (fish and aquatics instream flow);
2) location and extent of one- and two-dimensional geomorphology and aquatic
habitat modeling in project reaches, focus areas, and other study sites;
3) rationale and criteria for model selection including an overview of model
development;
4) for fluvial geomorphology modeling only, a detailed description of the processes
and methods by which ice and LWD would be incorporated into the modeling
approach (as described in our recommendations for Incorporating Large Woody
Debris and Ice Processes into Fluvial Geomorphic Modeling); and
5) documentation of consultation with the TWG, including how the TWG’s comments
were addressed.
- We expect additional detail on model parameterization, model calibration, model
validation, and sensitivity analysis would be included in the initial and updated study
reports.
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 2 February 2014 Draft
Interaction of Geomorphic Processes in the Mainstem and Tributaries
- We recommend the study plan be modified to include a defined approach to
evaluating geomorphic changes at the confluence of the Chulitna, Talkeetna and
Susitna rivers. The evaluation should extend from the mouth of both the Chulitna and
Talkeetna rivers to the potentially affected upstream reaches of these tributaries. We
recommend that AEA prepare a technical memorandum detailing a proposed approach
for evaluating geomorphic changes in the three rivers confluence area, including
explicitly stated objectives for evaluating geomorphic changes, an overview of the
technical approach, additional data collection required, models and model components
to be used, and additional analyses that would be conducted to address the stated
objectives. We recommend that AEA file by June 30, 2013, this technical memorandum
to include documentation and consultation with the TWG, including how the TWG’s
comments were addressed.
Incorporating Large Woody Debris and Ice Processes into Fluvial Geomorphic Modeling
- As noted above in our analysis and recommendations for Modeling in Focus Areas,
we are recommending that AEA file a technical memorandum with additional
information on AEA’s proposed model selection process. We recommend that an
additional provision be added to the technical memorandum requiring that AEA
describe in detail how ice and LWD would be incorporated into both one- and two-
dimensional modeling approaches. The technical memorandum should explicitly state
where and how each of the five scenarios for incorporating ice processes into one-
dimensional and/or two-dimensional fluvial geomorphology modeling would be
implemented, as well as details regarding where and how LWD pieces and/or
accumulations would be incorporated into two-dimensional modeling.
Operational Scenarios
- As discussed under the general comments section of this study plan determination, we
recommend the study plan be modified to include run-of-river operation.
In accordance with the April 1 SPD, on May 3 , 2013, AEA provided to the Technical Work
Group (TWG) participants for comment a Draft Fluvial Geomorphology Modeling Approach
Technical Memorandum (Geomorphology Modeling TM; Tetra Tech 2013h) that was developed
to provide responses to all April 1 SPD recommendations. The Draft Geomorphology Modeling
TM was made available on the Project website (http://www.susitna-watanahydro.org). Consistent
with the April 1 SPD, AEA allowed a minimum of 15 days for comment. The National Marine
Fisheries Service (NMFS) submitted comments on May 18, 2013. AEA also received comments
on the Draft Geomorphology Modeling TM from one individual and two non-government
organizations. Recommended modifications were addressed in detail in the Final
Geomorphology Modeling TM filed with FERC on June 30, 2013.
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The Final Geomorphology Modeling Approach TM and several other TMs developed by the
Geomorphology Study (ISR Study 6.5) to provide information to support the Fluvial
Geomorphology Modeling below Watana Dam Study are listed below:
• Development of Sediment Transport Relationships and an Initial Sediment Balance for
the Middle and Lower Susitna River Segments (Tetra Tech 2013a)
• Initial Geomorphic Reach Delineation and Characterization, Middle and Lower Susitna
River Segments (Tetra Tech 2013b)
• Reconnaissance Level Assessment of Potential Channel Change in the Lower Susitna
River Segment (Tetra Tech 2013c)
• Stream Flow Assessment (2013d)
• Synthesis of 1980s Aquatic Habitat Information (2013e)
• Mapping of Aquatic Macrohabitat Types at Selected Sites in the Middle and Lower
Susitna River Segments from 1980s and 2012 Aerials (2013f)
• Mapping of Geomorphic Features and Assessment of Channel Change in the Middle and
Lower Susitna River Segments from 1980s and 2012 Aerials (2013g)
• Fluvial Geomorphology Modeling Approach (2013h)
• Field Assessment of Underwater Camera Pilot Test for Sediment Grain Size Distribution
(2013i) (Note: Included as Attachment A)
Following the first study season, FERC’s regulations for the Integrated Licensing Process (ILP)
require AEA to “prepare and file with the Commission an initial study report describing its
overall progress in implementing the study plan and schedule and the data collected, including an
explanation of any variance from the study plan and schedule” (18 CFR 5.15(c)(1)). This Initial
Study Report (ISR) on Fluvial Geomorphology Modeling below Watana Dam has been prepared
in accordance with FERC’s ILP regulations and details AEA’s status in implementing the study,
as set forth in the FERC-approved RSP and as modified by FERC’s April 1 SPD, and includes
the Final Geomorphology Modeling TM filed with FERC on June 30, 2013 (Tetra Tech 2012)
(collectively referred to herein as the “Study Plan”).
2. STUDY OBJECTIVES
The overall goal of the Fluvial Geomorphology Modeling below Watana Dam Study is to model
the effects of the proposed Project on the fluvial geomorphology of the Susitna River to assist in
predicting the trend and magnitude of geomorphic response. More specifically, the purpose of
the modeling study, along with the Geomorphology Study (Study 6.5), is to assess the potential
impact of the Project on the behavior of the river downstream of the proposed dam, with
particular focus on potential changes in instream and riparian habitat. Whether the existing
channel morphology will remain the same or at least be in “dynamic equilibrium” under post-
Project conditions is a significant question in any instream flow study (i.e., Is the channel
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morphology in a state of dynamic equilibrium such that the distribution of habitat conditions will
be reflected by existing channel morphology, or will changes in morphology occur that will
influence the relative distribution or characteristics of aquatic habitat over the term of the
license? [Bovee 1982]). This key issue prompts four overall questions that must be addressed by
the two geomorphology studies:
• Is the system currently in a state of dynamic equilibrium?
• If the system is not currently in a state of dynamic equilibrium, what is the expected
evolution over the term of the license in the absence of the Project?
• Will and in what ways will the Project alter the equilibrium status of the downstream
river (i.e., what is the expected morphologic evolution over the term of the license under
with-Project conditions)?
• What will be the expected effect of the Project-induced changes on the geomorphic
features that form the aquatic habitat and therefore are directly related to the quantity,
distribution, and quality of the habitat?
The methods and results from the Geomorphology Study and the Fluvial Geomorphology
Modeling below Watana Dam Study address these questions.
Specific objectives of the Fluvial Geomorphology Modeling below Watana Dam Study are as
follows:
• Develop calibrated models to predict the magnitude and trend of geomorphic response to
the Project.
• Apply the developed models to estimate the potential for channel change for with-Project
operations compared to existing conditions.
• Coordinate with the Geomorphology Study to integrate model results with the
understating of geomorphic processes and controls to identify potential Project effects
that require interpretation of model results.
• Support the evaluation of Project effects by other studies in their resource areas providing
channel output data and assessment of potential changes in the geomorphic features that
help comprise the aquatic and riparian habitats of the Susitna River.
3. STUDY AREA
RSP Section 6.6.3 initially established the study area for this study. The Fluvial Geomorphology
Modeling below Watana Dam Study utilizes an approach in which the entire study length is
being assessed by a 1-D Bed Evolution Model to determine potential reach-level Project effects.
More detailed 2-D Bed Evolution modeling is being performed in locations referred to as “Focus
Areas”. The modeling approach is discussed in more detail in Section 4.1.2.1 and in the
Modeling Approach TM (Tetra Tech 2013h). Specific study areas are associated with each of the
two modeling scales.
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3.1. Downstream Study Limit
The study area for the Fluvial Geomorphology Modeling below Watana Dam was initially
identified in the RSP as the portion of the Susitna River from Watana Dam (Project River Mile
[PRM] 187.1 [RM 184]) downstream to PRM 79 (River Mile [RM] 75). This downstream limit
was set to extend the study into the upper portion of the Lower Susitna River Segment. This limit
extends the study 9 miles downstream of the lower limit of Geomorphic Reach LR-1. Initial
evaluation of information from the 1980s studies indicated that it was unlikely that Project
effects on the geomorphology of the Susitna River would extend downstream of Geomorphic
Reach LR-1. This initial assessment was based on the large introduction of sediment and water at
the Three Rivers Confluence where both the Chulitna and Talkeetna rivers approximately double
the flow in the Susitna River and increase the sediment supply by approximately a factor of five.
In response to the increase in sediment supply as well as a reduction in gradient, the form of the
Susitna River changes at the Three Rivers Confluence from a single channel to a braided
channel. The 15 miles of braided channel could buffer the downstream remaining portion of the
Susitna River from the changes in flow regime and sediment supply caused by the Project.
Further review of information developed during the 1980s studies and study efforts initiated in
2012 and completed in Q1 2013 (Tetra Tech 2013a through 2013g)—such as sediment transport
analyses, hydrologic analysis, assessment of channel change and comparison of habitat mapping
from the 1980s with current 2012 conditions in the Geomorphology Study (Study 6.5), and
additional 2012 habitat mapping (Study 9.9) operations modeling and the Open-water Flow
Routing Model (RSP Section 8.5.4.3)—were used to reassess the extent to which Project
operations could potentially influence habitats in the Lower River Segment. An assessment of
the downstream extent of Project effects was completed in Q1 2013 and the results presented in
technical memorandums (R2 Resource Consultants [R2] 2013a and R2 2013b) in collaboration
with the TWG. This assessment was supported by the results presented in the TMs prepared by
the Geomorphology Study (Tetra Tech 2013a through 2013g). The assessment guided the
decision to extend studies into the Lower River to PRM 29.9, and to the determination of which
geomorphic reaches were subject to reach and Focus Area level modeling of the Susitna River
fluvial geomorphology in 2013. Figure 3.1-1 shows the current limits of the Fluvial
Geomorphology Modeling below Watana Dam Study.
The 1-D Bed Evolution Model study area currently includes the entire Middle Susitna River
Segment from the Watana Dam site (PRM 187.1 [RM 184]) downstream to the Three Rivers
Confluence area (PRM 102.4 [RM 98]). It includes the majority of the Lower Susitna River
Segment from the Three Rivers Confluence area downstream to Susitna Station at PRM 29.9.
(Note: Modeling of Devils Canyon will not be performed because this reach is considered too
dangerous to perform cross-section and other surveys needed to develop the model. Devils
Canyon is assumed to be a stable, pass-through reach in terms of sediment transport due to the
high level of bedrock control and steep gradient present in this reach.)
The final check-in on the downstream study limit to be provided by the geomorphology studies
will be based on the results of the 1-D Bed Evolution Model. If the results of the 1-D modeling
effort show differences between the modeled existing and the modeled with-Project conditions
that are beyond the range of natural variability below PRM 29.9 (Susitna Station) in Geomorphic
Reach LR-5, the 1-D modeling will be continued farther downstream in the Lower Susitna River
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Segment in a next year of study. The criteria for determining what constitutes natural variability
will be made in collaboration with the licensing participants. As part of the process, a technical
memorandum documenting the 1-D modeling effort and its results will be prepared. Table 3.1-1
provides a summary of the steps and dates involved in the process that was used to assess and
adjust the downstream study limit in Q1 2013, and, if necessary, will be used to adjust the
downstream study limit for the Fluvial Geomorphology Modeling below Watana Dam Study in a
next year of study.
3.2. Focus Areas
The bed evolution modeling approach includes the application of a 1-D Bed Evolution Model to
predict the geomorphic response of the Susitna River to the Project for the entire study area
(PRM 187.1 to PRM 29.9 excluding Devils Canyon as noted above). To provide a higher level
of detail and to model physical processes not adequately represented in a 1-D Bed Evolution
Model, a 2-D Bed Evolution Model is being applied in the ten selected Focus Areas (R2 2013a
and R2 2013b for more details on Focus Area selection). Focus Areas involve portions of the
Susitna River and its floodplain where detailed study efforts are being jointly conducted by
several study teams including the Fish and Aquatics Instream Flow (Study 8.5), Riparian
Instream Flow (Study 8.6), Geomorphology (Study 6.5), Ice Processes in the Susitna River
(Study 7.6), Groundwater (Study 7.5), and Characterization and Mapping of Aquatic Habitats
(Study 9.9) studies. The Focus Areas are at the core of a highly integrated, multidisciplinary
effort to evaluate potential Project effects for key resource areas across a range of representative
sites.
The 2-D models—bed evolution and hydraulic—are being used to evaluate the detailed hydraulic
and sediment transport characteristics on smaller, more local scales where it is necessary to
consider the more complex flow patterns to understand and quantify the issue(s). The 2-D
models are being applied to each Focus Area, within the selected 1-D modeling study area. The
Focus Areas were selected to be representative of important habitat conditions and the various
geomorphic reach types. The Focus Areas were chosen jointly by the Fish and Aquatics Instream
Flow (Study 8.5), Riparian Instream Flow (Study 8.6), Geomorphology (Study 8.5), Ice
Processes in the Susitna River (Study 7.6), and Characterization and Mapping of Aquatic
Habitats Study (Study 9.9) studies to facilitate maximum integration of available information
among the studies. Sites were chosen such that there is at least one Focus Area for each
geomorphic reach (except reaches MR-3 and MR-4 where there are safety concerns associated
with Devils Canyon due to the extreme whitewater conditions) and the sites cover the range of
riverine aquatic habitat types (see R2 2013a and R2 2013b and ISR Study 8.5 Section 4.2.1.2.1).
The portions of the tributaries that fall within the Focus Areas are part of the 2-D model domain
including the current tributary delta or alluvial fan areas.
Selection of 10 Focus Areas was performed in Q1 and Q2 of 2013 in coordination with the
TWG. The process and results are documented in two TMs (R2 2013a and R2 2013b). The first
TM provides the initial recommendations for 10 Focus Areas and the second TM provides
adjusted locations based on input from the TWG. The resulting locations are provided in Figure
3.2-1.
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4. METHODS AND VARIANCES IN 2013
The Fluvial Geomorphology Modeling below Watana Dam is divided into three study
components:
• Bed Evolution Model Development, Coordination, and Calibration
• Model Existing and with-Project Conditions
• Coordination on Model Output
Each of these components is explained further in the following subsections. These study
components build on earlier efforts documented in technical memoranda (Tetra Tech 2012, Tetra
Tech 2013a through 2013g) performed under the Geomorphology Study (Study 6.5). These
technical memoranda (TMs) helped guide the development of this study. As examples, the
geomorphic reach delineation (Tetra Tech 2013b) was developed in 2012 in order to provide
other studies a tool to help stratify the Susitna River system including selection of Focus Areas.
The sediment transport TM (Tetra Tech 2013a) provides sediment transport relationships that
help define sediment supply to the bed evolution model developed in this study. The assessment
of potential channel change in the Lower Susitna River (Tetra Tech 2013c) was developed to
help inform the decisions on the downstream limit for the this study as well as several other
studies.
4.1. Study Component: Bed Evolution Model Development,
Coordination, and Calibration
The overall goal of the Bed Evolution Model Development, Coordination, and Calibration study
component is to develop numerical models that can accurately simulate fluvial geomorphic
processes that influence the morphology of the Susitna River channel and floodplain downstream
of Watana Dam.
4.1.1. Existing Information and Need for Additional Information
During the 1980s studies of the Susitna Hydroelectric Project, various efforts were carried out to
characterize sediment supply and sediment transport capacity. Modeling of hydraulics of the
Susitna River below the proposed Project, a necessary step in developing a sediment transport
model, was performed in the 1980s. One-dimensional HEC-2 hydraulic models were developed
in the 1980s to support the calculation of water-surface profiles and channel hydraulics (Acres
1983).
R&M Consultants, Inc. (1982a) considered three primary influences of the Susitna River
backwater on 19 tributaries discharging into it between the Devils Canyon dam site and the
Susitna-Chulitna confluence: (1) fish access into the streams, (2) sediment deposition at the
confluences, and (3) reduced flow velocity in the stream channel. Tributaries that were expected
to encounter a possible impact on Alaska Railroad structures crossing them were also considered.
Qualitative assessments of creek stability under post-Project conditions were made based on field
surveys and observations. These assessments included factors such as bed load transport, creek
hydrology, bed material, and confluence geometry. The qualitative assessments were followed
up with semi-quantitative analyses where determined necessary. These analyses included
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calculation of bed-material transport by relating flow and slope to sediment discharge and bed-
material size. Channel slopes were surveyed, mean annual flood peak flows were estimated
using regression equations, bed-material gradations were visually estimated, and pre-Project to
post-Project changes in Susitna River water-surface elevation at each tributary mouth were
calculated from hydraulic modeling simulations of the mean annual flood; sediment discharge
was not quantified. A rigorous mathematical development of sediment transport capacity was
determined to be beyond the scope of the study, so this previous work illustrates the need for
quantification of the sediment supply delivered from major tributaries to the Middle and Lower
Susitna River Segments.
R&M Consultants, Inc. (1982b) describes analyses of sedimentation within the proposed Watana
and Devils Canyon Reservoirs. The annual sediment load entering the reservoirs was estimated
using the flow-duration sediment-rating curve method for the nearest gaging stations; an areal
sediment yield was estimated for the tributary areas draining directly into the reservoirs. No
information is provided regarding the development of the sediment-rating curves or the flow-
duration curves. The average annual sediment loads are summarized in Table 4.1-1. The
sediment contributed by the tributaries directly to the reservoirs was estimated from the unit
sediment runoff per square mile between the U.S. Geological Survey (USGS) gages near
Cantwell and at Gold Creek (i.e., 425 tons of total sediment load per square mile per year).
Harza-Ebasco (1984) includes estimates of average annual sediment loads at the Watana Dam
site by interpolating the loads at the USGS gages near Cantwell and at Gold Creek. The loads at
the USGS gages were calculated using the flow-duration sediment-rating curve method.
Suspended-sediment measurements near Cantwell were collected between 1962 and 1972 and a
curve was visually fitted to all data points. Average annual sediment loads were calculated using
the suspended sediment-rating curve, the flow-duration curve (based on 13 years of
measurements: 1962 to 1972 and 1981 to 1982), and an assumed bed load equal to 3 percent of
the suspended load (Table 4.1-2). Suspended-sediment measurements at Gold Creek were
collected from 1949 to 1982; separate curves were visually fit to data collected from May
through October and November through April. Using the same methods as used near Cantwell,
the average annual loads were calculated. An areal scaling was used to interpolate the sediment
loading at the Watana Dam site, which is located between the two gages.
The differences in the sediment loads calculated in R&M Consultants, Inc. (1982b) and Harza-
Ebasco (1984) indicate the need to use updated measurements of sediment transport to refine the
sediment loading into Watana Reservoir, and the corresponding sediment loads conveyed
downstream to the Middle Susitna River Segment.
None of the reviewed studies from the 1980s include explicit calculations of sediment transport
capacity in the Susitna River downstream of the Watana Dam site at locations other than USGS
gages. However, samples of bed material and simulated hydraulics were used to infer
mobilization of bed material (as summarized in ISR 6.5 Section 4.3.1). Harza-Ebasco (1984)
includes sediment gradations derived from sieve analyses of 17 bed-material samples from the
mainstem Susitna River, 2 samples from the Chulitna River, and 29 samples from side channels
of the Susitna River upstream from the Three Rivers Confluence. R&M Consultants, Inc. (1985)
includes gradations derived from sieve analysis of multiple bed-material samples collected along
the length of 8 cross-sections located approximately between the Three Rivers Confluence and
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the USGS gage at Sunshine. R&M Consultants, Inc. (1982c) describes the development and
calibration of HEC-2 numerical hydraulic models for two reaches of the Susitna River: (1) the
upper study reach from Deadman Creek downstream to Devil Creek, and (2) the middle study
reach from the outlet of Devils Canyon downstream to the Susitna-Chulitna confluence. To
accommodate the island and split-channel conditions, separate models were developed for flows
above/below 20,000 cubic feet per second (cfs; the flow at which side channels were judged to
be hydraulically connected). Harza-Ebasco (1983) describes refinements to the R&M
Consultants, Inc. (1982c) HEC-2 models using new and updated cross-section geometry and
improved calibration datasets based on staff gage measurements. Calibration was focused on
adjustments to the initial estimates of Manning’s n-values. The Harza-Ebasco (1983) modeling
approach still relied on separate models for flows above/below 20,000 cfs. The models were
developed to simulate water-surface elevations, average channel velocities, and stage-discharge
rating curves at all surveyed sections between the mouth of Devils Canyon and the USGS gage at
Sunshine.
Holly et al. (1985) document the BRALLUVIAL numerical simulation program for computation
of long-term bed evolution in multiply-connected fluvial channels. The model code was
developed to forecast the effect of possible flow modulation by two proposed Susitna
hydropower dams on sediment deposition patterns in the highly braided 15-mile reach of the
Susitna River from the Chulitna–Talkeetna confluence downstream to the Sunshine Bridge. The
code was based on the sedimentation methodology previously developed for simple channels
(i.e., the IALLUVIAL code); however, it was necessary to develop a new water flow
methodology to handle multiple flow paths of the braided system. The resulting combination of
new and existing techniques was based on assumption of quasi-steady, one-dimensional flow,
and incorporated procedures for treatment of highly non-uniform sediments, sediment sorting,
bed armoring, flow-dependent friction factor, and alternate drying and flooding of perched
channels. The total load transport model and friction-factor relations previously developed were
re-calibrated for the limited Susitna bed-sediment data. Although preliminary tests were
performed as described in this report, actual use of the model was the responsibility of Harza-
Ebasco Susitna Joint Venture. Use of the model was reportedly described in a companion report,
but a copy of that report to review has not been located.
The lack of historical mobile bed modeling highlights the need to develop sediment transport
models that can simulate the geomorphic responses of the Susitna River to potential changes in
hydrology and sediment supply from existing conditions to post-Project conditions.
While the existing information just summarized provides useful context for developing and
calibrating these models, the uncertainty and limitations of the existing information confirm the
need for refined evaluations to provide the needed model input and calibration datasets. Both
1-D and 2-D Bed Evolution models are required to characterize the bed evolution for both the
existing and with-Project conditions in the Susitna River. This study component involves
selection and development of the bed evolution models.
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4.1.2. Methods
AEA implemented the methods as describe in the Study Plan with no variances. The Bed
Evolution Model Development, Coordination, and Calibration study component is divided into
three tasks:
• Development of Bed Evolution Modeling Approach and Model
• Coordination with other Studies on Processes Modeled
• Calibration/Validation of the Model
The first bullet includes the field data collection efforts that provided first-hand information to
assist in the development of the modeling approach, and ultimately, the models themselves.
4.1.2.1. Development of Bed Evolution Model Approach and Model Selection
This section provides an updated description of (1) the bed evolution model approach,
particularly in regard to the model selection process described in more detail in the Modeling
Approach Technical Memorandum (Tetra Tech 2013h); and (2) the methods for applying both
the reach-scale 1-D model and the local-scale 2-D bed evolution models. This section includes a
description of the tasks completed during 2013, tasks that are ongoing, and tasks that will be
completed during the next year of study. The tasks completed during 2013 are described in
Section 5 of this ISR.
Development of the bed evolution model for a dynamic system such as the Susitna River is a
complex undertaking that requires considerable investigation and coordination. The work in the
Middle and Lower Susitna River Segments contained in the Geomorphology Study (Study 6.5)
provides a considerable part of the required investigation. Based on the study results and input
from the Fish and Aquatics Instream Flow (ISR Study 8.5), including the Open-water Flow
Routing Model (ISR Study 8.5 Section 4.3), Riparian Instream Flow (ISR Study 8.6), Ice
Processes in the Susitna River (ISR Study 7.6), Characterization and Mapping of Aquatic
Habitats (ISR Study 9.9), and Fish Barriers in the Middle and Lower Susitna River and Susitna
Tributaries (ISR Study 9.12) studies, models will be developed that represent the physical
processes that control the dynamic nature of the Susitna River, and that will provide other studies
with the required information on the potential changes in the channel and floodplain for their
analyses.
Some of the important steps that will be considered in the development of the modeling approach
and model are as follows:
• Review and understand available data.
• Develop an understanding of the dominant physical processes and governing physical
conditions in the study reach.
• Coordinate with other studies to understand their perspectives on system dynamics, and
the physical features and processes that are important to their studies.
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• Identify an overall modeling approach that is consistent with the study goals, the
constraints on information that is currently available or can practically be obtained, and
the needs of the other studies.
• Identify a modeling approach that is consistent with the spatial and temporal scale of the
area to be investigated.
• Determine the spatial limits of the modeling effort.
• Determine the time scales for the various models.
• Review potential models and select a model(s) that meets the previously-determined
needs and conditions.
• Identify data needs and data gaps for the specific model and study area being
investigated.
• Collect the required data to fill data gaps.
• Develop the model input.
• Identify information to be used to calibrate and validate the model.
• Perform initial runs and check basic information such as continuity for water and
sediment, hydraulic conditions, magnitude of sediment transport, and flow distributions.
• Collaborate with other studies on initial model results.
• Refine model inputs.
• Perform calibration and validation efforts, to include comparison of modeled water-
surface elevations, in-channel hydraulic conditions (e.g., velocity and depth), sediment
transport rates, and aggradation/degradation rates with available measured data.
• Perform model runs for existing conditions to provide a baseline for comparison of with-
Project scenarios.
• Work with other studies to develop scenarios to evaluate the potential Project effects, and
apply the model to those scenarios.
• Coordinate with other studies to evaluate and define the appropriate format for
presentation of the model results.
• Develop and run additional scenarios, as necessary, based on results from the initial
scenarios and identified Project needs.
The following subsections (1) outline the identified issues considered, and (2) summarize the
development of the modeling approach, the model selection, and the model development.
Issues Considered: To develop the modeling approach, specific issues were identified and were
differentiated into reach-scale and local-scale because the scale influences the proposed
approach.
Reach-Scale Issues: Reach-scale issues refer to aspects of the system that involve the overall
behavior and general characteristics of the Susitna River over many miles. Each reach represents
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a spatial extent of the Susitna River that has a consistent set of fluvial geomorphic
characteristics. Reach-scale issues include the following:
• Historical changes in the system and the existing status with respect to dynamic
equilibrium.
• Changes in both the bed material (sand and coarser sizes) and wash (fine sediment) load
sediment supply to the system due to trapping in Watana Reservoir.
• Long-term balance between sediment supply and transport capacity and the resulting
aggradation/degradation response of the system for pre- and post-Project conditions.
• Changes in bed-material mobility in terms of size and frequency of substrate mobilized
due to alteration of the magnitude and duration of peak flows by the Project.
• Project-induced changes in supply and transport of finer sediments that influence
turbidity.
• Potential for changes in channel dimensions (i.e., width and depth) and channel pattern
(i.e., braiding versus single-thread or multiple-thread with static islands) due to the
Project and the magnitude of the potential change.
• Project-induced changes in river stage due to reach-scale changes in bed profile, channel
dimensions, and potentially hydraulic roughness.
Local-Scale Issues: Local-scale issues refer to aspects of the system that involve the specific
behavior and characteristics of the Susitna River at a scale associated with specific geomorphic
and habitat features. Local-scale issues are addressed using a more detailed assessment over a
finer Focus Area scale; however, these analyses must draw from and build upon the
understanding and characterization of the system behavior as determined at the reach-scale.
Local-scale issues include the following:
• Processes responsible for formation and maintenance of the individual geomorphic
features and associated habitat types.
• Potential changes in geomorphic features and associated aquatic habitat types that may
result from effects of Project operation on riparian vegetation and ice processes.
• Effects of changes in flow regime and sediment supply on substrate characteristics in off-
channel habitat units.
• Changes in upstream connectivity (breaching) of off-channel habitats due to alteration of
flow regime and possibly channel aggradation/degradation. These changes may induce
further changes in the morphology of off-channel habitats, including the following:
o Potential for accumulation of sediments at the mouth.
o Potential for accumulation of fines supplied during backwater connection with the
mainstem.
o Potential for changes in riparian vegetation that could alter the width of off-channel
habitat units.
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• Project effects at representative sites on the magnitude, frequency, and spatial distribution
of hydraulic conditions that control bed mobilization, sediment transport, sediment
deposition, and bank erosion.
• Potential for change in patterns of bed-load deposits at tributary mouths that may alter
tributary access or tributary confluence habitat, as discussed below.
Tributary confluences are areas of interest for determining the potential Project effects on
sediment transport and morphology. Modeling of tributary deltas is discussed as a separate topic
in Section 4.1.2.6.
Synthesis of Reach-Scale and Local-Scale Analyses: The final step in the development of the
modeling approach will be the synthesis of the reach-scale and local-scale analyses to identify
potential Project-induced changes in the relative occurrence of aquatic habitat types and
associated surface area versus flow relationships. In addition to the results of the hydraulic and
sediment transport modeling, this synthesis will require application of fluvial geomorphic
relationships to develop a comprehensive and defensible assessment of potential Project effects.
Development of Modeling Approach: The modeling approach considers the need to address
both reach-scale and local-scale assessments and the practicality of developing and applying
various models based on data collection needs, computational time, analysis effort, and model
limitations. Based on these considerations, the capabilities of 1-D and 2-D Bed Evolution
models, and the need to evaluate potential Project effects over the majority of the system and at
small habitat scales, a combination of 1-D and 2-D modeling approaches is required.
Considering the broad physical expanse of the Susitna River system, the general hydraulic and
sediment transport characteristics of the various geomorphic reaches that make up the overall
study area (ISR Study 6.5 Section 5.1) will be evaluated using 1-D computer models and/or
established hydraulic relationships. The 2-D models will be used to evaluate the detailed
hydraulic and sediment transport characteristics on smaller, more local scales where it is
necessary to consider the more complex flow patterns to understand and quantify flow
distribution, habitat, breaching, and erosion/deposition issues related to changing hydrology,
sediment supply, ice, and large woody debris (LWD) conditions.
The 2-D models will be applied to the 10 Focus Areas that are representative of important habitat
conditions, the various geomorphic reaches, associated channel classification types, and selected
primary tributaries. These Focus Areas were chosen in coordination with the licensing
participants and the Fish and Aquatics Instream Flow (Study 8.5), Riparian Instream Flow
(Study 8.6), Ice Processes in the Susitna River (Study 7.6), and Characterization and Mapping of
Aquatic Habitats (Study 9.9) studies to facilitate maximum integration of available information
between the studies. The selection of Focus Areas is documented in two technical
memorandums, the first filed in Q1 2013 (R2 2013a) and the second in Q2 2013 (R2 2013b) as
well as the Fish and Aquatics Instream Flow Study (ISR 8.5 Sections 4.1.2.3 and 5.1.3).
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The integrated approach incorporating 1-D modeling at the reach-scale and 2-D modeling at the
local-scale provides the following advantages:
• 1-D modeling will allow for efficient assessment of the hydraulic conditions and
sediment transport balance over the length of the study reach downstream of Watana
Dam.
• 1-D Bed Evolution Model uses cross-sectional data that are being obtained as part of the
Open-water Flow Routing Model (ISR Study 8.5 Section 4.3). (Note: the majority of the
sections were obtained in 2012 and 2013. Additional sections will be surveyed during
the next year of study.)
• The 1-D Bed Evolution Model will provide the boundary conditions for the 2-D model,
including starting water-surface elevations and upstream sediment supply.
• 2-D Bed Evolution modeling applied at the Focus Areas that are also chosen for the Ice
Processes in the Susitna River (ISR Study 7.6) and Riparian Instream Flow (ISR Study
8.6) studies will allow for the fullest level of integration of these efforts, particularly as
they relate to assessments of potential changes in channel width and pattern for this
study.
• 2-D modeling at the Focus Areas will provide an understanding of the hydraulic
conditions and sediment transport processes that contribute to formation of individual
habitat types.
• 2-D modeling provides a much more detailed and accurate representation of the complex
hydraulic interaction between the main channel and the off-channel habitats than is
possible with a 1-D model.
4.1.2.1.1. Model Selection
Many computer programs are available for performing movable boundary sediment transport
simulations. The choice of an appropriate model for this study depends on a number of factors,
including (1) the level of detail required to meet the overall project objective(s); (2) the class,
type, and regime of flows that are expected to be modeled; and (3) characteristics of the bed
material and wash load; and (4) the availability of necessary data for model development and
calibration. In addition, because of the wide range of sediment sizes present in the Susitna River,
both the 1-D and 2-D Bed Evolution models must be capable of routing sediment by size
fraction, and ideally be capable of addressing deposition of fine sediment (wash load). While 2-
D modeling provides the most comprehensive assessment of hydraulic and sediment transport
conditions in the study reach, the extent of required data, effort required for model development,
and computational time required for execution to model the entire system make this impractical.
Considering the very broad physical expanse of the overall Susitna River system, a one-
dimensional (1-D) computer model and/or engineering relationships that can be applied in a
spreadsheet application is the most practical approach to modeling overall system behavior at the
scale of the study reach. Two-dimensional (2-D) modeling is being used to evaluate the detailed
hydraulic and sediment transport characteristics that control the complex geomorphic features
and habitat at the local scale. A variety of candidate models were evaluated for application on
the Susitna River. Selection of the 1-D and 2-D Bed Evolution models for this study (Study 6.6)
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was initiated in 2013 and will be completed in the next year of study. Section 5.1.1.1 describes
the current progress on 1-D and 2-D Bed Evolution Model selection for this Study.
One-Dimensional (1-D) Bed Evolution Model Selection
Most 1-D movable-boundary sediment transport models (bed evolution models) are designed to
simulate changes in the cross-sectional geometry and river profile due to scour and deposition
over relatively long periods of time. In general, the flow record of interest is discretized into a
quasi-unsteady sequence of steady flows of variable discharge and duration. For each
computational time-step and corresponding boundary conditions (e.g., discharge and stage), the
water-surface profile is calculated using the step-backwater method or hydrodynamic equations
to compute the energy slope, velocity, depth, and other hydraulic variables at each cross-section
in the network. The sediment transport capacity is then calculated at each cross-section based on
input bed-material information and the computed hydraulics, and the aggradation or degradation
volume is computed by comparing the transport capacity with the upstream sediment supply (i.e.,
the supply from the next upstream cross-section for locations not identified as an upstream
boundary condition). The resulting aggradation/degradation volume is then applied over the
cross-section control volume (i.e., the sub-channel concept), and the shape of the cross-section is
adjusted accordingly. Where the sediment transport calculations are performed by size fraction,
the models are capable of simulating bed-material sorting and armoring. The computations
proceed from time-step to time-step, using the updated cross-section geometry and bed-material
gradations from the previous time-step.
One-dimensional (1-D) sediment transport models should not be applied to situations where 2-
and 3-dimensional flow conditions control the sediment transport characteristics because they do
not consider secondary currents, transverse movement and variation, turbulence, and lateral
diffusion; thus, the models cannot simulate such phenomena as point bar formation, pool-riffle
formation, and planform changes such as river meandering or local bank erosion. One-
dimensional models typically distribute the volume of aggradation or degradation across the
entire wetted portion of the channel cross-section after each time-step; thus, the effects of
channel braiding are also not directly considered. However, 1-D models are useful in evaluating
the general sediment transport characteristics and overall sediment balance of a given reach, and
they are also useful in providing boundary conditions for localized 2-D models.
One-dimensional models that were considered for this study included the U.S. Army Corps of
Engineers HEC-RAS (version 4.1; USACE 2010a) (version 4.2.0, beta release; USACE 2013),
the U.S. Bureau of Reclamation’s SRH-1D (version 2.8; Huang and Greimann 2011), DHI’s
MIKE 11 (version 2011; DHI 2011a), and Mobile Boundary Hydraulics’ HEC-6T (version
5.13.22_08; MBH 2008). More details and discussions regarding the potential benefits and
limitations of each of these models are included in a Tetra Tech TM (2013h). As described in
Section 5.1.1.1.1, the preferred models (HEC-6T and HEC-RAS version 4.2.0 beta) appear to
best meet the criteria described below and are well suited for simulating conditions on the
Susitna River. Final selection between these two models will occur in the next year of study.
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The criteria used for selecting a 1-D Bed Evolution Model for this Project were primarily based
on required functionality given the specific conditions of the Susitna River and its tributaries
(Tetra Tech 2013h):
• The model must accommodate sufficiently large number of cross-sections to model over
100 miles of river including split-flow reaches.
• The model must be capable of storing sufficiently large number of hydrograph ordinates
to model flows over the 50-year license period.
• The model must be capable of simulating sufficient number and range of sediment sizes
to represent the range of materials.
• The model must include either (or both) the Parker (1990) or Wilcock and Crowe (2003)
bed-load sediment transport equations because these are the most applicable to the range
of coarse bed conditions in the Susitna River and tributaries.
• Closed-loop sediment transport capability must be included to model sediment
transported around islands and in multiple channel reaches common in the Lower Susitna
River Segment, but also present in the Middle Susitna River Segment.
There are also several desirable characteristics that influenced the decision about whether models
are otherwise similar in their capabilities and performance. The desirable characteristics
included public domain, high-level project experience with the model, unsteady flow routing
capabilities, and advanced graphical user interface for model input and review of results. HEC-
RAS Version 4.2.0 beta has all four of these characteristics while HEC-6T does not have an
advanced graphical user interface or unsteady flow routing capabilities. Whether HEC-6T or
HEC-RAS 4.2.0 beta are ultimately used for the final modeling, the model development is most
efficiently performed using the HEC-RAS version.
Two-Dimensional (2-D) Bed Evolution Model Selection
The 2-D models provide a much more detailed and accurate representation of the flow field than
1-D models because they predict both the magnitude and direction (in the horizontal plane) of
the velocity, whereas 1-D models only predict magnitude of velocity in the downstream
direction. Because the 2-D models require the complete bed topography at the resolution of the
mesh, they also provide a more accurate representation of velocity, flow depth, and water-surface
elevation throughout the model domain. The 2-D models vary water-surface elevation and
distribute velocity based on the equations of motion (continuity and Newton’s second law) and,
therefore, account for flow conditions upstream and downstream of the location of interest. As a
result, 2-D models are superior in defining detailed hydraulic conditions in areas of special
interest such as key habitat units.
The 2-D models are often categorized based on the solution technique and grid structure. Finite
difference models use a regular grid, which simplifies the solution but limits the level of detail
that can be achieved. Finite element and finite volume models use an irregular mesh that allows
for more detail in areas of interest or in areas where there is appreciable variability. A subset of
finite element models uses a curvilinear grid, which shares advantages and disadvantages of both
regular grid and irregular mesh. For the requirements of this project, only models that use an
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irregular mesh are considered because of the highly variable channel and floodplain
configurations (main channel, side channels, side sloughs, upland sloughs, tributaries, islands,
and floodplains) and the need to provide accurate and detailed results for habitat evaluation.
The 2-D hydraulic models of a specific location should be developed to accurately represent the
geometry (bathymetry and topography) and variability of flow resistance, with appropriate
boundary conditions. The mesh should include greater detail in areas with appreciable
variability in geometry, velocity magnitude, velocity direction, depth, and roughness. The
required boundary conditions include downstream water-surface elevation and upstream
discharge (mainstem and tributary sources). The model boundaries should be located where flow
is generally one-dimensional, although this requirement is not absolute and the effects can be
reduced by extending the model limits upstream or downstream from the areas of interest. 2-D
bed evolution models must include good quality hydraulic modeling capability, and they must
accurately represent surface and subsurface sediments, sediment depths, erodibility, and
appropriate starting and boundary conditions. 2-D bed evolution models are typically fully
dynamic, which is a requirement for sediment routing, though many can be operated in a steady
state. A sediment transport simulation routes the sediment through the network and adjusts the
elevation of the grid points (nodes) due to erosion and deposition. Modeled changes in node
elevations provide a feedback on the hydraulic simulation due to changes in flow depth and
conveyance. Unlike 1-D bed evolution models, which aggrade or degrade the wetted portion of
each cross section in concert, 2-D models adjust nodes individually based on the spatial
variability of velocity, depth, sediment supply, and sediment transport capacity.
A full description of the candidate 2-D bed evolution models is provided Tetra Tech (2013h).The
following 2-D models were considered for this study:
• SRH-2D Version 3 (USBR)
• ADH version 3.3 (USACE)
• MD_SWMS (USGS)
• MIKE 21 (Danish Hydraulic Institute)
• River2D (University of Alberta)
The criteria for selecting a 2-D bed evolution model for this project are primarily based on
required functionality based on the specific conditions of the Middle Susitna River Segment.
The required characteristics to include:
• Capability for sufficiently large number of elements to model the Focus Areas at the
required spatial resolution.
• Flexible mesh (irregular mesh) to accurately depict geometric and hydraulic variability.
• Capability to simulate a sufficient number and range of sediment sizes to represent the
range of materials in each Focus Area.
• Sediment transport calculations must be performed by size fraction, especially to simulate
bed-material sorting and armoring processes in coarse bed channels.
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• The model must include either (or both) the Parker (1990) or Wilcock and Crowe (2003)
bed load sediment transport equations, as these are the most applicable to the range of
coarse bed conditions in the Susitna River and tributaries.
• The model must be numerically stable under a wide range of flow conditions, especially
as portions of the network wet and dry.
As with 1-D bed evolution models, there are several desirable characteristics that influenced the
decision if models are otherwise similar in their capabilities and performance. The desirable
characteristics include: public domain, high level of experience with the model, moderate to fast
execution speed, and advanced graphical user interface for model input and reviewing results.
During 2013, based upon analysis and as explained in Section 5.1.1.1.2, AEA selected River2D
and SRH-2D models as the preferred 2-D bed evolution models for this study (Tetra Tech
2013h). Final selection between these two models will occur in 2014.
4.1.2.1.2. Model Development
Overview of 1-D Bed Evolution Model Development
The following steps are being followed to develop the 1-D Bed Evolution Model. With few
exceptions (as noted) the model development is very similar regardless of the selected model.
An overview of calibration and validation is included below and is discussed in more detail in
Section 4.1.2.5.1. Review and quality control procedures will be implemented throughout the
model development process and are not indicated as individual steps. Section 5.1.1.2.1 provides
the progress in 2013 on the following steps with significant progress having been made in steps 1
through 5. The steps are (Tetra Tech 2013h):
1. Determine the overall model layout.
• Downstream boundary selected at a location of known stage-flow conditions.
• Upstream boundary location(s) of known discharge and sediment supply information.
• Tributaries that will be modeled geometrically with sediment routing.
• Flow change locations of tributaries that are modeled as flow and sediment inputs.
• Identification of split flow reaches around islands or in multiple-channel locations.
2. Develop cross-section data.
• Determine cross section locations to represent the channel network.
• Obtain channel cross-sectional geometry from land and bathymetric survey data.
• Extend surveyed channel cross sections over islands and into floodplains using land-
based survey and light detecting and ranging (LiDAR) data.
• Determine channel and floodplain flow distances between cross sections.
3. Develop flow resistance (roughness) data for cross sections.
• Channel base roughness based on bed-material size.
• Adjust base roughness to account for other sources of flow resistance such as channel
irregularities, obstructions (including LWD), bed forms, and channel sinuosity. Note:
project-related changes in amounts of LWD and sediment size can be related to flow
resistance values.
• Channel bank and floodplain (overbank) roughness based on land use, vegetative
ground cover, and obstructions using field observations and aerial photography.
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4. Develop bed and bank material gradation and layer information.
• Surface sampling,
• Subsurface sampling, and
• Bank material samples.
5. Develop inflow hydrographs and sediment inflows for existing and with-Project
conditions.
• For quasi-unsteady models, develop step hydrographs for the main channel and
tributary inputs.
• For fully unsteady models, use complete flow hydrographs.
• Develop sediment inflow rating curves based on tributary models or gaging station
records that include sediment measurements.
6. Other considerations.
• Bridge constrictions and geometries.
• Ineffective flow areas around bridges and other rapid expansion and contraction
areas.
• Use of depth- or flow-variable roughness input.
7. Test the hydraulic model over a range of flow conditions.
• Evaluate cross-sectional spacing to determine the need for interpolated cross sections.
• Review for potential geometric input errors in reach lengths or station-elevation data
in areas of appreciable change or instability in hydraulic results.
8. Calibrate and validate the hydraulic model.
• Adjust flow resistance input values (within reasonable limits) to calibrate the
hydraulic results using available data including:
- Water-surface elevations at the time of cross-sectional survey,
- Water-surface elevations collected at other flows,
- Gaging station records,
- Water level loggers at Focus Areas and other locations,
- Discharge and velocity measurements including main channel and lateral features,
and
- High-water marks reported from extreme flood events.
9. Test the sediment transport model.
• Conduct a sediment transport time-step sensitivity analysis to evaluate appropriate
computational time steps for different flow magnitudes.
10. Calibrate and validate the sediment transport model.
• Adjust sediment input values, bed layer properties, sediment transport time step
(within reasonable limits) to calibrate the hydraulic results using available data
including:
- Gage station measured sediment loads, specific gage plots, flow area, width,
depth, and velocity measurements,
- Comparison of cross sections, and
- Longitudinal profiles.
11. Run and evaluate the results of the sediment transport simulations.
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Overview of 2-D Model Development
The following steps are being followed to develop the 2-D Bed Evolution and Hydraulic models
of the Focus Areas. An overview of model calibration and validation is included below and is
discussed in more detail in Section 4.1.2.5.2. Review and quality control procedures will be
implemented throughout the model development process and are not indicated as individual
steps. Section 5.1.1.2.2 provides the progress in 2013 on the following steps with significant
progress having been made in steps 1 through 6 and 8. The steps are (Tetra Tech 2013h):
1. Determine the overall model layout.
• Downstream boundary stage-flow conditions developed from 1-D Bed Evolution
Model.
• Upstream (i.e., inflowing) discharge and sediment supply from 1-D Bed Evolution
Model.
• Tributary flow and sediment input from tributary models.
2. Develop geometric base data.
• Data from TIN (Triangulated Irregular Network) surface representation from land and
bathymetric survey including necessary break lines, and
• Data from LiDAR bare-earth dataset for island and floodplain areas not surveyed.
3. Develop model network.
• Determine node and element locations and configurations to accurately represent
geometry (bathymetry and topography) and changes in roughness. This may be either
a network of triangular elements or a combination of triangular and quadrilateral
elements, depending on the selected model.
• Refine the network in areas of appreciable change or areas of significant habitat
interest.
• Determine the node elevations from the geometric data.
• Review mesh quality to assure that element size transitions and other modeling
requirements are reasonably met. These include increased mesh refinement where
there is appreciable geometric change or where velocity magnitude or directions
changes occur. Identifying where additional model refinement is needed is somewhat
based on experience and judgment. Large element sizes may miss large-scale flow
separation (circulation) or may have numerical instabilities (oscillating or greatly
changing velocities). If the instabilities are too large the model will terminate. Areas
of instability are easily identified in the model results and these areas will be refined.
The model results will also be reviewed to determine if there are currents that are not
“reasonably” depicted based on our experience and these areas will be refined.
4. Develop flow resistance (roughness) and turbulence stress data.
• Channel base roughness based on bed-material size.
• Adjust base roughness to account for other sources of flow resistance such as
obstructions (including LWD) and bed forms. Note: Project-related changes in
amounts of LWD and sediment size can be related to flow resistance values. Also
note that LWD will be simulated by including large debris areas as part of the
geometry.
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• Channel bank and floodplain (overbank) roughness based on land use, vegetative
ground cover, and obstructions using field observations and aerial photography.
• Turbulence stress data, such as eddy viscosity coefficients, are used to incorporate
internal flow stresses. Reasonable values depend on each model’s numerical
representation of these stresses. ADCP data will be used to calibrate these
coefficients.
5. Develop bed-material gradation and layer information.
• Surface sampling conducted throughout the channel network,
• Subsurface sampling, and
• Bank material samples.
6. Develop water and sediment inflows for existing and with-Project conditions.
• For fully unsteady models, use complete flow hydrographs.
• Steady flow simulations will be performed for habitat analysis based on the range of
flows in the simulation record.
• Develop sediment inflow rating curves based on tributary models and from the 1-D
Bed Evolution Model.
7. Other considerations.
• Ice jam breakup hydrographs,
• Ice jam blockage of main channel or lateral features causing redistribution of flow,
• LWD as obstructions or changes in roughness, and
• Erodibility of floodplain areas.
8. Test the hydraulic model over a range of flow conditions.
• Further evaluate mesh quality and the need for additional mesh refinement for areas
with appreciable changes in velocity magnitude or direction to adequately capture
flow transitions.
9. Calibrate and validate the hydraulic model.
• Adjust flow resistance input values (within reasonable limits) to calibrate the
hydraulic results. Calibration and validation will be performed using available data
including:
- Measured water-surface elevations throughout the focus areas during site survey
and water-surface elevations measured at other times.
- Measured velocities collected using acoustic Doppler current profiler along
selected cross sections and longitudinal profiles. Note that flow resistance values
in 2-D models are often lower than comparable 1-D models because 2-D models
directly account for processes that 1-D models must treat as lumped flow
resistance parameters.
- Water-level loggers.
- Discharge distribution between main channel and secondary channels.
- High-water mark information if available.
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Test the sediment transport model.
• Conduct a sediment transport time-step sensitivity analysis to evaluate appropriate
computational time steps for different flow magnitudes. These tests identify the
longest stable time-step for model applications.
10. Calibrate and validate the sediment transport model.
• Adjust sediment inflow rates and sizes, bed layer properties, sediment transport time
step (within reasonable limits) to calibrate the hydraulic results using available data
including:
- Main channel bed level changes observed in the 1-D Bed Evolution Model,
- Comparisons of cross sections using 1980s and current data and between the 1-D
and 2-D bed Evolution Models, and
- Longitudinal profiles.
11. Run and evaluate the results of the sediment transport simulations.
4.1.2.2. Coordination with other Studies
As previously discussed, a combination of 1-D and 2-D Bed Evolution models are being used to
assess potential changes in the aggradation/degradation behavior and related processes in the
Susitna River downstream from Watana Dam due to the potential size and complexity of the
system to be modeled. As a result, the modeling approach uses a reach-scale 1-D Bed Evolution
Model to evaluate the potential effects of the Project on the overall aggradation/degradation
behavior of the study reach, and a series of representative, local-scale 2-D Bed Evolution models
at key locations where the dynamic behavior of the channel and habitat cannot be adequately
assessed using the 1-D modeling approach or are better assessed using a 2-D model. The 1-D
Bed Evolution Model provides boundary conditions for the individual 2-D Bed Evolution
Models. Because of this modeling approach, it is important to coordinate with other studies
because results from the detailed 2-D Bed Evolution Model are only available at specified
locations that have been selected (e.g. Focus Areas) identified by the Fish and Aquatics Instream
Flow (Study 8.5), Riparian Instream Flow (Study 8.6), Ice Processes in the Susitna River (Study
7.6), and Characterization and Mapping of Aquatic Habitats (Study 9.9) study teams and in
consultation with the licensing participants. Section 5.1.2 describes the coordination activities
conducted in 2013. Table 4.1-3 summarizes the interactions of modeling between the fluvial
geomorphology modeling and other study components. Model inputs are divided into four types
of boundary conditions including hydrology, hydraulic, sediment, and geometry, and the source
of the input is identified. The results of each fluvial geomorphology model are also summarized
including the type of result and the recipient study component. The comprehensive modeling
approach is described in detail in Tetra Tech (2013h).
Though not specifically included in Table 4.1-3, additional 2-D Bed Evolution modeling will be
conducted for a range of ice blockage and breakup conditions to evaluate erosion and deposition
potential. Also not included in the table are changes in LWD that may occur over time.
Descriptions of LWD and ice effects on sediment transport and model simulations are described
in Sections 4.1.2.7 and 4.1.2.8.
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Focus Areas have been identified (R2 2013a, R2 2013b), with each covering a length of river on
the order of one to several miles that includes a representation of each geomorphic reach
(excluding Devils Canyon) in the Middle Susitna River. The 2-D Bed Evolution modeling will
be applied at each of the Focus Areas. During the Q1 2013 TWG meetings adjustments of the
proposed Focus Areas were finalized. The Focus Areas also included selected primary tributary
confluences. Coordination among the studies was necessary to ensure efficient collection of
field data, because a considerable amount of the data necessary for development and calibration
of the 1-D and 2-D Bed Evolution models are either required for the other studies, or are more
easily obtained along with data that are required for those studies. For example, the Fish and
Aquatics Instream Flow Study obtained velocity magnitude and direction, flow depth, and
discharge measurements, the data from which would be very useful for calibration of the 2-D
models. The collection of the cross sections for the 1-D model and the bathymetry and
topography for the 2-D model are also being collected under the Fish and Aquatics Instream
Flow Study. In the winter of second study season, this study will collect subaqueous bed-material
data for the modeling by lowering a laser/camera through the ice thickness transect holes that
will be bored in conjunction with winter data collection by the Ice Processes in the Susitna River
Study (Study 7.6).
The temporal resolutions for model execution were selected to ensure model stability and proper
representation of important variability in flow conditions (e.g., daily fluctuations associated with
load-following). The overall time-scale for model execution is also an important factor. Because
a key purpose of the 1-D Bed Evolution model is assessment of the long-term sediment balance
in the study reach, this model is being executed for a continuous period of 50 years to represent
the length of a FERC license. On the other hand, due to the computational requirements of the
2-D Bed Evolution Model, much shorter time-periods are being evaluated.
Close coordination between the study leads and key study team members has been conducted
and will continue throughout the model development process. It is important that all the study
teams have an understanding of the capabilities and limitations of the models, and the
information that will be provided by each model. This is being accomplished through frequent
informal communication and more formal Technical Workgroup meetings. The study leads and
other key participants have and will continue to spend time together in the field to develop a
practical understanding of each study’s needs.
An important aspect of coordination between other studies was to establish which models will be
the source for what type of information. There are a number of hydraulic models being applied
to various aspects of this study. In order to avoid inconsistencies in reported information such as
flows and stage, the model that will take precedence for reporting of information has been
established. Table 4.1-4 is an update of the model precedence. In the event that the precedence
established in the table changes, a revised table will be provided.
Due to application of several hydraulic models, there will be opportunities to perform cross-
checking between models. For instance, water surface elevations and stage can be checked
between the mainstem Open-water Flow Routing Model, 1-D Bed Evolution Model, and the 2-D
River Water Quality Model. If there are significant discrepancies, then parameters within the
models will be checked and adjusted if necessary. In some cases, the discrepancies may be
explained by the formulation of the models or the resolution of the data used by each model.
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4.1.2.3. Model Resolution and Mesh Size Considerations
As described in Section 5.1.3, required model resolution and mesh sizes were identified in 2013
for 2-D Hydraulic and Bed Evolution models. Selection of the appropriate mesh size for the 2-D
models is dictated by several factors including the following:
1. The size and complexity of the site features of primary interest.
2. The overall area of the site.
3. The desired resolution of output information such as velocity, depth, and bed-material
gradation.
Factors that can also influence mesh resolution, subject to meeting the needs indicated by the
above critical factors include:
4. Limitations on the maximum number of elements that the model can simulate.
5. Model execution time.
In general, the mesh resolution in any particular portion of the model should be consistent with
the dimension of the scale of the processes that are being analyzed (Pasternack, 2011; Horritt, et
al, 2006). For example, bed evolution modeling to predict aggradation/degradation in the main
stem can typically be performed using a relatively coarse mesh because the topographic and
hydraulic variability is less pronounced than in smaller habitat features where a relatively high
resolution mesh is necessary to describe the hydraulic variability that is important to habitat
quality and processes. The need to provide a high level of spatial resolution to satisfy items 1, 2,
and 3 above to develop and accurate model can push the limitations imposed by items 4 and 5
above. One approach to avoid trade-offs between model complexity and physical limitations of
the model is to use a variable mesh (also referred to as flexible mesh) that allows a finer mesh to
be applied in areas where either the information desired or the condition being modeled requires
higher spatial resolution (i.e., a finer mesh). The 2-D models being considered for this study
allow the use of a variable mesh.
Areas that will require finer mesh sizes include the following:
• Side sloughs
• Upland sloughs
• Smaller side channels
• Spawning areas
• Tributary mouths
• Locations where circulation is of interest such as eddies between the main channel and
backwater areas
• Other specific habitat features of interest
Areas where coarser spatial resolution may be appropriate include the following:
• Main channel
• Floodplains
• Large side channels
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The RSP indicated that a single mesh could be used for both the habitat and bed evolution
modeling but that some Focus Areas may require different resolution meshes. However, it is now
anticipated that separate habitat (hydraulic) and bed evolution models will be developed for each
Focus Area. A higher-resolution mesh will be used to evaluate detailed hydraulic conditions for
use in assessing factors such as mobilization of spawning gravels in the side sloughs and side
channels where channel widths and depths are small relative to the main channel and connections
between side channels and side sloughs and at the tributary mouths where circulation plays a key
role. The resolution of the hydraulic mesh size was coordinated with the Fish and Aquatics
Instream Flow Study (ISR Study 8.5) to identify the areas requiring finer mesh resolution as well
as the mesh sizes. Due to model size limitations and/or the long simulation times associated with
detailed meshes, a coarser mesh will be used for the bed evolution modeling because issues
related to bed evolution associated with sediment transport processes can be adequately
addressed at a coarser scale. The use of two different mesh resolutions achieves the best
combination of model results and accuracy within available computer and model limitations.
4.1.2.4. Focus Area Selection
The use of “Focus Areas” to conduct concentrated interdisciplinary studies at selected areas
within the study area was introduced in RSP Study 6.6 Sections 3.1 and 4.1.2.4. The selection
was further detailed and refined in two technical memorandums filed in Q1 2013 (R2 2013a) and
Q2 2013 (R2 2013b). A total of 10 Focus Areas were selected and presented in R2’s (2013a)
March technical memorandum, Selection of Focus Areas and Study Sites in the Middle and
Lower Susitna River for Instream Flow and Joint Resource Studies—2013 and 2014. These
selected Focus Areas were modified in May 2013 (R2 2013b) and stand as the working locations
for the 10 Focus Areas. Explanation and methods describing the modifications can be found in
the aforementioned technical memorandum (R2 2013b) and ISR Study 8.5 Sections 4.1.2.3 and
5.1.3.
4.1.2.5. Model Calibration and Validation
Calibration and validation of the 1-D and 2-D Bed Evolution models is a stepwise process.
These efforts have been initiated in 2013 and preliminary results are discussed in Section 5.1.5.
Calibration is used to confirm the precision of model results, whereas validation is used to
confirm the accuracy of model results. Table 4.1-5 provides a general summary of the sources
and types of datasets that will be available to calibrate and validate the 1-D and 2-D models. For
both the 1-D and 2-D models, the sediment transport routines rely on simulated hydraulics, so
the hydraulic components of the models will be calibrated and validated before the sediment
transport components are calibrated and validated. The following subsections describe the
model calibration and validation methodology for both the1-D and 2-D models.
4.1.2.5.1. One-Dimensional (1-D) Bed Evolution Model
Discharges along the study reach will be obtained from the three Susitna River USGS gages and
will be used as boundary condition data for the 1-D Bed Evolution Model. These gages will also
provide a continuous record of stages and water-surface elevations at the gage locations that can
be used as calibration data. These calibration data will be supplemented with stage data from the
“Surface Water Stations” that were established in the Middle and Lower Susitna River segments
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in 2012 as part of the Instream Flow Study (ISR Study 8.5). A total of 13 stations, complete with
pressure transducers, were initially established in 2012; although it is expected that water level
data will be available for only 8 of these stations due to loss of the pressure transducers.
Additional sources of water-level data for model calibration will include water-surface elevations
surveyed during the cross-section and bathymetric surveys in 2012 and 2013 and also include
water surface elevation data collected at the “Focus Area Stations” established in 2013 as part of
the Groundwater Study (ISR Study 7.5). Some of these “Focus Area Stations” are equipped with
pressure transducer transducers.
Specific calibration and validation criteria will be established for the 1-D model during the
model development phase. The hydraulic component of the 1-D Bed Evolution Model will be
calibrated by adjusting the flow resistance and other loss coefficients (within reasonable limits)
so that the predicted water-surface elevations are within an established tolerance of the measured
or surveyed water-surface elevations (i.e., the selected calibration criteria). The hydraulics will
be calibrated to as wide a range of flow conditions as is reasonable given the available
calibration datasets. However, more weight will be given to calibrating to moderate and high
flows because of their influence on the mobilization and transport of sediment. The hydraulics
will be validated following the same procedure as used for calibration except that a separate
validation dataset will be used. In addition to the formal calibration and validation processes, the
simulated water-surface elevations will be compared to water-surface elevations generated by the
Open-water Flow Routing Model (ISR Study 8.5 Section 4.3) to ensure that the models are
producing consistent results. The sediment transport portions of the 1-D Bed Evolution Model
will be calibrated using (1) available sediment transport measurements and the associated
sediment-rating curves at USGS gaging stations for both bed load and suspended load, mean bed
elevation profiles from 1982and 2012 surveys, and (3) comparisons of 1980s and 2012 bed
surface gradations. For coarse-grained rivers such as the Susitna River, the bed-material load
transport is dominant with respect to channel forming processes, so only bed material will be
considered in the calibration and validation processes. However, the fine-grained suspended
load (i.e., wash load) may be important in evaluating the changes to other features including
turbidity, instream habitat, side channels, sloughs and floodplains, so wash load will be
considered in the riverine water quality modeling (ISR Study 5.6 Section 4.8). The sediment
transport components will be validated, to the extent that available information allows, by
comparing modeled and measured (or if necessary, qualitatively observed) changes in bed
elevations and bed-material gradations from the Geomorphology Study (Study 6.5), by making
model runs for specific time-periods. Pending data availability, comparison of simulated and
measured sediment transport will be considered for the validation process. If additional data is
collected or identified that could improve the calibration and validation of the sediment transport
component of the model, it will be considered.
4.1.2.5.2. Two-Dimensional (2-D) Bed Evolution Model
As noted in Section 4.1.2.1 (The hydrodynamic component of the 2-D models will be calibrated
by adjusting the flow resistance input values (within reasonable limits) so that the predicted
water-surface elevations match, as reasonably as possible, the measured water-surface
elevations. The discharges in the main and secondary channels measured using the ADCP will
be compared to the predicted flow distributions. In addition, the measured velocities collected
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using ADCP along selected cross sections and longitudinal profiles will be compared to the
predicted velocities at the same discharge.
Calibration of the velocities and depth are critical to the Fish and Aquatics Instream flow Study.
Calibration of the flow depths is achieved directly through calibration of the water-surface
elevations. Calibration of the local flow velocities will be achieved by comparing predicted
velocities from the 2-D models with measured velocities at the key locations from the field data
collection, including ADCP and current meter data. PHABSIM studies typically require velocity
measurements collected during at least three flows levels (low, medium, and high discharges).
Calibration activities for this study will include all available flow data. Pasternack (2011)
provides guidelines for evaluating 2-D model performance with respect to the velocity
magnitude. These guidelines suggest that the calibration is reasonable when the following
criteria are met:
• Variance (r2) between the predicted and corresponding measured values is in the range of
0.4 to 0.8.
• Median and mean error of individual points is in the range of 15 to 30 percent. Pasternak
(2011) also notes that the relative error for low velocity conditions is typically much
greater than for normal to high velocity conditions.
The sediment transport portions of both the 1-D and 2-D Bed Evolution Model will be first
calibrated based on the available measured sediment transport data and the associated sediment-
rating curves for both bed load and suspended load. For coarse-grained rivers such as the
Susitna River, the bed-material load transport is dominant with respect to channel forming
processes; however, the fine-grained suspended load (i.e., wash load) may be important in
evaluating the changes to other features including turbidity, instream habitat, side channels,
sloughs and floodplains. The sediment transport model will also be validated, to the extent that
available information allows, by comparing modeled and measured (or if necessary, qualitatively
observed) changes in bed elevations and bed-material gradations from the Geomorphology Study
(Study 6.5), by making model runs for specific time-periods. This effort will include comparison
of 1980s and current 2012 transect data if sufficient data are available.
4.1.2.6. Tributary Delta Modeling
Section 5.1.6 describes the tributary delta model development performed at 11 tributaries during
2013. Additional tributaries will be modeled in the next year of study. Determination of
tributary sediment loads has been the focus of 2013 activities and other tasks, such as the
modeling of delta deposits and potential for barriers to fish access, will also be investigated in
the next year of study.
Under post-Project conditions, tributaries are expected to be the primary source of bed-material
sediment to the Middle Susitna River Segment. The sediment supply from the tributaries is
important not only as input to the bed evolution modeling of the Susitna River, but also to
assessing potential Project effects on the ability of fish to access the tributaries and the extent of
clear water habitat associated with some tributary confluences. The post-Project flow regime has
the potential to change the elevation and location where sediment loads from tributaries are
initially deposited because the mainstem may be at a different stage relative to pre-Project
hydrology when the tributaries are at peak flow. Potential changes in deposition patterns
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correspond to potential changes in sediment delivery from the tributaries into the mainstem.
Additionally, the ability of the mainstem to mobilize and transport sediment deposited in
tributary deltas may also be altered by the post-Project hydrology. Modeling sediment transport
and deposition processes at select tributary mouths in the Middle and Lower Susitna River
Segments is therefore necessary. Assessing fish access into tributaries that drain directly into
Watana Reservoir is based on tributary delta modeling as described in the Geomorphology Study
(ISR 6.5 Section 4.8.2.2) and the methods are being closely coordinated between studies.
As a precursor to modeling geomorphic changes at select tributary deltas, the sediment supply to
the deltas must be characterized; a numerical modeling approach is being used for this purpose.
Numerical modeling of sediment supply will be carried out using software such as HEC-RAS
(USACE 2010a), SAMWin (Ayres Associates 2003), or spreadsheet applications coupling HEC-
RAS hydraulic results with an applicable transport function. Model inputs will include tributary
channel geometry, energy loss parameters, bed-material gradation, tributary hydrology, and an
appropriate sediment transport function. Simulated hydraulics will be calibrated where
calibration datasets exist; lacking datasets to calibrate the simulated sediment transport, the
modeled sediment transport capacities can only be reviewed and adjusted based on professional
judgment. In addition to quantifying the sediment supply to the tributary deltas, the modeling
results will be used to develop sediment supplies for other non-modeled tributaries to quantify
inputs to the bed evolution models. For example, the calculated unit-sediment yields at the
modeled tributaries will be regressed against factors such as contributing drainage area and
watershed slope to develop regression relationships. If robust relationships can be identified,
these relationships will be applied to the non-modeled tributaries. Alternate approaches to
quantifying sediment yield may also be considered, such as previous studies of regional sediment
yields (Guymon 1974).
Once the sediment supplies at the selected tributaries have been characterized, tributary delta
modeling will be carried out. The tributaries to be modeled were preliminarily selected in
conjunction with the instream flow and fish and aquatic resources studies and the licensing
participants based on existing fish use and the potential for Project effects. Final selections are
being confirmed based on observations during reconnaissance of existing delta morphology and
estimates of potential Project effects on the ability of fish to access the tributaries.
At the selected tributaries, a numerical model will be developed to characterize changes in delta
morphology using (1) estimated bed-material supply from the tributary, (2) the topography and
the bathymetry of the existing confluence, (3) measurements of the characteristics of the existing
tributary deposits, and (4) the ability of the mainstem in the area of the confluence to mobilize
and transport those deposits. The approach includes field observations to characterize the
sediment transport regime as a basis for identifying appropriate methods of estimating bed-
material transport. Surveys of tributary channel geometry and sampling of bed material
gradations will be coupled with an appropriate bed-material transport function to calculate
sediment yield rating curves. Hydrology synthesized for ungaged tributaries will be provided
(ISR Study 8.5 Section 8.5.5.3). The topography in the area of the expected delta will be based
on surveys or LiDAR-derived mapping. Slopes and gradations of existing tributary deposits will
be collected during field surveys. The ability of the mainstem in the area of the confluence to
mobilize sediment deposited on the deltas will be quantified using numerical 1-D hyd raulic
models. The models will be used to identified the riverward extent of the delta foreset slope
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under various post-Project hydrologic conditions. The estimates, measurements, and modeling
results will provide a basis for characterizing how Project operations at different points in time
affect the formation of tributary deposits. Volumes of sediment will be distributed within the
confining topography considering topset and foreset slopes affected by Project operations to
estimate delta morphologies. Tributary confluences in Focus Areas will be simulated as part of
the 2-D Bed Evolution modeling effort to provide detailed information on delta evolution.
4.1.2.7. Large Woody Debris Modeling
Large woody debris modeling will be performed during the next year of study. Mapping of large
woody debris has been conducted as part of Geomorphology Study using the methods presented
in Section 4.9 and corresponding results presented in Section 5.9 of the ISR Study 6.5. The
assessment of the Project effects on the large woody debris processes within the Middle Susitna
River will be assisted by the Fluvial Geomorphology Modeling below Watana Dam Study,
recognizing that bank erosion is a key process in large woody debris recruitment. Both the 1-D
and 2-D hydraulic model results will be used to estimate changes in bank erosion rates by using
the model output, along with the long-term pre- and post-Project flow records and measurements
of the channel planform, to estimate pre- and post-Project Bank Energy Indices (BEI) (Mussetter
et al. 1995; Mussetter and Harvey 1996). The BEI values for relevant periods will be correlated
with historic bank erosion rates determined from the available aerial photography. Anticipated
changes in the erosion rates, and thus, this aspect of large woody debris recruitment, under
Project conditions will then be estimated based on the correlation results and the Project-
conditions BEI values. A similar approach will be used to evaluate large woody debris
recruitment at the local scale at the Focus Areas using output from the 2-D model where various
levels of large woody debris are present based on the localized hydraulic and scour conditions.
This information will be provided to the Fish and Aquatics Instream Flow Study for
quantification of the change in habitat resulting from Project-induced changes in large woody
debris. Review of the overall role of large woody debris in formation and maintenance of the
geomorphic features and the potential impacts of changes in the large woody debris supply on
these features will be identified using model results and the analysis described in the
Geomorphology ISR (Study 6.5) Section 4.9.
In developing the change in large woody debris supply under the post-Project condition, the
primary questions are the sources of the large woody debris, the current rate of large woody
debris loading to the river, and the impact of the Project on the large woody debris loading rate.
The existing supply of large woody debris from recruitment within the Middle Susitna River
Segment and from upstream of the Watana Dam site (PRM 187.1 [RM 184]) will be estimated in
the Geomorphology Study (ISR Study 6.5 Section 4.9). The Project will change the upstream
supply of large woody debris by retention in the reservoir. Project operations may also change
large woody debris recruitment from bank erosion. Changes in bank erosion can be addressed by
an assessment of the pre- and post-Project rates of erosion of vegetated geomorphic surfaces
(vegetated islands and floodplain segments) that deliver large woody debris to the river. The
rates of bank erosion and thus large woody debris loading can be ascertained by comparison of
time sequential aerial photography, the turnover analysis in the Geomorphology Study (ISR
Study 6.5 Section 4.4) in conjunction with an estimate of the density of the vegetation (volume
and sizes of the trees) growing on the geomorphic surfaces from the Riparian Instream Flow
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Study (Study 8.6) and the Riparian Vegetation Study Downstream of the Proposed Watana Dam
(Study 11.6).
The impacts of the Project on the rates of bank erosion and large woody debris recruitment will
be semi-quantitatively addressed with a comparison of pre- and post-Project Bank Erosion Index
(BEI) (Mussetter et al. 1995; Mussetter and Harvey 1996) values at specific sites along the river
where the output from both 1-D and 2-D models will be used to compute the pre- and post-
Project BEI values. The BEI is an index of the total energy applied to the banks at specific
locations, and is computed based on the hydraulic characteristics of the channel, the channel
planform, and the magnitude and duration of flows (Mussetter and Harvey 1996). The BEI
values will be calibrated with site-specific bank erosion rates determined from the aerial
photography-based turnover analysis. The pre-Project rate of large woody debris recruitment
from bank erosion along the mainstem Susitna River will be scaled using the ratio of the pre- and
Post-Project BEI based erosion rate estimates to develop the post-Project rate of large woody
debris recruitment. These data will be incorporated into the analysis of pre- and post-Project
large woody debris loading from all mechanisms as described in the Geomorphology Study (ISR
Study 6.5 Section 4.9).
A detailed survey of large woody debris within 7 Focus Areas was performed as part of the
fieldwork in 2013 as described in the Geomorphology ISR Section 4.9 and the remaining Focus
Areas will be included in a next year of study. This information will be used to incorporate large
woody debris within the 2-D Bed Evolution Model mesh. This will permit determination of the
influence on flow patterns, local hydraulics, and scour that accumulations of large woody debris
have. At selected Focus Areas, adjustment of the amount of large woody debris at the site will
be performed and the 2-D Bed Evolution Model executed again for a range of hydrologic
conditions. The resulting comparison of flow patterns, local hydraulics, and scour between the
various large woody debris densities will assist in determining the potential influences the
change in density of large woody debris at the site may have on the geomorphic features
associated with the aquatic habitats. These results will be provided to the Fish and Aquatics
Instream Flow Study to develop estimated changes in the aquatic habitat indicators (ISR Study
8.5 Section 4.6).
Large woody debris will also factor directly into the 1-D and 2-D Bed Evolution and Hydraulic
Model parameters. At the reach-scale, large woody debris increases overall flow resistance,
reduces velocity, and reduces sediment transport (Smith et al. 1993, Shields and Grippel 1995;
Assani and Petit 1995; Buffington and Montgomery 1999). The cumulative drag force of debris
in a particular reach will be distributed over the reach by equating area-distributed drag force to
the equivalent shear stress to compute an incremental increase in flow resistance associated with
the LWD (Hygelund and Manga 2003). For existing conditions, the amount of debris, type of
obstruction, size, and other attributes will be used to evaluate the contribution of debris to total
flow resistance. The input flow resistance coefficients will then be modified in the Project-
conditions models to reflect changes in LWD due to the Project by proportioning the amounts of
debris and the resulting total flow resistance based on the altered LWD supply. Depending on
the relative LWD supply, effects on reach-average hydraulics may be negligible in some areas,
but could be significant in others. In general, LWD supply from upstream of the dam will be
eliminated by the Project, but LWD supplied from tributaries downstream from the dam will be
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unchanged. If bank erosion rates decrease based on the BEI analysis, then this supply will also
be reduced.
4.1.2.8. Wintertime Modeling and Load-Following Operations
Wintertime conditions analysis of erosion and deposition processes will be performed, if needed,
during the next year of study. It is currently not proposed to execute the bed evolution models—
either 1-D or 2-D—during the winter period when flows are low and the bed material is not
mobilized. However, if the Characterization of Bed-Material Mobility component of the
Geomorphology Study (ISR Study 6.5 Section 4.3.2.3) indicates that the bed material is
mobilized during winter-time flows, including higher than existing flows due to load-following,
the sediment transport modeling will be extended to include the winter flow period. One winter
operational issue of potential importance is the resuspension of fine sediments during load-
following that could result in increased turbidity during the early portion of the otherwise clear
water conditions during the winter months. To address this, an effort to model the resuspension
of fines can be undertaken with the 1-D Bed Evolution Model and possibly the 2-D Bed
Evolution Models for the early portion of the winter period. This effort could include
investigation of a controlled release to flush the fines from the system prior to commencement of
winter load-following operations. Decisions on continuing the 1-D and 2-D bed evolution
modeling into the winter period will be made in consultation with the licensing participants and
in coordination with the Fish and Aquatics Instream Flow (Study 8.5), Instream Riparian Flow
(Study 8.6), Ice Processes in the Susitna River (Study 7.6), and Characterization and Mapping of
Aquatic Habitats (Study 9.9) studies.
Other aspects of winter and spring conditions that affect geomorphic processes will also be
considered for 1- and 2-D bed evolution modeling. As part of the Ice Processes in the Susitna
River Study (Study 7.6), predictive ice, hydrodynamic and thermal modeling using River1D is
planned for the Middle River between the proposed dam and the Three River Confluence near
Talkeetna (ISR Study 7.6 Section 4.6). Additional ice-related, reach-scale modeling will be
performed as part of the Fluvial Geomorphology Modeling below Watana Dam Study. It is
tentatively assumed that the existing bed material is stable (i.e., below incipient motion
conditions) under ice conditions, due to reduced velocities and shear stresses associated with low
river flows and the ice cover. The validity of this assumption under both existing and with-
Project conditions will be tested by performing an incipient motion analysis using shear stress
results from the River1D modeling. If the results indicate that substantial sediment transport
should occur at the reach scale, the 1-D Bed Evolution Model will be adjusted to incorporate
appropriate rates of sediment transport for ice covered conditions. 1-D dynamic hydraulic
modeling will also be performed of ice jam breakup surges to develop inflow hydrographs for
2-D dynamic hydraulic models. The 1-D hydraulic modeling will be performed using HEC-RAS
and will be similar to dam break simulations of the rapidly released water stored above the ice
jam.
Ice processes influence both the channel morphology and riparian vegetation. For example, ice
can prevent vegetation from establishing on bars by annually shearing off or uprooting young
vegetation. Similarly, ice can scour vegetation from the banks, increasing their susceptibility to
erosion. Both of these influences can affect channel morphology. Ice jams can also directly
influence the channel morphology by diverting flows onto the floodplain where new channels
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can form, particularly when the downstream water-surface elevations are low, allowing the
return flows to headcut back into the floodplain. Ice can also move bed material that would not
be mobilized under open-water conditions by rafting large cobbles and boulders.
The Geomorphology studies (Studies 6.5 and 6.6) and Ice Processes in the Susitna River Study
(Study 7.6) are working together to identify the key physical processes that interact between the
two. A significant portion of the influences of ice processes on morphology are directly related
to their effects on riparian vegetation. The Geomorphology and Ice Process studies are also
coordinating with the Riparian Instream Flow Study (Study 8.6) to identify and interpret
evidence of ice conditions such as ice scarring locations and elevations on trees. Additional
influences of ice processes that may be incorporated into the 2-D modeling include:
• Simulation of the effects of surges from ice jam breakup on hydraulics, sediment
transport and erosive forces using unsteady-flow 2-D modeling with estimates of breach
hydrographs.
• Simulation of the effects of channel blockage by ice on the hydraulic and erosion
conditions resulting from diversion of flow onto islands and the floodplain.
• Use of the detailed 2-D model output to assess shear stress magnitudes and patterns in
vegetated areas, and the likelihood of removal or scouring.
• Use of the detailed 2-D model output to assess shear stress magnitudes and patterns in
unvegetated areas, and the likelihood of direct scour of the boundary materials.
• Application of the 2-D model to investigate whether ice jams are a significant contributor
to floodplain and island deposition as a result of ice jams inundating these features and
causing sedimentation.
The analyses of ice-affected morphologic change will rely on observations and information from
the Ice Processes in the Susitna River Study, the Riparian Instream Flow Study, and
geomorphology field work (Section 4.1.2.9). The results of River1D and River2D simulations,
performed by the Ice Processes in the Susitna River Study (Study 7.6), will also be used. The
information to be developed for both existing and with-Project scenarios will include: (1) size,
location, and frequency of ice jams, (2) location, extent, and duration of bank attached ice, (3)
location, extent, and duration of ice blockage in main versus secondary channels, (4) model
output from River1D and River2D ice model simulations, (5) estimates of fine-sediment
concentrations during ice cover conditions, and (6) field observations of the impacts of ice
movement or flow diversion on floodplain areas. The types of analyses and specific conditions
to be evaluated will be coordinated with the other study teams and agencies as information from
the 2013 field season is evaluated.
4.1.2.9. Field Data Collection Efforts
The field data collection effort to support both the Geomorphology Study and the Fluvial
Geomorphology Modeling below Watana Dam Study is presented in this section. The majority
of this effort was conducted during the 2013 field season but no data were collected in areas
where access was not obtained. If the subsequent need for additional data is identified during the
model development process, Focus Areas are modified, or the downstream limit of the 1-D Bed
Evolution Model is extended below PRM 29.9, additional data will be collected during the next
year of study. Section 5.1.9 includes the results of 2013 data collection efforts. The methods
described below will be also used in the next year of study.
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Much of the data collection performed in this task is being shared with and used by other studies
including Fish and Aquatics Instream Flow (Study 8.5), Riparian Instream Flow (Study 8.6),
Groundwater (Study 7.5), and Ice Processes in the Susitna River (Study 7.6) studies. The
exchange of data between these studies is highest at the Focus Areas.
At the start of the summer 2013 field season, a reconnaissance of the entire Fluvial
Geomorphology Modeling below Watana Dam study area (PRM 187.1 to PRM 79[RM 184 to
RM 75]) as well as the remainder of the Lower Susitna River Segment (PRM 79 to PRM 3.3[RM
75 to RM 0]) was conducted. This site reconnaissance was carried out to observe, characterize
and inform the following:
• Hydraulic and geomorphic controls (natural and man-made) that influence sediment
transport conditions.
• Verification of mapping of geologic and geomorphic features performed in the
Geomorphology Study.
• Hydraulic roughness conditions along the main channel and in the overbanks.
• Variations in bed-material size.
• The sediment transport regime and areas that appear to be in equilibrium, or are
aggradational or degradational.
• Areas that are not in equilibrium, qualitative assessment of the degree of erosion or
deposition.
To support the site reconnaissance as well as all other field data collection activities, maps of the
study area were developed to assist crews during field activities. The mapping included
topography (from available LiDAR), aerial photo base layer, geologic units and controls,
geomorphic features, aquatic habitat types, geomorphic reach boundaries, existing cross-section
locations, proposed supplemental cross-section locations, survey control points, focus site
locations, location of installed instrumentation, private land holdings and safety related
information.
Beyond the general site reconnaissance, detailed information was collected to support the
development of the 1-D Bed Evolution Model for the entire study area and the Focus Areas
where 2-D Bed Evolution Model will be applied. Additional data was also collected for the
tributary confluences that are identified for modeling. Field data collected for each of the study
components are provided below.
4.1.2.9.1. 1-D Bed Evolution Model
The primary field data collected in 2013 in support of the 1-D Bed Evolution Model include the
following:
1. Supplemental cross-sections. The supplemental cross-sections were surveyed as part of
Study 8.5 (ISR Study 8.5 Section 4.3).
2. Bed-material samples along the main channel and tributaries
a. Surface pebble count (Wolman count)
b. Subsurface bulk samples
3. Bank material samples
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4. Spot elevations to verify LiDAR in the area of the supplemental cross-sections (ISR
Study 8.5 Section 4.3). LiDAR are being used to provide the floodplain portion of the
cross-sections. LiDAR verification is discussed in Section 4.1.2.9.5.
5. Estimation of n-values at supplemental cross-sections
6. Observations of depositional or erosional features at the supplemental cross-sections
7. Water-surface elevations
Supplemental Cross Sections
Supplemental cross-sections are required to provide the level of detail in the hydraulic model
necessary to properly model sediment transport conditions. The cross-sections collected in 2012
for the Open-water Flow Routing Model (ISR Study 8.5 Section 4.3) will be used in
development of the 1-D Bed Evolution Model; however, their spacing is such that additional
cross-sections were collected in 2013 to complete the 1-D Bed Evolution Model. There were 88
cross-sections surveyed in 2012 between PRM 80 and 188 (RM 75 and RM 184) (excluding the
12-mile length of river in the Devils Canyon area) with an average spacing of just over 1 mile.
The minimum and maximum spacing between the cross-sections was 0.1 and 3 miles,
respectively. Supplemental cross-sections were surveyed in 2013 and additional cross sections
will be surveyed during the next year of the study to complete the cross-sectional database for
the 1-D Bed Evolution Model. Presently, approximately 40 cross sections have been identified
for survey during the next year of the study with a dozen in the Lower River and the remainder
in the Middle River. The locations of cross sections to be surveyed during the next year of the
study will be finalized based on initial runs of the Open-water Flow Routing Model (ISR Study
8.5 Section 4.3) and the 1-D Bed Evolution Model. The bathymetric and topographic data
collected at the Focus Areas are another source of geometric data for the 1-D Bed Evolution
Model.
Tributary cross-sections surveys were conducted to provide input to the HEC-RAS models,
which in turn being used in conjunction with the tributary sediment sampling and flow
hydrographs to estimate the tributary sediment loads.
Bed-material Sampling
Bed-material samples distributed throughout the study area were collected to support the 1-D
Bed Evolution Model development. In general, sample sites were located approximately every
2 miles throughout the Middle River (below PRM 146.6) and approximately every 3 miles
throughout the Lower River (between the Yentna Confluence and Three Rivers Confluence). In
general, three surface and 1 subsurface samples were collected at each bed-material sample site.
Characteristics of the substrate making up these features were measured using techniques
appropriate to the size range of the material at that location.
In coarse-grained areas, defined by a definite clast-supported, cobble-gravel armor layer, surface
samples were taken using the pebble count method (Wolman 1954) for a minimum of 300
measurements per sample site. The measurements were collected by using a gravelometer along
three 100-foot transects oriented parallel to flow at heads of bars and islands. Where individual
particles exceeded the size of the gravelometer (256 mm), a metric tape was used to measure the
b-axis of the particle. Where individual particles located on transects were less than 2 mm in
diameter (i.e. sand), the particle was noted on the field form but was not included in determining
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the gradation of the surface sediments. Instead, the less than 2 mm particles were removed until
a particle greater than 2 mm in size was identified below the finer sediments. This particle was
then measured and included in the gradation. In general, when the sampled surface was above
water, each transect was placed along the particle imbrication axis located on the Left, Center,
and Right sides (orientation defined looking downstream) of the sampled area (see Figure 4.1-1).
In addition, transects were established such that they encompassed any obvious variability across
the sample surface. Sampling was performed at 1-foot increments along each 100-foot transect
for a total of 300 measurements. An example field data sheet is illustrated in Figure 4.1-2. If a
particle spanned more than the 1-foot interval along a transect, it would be counted for each
interval intersected. If the sampled area was less than 100 feet in length, two 50-foot parallel
transects were established less than 10-feet apart. If a transect tape could not be placed due to a
below-water sample area, a random step method was performed.
In areas where the surface material was sufficiently fine, defined by greater than 20 percent sand
and fine- to medium-gravel, bulk samples were collected for laboratory grain size analysis. A
bulk sample would be gathered by excavating at least 10 pounds of sediment from the sampled
area. The sediment was placed in a sample bag with an aluminum tag identifying the date, river,
PRM, sample type, sample name, and field team identification. The tag information was verified
before being placed in the sample bag. A GPS point was taken at each subsurface sample
location.
Considering the generally coarse-grained nature of the substrate in the Susitna, Chulitna,
Talkeetna and Yentna rivers, bed-material sampling was conducted using a combination of
surface and subsurface sampling. After completion of surface sampling in each area, the surface
armor layer at the 50-foot interval on the center transect was removed and a sufficient quantity of
material based on the sizes of the sediments in the surface gradations (generally between 400 and
500 lb) was excavated from the site. The minimum weight of the bulk sample was based on
ASTM D75-71 guidelines. Figure 4.1-3 and Figure 4.1-4 identify the basis for determining
sample depth and sample weight and is summarized in Table 4.1-6.For practical purposes, an
upper limit for minimum sample weights was set at about 400 pounds. The bulk sample was
weighed with a field scale to determine the total bulk weight. Particles larger than 45 mm were
separated into size classes using a gravelometer. Particles smaller than 45mm and larger than 16
mm were field sieved into size classes. The individual size classes were weighed and recorded.
The remaining sample consisting of the less than 16 mm size class was weighed and recorded.
The less than 16 mm material was then re-mixed with a shovel and a bulk sample, of
approximately 10 pounds or more, was collected for further laboratory sieve analysis. The
difference in wet (field condition) and dry weights of the collected sample were used to estimate
the dry weight of the entire less than 16mm fraction to enable the gradation of the entire bulk
sample to be determined. For quality control purposes, the total weight of the subsurface sample
was compared against the sum of the weights for each particle class size. A 2-percent tolerance
between the initial and final sample weights was used. This check was performed in the field.
An example of a complete subsurface field data form is identified in Figure 4.1-5.
At each bed-material sample site a GPS point was taken as well as photographs of the subsurface
sample pit, overview photos of the subsurface sample location which included the bar/island
surface at the sampling site, overview photos upstream and downstream of the sampling location
and photos of relevant general site conditions.
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Based on the collected field data, the overall gradation was later determined by combining the
field-measured coarse fraction and laboratory-analyzed fine fraction into a single gradation based
on the relative weights of each in the original field sample.
Bed-material data in the main channel is difficult to measure under open-water conditions on the
Susitna River. During the open-water period, flows are typically high and associated higher river
stages make shallow water or dry pebble count methods in the deeper parts of the channel not
feasible. Turbidity associated with the open-water period glacial melt and runoff significantly
reduces visibility, and prevents the use of alternative sampling methods such as the use of
underwater cameras. However, during the wintertime ice-covered period, the turbidity is about
100 times less (Tetra Tech 2013i – Attachment A) and visibility is good.
The Fluvial Geomorphology Modeling below Watana Dam Study worked with the Fish and
Aquatics Instream Flow Study (ISR Study 8.5) and Ice Processes in the Susitna River (ISR Study
7.6) in the winter of 2013 to determine whether subaqueous bed-material gradations could be
determined in the main channel under iced-over conditions using a camera equipped with two
lasers to provide scale. The pilot wintertime bed-material sampling was performed using several
underwater cameras and parallel lasers submersed through augered holes in the ice above the
main channel at ESS40 near PRM 107 and at FA-104 (Whiskers Slough) near PRM 105 (Tetra
Tech 2013i – Attachment A). The underwater cameras were used to acquire images of bed
material that could be analyzed based on the type of camera used, method of scene illumination,
and resolution of separate grain sizes. The parallel lasers were used to project a constantly spaced
scale reference onto each image, with a distance of 4 inches between the lasers. In addition, the
following study goals were evaluated:
• whether or not frazil ice, turbidity, or other moving material interfere with the acquisition
of images,
• how much time is required to collect sample images at a site,
• whether or not main channel velocities are too high for securing and operating camera
and laser equipment mounted to a pole lowered to the bed, and
• identification of other challenges or constraints to performing underwater camera
sampling of main channel bed material during the winter.
Different equipment combinations were used for bed-material image sampling, including four
cameras, one set of two green lasers, and three underwater light sources. The cameras used
included a GoPro Hero3 Black Edition (GoPro), a SplashCam Deep Blue Pro (SplashCam), a
Deep Sea Power & Light Wide-I SeaCam (Wide-I), and an AquaVu camera. The lasers were
Deep Sea Power & Light SeaLaser 100’s. The lights used were two Princeton Tec scuba
flashlights, a Brinkman Q-Beam Starfire II, and LED lights integrated on the AquaVu camera.
Additionally, both 8-inch and 10-inch diameter power ice augers were used to drill holes through
the ice and Marshalltown aluminum push button handle sections were used to deploy the
equipment through the holes in the ice. A ruggedized laptop was used to record images from the
SplashCam, Wide-I, and AquaVu cameras since these cameras did not have internal storage
media. The GoPro camera did have internal storage media for recording images acquired.
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Bank Material Sampling and Bank Observations
Bank observations were performed throughout the Middle Susitna River Segment below PRM
146.6. Observations were performed primarily at cross-section locations and intended to
document any substantial changes in bank and floodplain material within the various geomorphic
reaches along the river. Data recorded included a floodplain/island description, an estimate of
roughness (Manning’s n value) along the floodplain/island, stratigraphic section of the bank,
height and angle of the bank, and any other general observations including high-water marks and
effects of ice processes. Figure 4.1-6 shows an example of a bank observation data sheet.
Periodic bank samples were taken in addition to bank observations. However the concentrated
effort for bank sampling during the 2013 field data collection effort was performed in the Focus
Areas. See Section 4.1.2.9.2 Focus Areas below for detailed methods on bank sampling.
Some additional bank observations were recorded along the Middle Susitna River. These
included identification of eroding banks, bedrock outcrops, and riprap protected banks. This
effort was performed throughout the Middle River downstream of PRM 146.6.Visibly eroding
banks, areas of riprap bank protection, and rock outcrops were identified and marked on a set of
field maps covering the Middle River in primary channels accessible by boat. Within the Focus
Areas, the locations of eroding banks were identified and mapped as part of the Geomorphology
Study (ISR Study 6.5).
Spot Elevations for LiDAR Verification
Surveys of spot elevations were performed throughout the study area as part of the survey efforts
(see sections 4.1.2.9.1.1 and 4.1.2.9.2.1) conducted under Study 8.5 Section 4.3. Section
4.1.2.9.5 provides additional detail on the LiDAR verification and acquisition.
Manning n Estimation
Manning n values were estimated during bank observations (Section 4.1.2.9.1.3). A range of
values were identified based on vegetation density and ground surface variability. These values
were recorded on bank observation data sheets. Channel Manning n values will be developed as
part of the model calibration and validation process (Section 4.1.2.5).
Erosional and Depositional Features
Erosional and depositional features (eroding banks or pointbar accretion) were recorded on the
bank observation data sheet (Section 4.1.2.9.1.3). In addition to individual cross sections, the
main channel banklines were mapped in field maps as erosional, protected by riprap, or
controlled by rock outcrops during transit along the river.
Water Surface Elevations
Water surface elevations were primarily collected at part of cross section surveys conducted as
part of Study 8.5 (see section 4.1.2.9.1.1 above). The Study 8.5 efforts also included additional
surveys of water surface elevations at different times so that many cross sections had 2 or 3
water surface elevations for model calibration and validation purposes. As part of this study,
some cross section observations (Section 4.1.2.9.1.3) included water surface elevation surveys
and a concentrated effort of these surveys was conducted during high flow conditions. When
cross sections were surveyed as part of this study the cross section endpoints were used as the
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control point and a level loop was performed between the control point and the water’s edge.
The date and time of each survey was recorded to assign an approximate discharge to each
measurement.
4.1.2.9.2. Focus Areas
The primary field data collected at the Focus Areas by the Geomorphology and Fluvial
Geomorphology Modeling below Watana Dam studies included the following:
1. A combination of bathymetry (single beam), cross-section data, and spot elevations
necessary to develop a TIN for the portion of the site for which LiDAR is not available.
(These included the main channel, side channels, side sloughs, upland sloughs,
tributaries, and open water areas that were inundated at the time the LiDAR was
acquired.) Note: These data were collected as part of Study 8.5 (ISR 8.5 Section
4.6.1.2.2).
2. All obstructions in the off-channel habitats such as beaver dams were documented.
3. Large woody debris survey and characterization of its influence on the geomorphology of
the channels, side channels and sloughs (Also see Study 6.5 ISR Section 4.9).
4. Bed-material samples in the main channel, sloughs, and side channels
a. Surface pebble count (Wolman count)
b. Subsurface bulk samples
c. Winter sampling in conjunction with the Ice Processes in the Susitna River Study
(Study 7.6) (see 1-D Bed Evolution Model field data section (Section 4.1.2.9.1)
and description of geomorphic mapping below)
5. Bank material samples.
6. Spot elevations collected in the Focus Areas as well as part of the 1-D cross section
surveys are being used to verify LiDAR. The elevation data were collected as part of the
Fish and Aquatics Instream Flow Study (Study 8.5 ISR Sections 4.3 and 4.4). The
LiDAR verification is presented in Section 4.1.2.9.5.
7. Estimation of n-values in the channels, side channels, sloughs, and tributaries.
8. Observations on depositional or erosional features.
9. Field verification, and correction and/or mapping if necessary, of the geomorphic
features, geologic controls, and terraces previously identified from available information
for the Focus Area.
10. ADCP measurements to calibrate and determine the accuracy of the 2-D Hydraulic
Model velocities. Note: These data were collected as part of Study 8.5 (ISR Section 4.6).
11. Installation of level loggers and associated readings to support calibration of water
surface elevations produced by the 2-D model. Note: These data were collected as part of
Studies 7.5 (ISR 7.5 Section 4.5), 8.5 (ISR 8.5 Section 4.3, 4.4 and 4.5) and 8.6 (ISR 8.6
Section 4.6).
12. Current meter measurements of velocity were considered for areas where the ADCP
cannot be used. (Note: The areas where ADCP data were collected were deemed
sufficient for model calibration purposes and no current meter measurements were
collected in 2013).
13. Identification and mapping of evidence of ice processes at the site along with
observations of their potential influence on the geomorphology of the Focus Area
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(Additional information from Studies 7.6 (ISR 7.6 Sections 4.1 and 4.2) and 8.6 (ISR 8.6
Section 4.4.4.1).
14. Any evidence of past extreme events.
15. Overall narrative description and assessment of the geomorphology of the Focus Area
including identification of key physical processes and controls.
16. Spot surveys water surface elevations
Geomorphic mapping of the Focus Areas was conducted during the field data collection at an
appropriate level of resolution to delineate the key geomorphic features that influence the
dynamics and the distribution of aquatic and riparian habitats at the site. This mapping included
features at the scale of the individual habitat units on the order of the channel width in side
channels and sloughs, banklines, large LWD clusters, and other features including lateral and
vertical controls. Detailed topography and bathymetry were collected at the Focus Areas as part
of the Ice Processes in the Susitna River (ISR Study 7.6 Sections 4.1 and 4.2) Fish and Aquatics
Instream Flow Study (ISR Study 8.5 Section 4.4.6.1.2.2)
Bathymetric and Land Survey
Bathymetric, land, and LiDAR surveys were performed to develop a TIN (Triangulated Irregular
Network) of the Focus Areas. The bathymetric and land surveys were conducted as part of the
survey efforts in Study 8.5. The LiDAR acquisition was performed as part of this study and is
described in Section 4.1.2.5.9. The bathymetric survey included below-water areas in the main
channel using cross sections surveyed at approximate 200-ft spacing. The cross section spacing
was reduced to approximately one-half channel width in side channels and other lateral features.
The land survey included near-shore below water shots, water’s edge, top-of-bank, and
breakpoints between the water’s edge and top-of-bank. Land survey was also performed in
shallow side channels inaccessible by the bathymetric survey boat.
Mapping of Obstructions
Beaver dams in the off-channel habitats were documented using field photographs, GPS
waypoints, and field observations which included identifying if the beaver dam appeared active,
inactive, or unknown. Where possible, a height of the beaver dam was measured with a stadia
rod.
Large Woody Debris Mapping
Large woody debris surveys were performed at seven Focus Areas in 2013. Additional surveys
and characterization of LWD was performed outside of the Focus Areas in both the Middle and
Lower River. Methods, sample areas, and study area maps for the LWD survey are provided in
Appendix D of ISR Study 6.5.
Bed-material Sampling
Bed-material sampling within Focus Areas was conducted to characterize the bed materials in
the main channel, side channels, sloughs, and tributaries. Sediment sampling (involving a
combination of surface and subsurface sampling) was conducted in at least 4 locations along the
main and primary side channels. At least two bed-material samples were collected along the
main channel using the sediment sampling procedures identified in Section 4.1.2.9.1, which
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consisted of three pebble counts along 100-foot transects and one subsurface sample at the
50-foot interval of the center transect).
To characterize the bed materials in the side (secondary) channels, additional surface samples
and subsurface samples were collected above and below water. The above water sampling was
conducted at the heads of bars and dry channels, and the below water sampling was conducted in
riffles and runs. Like the bed-material sampling identified in Section 4.1.2.9.1, surface sampling
in secondary channels required identifying if the substrate was either coarse grained (definite
clast supported cobble-gravel armor layer) or fine grained (greater than 20 percent sand and fine-
to medium- gravels). If coarse grained, a pebble count was conducted along one 100-foot
transect placed along the imbrication axis. If the sample area above water was less than 100 feet
long, multiple smaller transects that fit the sample area were established and 100 measurements
were collected. If the sample area was below water, the random step method was used. Because
some of the surface sampling was performed at the base of banks, care was taken to ensure that
in-place particles were being measured and not particles dislodged from above. Where larger
particles that could not be picked up were present, the median (b) axis was measured using a
metric tape. Pebble counts were recorded on field data sheets (previously presented Figure
4.1-2).
The subsurface sampling locations (with the exception of the 2 sample sites collected along the
main channel in conjunction with the 1-D Bed Evolution Model data collection effort) were
broken into two categories: (1) locations with an armor layer, or (2) locations within a
sufficiently fine-grained surface layer. In subsurface sample locations with an armor layer, one
pebble count (method identified in the preceding paragraph) was performed. The subsurface
sample pit was excavated at the center of the transect line. Field sieve procedures followed those
identified in Section 4.1.2.9.1. In locations with sufficiently fine-grained material, a bulk sample
was collected and placed in a sample bag with an etched aluminum tag identifying PRM
(approximated since location was off the main thalweg), date, Focus Area, and sample name.
Additionally, a GPS point was taken.
Bank Material Sampling
Bank samples were collected throughout the 7 Focus Areas studied in 2013 and effort was made
to represent the various geomorphic surfaces. The samples were typically collected at nearly
vertical, exposed banks on floodplains and islands. A scaled photo and GPS waypoint were taken
and the bank stratification was described in a field book. A 5-10 lb bank sample was collected
and placed in a sample bag with an etched aluminum tag identifying PRM, date, Focus Area and
sample name.
Spot Elevations for LiDAR Verification
Surveys of spot elevations were performed throughout the study area as part of the survey efforts
(see sections 4.1.2.9.1.1 and 4.1.2.9.2.1) conducted under Study 8.5 Section 4.3. Section
4.1.2.9.5 provides additional detail on the LiDAR verification and acquisition.
Manning n Estimation
Manning n values were estimated at cross sections for overbank areas based on vegetation
density and ground surface irregularity (see Section 4.1.2.9.1.5). The overbank conditions at
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Focus Areas were mapped and will have Manning n values that are consistent with the 1-D
models. Manning n values in the main channel bed and along lateral features will be developed
primarily during model calibration based on surveyed water surface elevations (4.1.2.9.2.16) and
ADCP velocity and discharge measurements (4.1.2.9.2.10).
Bank Material Sampling
Bank materials were sampled along the main channel and side channels within the Focus Areas.
In most cases a single bank sample was collected but when there appeared to be appreciable
vertical chance the bank was sampled in two or three vertical locations.
Field Verification and Mapping of Geomorphic Features
Field verification of geologic features that provide lateral and vertical controls of the Susitna
River was performed as described in ISR 6.5 Section 4.1.2.3 Geomorphic Characterization of the
Susitna River. See ISR 6.5 Section 4.1.2.3.1 Surficial Geology for corresponding methods.
ADCP Velocity Measurements
ADCP velocity measurements were collected as part of ISR Study 8.5 (See Study 8.5 Section
4.6). These data were collected at cross sections and along the channels within the focus areas.
The individual velocity measurements provide depth-averaged velocity magnitude and direction
data that will be compared to the velocity magnitude/direction results of the 2-D models for
calibration and validation. The cross sectional ADCP data will also be used to calculate
discharge in the main channel and side channels to compare with the flow distributions computed
by the models.
Level Loggers
Level logger data were collected as part of Studies 7.5 (ISR Section 4.5), 8.5 (ISR Section 4.3,
4.4 and 4.5) and 8.6 (ISR Section 4.6). The stage data collected by these will be available for
calibration of the 1-D and 2-D models.
Current Meter Velocity Measurements
No current meter velocity measurements were made in 2013 because the areas where ADCP data
were collected were deemed sufficient for model calibration and validation purposes.
Mapping of Evidence of Ice Processes
Identification and mapping of effects of ice processes on geomorphology was performed during
geomorphic surface mapping of Focus Areas. Evidence of ice scars, ice eroded banks, overbank
sand deposition, and ice rafted cobbles and boulders were noted in field books, photographed,
and mapped on Focus Area mapbooks. The ice-specific observations help provide an
understanding of ice processes and geomorphology on the Susitna River (ISR Study 6.5 Sections
5.1.3.2 and 6.1.3.2). Mapping of evidence of ice processes was also performed by the Riparian
Instream Flow Study (ISR Study 8.6 Section 4.4.4.1)
Evidence of Extreme Events
Evidence of past extreme events was noted in fieldbooks and on Focus Area geomorphic surface
mapping. The information used, in part, to classify the geomorphic surfaces.
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Geomorphic Narrative and Characterization
Geomorphic mapping was conducted in the field which included documentation and mapping of:
geomorphic surfaces, eroding banks, effects of ice processes, types of channels, locations of
lateral weirs (berms) and general site specific information. The Geomorphology Study presents a
detailed description of this effort (ISR Study 6.5 Section 4.1.2.3). In addition, bank heights of the
various geomorphic surfaces were measured using a stadia rod and inclinometer. The bank
heights were measured relative to water-surface elevation and were converted to an elevation
using the daily discharge at Gold Creek on the day of measurement and stage-discharge rating
curves (ISR Study 6.5 Appendix A.3) developed from the preliminary Open-water Flow Routing
Model. Because bank heights were measured on multiple days at different discharges and
throughout the Focus Areas, the stage-discharge rating curve that was closest to the center of the
Focus Area was used. It is recognized that this will tend to overestimate the surface heights in
the downstream portions of the Focus Area and underestimate the surface heights in the upstream
portions of the Focus Area; more precise surface heights will be developed based on the output
from the 1-D and 2-D hydraulic models and using either the 2013 LiDAR or the indexed 2011
MatSu LiDAR data.
Surveys of Water Surface Elevations
Water surface elevations were surveyed during the data collection efforts by this study and
during data collection efforts by other studies. Edge-of-water was surveyed during the
bathymetric surveys (Section 4.1.2.9.2.1) and at the main and side channel cross sections during
ADCP data collection (Section 4.1.2.9.2.10). Additional water surface elevations were surveyed
as part the data collected in Focus Areas by this study. When elevations were surveyed as part of
this study a control point was set and a level loop was performed between the control point and
the water’s edge. The control point was surveyed later to establish the elevation in the project
datum. The date and time of each survey was recorded to assign an approximate discharge to
each measurement.
4.1.2.9.3. Tributary Deltas
A site reconnaissance and data collection was conducted at key tributaries that were identified to
have the potential to deliver significant quantities of sediment to the reach and/or importance to
other study teams. The data collected included cross-section surveys, surface and sub-surface
bed-material sampling, and observations and photographs of erosional and depositional features.
The tributary study sites were selected by the Team Leader and were typically located outside of
the backwater influence of the Susitna River and upstream of fan heads adequately quantify
sediment input from the tributary. The cross-sections locations were selected to include the
hydraulic controls and channel sections that were representative of the sediment transport
conditions. In general, the cross-sections extended across the channel onto the
floodplains/terraces and the cross-section spacing was on the order of 1 to 2 channel widths.
Typically 4 to 10 cross-sections were surveyed at each site with an average cross-section spacing
of 1 to 3 times the active channel widths, depending on the site complexity. The surveys were
conducted using standard engineering survey techniques using a survey level, survey rod and
tape measure with closed level loops.
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Surface and sub-surface bed-material samples were collected to characterize the gradation of the
sediments along the surveyed reach, and included at least one representative sample of the
surface material on the fan at the interface with the Susitna River. Additional pebble counts were
conducted at some sites to quantify the roughness characteristics of the channel.
4.1.2.9.4. Field Data from Other Studies
In addition to the above field data collected as part of the Geomorphology Study (Study 6.5), the
following data collected by the Fish and Aquatics Instream Flow (Study 8.5), Riparian Instream
Flow (Study 8.6), Ice Processes in the Susitna River (Study 7.6), and Groundwater (Study 7.5)
studies are available to support the Fluvial Geomorphology Modeling below Watana Dam Study.
The following data have been obtained from the various studies:
• Open-water Flow Routing Model cross-sections collected in 2012 (ISR Study 8.5 Section
4.3).
• Fish and Aquatics Instream Flow Study supplemental transects collected in 2013 (ISR
Study 8.5 Section 4.3).
• Information developed in the Geomorphology Study on channel changes that have
occurred since the 1980s (ISR Study 6.5 Section 4.4).
• Information developed in the Geomorphology Study on the physical processes most
important to accurately modeling the study reach (ISR Study 6.5 Section 4.1).
• Bathymetric and topographic survey information collected in the Focus Areas to
represent the geometry of the Focus Areas (ISR Study 8.5 Section 4.6).
The following data are being obtained:
• Hydraulic calibration information used in the development of the Open-water Flow
Routing Model including water surface elevations and associated discharges (ISR Study
8.5 Section 4.3).
• Information describing the influence of ice processes on channel and floodplain
morphology (ISR Study 7.6 Sections 4.1 and 4.2 and ISR Study 8.6 Section 4.4.4.1).
• Information describing the influence of riparian vegetation on channel and floodplain
morphology (ISR Study 8.6).
• Soil classification and gradations from Riparian Instream Flow Study test pits in the
floodplain and on islands (ISR Study 7.6 Section 4.5).
• Thickness and aging of floodplain and island deposits from the Riparian Instream Flow
Study (ISR Study 7.6 Section 4.5).
• Mapping of vegetation and associated age classes from the Riparian Vegetation Study
Downstream of Watana Dam (ISR Study 11.6 Section 4.1) and the Riparian Instream
Flow Study (ISR Study 8.6 Section 4.5). The velocity and depth measurements collected
by the Fish and Aquatics Instream Flow Study to characterize habitat for calibrating the
hydraulic model(s) (ISR Study 8.5 Section 4.6).
• Data collected on the distribution of flow between the main channel and off-channel
habitat to help calibrate the hydraulic portion of the 2-D model (ISR Study 8.5 Section
4.6).
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4.1.2.9.5. LiDAR Verification and Acquisition
Two LiDAR data sets are available for various portions of the Susitna River. The Matanuska-
Susitna Borough (Mat-Su) LiDAR was acquired in 2011 and AEA acquired higher density
LiDAR in 2013 (SuWa LiDAR). The original Mat-Su LiDAR was not indexed or verified using
surveyed ground points. AEA decided to acquire the high-density LiDAR to provide more
accurate information, but unfavorable conditions limited the amount of LiDAR that was acquired
in 2013. Therefore, in order to supplement the 2013 LiDAR data, the Mat-Su LiDAR was
indexed and the verification process for the 2011 Mat-Su LiDAR was repeated. The following
sections describe the methods for acquiring and processing the Su-Wa and for verifying and
indexing the Mat-Su LiDAR.
LiDAR Acquisition and Processing
Keystone Aerial Surveys acquired LiDAR data with an Optech ALTM Gemini Airborne Laser
Terrain Mapper System. The system includes an Inertial Measurement Unit (IMU), a 33-167kHz
laser rep rate, multi-pulse capability and four returns from each outgoing pulse. The data were
collected to meet a minimum of 8 points per square meter density at 800 meters Above Ground
Level (AGL) to support the project requirements.
The overall acquisition area was broken up into 13 priority areas. The total 2013 LiDAR area
was 557 square miles. Of that, 371.5 square miles were within the river corridor and 185.5
square miles were within the reservoir area. Priority areas were determined by the study teams
and ranked in order of importance to schedule. The project flight plan required that with
favorable weather and river flow conditions the priority areas would be flown in order, but that
areas with lower priority would be flown when unfavorable conditions limited access elsewhere.
The LiDAR acquisition also required low flow conditions to maximize LiDAR point returns on
the bare ground along the river. The flow levels were determined by 3 USGS gage stations along
the Susitna River. The Middle Susitna River was to be acquired at less than 17,000cfs (+/- 10%)
from the Gold Creek gage. The Talkeetna River was to be acquired at less than 20,000cfs at the
Gold Creek gage and the Chulitna was to be acquired at less than 15,000cfs at the Chulitna Gage.
The Lower Susitna River was to be acquired at less than of 55,000cfs (+/- 10%) at the Sunshine
Gage. There was also a tidal requirement from PRM 0 to 17. These areas were only to be
acquired during time windows around low tide.
The airborne LiDAR dataset was requested to meet the specifications shown in Table 4.1-7.
Upon receipt of the collected data, LiDAR and GIS specialists review the acquisition report and
confirm the results by performing an initial quality assurance and quality control assessment.
This assessment verifies LiDAR point cloud data coverage within the project area, point density,
vertical accuracy, accurate matching between flight lines, compliance with the ASPRS LAS
v.1.2 technical specifications document, and other specifications requested for the 2013 Susitna-
Watana project.
Once the initial quality assurance and quality control assessments were performed and the
LiDAR data were validated, the unclassified LiDAR point cloud files (LAS) were prepared for
an initial clean-up. All pulses were merged into the “Unclassified” or “Default” class (ASPRS
Class 1) to be used by the ground classification routine. A rough minimum elevation threshold
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filter was applied to the entire dataset in order to eliminate the most extreme low/high point
outliers. A second clean-up process was applied to search for isolated and low points using
several algorithm iterations using Terrascan macros. The “Low Points” macro searches for
possible error points that were clearly below the ground surface. The “Isolated Points” macro
then searches for points that were without any neighbors within a specified radius. The “Low
Points” as well as the “Isolated Points” were classified into the “Noise” class (ASPRS Class 7),
which excludes them from subsequent steps.
A first classification process (unsupervised) was performed using all points in the previously
cleaned “Unclassified”/”Default” class (ASPRS Class 1). Each laser return was assigned an
“echo”: Only, First-of-Many, Last-of-Many, or Intermediate. To begin classification, the ”First-
of-Many” and ”Intermediate” returns were removed from consideration as Bare-Earth points by
assigning them to the Medium Vegetation class. The remaining points, the “Only” and “Last-of-
Many” returns were placed in the “Unclassified”/”Default” class (ASPRS Class 1). The Bare-
Earth class was developed from this set of returns by an iterative method. First, a rectangular
filter was passed over the points in the “Unclassified”/”Default” class (ASPRS Class 1) , and a
set of local low points was selected to seed the Bare-Earth class. Then the rest of the points in
“Unclassified”/”Default” class (ASPRS Class 1) were compared to the triangulated surface
defined by the set of Bare-Earth points, and those that were found be close enough to fall within
an acceptable angle and height of the surface were added to the Bare-Earth class (ASPRS Class
2). The process was repeated with the expanded Bare-Earth class until the number of points
being added to the Bare-Earth class declines. Standard practice in the LiDAR industry
acknowledges that no ground classification is perfect. Valid ground points on edges or sharp
features are commonly misclassified by LiDAR point cloud processing software packages,
leaving blank areas (gaps) in the ground surface. Using proprietary techniques, potential
anomalies (e.g., artificial pits, “spikes” on the ground, etc.) were identified during the first
classification process (unsupervised) to be corrected in further steps. The application of those
techniques provides a semi-automated quality control of the first point cloud classifications and
improves the efficiency of the next classification process.
After the unsupervised classification, a second classification process was applied (supervised),
where the Bare-Earth model class (ASPRS class 2) were inspected in a tile-by-tile basis and
edited as necessary. The Bare-Earth model was visualized as a triangulated irregular network
surface (TIN) with contours and potential gap polygons overlaid. Irregularities or voids in the
ground surface were subjected to special scrutiny, typically by generating and studying sectional
views of the questionable area. Incorrectly classified points were reclassified as necessary, and
the classification routine was re-run locally to correct nearby points. This careful review of each
tile is central to making a consistently high-quality DEM.
The LiDAR point classification process was complete by performing a second vertical accuracy
assessment using only points classified as Bare-Earth (ASPRS Class 2), and exporting the
LiDAR-derived data to create the final deliverables.
2011 Mat-Su LiDAR Verification
Ground survey data collected in 2013 as part of the Fish and Aquatics Instream Flow Study cross
section and Focus Area survey efforts (ISR Study 8.5 Sections 4.3, 4.4 and 4.6.1.2.2) were used
as a control to evaluate the 2011 Matanuska-Susitna Borough LiDAR data. The verification was
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based on the comparison of ground survey points collected in the Lower and Middle Susitna
River areas with a Triangulated Irregular Network (TIN) constructed from LiDAR points around
each survey point. Figure 4.1-7 shows the locations of the ground control points. The 522
ground survey points were classified according to major land cover types found in both the
Lower and Middle Susitna River, in order to perform the three vertical accuracy tests for a
LiDAR dataset recommended by the National Digital Elevation Program (NDEP) and adopted
by ASPRS, which are:
a. Fundamental Vertical Accuracy (FVA)
b. Supplemental Vertical Accuracy (SVA)
c. Consolidated Vertical Accuracy (CVA)
There are three major land cover types in the Lower and Middle Susitna River areas,
a. Open terrain
b. Brush land/Low vegetation
c. Forest land
As shown in Figure 4.1-7, 522 ground survey points were used for the verification of the 2011
Mat-Su LiDAR. Figures 4.1-8 and 4.1-9 show examples of the ground survey points the
Whiskers Slough Focus Areas (FA 104). The Fundamental Vertical Accuracy was performed by
comparing the 174 ground survey points collected on open terrain land cover to the Triangulated
Irregular Network (TIN) constructed from the classified LiDAR point cloud (ASPRS point class
2) in a radius of 30 feet for each point. Fundamental Vertical Accuracy measures vertical
accuracy in areas of open terrain. The fundamental accuracy is the value by which vertical
accuracy can be equitably assessed and compared among different datasets.
Supplemental Vertical Accuracy measures the vertical accuracy in ground cover categories other
than open terrain. The Supplemental Vertical Accuracy test was performed by comparing the 348
ground survey points collected on forest and brush land cover to the Triangulated Irregular
Network (TIN) constructed from the classified LiDAR point cloud (ASPRS point class 2) in a
radius of 30 feet for each point.
The Consolidated Vertical Accuracy was performed by comparing all 522 ground survey points
collected on all the land cover types to the Triangulated Irregular Network (TIN) constructed
from the classified LiDAR point cloud (ASPRS class 2) in a radius of 30 feet for each point. For
comparison, Table 4.1-8 shows the vertical accuracy limits and the equivalent contour intervals.
All vertical accuracy tests were performed in an automated fashion using the industry standard
LiDAR processing software Terrascan.
2011 Mat-Su LiDAR Indexing
The 2011 Matanuska-Susitna (Mat-Su) Borough LiDAR dataset was indexed in order to improve
on the vertical accuracy of this data set. Indexing is an elevation adjustment to true ground using
surveyed data. The indexing process started by reshaping and renaming the 2011 Mat-Su
LiDAR dataset according to the 2013 Susitna-Watana (Su-Wa) LiDAR files index.
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The retiled and renamed version of the 2011 Matanuska-Susitna Borough LiDAR dataset was
compared against 525 ground survey points collected in 2013 on open terrain land cover type,
distributed over the study area between PRM 31 and PRM 147. This comparison was performed
similarly to the process explained in the 2011 Mat-Su LiDAR Verification (Section 4.1.2.9.5.2)
by subtracting the laser point cloud elevation at known locations from the ground survey point
elevations in order to obtain the average elevation difference (Mean). The average elevation
difference was subtracted from the LiDAR point cloud elevation values in order to adjust them to
true ground. This process is also called ‘Datum shift’.
Once the vertical Datum shift was applied, the indexed LiDAR dataset was compared against the
174 ground survey points on open terrain land cover type utilized for the 2011 Mat-Su LiDAR
verification. With the statistical results of the comparison, a final inspection of the extreme
elevation difference values is performed in order to remove outliers within the ground survey
point dataset. According to ASPRS “An outlier is an error of major proportion, normally
identified and removed during editing or quality control processing. A potential blunder may be
identified as any error greater than three times the standard deviation (3 Sigma) of the error.
Errors greater than three times the standard deviation should be analyzed to determine the
source of the blunder and to ensure that the blunder is not indicative of some unacceptable
source of systematic error”(ASPRS 2004). Potential outliers were analyzed before removing
from the ground survey verification dataset.
4.1.2.10. Information Required
In addition to the field data collection effort described in the previous section, the following
existing information is being used to conduct this study:
• Historical and current aerial photographs (ISR Study 6.5 Sections 4.4, 4.5 and 4.7).
• Historical channel cross-sections (ISR Study 6.5 Section 4.3).
• LiDAR to develop sub-aerial topography and extend surveyed transects across the
floodplain (2011 Mat-Su and 2013 Su-Wa LiDAR described in Section 4.1.2.9.5).
• Extended flow records from USGS mainstem and tributary gages (ISR Study 6.5 Section
4.6 and ISR Study 8.5 Section 4.3).
• Estimated flows from key ungaged tributaries that will be accounted for in the water and
sediment inflows, and where potential development of tributary fans is to be evaluated
(ISR Study 8.5 Section 4.3).
• Historical bed-material sample data (ISR Study 6.5 Section 4.1).
• List of key indicators from the other studies (Fish and Aquatics Instream Flow Study
(Study 8.5), Riparian Instream Flow Study (Study 8.6), Ice Processes in the Susitna River
Study (Study 7.6), and Groundwater Study (Study 7.5)) to ensure that the models are
structured to either directly quantify the indicators or provide quantitative data from
which the indicators can be quantified using other relationships outside the context of the
model.
4.1.3. Variances from Study Plan
No variances from the methods occurred during the implementation of this study component in
2013. While land access was not available for portions of the river and tributaries adjacent to
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Cook Inlet Regional Working Group (CIRWG) lands in 2013, this was not considered a variance
because this study was designed to collect data over multiple years.
4.2. Study Component: Model Existing and with-Project Conditions
AEA implemented the methods as described in the Study Plan, with no variances. The methods
are included in the RSP Section 6.6.4.2 and additional detail is provided in the modeling
approach technical memorandum (Tetra Tech 2013h). Because this study component will be
conducted in the next year of the Study, the only analysis that has been performed relates to the
selection of hydrologic conditions that will be simulated in the 1-D reach-scale modeling and
2-D local-scale modeling. The hydrologic analysis, which is included as Appendix E,
recommends which 50-year period will be included for reach-scale modeling and the
representative years for local-scale modeling.
The goal of the Model Existing and with-Project Conditions study component is to provide a
baseline and series of with-Project scenarios of future channel conditions for assessing channel
change. The extent of the study area is the Susitna River downstream of Watana Dam, the
specific downstream boundary of which was determined in study component Bed Evolution
Model Development, Coordination, and Calibration.
4.2.1. Existing Information and Need for Additional Information
Once the 1-D and 2-D Bed Evolution Models are developed in the previous study component,
the model will be run for the existing condition (the Susitna River without Watana Dam in place)
in order to establish a baseline for comparison with Project model runs. The model will also be
run for various Project scenarios to determine the potential effects of the Project on the fluvial
geomorphology of the Susitna River.
4.2.2. Methods
4.2.2.1. Existing Conditions – Base Case Modeling
The Study Plan includes five operation scenarios. The first is the existing conditions or without-
Project scenario. This scenario provides the baseline against which all other with-Project
scenarios are compared against to identify Project effects.
The time period and representative hydrologic conditions to be assessed with the bed evolution
model will be determined through coordination with the Technical Workgroup, based on the
availability of data, study objectives, and model limitations. The hydrologic inputs for the
various with-Project scenarios will be obtained from the Reservoir Operation Model (ISR Study
8.5 Section 4.3) and Open-water Flow Routing Model (ISR Study 8.5 Section 4.3) and the model
run for flows representative of each scenario. A 50-year, continuous period of record that
represents the length of the FERC licensing period will be used for the 1-D bed Evolution
Modeling, and shorter modeling periods will be used for the 2-D Bed Evolution Model due to
computational limitations. The 50-year period will be divided into three points in time to provide
comparison: year-0, year-25, and year-50. As previously indicated, the 1-D model will be
applied to address the analysis of reach-scale issues and the 2-D model to address local-scale
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issues. Section 5.2.1 provides the preliminary results of the selection of the 50-year hydrologic
record for 1-D Bed Evolution Modeling.
The shorter periods for the 2-D Bed Evolution Model will include specific years or portions of
annual hydrographs for selected years of wet, average, and dry hydrologic conditions and warm
and cool Pacific Decadal Oscillation (PDO) phases. Therefore, up to six annual hydrologic
conditions will be considered. (The inclusion of the warm and cool PDO phases was requested
by NOAA-NMFS and USFWS in the May 31, 2012, study requests; the rationale for the request
was discussed at the June 14, 2012 Water Resources TWG meeting and it was agreed that the
PDO phases would be included in the suite of representative annual hydrologic conditions.)
Other scenarios might include rapid release of flows from an ice jam or larger flood events that
are not contained in the period of the hydrologic record chosen for simulation. Section 5.2.1
provides the preliminary results of the selection of representative annual hydrologic conditions
for 2-D modeling.
Each run will be subjected to a quality control process to ensure that the appropriate data were
used and model outputs are reasonable. Naming conventions for the model input and output
files for the various scenario files will be applied so that files can be easily archived and
retrieved in the future.
4.2.2.2. Future Conditions – with-Project Scenarios
The four with-Project scenarios will represent a maximum load-following, an intermediate load-
following, a base-load, and a run-of-river scenario. The four with-Project scenarios will provide
an understanding of the range of potential Project effects. Similar to the existing conditions, the
with-Project scenarios will be modeled with both the 1-D Bed Evolution Model to determine the
reach-scale Project effect and the 2-D Bed Evolution Model to determine the local-scale Project
effects. The with-Project scenarios will be evaluated over the same time periods as the existing
conditions base case.
4.2.2.3. Uncertainty
To assist in identifying and understanding uncertainties, sensitivity analysis will be performed
for the 1-D and 2-D Bed Evolution modeling efforts by varying key input parameters within the
range of physically reasonable values. Additionally, the 50-year simulation period to be used for
the 1-D bed evolution model includes a broad range of hydrologic conditions, and will be used to
assess the sensitivity of the study reach to hydrologic variability. Variation in response to up to
six representative years (wet, average, and dry for warm and cool PDO) based on both the 1-D
and 2-D Bed Evolution Model results will also provide an understanding of the uncertainty
associated with hydrologic conditions. Specific parameters that will be varied in the uncertainty
analysis include hydraulic roughness coefficients, magnitude and gradations of inflowing
sediment loads, substrate size gradations, and dimensionless critical shear (i.e., Shields) values
depending on the selected transport equation. Section 6.2.3 includes further discussion of the
evaluation of uncertainty in the 1-D and 2-D Bed Evolution models.
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4.2.2.4. Synthesis of Reach-Scale and Local-Scale Analyses
In general, based on the spatial resolution of the input and output data, the 1-D Bed Evolution
Model results are used to facilitate analysis of processes at the reach-scale, while the 2-D Bed
Evolution Model is used for local-scale analysis. It is important to recognize that the
downstream stage and upstream discharge boundary conditions for the local-scale 2-D models
will be taken from the Open-water Flow Routing Model, and the inflowing sediment loads will
be taken from the 1-D Bed Evolution Model, ensuring consistency at the model boundaries.
Although this is not anticipated, it may be necessary to take downstream stage boundary
conditions from the 1-D Bed Evolution Model for purposes of analyzing future conditions if this
model shows sufficient change over the duration of the model runs. If the 1-D Bed Evolution
Model indicates that there is sufficient bed change to warrant adjustments to the 2-D model
downstream stage boundary conditions, then the geometry of the 2-D models will also have to be
modified. As shown in Figure 4.2-1, this potentially would occur at the year-25 and year-50
points in time. This would also affect the 2-D Hydraulic Models that will provide hydraulic
input to the fish habitat analyses and could also affect ice processes, flow routing, and
groundwater models. In addition, results from the 1-D Bed Evolution Model are compared
within the 2-D model domain to further ensure consistency. This comparison often leads to
important adjustments to one or both of the models to improve consistency and predictive
quality.
As described in the Section 4.1.2.4, the Focus Areas have been selected to represent the range of
geomorphic and habitat conditions that occur within the study area. The detailed analysis at
these sites that relies on the 2-D model results will be extrapolated to the overall study reach
using the 1-D model results and other relevant information from the Geomorphology (Study 6.5),
Fish and Aquatics Instream Flow (Study 8.5), Riparian Instream Flow (Study 8.6), Ice Process in
the Susitna River (Study 7.6) studies, where appropriate, to quantify anticipated Project impacts
at the Study Reach Scale.
4.2.2.5. Information Required
The following available existing information is needed to conduct this study:
• The calibrated existing conditions model(s) developed in the previous tasks, including the
data used to develop them.
• Extended flow records for mainstem gages and major tributaries for existing conditions.
• Sediment inflow rating curves for the major tributaries.
• With-Project mainstem flows corresponding to the periods and locations in the extended
flow record.
• The with-Project sediment outflow rating curve from Watana Dam.
• List of key indicators from the other studies (Fish and Aquatics Instream Flow Study
(Study 8.5), Riparian Instream Flow Study (Study 8.6), Ice Process in the Susitna River
Study (Study 7.6), Groundwater Study (Study 7.5)) to ensure that the models are
structured to either directly quantify the indicators or provide quantitative data from
which the indicators can be quantified using other relationships outside the context of the
Fluvial Geomorphology Modeling below Watana Dam Study.
• Data on PDO index during the extended flow record.
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4.2.3. Variances from Study Plan
No variances from the methods occurred during the implementation of this study component in
2013.
4.3. Study Component: Coordination and Interpretation of Model
Results
The goal of this study component is to ensure that the information from Geomorphology Study is
properly considered and incorporated into the modeling studies, that the results from the
modeling studies are used to update and refine the understanding of key processes identified in
the Geomorphology Study, and to provide the necessary results to the other resources studies that
will require knowledge, and where possible and appropriate, quantification of potential natural
and Project-induced geomorphic changes. The extent of the study area is the Susitna River
downstream of Watana Dam (PRM 187.1) to Susitna Station (PRM 29.9).
4.3.1. Existing Information and Need for Additional Information
Several studies require the results of the Fluvial Geomorphology Modeling below Watana Dam
Study to conduct their efforts. These include the Fish and Aquatics Instream Flow (Study 8.5),
Groundwater (Study 7.5), Riparian Instream Flow (Study 8.6), and Ice Processes in the Susitna
River (Study 7.6) studies. The primary concern is whether the Project will affect aspects of the
channel morphology including, but not limited to, substrate characteristics, cross-sectional
geometry, connectivity with off-channel habitats, and in the most general sense, the formation,
maintenance and distribution of geomorphic features that comprise the aquatic and riparian
habitats.
4.3.2. Methods
As discussed in Study 6.5 ISR Section 4.11, initial work for the Geomorphology Study identified
the specific geomorphic processes that affect aquatic and riparian habitat, channel stability and
related issues that require further quantification, identified a significant portion of the data needs,
and provided the basic information and context for the Fluvial Geomorphology Modeling below
Watana Dam Study. During the Fluvial Geomorphology Modeling below Watana Dam Study,
results from the Geomorphology Study are used in conjunction with knowledge of the specific
needs of the other resource teams to insure that the models are developed in an appropriate
manner to address the key issues and to provide a reality check on the model results. After
completion of the modeling, the study team will use the results from both studies in an integrated
manner to provide interpretations with respect to the issues that must be addressed, including
predictions of potential changes to key geomorphic features that comprise the aquatic and
riparian habitat. This information is then provided to the other resource teams for use in their
evaluation of potential project effects.
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4.3.2.1. Integration of Geomorphology and Fluvial Geomorphology Modeling below
Watana Dam Study Results
The purpose of this task is to integrate the Geomorphology and Fluvial Geomorphology
Modeling below Watana Dam Studies to insure that results from both studies are used in a
coordinated manner to identify and, to the extent possible, quantify drivers for the existing
conditions and the potential influence of the Project on key geomorphically related habitat
features. Study 6.5 ISR Section 4.11 provides a detailed discussion of the specific aspects of the
Geomorphology Study that will be used to guide development of the models and interpretation of
the model results for the Fluvial Geomorphology Modeling below Watana Dam Study,
particularly as they relate to the geomorphically-based habitat indicators. Additional examples
of key coordination activities between the two studies include the following (note that other
activities may be identified as the study teams gain additional understanding of the key processes
that drive existing conditions and potential Project effects):
• The LWD component of the Geomorphology Study is providing information on the status
of LWD recruitment to the project reach and the effects of LWD on geomorphic
processes, Manning’s n values and in-stream habitat (Study 8.5) under existing
conditions and qualitative information about the potential effect of the Project on future
LWD recruitment and hence geomorphic processes, Manning’s n values and in-stream
habitat. Results from the bed evolution modeling, as well as the Ice Processes in the
Susitna River Study (Study 7.6) and Riparian Instream Flow Study (Study 8.6), will
provide quantitative estimates of certain key processes (fluvial and ice) that affect LWD
recruitment under both existing and Project conditions, including potential changes in
bank erosion rates.
• The Geomorphology Study is identifying key locations that control connectivity between
the main channel and the side channels, side sloughs and upland sloughs, and will assess
how these locations have evolved over the period of coverage of the historical aerial
photography as well as in terms of the channel evolution model developed in the
Geomorphology Study (Study 6.5) ISR (Section 4.1.2.3). In a next year of study, the
Fluvial Geomorphology Modeling below Watana Dam Study will quantify the hydraulic
and sediment transport behavior of the existing locations, and will provide quantitative
projections of how these areas will change in the future under both existing (no Project)
and Project conditions based on the bed evolution modeling results as well as the results
of the River1D Ice Processes Model and the River2D Focus Area Models (Study 7.6).
• The Geomorphology Study, coupled with the field data collection activities for the
Fluvial Geomorphology Modeling below Watana Dam Study, is identifying the
geomorphic characteristics (i.e., channel geometry, gradient, substrate, bank material and
vegetation) that are important drivers of habitat conditions within the side channels, side
sloughs, and upland sloughs under existing and Project conditions. The modeling,
particularly 2-D bed evolution modeling being implemented at the Focus Areas, will
provide a means of directly quantifying these processes by providing detailed hydraulic
information and projections of changes in substrate, bed elevations, and hydraulic
connectivity with the mainstem. This will include quantification of the frequency and
duration of substrate mobilization and the potential for fines infiltrations and flushing in
spawning areas. Other aspects, such as potential changes in channel width, will be
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estimated based on a combination of the model output and relevant geomorphic
relationships.
4.3.2.2. Coordination of Results with Other Resources Studies
The Fluvial Geomorphology Modeling below Watana Dam Study and Geomorphology Study
(Study 6.5) teams are interacting extensively with the Water Quality Modeling (Study 5.6),
Open-water Flow Routing Model (Study 8.5 Section 4.3), Fish and Aquatics Instream Flow
Study (Study 8.5), Riparian Instream Flow Study (Study 8.6), Groundwater Study (7.5), Ice
Processes in the Susitna River Study (Study 7.6), and Characterization and Mapping of Aquatic
Habitats (Study 9.9) study teams. The types of interaction vary depending on the specific study,
but a considerable amount of physical data describing the physical characteristics and dynamics
of the system, including transects, topography/bathymetry, substrate characterization, aerial
photography, and pre- and post-Project flows generally are being shared. Selection of joint Focus
Areas for detailed studies was an important aspect of the collaboration (R2 2013a, R2 2013b).
By selecting common sites, the potential for exchange of information between the study teams is
being maximized to ensure the most effective, integrated, and extensive use of Focus Area data.
Because of the detailed spatial nature of the information produced by the models, GIS is an
important tool for visually illustrating and conveying model results for use in the other studies.
Development of the plan for transferring results in a manner that facilitates efficient and effective
use by other studies requires considerable effort. The details of the plan are being worked out as
the overall modeling approach is being developed through informal coordination with the
respective study teams, internal team meetings, the November 2013 Instream Flow Study
Technical Team meeting, the Technical Workgroup meetings and the Proof of Concept effort in
progress. This latter effort is a demonstration of the initial integration of the various modeling
efforts being conducted under the Fish and Aquatics Instream Flow Study (Study 8.5), the Ice
Processes in the Susitna River Study (Study 7.6), Groundwater Study (Study 7.5), Water Quality
Modeling Study (Study 5.6), Geomorphology Study (Study 6.5) and Fluvial Geomorphology
Modeling below Watana Dam Study.
The 1-D and 2-D Bed Evolution models provide quantitative predictions of a range of key
variables that are directly related to the geomorphic and habitat conditions along the study reach
at a range of spatial and temporal resolutions (previously presented Table 4.3-1 and Table 4.3-2).
As noted in Table 4.3-1, the values of many of these variables can be used directly to assess
geomorphic and habitat conditions, while additional analysis of other variables outside the
context of the model is required to obtain useful predictions (Table 4.3-2). The output variables
can be broadly grouped into hydraulic conditions (water-surface elevations, depth, velocity, bed
shear stress) and sediment transport/bed morphology conditions (substrate size gradations,
sediment transport rates, changes in bed elevation).
Open-water Flow Routing Model (RSP Section 8.5.4.3): It is anticipated that the Open-water
Flow Routing Model will provide the pre- and post-Project hydrology information for all studies,
including the Fluvial Geomorphology Modeling below Watana Dam Study. This hydrology
information will include mainstem pre- and post-Project flows at various points along the study
area and inflows for gaged and ungaged tributaries. This information will be provided for the
50-year, extended flow record.
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For the Fluvial Geomorphology Modeling below Watana Dam effort, the upstream boundary
condition at PRM 187.1 (RM 184) will be the existing condition or pre-Project daily flows from
the extended flow record. For the post-Project condition, the upstream boundary condition will
be the average daily releases from Watana Dam unless load-following scenarios are evaluated.
In the latter case, the Project outflows will need to be on an hourly or possibly finer time
increment. Estimated daily inflows from tributaries provided by the Open-water Flow Routing
Model will be input along the length of the 1-D Bed Evolution Model and may be inputs to the
localized 2-D Bed Evolution models depending on the location and specific issues to be
addressed.
Fish and Aquatics Instream Flow Study(Study 8.5): The primary initial interaction with the Fish
and Aquatics Instream Flow Study was in the selection of the Focus Areas for detailed study.
Part of the selection process considered the use of the specific sites as well as the types of habitat
present at the site by target fish species. The local-scale 2-D models will be used to evaluate
instream habitat quality on a spatially-distributed basis rather than the cross-sectional-based
approach used in traditional Instream Flow Incremental Methodology (IFIM) studies.
For the Fish and Aquatics Instream Flow Study, an assessment of whether the current channel
geometry and substrate characterization used in evaluation of habitats will remain relatively
unchanged over the period of the license under both the pre- and post-Project conditions is
important. The Geomorphology Study is determining the equilibrium status of each reach such
that the distribution of habitat conditions over the timeframe of the license (assumed to be 50
years, corresponding to the maximum FERC licensing period) will be adequately reflected by
existing channel morphology. If it is determined that the river is not in a state of dynamic
equilibrium, the Geomorphology studies (Study 6.5 and Study 6.6) will provide projections of
the direction and magnitude of the changes under both existing and Project conditions. Changes
in the relative occurrence of aquatic habitat types and the associated surface area versus flow
relationships that may occur as a result of the Project are an important outcome of these studies.
As part of this evaluation, pre- and post-Project changes in channel dimensions (width and
depth) and the proportion and distribution of geomorphic features and habitat types will be
estimated for each of the delineated reach types using the channel classification system
developed for the Susitna River (Tetra Tech 2013c). This will provide the Fish and Aquatic
Instream Flow Study with an important part of the information required to evaluate the post-
Project effects on aquatic habitat. Other important information to be provided by the Fluvial
Geomorphology Modeling below Watana Dam study for the Fish and Aquatics Instream Flow
Study includes the following:
• Identification of zones of substrate mobilization, deposition, and scour at the reach scale
for pre- and post-Project flow regimes.
• Potential changes in off-channel habitat connectivity due to aggradation and degradation.
• Pre- and post-Project changes in spatial and seasonal patterns of the fine sediment (wash
load) transport and the associated Project effects on turbidity.
• Changes in substrate composition in both the main channel and off-channel habitats.
• Pre- and post-Project large woody debris (LWD) recruitment and transport.
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Riparian Instream Flow Study (Study 8.6): Riparian vegetation plays a large role in the
development of islands and off-channel habitats, primarily by protecting surfaces from erosion
and promoting sediment deposition. Vegetation can also contribute to channel narrowing by
encroaching onto bars and islands and riverward growth of banks through trapping of sediments.
Conversely, changes in the flow regime and/or ice processes can alter riparian vegetation
patterns, including the extent, species composition, and age-classes; thus, there is a feedback
mechanism between the two processes. As a result, the influence of riparian vegetation on the
morphology of the Susitna River is an important consideration in these studies. The Riparian
Instream Flow Study, Geomorphology and Fluvial Geomorphology Modeling studies are being
closely coordinated because of the interactions described above. The collaboration began with
coordinated selection of the Focus Area among the Riparian Instream Flow Study, Ice Processes
in the Susitna River Study, Geomorphology Study and Fluvial Geomorphology Modeling below
Watana Dam Study teams. By analyzing the same Focus Areas in a coordinated manner, the
teams are developing an understanding of the interaction between the processes that are
responsible for creation and maintenance of the islands and off-channel habitats (See ISR 6.5
Section 4.1.2.3). Estimates of the ages of island and floodplain surfaces from the Riparian
Instream Flow Study based on dendrochronology as well as short-lived isotope dating of
floodplain and island sediments, combined with the inundation frequencies from the 1-D and 2-D
modeling, are greatly facilitating this effort by helping to identify rates of sediment deposition
and reworking of these surfaces. Similarly, profiling of deposited sediments in the riparian
corridor to identify the types of sediments that make up the floodplain contribute to the
understanding of the physical processes and development of the functional model for linkage of
the geomorphology, riparian vegetation, and ice processes.
The results of the Fluvial Geomorphology Modeling below Watana Dam Study along with
applicable geomorphic principles will be applied to interpret model results. An understanding of
the geomorphology of the system will also be used to provide a reality check on the extent of
changes indicated by the modeling.
Examples of the linkage between the Riparian Instream Flow Study and the Fluvial
Geomorphology Modeling below Watana Dam Study include the following:
• Altering Manning’s n-values to represent establishment (increased n) or removal
(decreased n) of vegetation.
• Application of shear stress parameter to determine the erodibility of banks and potential
influence of and on vegetation.
• Interpretation of flow and sediment transport patterns to determine areas of sediment
deposition within and adjacent to vegetation.
• More accurate water-surface elevations and flow distributions from the local-scale 2-D
models than is provided by the 1-D models for periods when the flows only partially
inundate the riparian corridor.
• Estimation of the change in the rate of floodplain and island building under the with-
Project condition and between various operational scenarios. This can be accomplished
by scaling the historical rates of sedimentation developed from the Riparian Instream
Flow Study by the ratio of the with-Project rate of sediment delivery to the floodplain
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surfaces to the existing rate. The 2-D model will be applied to simulate sediment delivery
to the floodplains and islands.
• Use of geomorphic threshold relationships to understand the potential for removal of
vegetation by the flows and the potential for additional channel narrowing due to changes
in the vegetation patterns.
Ice Processes in the Susitna River Study (Study 7.6): Ice processes influence both the channel
morphology and riparian vegetation. For example, ice can prevent vegetation from establishing
on bars by annually shearing off or uprooting young vegetation and or retarding vegetation
succession. Similarly, ice can scour vegetation from the banks, increasing their susceptibility to
erosion. In both examples these influences affect channel morphology. Ice jams can also directly
influence the channel morphology by diverting flows onto floodplains where new channels can
form, particularly when the downstream water-surface elevations are low, allowing the return
flows to headcut back into the floodplain. Ice can also move bed-material that would normally
not be mobilized by rafting large cobbles and boulders. Ice may also be responsible for initiating
channel avulsion.
There is ongoing close collaboration between the Geomorphology (Study 6.5) and Ice Processes
in the Susitna River (Study 7.6) studies to identify the key physical processes that interact
between the two. Working together to analyze the conditions at the Focus Areas is a key part of
this collaboration. A significant portion of the influences of ice processes on morphology are
directly related to their effects on riparian vegetation and sediment deposition. Additionally,
influences of ice processes beyond the riparian vegetation issues that may be incorporated
directly into the Fluvial Geomorphology Modeling Study may include the following:
• Simulating the effects of surges from ice jam break-up on hydraulics, sediment transport,
and erosive forces using unsteady-flow 2-D modeling with estimates of breach
hydrographs.
• Simulating the effect of channel blockage by ice on the hydraulic and erosion conditions
resulting from diversion of flow onto islands and the floodplain.
• Use of the 2-D model output to assess shear stress magnitudes and patterns in vegetated
areas, and the likelihood of removal or scouring.
• Use of the 2-D model output to assess shear stress magnitudes and patterns in
unvegetated areas, and the likelihood of direct scour of the boundary materials.
• Application of the 2-D model to investigate whether ice jams are a significant contributor
to floodplain and island deposition as a result of ice jams inundating these features and
causing sedimentation.
Water Quality Modeling (Study 5.6): The Fluvial Geomorphology Modeling below Watana Dam
Study has two primary areas of interaction with the Water Quality Modeling Study (Study 5.6).
The first involves the determination of reservoir sediment trap efficiency. The Environmental
Fluid Dynamics Cod (EFDC) model that is being used for studying the water quality of the
reservoir, Middle and Lower Susitna River Segments is being used to perform the final
determination of reservoir sediment trap efficiency. This model is referred to as the 3-D
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Reservoir Water Quality Model. This model will provide a more accurate determination of the
fine sediment settling than use of the empirical equations that are described in RSP Section
6.5.4.8.2.1 that will be used for the initial estimate of trap efficiency. The Geomorphology Study
(Study 6.5) will provide the Water Quality Modeling Study (Study 7.6) with the sediment inflow
to the reservoir based on the sediment supply analysis conducted in Tetra Tech 2013a. If
necessary, the effects of glacial surges on sediment supply will be incorporated into the reservoir
sediment supply by coordination with the Glacier and Runoff Changes Study (Study 7.7).
The second area of interaction is the routing of fine sediment, silt and clay, downstream. Both
the 1-D Bed Evolution Model from this study and the 2-D version of the EFDC model from the
Water Quality Modeling Study will route portions of the fine sediment load in the Middle
Susitna River Segment and the Lower Susitna River Segment. This model is referred to as the 2-
D River Water Quality Model. The Water Quality Modeling Study models are focused on the silt
and clay portion (finer than 0.0625 mm) of the fine sediment load in order to estimate the Project
effects on turbidity. The Fluvial Geomorphology Modeling below Watana Dam Study is
primarily interested in fine sediment load in the sand range (0.0625mm to 2mm) to evaluate
Project effects on the volumes of sediment available for deposition in the main channel, off-
channel and floodplain areas. The two models will overlap in the routing of the very fine sand
range (0.0625mm to 0.125mm).The results of each model for the very fine sand range in terms
volumes and concentrations will be compared to insure consistency.
4.3.2.3. Information Required
The following available existing information is needed to conduct this component of the
modeling study:
• Study plans, technical memorandums, and reports for other studies
The following additional information is being obtained to conduct this component of the
modeling study:
• Locations of sites for other studies
• Lists of output required for other studies, including list of key habitat indicators.
• Output formats required for other studies
• Schedule dates for providing output
4.3.3. Variances from Study Plan
AEA implemented the methods as described in the Study Plan with no variances.
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5. RESULTS
5.1. Study Component: Bed Evolution Model Development,
Coordination, and Calibration
The preliminary results of the three tasks of this study component are discussed below. The
modeling approach has been more thoroughly defined with input from the other study
components and agencies. Initial model development has occurred and test simulations have
been performed, but final development and calibration has not as yet been conducted.
5.1.1. Development of Bed Evolution Model Approach and Model Selection
This section documents the results of the selection of the 1-D and 2-D Bed Evolution modeling
software for the project and the model development conducted to date. More detail is provided in
Tetra Tech (2013h).
5.1.1.1. Model Selection
5.1.1.1.1. One-Dimensional (1-D) Bed Evolution Model Selection
The HEC-6T software was initially selected for the 1-D Bed Evolution modeling (Tetra Tech
2013h); subsequently the selection was revised to HEC-RAS Version 4.2.0 beta based on it being
made available to the Geomorphology Study team (Table 5.1-1). Whether HEC-6T or HEC-
RAS Version 4.2.0 are ultimately used for final modeling, the model development is most
efficiently performed using the HEC-RAS interface.
5.1.1.1.2. Two-Dimensional (2-D) Bed Evolution Model Selection
Two 2-dimensional sediment transport models (River2D and SRH-2D) were selected for further
evaluation based on recommendations reported in the Fluvial Geomorphology Modeling below
Watana Dam Approach technical memo (Tetra Tech 2013h). Originally, there were five 2-D bed
evolution models considered for the study, however, three of these models were dropped because
they did not meet the selection criteria. A full description of the River2D and SRH-2D models is
provided Tetra Tech (2013h) and a summary of the model evaluation criteria is listed in Table
5.1-2. An evaluation of the SRH-2D and River2D models is underway with habitat and sediment
transport meshes being constructed for both models for FA-104 (Whiskers Slough) and FA-128
(Slough 8A), resulting in a total of 8 models.
5.1.1.2. Model Development
5.1.1.2.1. Overview of 1-D Bed Evolution Model Development
Model development effort conducted in 2013 thus far has followed the steps 1 through 3 outlined
in Section 4.1.2.1.2 and in the Fluvial Geomorphology Modeling Approach (Tetra Tech 2013h).
1. Determine the overall model layout.
• The model domain extends from Susitna River PRM 29.9 to Susitna River PRM
187.1. The downstream boundary was selected to correspond with a location of
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known stage-flow conditions, namely the USGS gage at Susitna Station (USGS Gage
15294350). The upstream boundary is located at the site of the proposed Watana
Dam, and therefore corresponds with a location of known discharge and sediment
supply for both the pre- and post-Project conditions. Discharge at this location for
both the pre-Project and post-Project conditions will be provided by the Open Water
Flow Routing and Reservoir Operations Modeling (ISR Study 8.5 Section 4.3).
• Sediment supply for the pre-Project condition will be developed by scaling the
sediment-rating curves for the Susitna River at Gold Creek USGS gaging station.
Sediment supply for the post-Project condition will be provided by the Water Quality
Modeling Study (ISR 5.6).
• The tributaries that will be incorporated as reaches with moveable bed in the 1-D Bed
Evolution Model include the Talkeetna River and the Chulitna River. Other Susitna
River tributaries will be included in the model as flow and sediment inputs, but will
not be included in the model for hydraulic or sediment routing. At this time, twenty
(20) tributaries have been identified for inclusion in the model as a flow and sediment
input, as listed in Table 5.1-3. Sediment-rating curves will be developed for each of
these tributaries as part of this study; however, the tributary hydrologic flow series
will be developed as part of the Fish and Aquatics Instream Flow Study (ISR Study
8.5 Section 4.3).
• Preliminary split flow reaches for the Susitna River and Talkeetna River were
identified for inclusion in the reach scale 1-D Bed Evolution Model, as shown in
Figures 5.1-1 through 5.1-8. A total of fourteen (14) preliminary split flow reaches
were identified on the Susitna River and one (1) split flow reach was identified on the
Talkeetna River. No split flow reaches were identified within approximately the
downstream-most 10 miles of the Chulitna River included in the model. On the
Susitna River, split flow reaches were identified if (1) they are located within a focus
area, or (2) if they are located where a modeled tributary (see Table 5.1-3) enters the
Susitna River, thus ensuring that the sediment and discharge from the tributary enters
the appropriate channel (main channel or side channel). As the model development
progress, these split flow delineations may be revised and additional split flow
reaches may be added.
2. Develop cross-section data.
• Preliminary Susitna River, Talkeetna River and Chulitna River cross section locations
were identified to represent the channel network. A total of 242 cross sections were
identified for the Susitna River; a total of 14 cross sections were identified for the
Talkeetna River, and a total of 17 cross sections were identified for the Chulitna
River (see Figures 5.1-1 through 5.1-8). The upstream modeled extent on the
Chulitna River is approximately 10 miles upstream of the confluence with the Susitna
River, at a location of channel narrowing. The upstream modeled extent on the
Talkeetna River is the existing USGS gaging station. During model development, it
will be necessary to interpolate additional cross sections between the surveyed cross
sections to maintain model stability. These preliminary locations include
hydrographic cross section surveys that were completed in 2012 and 2013. These
preliminary locations also include hydrographic cross section surveys that may be
collected in a next year of the Study.
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• Only a portion of each cross section has been/will be field surveyed, generally the
below-water areas and the exposed gravel bars. For input to the model, the field
surveyed data will be merged with the LiDAR data to create a composite cross
section. Figure 5.1-9 is an example of a merged cross section at PRM 117.9. Several
cross section locations, namely in the Chulitna River and in Devils Canyon, will not
have hydrographic surveys available. For the Chulitna River sections, bathymetric
geometry will be developed from the LiDAR data and surveyed bathymetry from the
lower Chulitna River. The LiDAR data will be used to estimate water-surface slope
(elevation drop over channel distance). Using slope, roughness, discharge, and flow
top-width, the flow area will be estimated to calculate an average depth at each cross
section. The channel form from the surveyed cross sections will used to guide the
development of the below water channel shape. This approach is feasible because the
LiDAR will be collected at low flow when depths are shallow on this wide and
braided section of the Chulitna River. Within Devils Canyon, no bathymetric
geometry will be estimated; this approximation is suitable since the reach is bedrock
lined and will convey sediment without appreciable changes in channel geometry.
• Preliminary flow paths were delineated to represent the main channel and floodplain
areas. These flow paths provide the basis for stationing between cross sections; the
different floodplain and channel paths allow for different distances. The channel flow
path was delineated with consideration of its use for representing the volume of bed-
material (i.e., length of channel multiplied by the width between moveable bed
limits); this consideration was particularly important in the Lower Susitna River
Segment where multiple braided channels exist within the banks of the main channel.
The floodplain flow paths are supposed to follow the centroid of flow in the
overbank; during model development these flow paths may be revised if preliminary
results show appreciable different flow centroids.
3. Develop flow resistance (roughness) data for cross sections.
• Preliminary initial estimates of the Manning’s roughness coefficient for the channel
and the floodplain were defined and are summarized in Table 5.1-4. The Manning’s
roughness coefficient is one of the parameters that will be used to calibrate the
hydraulics of the 1-D Bed Evolution Model. As such, the preliminary initial
estimates listed in Table 5.1-4 are simply a starting point from which to initiate model
calibration.
5.1.1.2.2. Overview of 2-D Bed Evolution Model Development
As described in Section 5.1.1.1.2, River2D and SRH-2D are being evaluated the input data,
model parameters and model output for both of the preliminarily selected modeling software are
generally similar; some differences in the models are described in the following discussion. The
types of data used to develop the models are summarized in Table 5.1-5.
A preliminary SRH-2D habitat model (hydraulic fixed bed model) of FA-104 (Whiskers Slough)
has been developed and run and is used as an example in the following discussion to show the
2-D Bed Evolution Model development steps. The Whiskers Slough Focus Areas was selected
through coordination with the Fish and Aquatics Instream Flow Study (Study 8.5) because it was
the first to have complete bathymetry and LiDAR and was used to demonstrate linkage between
hydraulic results and habitat analyses for the Modeling Technical Team Meeting on
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November 13–15, 2013. The model development follows Steps 1 to 5 outlined in Section
4.1.2.1.2 and in the Fluvial Geomorphology Modeling Approach (Tetra Tech 2013h).
1. Determine the overall model layout.
• Downstream boundary stage-flow conditions were developed from Open-water Flow
Routing Model developed by R2 Resource Consultants, Inc.
• For the purpose of the example runs for the Technical Team Meeting, the upstream
(i.e., inflowing) discharges for the habitat analysis (2,000, 6,000, 14,000 and 24,000
cfs) were specified by the Fish and Aquatics Instream Flow Study team and a
discharge of 100,000 cfs was selected by this study to perform an initial evaluation of
the channel capacity.
• Applicable inflows from Whiskers Creek tributary were also included.
2. Develop geometric base data.
• Data from TIN (Triangulated Irregular Network) and 2013 LiDAR survey were used
to assign elevations to the mesh nodes. Figure 5.1-10 shows a TIN that was developed
from the land and bathymetric survey data collected by Brailey Hydrologic
Consultants and Geovera. The TIN was used to assign elevations primarily to the in-
channel portions of the 2-D model. Figure 5.1-11 shows the 1-foot contour mapping
for FA-104 (Whiskers Slough) developed from the TIN.
• Data from the 2013 LiDAR bare earth data set was used to assign elevations to the
un-surveyed island and floodplain areas. Figure 5.1-12 shows a 2-foot interval
contour mapping developed from the LiDAR data that was used to assign elevations
primarily to the un-surveyed island and floodplain areas of the 2-D model.
3. Develop model network.
• The mesh extents are evaluated on a site-by-site basis. For example, the downstream
boundary of the 2-D model is located at the downstream boundary of the Focus Area
(Figure 5.1-13), whereas, the upstream boundary of the 2-D model is located
approximately 1.4 miles upstream of the Focus Area boundary to provide better
prediction of the flow distribution in the vicinity of the upstream end of the Focus
Area and to evaluate the channel capacity between the upstream end of the Focus
Area and the upstream end of the model.
• The node and element locations and configurations are located to accurately represent
the channel and overbank topography and changes in roughness. The SRH-2D
meshes are composed of triangular and quadrilateral elements whereas the River2D
meshes are composed entirely of triangular elements. The meshes are refined in areas
of appreciable change or areas of significant habitat interest.
• Node elevations were determined from the TIN and LiDAR from Step 2, above.
• A review of the mesh quality was conducted to ensure that element size transitions
and other modeling requirements are reasonably met. These include increased mesh
refinement where there is appreciable geometric change or where velocity magnitude
or directions changes occur.
4. Develop flow resistance (roughness) and turbulence stress data.
• The bed-material sizes are being evaluated and will be used in conjunction with the
substrate mapping to develop channel roughness values.
• The channel bank and floodplain (overbank) roughness values were developed based
on land use, vegetative ground cover, and obstructions using field observations and
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aerial photography. Initial Manning’s n-values (Table 5.1-4) have been developed and
correlate to the geomorphic surface mapping (Figure 5.1-14). The Manning’s n-
values will be adjusted on a site-by-site basis, including potential influence from
LWD, during model calibration.
• The two models under consideration apply different methods to predict the turbulence
energy losses. The SRH-2D model uses turbulence models (parametric or k-ε) and the
River2D model uses eddy viscosity coefficients. The parameters in turbulence models
and/or the eddy viscosity coefficients will be calibrated using the ADCP data, which
was not yet processed during this preliminary example run.
5. Develop bed and bank material gradation and layer information.
• The bed surface, sub-surface and bank material sampling data will be evaluated in
conjunction with the channel substrate mapping to develop spatially representative
sediment gradations and bed layers for input to the bed evolution models. For the
initial model runs, a uniform n-value of 0.03 was applied to the main and side
channels (Table 5.1-4).
5.1.2. Coordination with other Studies
The coordination between various studies has contributed greatly to development of the Fluvial
Geomorphology Modeling Study below Watana Dam. The nearly continuous coordination has
taken place with the Geomorphology Study (Study 6.5), Fish and Aquatics Instream Flow Study
(Study 8.5), Riparian Instream Flow Study (Study 8.6), Ice Processes in the Susitna River Study
(Study 7.6), Groundwater Study (Study 7.5), Water Quality Modeling Study (Study 5.6), and
Characterization and Mapping of Aquatic Habitats (Study 9.9). Coordination has also occurred
with the Glacier and Runoff Changes Study (Study 7.7), Study of Fish Distribution and
Abundance in the Upper Susitna River (Study 9.5), Study of Fish Distribution and Abundance in
the Middle and Lower Susitna River (Study 9.6), Study of Fish Passage Feasibility at Watana
Dam (Study 9.11), Study of Fish Passage Barriers in the Middle and Lower Susitna River and
Susitna Tributaries (Study 9.12), Eulachon Run Timing, Distribution and Spawning in the
Susitna River (Study 9.16), Cook Inlet Beluga Whale Study (Study 9.17), Riparian Vegetation
Study Downstream of the Proposed Watana Dam (Study 11.6), River Recreation Flow and
Access Study (Study 12.7), Probable Maximum Flood Study (Study 16.5) and Special Seismic
Hazard Study (Study 16.6).
As examples of the outcome of this coordination the following items are listed:
• Modeling Approach TM (Tetra Tech 2013h)
• Selection of Focus Areas and their extents (R2 2013a and 2013b)
• Extension of the downstream study limits for the 1-D Bed Evolution Model
• Identification of appropriate 2-D Bed Evolution and Hydraulic models mesh size
• Continued development of the Proof of Concept modeling effort
• Selection of representative hydrologic years (wet, average and dry) and the 50 year
record
• Identification of model precedence for various parameters
• Selection of Middle and Lower River tributaries for analysis in the Fluvial
Geomorphology Modeling below Watana Dam Study
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A large portion of the data being used by the Fluvial Geomorphology Modeling below Watana
Dam Study was collected partially or in cooperation with other studies. This includes:
• Survey of 1-D Bed Evolution Model mainstem and tributary cross sections
• Survey 2-D Bed Evolution Model (Focus Area) bathymetry and topography
• 1-D and 2-D model calibration information including:
Spot survey of water surface elevations
Continuous recordings of water surface elevations
Flow distribution and split flow locations
Velocity and depth ADCP measurements in Focus Areas
• Ages of floodplain surfaces
• Stratigraphy of floodplain deposits
• Gaging of tributary flows
• Evidence and influences of ice processes including:
Mapping of ice scars
Locations and characteristics of current and historical breakup jams
Hydraulic conditions during ice cover
• Mapping of floodplain vegetation
• Mapping of substrate (bed material) in Focus Areas
As the studies progress in a next year of study, the level of coordination and integration will
continue to increase among the various studies. Section 5.3 provides a description of the
Coordination and Integration of Modeling Results.
5.1.3. Model Resolution and Mesh Size Considerations
The flexible mesh formulation available in the SRH-2D and River2D models is ideal for
obtaining detailed results in areas of significant change or interest. As mentioned previously, an
initial SRH-2D habitat model has been developed and run. Figure 5.1-13 (previously presented)
shows the extents and mesh resolution of the SRH-2D habitat model which contains
approximately 164,000 elements.
Based on input from the aquatic and riparian habitat analysis teams, and specified in the Fluvial
Geomorphology Modeling Approach (Tetra Tech 2013h), the elements in the habitat mesh range
in size from approximately 5 to 100 feet. Areas were identified by the aquatic habitat team
members (Figure 5.1-15) to be modeled at the specified mesh resolution of 6.5 feet (2 m), which
is sufficient to describe the variability in hydraulic conditions that is necessary for the habitat
analysis. Figure 5.1-13 is an example of the mesh requirements of the 2-D Hydraulic Models
used for aquatic habitat analysis; the darker areas located within the FA represent the fine mesh
(Figure 5.1-15). Figure 5.1-16 shows a close up view of the fine mesh in the FA-104 (Whiskers
Slough) SRH-2D model near the mouth of Whisker Creeks. Element sizes of up to 30 feet
(~10 m) are used for the non-habitat areas of the main channel, and up to 100 feet (~30 m) in
floodplain areas. The element sizes transition smoothly between these ranges to maintain good
mesh quality.
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For the 2-D Bed Evolution Models, the element sizes are as large as practicable, but with
sufficient detail to represent variability in bathymetry, topography, roughness, and bed
composition. Figure 5.1-17 shows an example of the coarser mesh developed for the SRH-2D
sediment transport model. The size of the elements in the main channel are on the order of 50 to
75 feet in width and the mesh contains approximately 10,000 elements, which is significantly
less than the 16,000 element limit of SRH-2D.
5.1.4. Focus Area Selection
Table 5.1-6 lists the Focus Areas, the upstream and downstream limits, the associated
geomorphic reach, and the geomorphic reach type. The Focus Areas represent five areas within
the SC2 reach type, four within the SC3 reach type, and one within the transitional MC1/SC2
reach type. The SC1 channel type is very confined and typically single channel and therefore 1-D
Bed Evolution Modeling efforts are adequate to identify project effects. The locations of the
Middle Susitna River Segment Focus Areas are shown on Figure 5.1-18. More detailed maps
that show individual proposed Focus Areas on recent (2011) color aerial photographs are
provided in the Fish and Aquatics Instream Flow Study (Study 8.5 ISR Section 4.2.1.2.1).
The upstream boundary of the FA-104 (Whiskers Slough) 2-D Bed Evolution model is located
approximately 1.4 miles upstream of the Focus Area boundary. The upstream boundary for the 2-
D model was moved to evaluate the main channel discharge required to initiate flow into an
upland side slough located on the right overbank. The downstream boundary of the FA-104
(Whiskers Slough) 2-D model is located at the Focus Area boundary.
At FA-128 (Slough 8A) the downstream boundary of the Focus Area is located near the
downstream end of an island. The 2-D Bed Evolution model boundary was moved approximately
250 feet downstream of the Focus Area boundary (and island) to provide more uniform hydraulic
conditions across the channel and better prediction of the hydraulic conditions at the Focus Area
boundary. The upstream 2-D model boundary of the FA-128 (Slough 8A) coincides with the
Focus Area boundary. The mesh extents of the other Focus Area 2-D Bed Evolution Models are
being evaluated on a site-by-site basis and it may be necessary to extend the model boundaries
outside of the Focus Areas to improve the model performance.
This expansion of efforts outside the Focus Area boundaries has already been applied to a
portion of the Geomorphology Study. In order to adequately develop a geomorphic narrative for
the Focus Areas (i.e. identify geomorphic trends and processes), the area of study was extended
either upstream, downstream or both, from the Focus Area boundaries. These expanded areas of
geomorphic study are hereby referred to as Geomorphic Assessment Areas (GAAs) and
correspond with each of the 2013 studied Focus Areas. Table 5.1-7 identifies each GAA and
defining PRM boundaries. Names of GAAs correspond to the numerical and common naming
convention for Focus Areas. The geomorphic characterization of the 7 Focus Areas and the
corresponding GAAs is provided in Geomorphology Study (ISR 6.5 Sections 4.1.2.3 and 5.1.3).
5.1.5. Model Calibration and Validation
This section briefly describes the model calibration and validation results to date for both the
reach-scale 1-D Bed Evolution Model and the 2-D Bed Evolution and Hydraulic models.
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5.1.5.1. One-Dimensional (1-D) Model
The reach-scale 1-D Bed Evolution model is currently in the process of being developed.
Preliminary model calibration and validation will be performed in 2014 from PRM 187.1 to
PRM 29.9 per the procedures outlined in the 1-D Bed Evolution Model development (Section
4.1.2.5.1 and Tetra Tech 2013h).The results will be reported on in 2014 as part of the Proof of
Concept for the overall aquatic resources modeling effort. There are therefore no model
calibration and validation results to present at this time.
5.1.5.2. Two-Dimensional (2-D) Bed Evolution Model
Through 2013, the model development process for both FA-104 (Whiskers Slough) and FA-128
(Slough 8A) has concentrated on the development of the hydraulic and sediment transport
meshes. The initial step in the calibration process has been started at FA-104 (Whiskers Slough)
as models runs for three n-values have been conducted. The 2-D Bed Evolution models are
being calibrated and validated following the procedures outlined in 2-D model development
(Section 4.1.2.5.2 and Tetra Tech 2013h). Velocities and flows from ADCP measurements are
being used to calibrate the split flows between the various channel elements and velocities and
velocities and locations within the mesh. Figure 5.1-15 (previously presented shows locations of
the ADCP measurements being used in FA-104 (Whiskers Slough) for this purpose.
The SRH-2D habitat model was run using the parameters described previously for the specified
habitat flows of 2,000, 6,000, 14,000, and 24,000 cfs. In addition, the model was run at 100,000
cfs (the 100-year peak flow event is 98,000 cfs) to provide an estimate of the channel capacity
and overtopping discharges of the geomorphic surfaces.
Figures 5.1-19 and 5.1-20 show the predicted depth and velocity distributions, respectively, at
24,000 cfs. In general, the depths in the main channel range from 6 to 12 feet and the velocities
range from 4 to 7 fps. The model output at 100,000 cfs indicates that the flow depths range up to
20 feet near the upstream end of the model (Figure 5.1-21)and velocities generally range from 8
to 13 fps along the main channel (Figure 5.1-22). Although these results are preliminary, they
indicate that open-water conditions may not significantly inundate island and overbank areas at
this Focus Area even at 100-year flow conditions.
5.1.6. Tributary Delta Modeling
Preliminary selections of 20 tributary deltas to be modeled were based on existing fish use and
the potential for Project effects, as determined in coordination with the instream flow and fish
and aquatic resources studies and the licensing participants (Table 5.1-3). The preliminary
selections included 5 tributaries to the Lower River (Figure 5.1-23), and 15 tributaries to the
Middle River, of which 11 enter the Susitna River within a focus area (Figure 5.1-24).
Reconnaissance was planned for 13 tributary deltas during the 2013 field season (Table 5.1-6);
however, reconnaissance was carried out at 10 tributaries to the Middle River, and only two
tributaries to the Lower Susitna River Segment (Table 5.1-8). Due to private landowner access
issues at Birch Creek in the Lower River, no reconnaissance or survey could be conducted. Due
to access limitations upstream of PRM 146.1 during the 2013 field season, data collection at five
of the selected Middle River tributaries could not be conducted, but is planned for in a next year
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of the study. Thus, final selections were confirmed at 11 of the 12 tributaries where
reconnaissance was carried out during 2013. Observations made during the reconnaissance at
the unnamed tributary (PRM 115.4) confirmed that no appreciable amount of sediment was
delivered from the watershed, and that no delta was present. It was decided that there would be
no value in modeling this tributary to characterize sediment loading for input to the 1-D and 2-D
Bed Evolution models (Section 4.1.4). This decision was coordinated with the Study of Fish
Passage Barriers in the Middle and Upper Susitna River and Susitna Tributaries (Study 9.12),
and since this tributary is not included within the scope of that study, there is no need to assess
potential Project effects on the ability of fish to access the tributary. Thus, the unnamed tributary
(PRM 115.4) will be excluded from tributary delta modeling.
HEC-RAS models have been developed for 11 tributaries near their confluences with the Susitna
River (Table 5.1-8); nine models are for tributaries to the Middle Susitna River Segment and the
remaining two models are for tributaries to the Lower Susitna River Segment. In general, the
cross section geometry and bed profiles were surveyed during the 2013 reconnaissance. Energy
losses in the models were quantified using (1) roughness heights based on average bed surface
gradations sampled during the reconnaissance, and (2) expansion and contraction coefficients
based on professional judgment. Downstream boundary conditions for the models were set to
normal depth. Preliminary hydraulic calibration was completed by adjusting initial roughness
heights so that the simulated water-surface profiles visually aligned with surveyed water-surface
elevations. The hydraulic calibration is limited because flows during the surveys were not
measured; rather, the flows were visually estimated. Preliminary hydraulic calibration could not
be completed for tributaries that were dry. Sieve analysis results for the finer gravel and sand
component of the bed material have only recently been returned from the lab, so the sediment
transport analyses are just now getting underway. Bed-material sediment transport curves have
not yet been developed, but the calculations of sediment loading are also awaiting the
synthesized flow series (ISR Study 8.5 Section 4.3).
The hydraulic models developed for the two tributaries to the Lower Susitna River Segment
(Deshka River and Trapper Creek) have greater modeled lengths than the models for the nine
tributaries to the Middle Susitna River Segment (Table 5.1-6). These greater lengths were
necessary to encompass (1) potential post-Project backwater effects and (2) holding habitat for
targeted fish species accessing the tributaries. Since these tributary channels cross the extensive
floodplains along the Lower Susitna River, the slope of the channels is approximately two orders
of magnitude flatter than the tributary channels that enter the Middle Susitna River, so the
potential backwater influence could affect greater tributary channel length. The Deshka River
hydraulic model was developed from nine cross section surveys that were conducted on October
4, 2013 by Geovera LLC as part of the Fish and Aquatics Instream Flow Study (Study 8.5).
Geometry for a tenth cross section, located just upstream of the confluence with the Susitna
River, was estimated from depth readings taken from a boat traveling across the river by Tetra
Tech on September 26, 2013. The hydraulic model includes the lower 5.8 miles of the Deshka
River. The Trapper Creek hydraulic was developed from a total of 14 cross section surveys, 4 of
which were conducted between June 16th and June 20th, 2013 by Geovera LLC as part of the Fish
and Aquatics Instream Flow Study (Study 8.5) and 10 of which were conducted by Tetra Tech
between September 20th and September 23rd, 2013. The hydraulic model includes the lower 0.5
miles of Trapper Creek. Hydraulic calibration of both the Deshka River and Trapper Creek
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models is currently underway, using flow rates from installed flow gages and water surface
elevations surveyed during the cross section surveys.
Since the estimates of sediment loading are an input to modeling tributary deltas, and the
sediment loads are not yet quantified, no delta modeling results are available.
5.1.7. Large Woody Debris Modeling
There are as yet no results relevant to LWD modeling. The existing conditions models will have
calibrated Manning n values that include LWD effects. For simulations of operational scenarios,
the channel roughness parameters will be evaluated and adjusted based on anticipated changes in
LWD loading. There is significant information regarding LWD in the Geomorphology Study
(ISR 6.5 Section 5.9 and Appendix D).
5.1.8. Wintertime Modeling and Load-Following Operations
There are no results to report on any of the winter conditions modeling or load-following
operations. These operational scenario simulations will be conducted after calibrated existing
conditions models are developed. Winter condition models will also be developed after open
water models are developed as part of this study component and information is available from
the Ice Processes in the Susitna River Study. The Fluvial Geomorphology Modeling below
Watana Dam Study will not be executing winter load-following models, but will use results from
the Ice Processing in the Susitna River (ISR Study 7.6) modeling to evaluate the potential for
mobilization of bed material during winter load-following operations.
5.1.9. Field Data Collection Efforts
Field data presented in this section were collected in 2013 to support both the Geomorphology
Study and the Fluvial Geomorphology Modeling below Watana Dam Study. The types of data
include:
1. Inputs to the 1-D Bed Evolution Model
a. Hydraulic observations, and
b. Sediment sampling
2. Characterization of Focus Areas
3. Characterization of tributary deltas
4. Data collected from other studies, and
5. LiDAR verification and acquisition
5.1.9.1. Inputs to 1-D Bed Evolution Model
Field data were collected in 2013 to support the development and calibration of the hydraulic
component of the 1-D Bed Evolution Model, as well as the development of the sediment
transport component of the model.
Hydraulic Observations: Hydraulic observations were conducted in the Lower and Middle
Susitna River Segments and at the Focus Areas. These observations included a combination of
the following: characterization of the bank and overbank roughness, water-surface elevation
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measurements, and characterization of the bank geometry. Twenty cross-section roughness
observations and water-surface measurements were collected along the Susitna River and 8
cross-section roughness observations and water-surface measurements were collected at the
Focus Areas (Table 5.1-9). A total of 85 water-surface elevation measurements were collected at
65 locations as part of the Geomorphology and Fluvial Geomorphology Modeling below Watana
Dam studies (ISR Section 6.5 and 6.6, respectively) (Appendix D). Repeat measurements were
collected at 17 locations and at varying discharges. Forty of the 85 water-surface elevations
measurements, were collected between PRM 101.5 and PRM 143.9 during the mid-August high
water period when the discharge at Gold Creek gage varied from 30,000 cfs to 43,600 cfs; these
measurements will provide valuable data to calibrate the 1-D and 2-D Bed Evolution models.
Bank profile observations were conducted at 30 locations along the Susitna River and at 6
locations in the Focus Areas.
Sediment Sampling: A summary of the number of sediment samples collected along the Susitna
River and tributaries is summarized in Table 5.1-10. Figure 5.1-25 shows an example of the
number and spatial distribution of the sediment sampling conducted at FA-104 (Whiskers
Slough). The locations and representative grain sizes of the surface (pebble counts) and
subsurface samples measurements (bulk samples and sieve samples) are reported in tables in
Appendix A and mapping of the sediment sampling locations in the other 6 Focus Areas are
shown in Appendix B.
Eighty-three surface (pebble counts) and associated subsurface samples (sieve samples) were
collected along the Susitna River and tributaries (Table 5.1-10). It is important to note that
typically 3 pebble counts were collected at each subsurface sampling location. The 3 pebble
counts were combined into a single representative sample, and therefore, the total number of
pebble counts is underrepresented in Table 5.1-10. A total of 314 pebble counts were collected in
2013. Of the 83 co-located surface/subsurface measurements, 16 were collected in the Lower
River, 22 were collected along the Middle River in areas outside of the Focus Areas, 32 samples
were collected in the Focus Areas and 13 were collected at tributaries.
An additional 56 surface samples (pebble counts) were collected along the Susitna River with 5
of these in the Middle River outside of the Focus Areas, 51 in the Focus Areas, and 12 at the
tributaries (Table 5.1-10).
One bulk sample was collected along the Susitna River, two were collected at FA-104 (Whiskers
Slough) and 11 were collected at tributaries.
Tests of subaqueous image acquisition of bed material at FA-104 (Whiskers Slough) near PRM
105 and at discharge measurement transect ESS40 near PRM 107 was performed on March 20
and 21, respectively. The images were acquired by auguring holes through the ice and lowering a
pole attached with a camera, light and dual laser beams. A total of 5 combinations of camera
type, camera mode, and light type were tested for acquiring bed-material images at Whiskers
Slough site and 10 combinations were used at the ESS40 site. Each location offered varied water
depth and velocities, frazil ice and ice thickness conditions. The images were reviewed and
assigned quality grades ranging from poor to fair to good, with grades of good being useful for
determining channel bed gradation.
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At the Whiskers Slough site, only one combination achieved the image quality grade of good.
That combination was with the GoPro camera, operated in video mode, and using the Princeton
Tec scuba flashlights (Figure 5.1-26). Frazil ice, turbidity, and other moving objects were not an
issue at this site, located off of the main channel. Additionally, water velocities were low and not
an issue for securing or operating the equipment.
At the ESS40 site, all combinations with the GoPro camera achieved a grade of good for image
quality. Similarly for the AquaVu camera, nearly all combinations achieved the grade of good
with the exception of the combination including the AquaVu camera with the Princeton Tec
scuba flashlights. Both combinations tested for the Wide-I and SplashCam were unsuccessful
and images could not be acquired with this equipment at ESS40.Good scene illumination was
available and both the AquaVu and GoPro cameras without lights achieved good image quality
grades. Figure 5.1-27 illustrates an example of the GoPro streambed-material sample image
acquired at ESS40 with the use of underwater lights, and Figure 5.1-28 is an example of the
GoPro acquired sample image without the use of lights. The sample hole at ESS40 had a water
depth of 10.4 feet and included an ice thickness of approximately 3.8 feet, minimal snow cover,
and some frazil ice. High flow velocities were also present, but did not impact the use of
submerged equipment, which could be kept vertical during insertion and removal from the ice
hole.
A total of 63 bank material samples were collected in the Middle Susitna River. All but6 samples
were collected at Focus Areas. At some bank locations, multiple samples were collected to
characterize the different materials comprising the bank. For example, at Whiskers Creek, there
were 4 locations that up to 3 samples were collected (Figure 5.1-25). The results from the
laboratory sieving of all the collected samples has been completed and a list of the samples and
gradation characteristics are listed in Appendix C.
5.1.9.2. Focus Areas
The data collected in the Focus Areas was conducted as part of the overall data collection effort
and was collected by various studies including the Geomorphology and Fluvial Geomorphology
Modeling below Watana Dam Studies (ISR Study 6.5) and the Fish and Aquatics Instream Flow
Study (Study 8.5). The data collected within the Focus Areas has been described elsewhere in
this report and by other studies. The following data were collected (Note: The numbering follows
the items listed in Section 4.1.2.9.2.):
1. Bathymetry (single beam), cross-section data, and spot elevation data were collected and
reported by the Fish and Aquatics Instream Flow Study (ISR Study 8.5).
2. Documentation of the obstructions in the off-channel habitats was conducted as part of
the Geomorphology Study and is reported in ISR Study 6.5 (Section 5.1.3).
3. Large woody debris survey and characterization was conducted and is reported in ISR
Study 6.5 (Section 5.9).
4. Bed-material samples in the main channel, sloughs, and side channels was conducted and
reported in Section 5.1.9.1.
5. Bank material sampling was conducted and reported in Section 5.1.9.1.
6. Spot elevations to verify LiDAR in the Focus Area were conducted and reported in
Section 5.1.9.5.
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7. Estimation of n-values in the channels, side channels, sloughs, and tributaries was
conducted and reported in Section 5.1.9.1.
8. Observations on depositional or erosional features were conducted in the Geomorphology
Study and are reported in ISR Study 6.5 Section 5.1.3.
9. Field verification, and correction and/or mapping of the geomorphic features, geologic
controls, and terraces were conducted and are reported in the Geomorphology Study and
are reported in ISR Study 6.5 Section 5.1.3.
10. ADCP measurements were collected by the Fish and Aquatics Instream Flow Study (ISR
Study 8.5).
11. Installation of level loggers and associated readings to support calibration of water
surface elevations was conducted by the Fish and Aquatics Instream Flow Study (Study
8.5) and Groundwater Study (Study 7.5).
12. Current meter measurements of velocity were not collected because all velocity
measurements were conducted using ADCP by the Fish and Aquatics Instream Flow
Study (Study 8.5).
13. Identification and mapping of evidence of ice processes at the site along with
observations of their potential influence on the geomorphology of the Focus Area were
conducted as part of the Geomorphology Study and are reported in ISR Study 6.5
(Section 5.1.3) in the Ice Processes in the Susitna River Study (Study 7.6) and in the
Riparian Instream Flow Study (Study 8.6).
14. Evidence of past extreme events was documented as part of the Geomorphology Study
and reported in ISR Study 6.5 Section 5.1.3.
15. An overall narrative description and assessment of the geomorphology of the Focus Area
including identification of key physical processes and controls was developed as part of
the Geomorphology Study and reported in ISR Study 6.5 Section 5.1.3.
16. Water surface elevations were measured and reported by the Fish and Aquatics Instream
Flow Study (Study 8.5) and by the Fluvial Geomorphology Modeling below Watana
Dam Study (Section 5.1.9.1).
5.1.9.3. Tributary Deltas
Nine tributaries were surveyed in the Middle Susitna River between PRM 105.1 and PRM 144.6,
and two tributaries were surveyed in the Lower Susitna River Segment. It was originally
anticipated that 20 tributaries would be surveyed (Table 5.1-3), however, for various reasons,
including limited access, 9 tributaries were not surveyed in 2013. Preliminary hydraulic models
have been developed for each of the 11 surveyed tributaries. Table 5.1-8 summarizes the number
of cross-sections, length of the study reach (model length), average channel width, and average
channel gradient of the tributary delta sites, and Table 5.1-11 summarizes the associated
sediment gradation parameters of the surface and subsurface samples at the tributary delta study
sites.
5.1.9.4. Field Data from Other Studies
Field data collected from other studies include:
1. Cross section surveys (Study 8.5)
2. Bathymetric surveys within Focus Areas (Study 8.5)
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3. Water-surface elevation (WSE) measurements (Studies 8.5 and 7.5)
4. Bed-material (substrate) mapping (Study 8.5)
5. Acoustic Doppler Current Profiler (ADCP) measurements (Study 8.5)
6. Stage hydrographs (Studies 8.5 and 7.5), and
7. Sediment transport measurements performed by the USGS (Study 6.5)
Cross section surveys: A total of 91 cross sections were surveyed in 2013 to support the
development of the 1-D Bed Evolution Model: 79 sections along the Susitna River, 2 sections
along the Chulitna River, and 10 sections along the Talkeetna River. Fifty (50) cross-sections
were surveyed in the Lower Susitna River Segment between PRM 29.9 and PRM 102.4, and 29
cross-sections were surveyed in Middle Susitna River Segment between PRM 102.7 and PRM
146.1 (Table 5.1-12). Table 5.1-12 also shows the cross sections that were surveyed in 2012.
PRMs are under development for the Chulitna River and the Talkeetna River, so PRMs for the
surveyed sections on these rivers are not yet available. The surveys were conducted as part of
the Fish and Aquatics Instream Flow Study (Study 8.5).
Bathymetric surveys within Focus Areas: The bathymetry survey data for each Focus Area
that was collected as part of ISR Study 8.5 has been provided in a TIN format. The in-channel
bathymetry will be merged with the overbank LiDAR data to create a combined TIN surface.
The surface will be used to develop the 1-D and 2-D Bed Evolution and Hydraulic models and
will be provided to other studies including the Ice Processes in the Susitna River (Study 7.6) and
the Groundwater Study (Study 7.5).
Water-surface elevation (WSE) measurements: WSE measurements were collected during the
Focus Area surveys as part of the Fish and Aquatics Instream Flow Study (Study 8.5). The
measurements were collected along the main channel, side channels, and upland sloughs; the
data were provided in an AutoCAD file containing the Focus Area survey data. Table 5.1-13 lists
the number of water-surface elevation measurements collected at each Focus Area. The date and
associated discharge for measurements will be obtained.
WSE measurements collected during the ADCP surveys as part of the Fish and Aquatics
Instream Flow Study (Study 8.5) has been provided in a spreadsheet format. Table 5.1-14
summarizes the number of measurements collected, the date of the survey and the coincident
discharge at the Gold Creek gage.
Bed-material (substrate) mapping: Bed-material mapping was conducted as part of the Fish
and Aquatics Instream Flow Study (Study 8.5) to spatially characterize the bed material. The
bed-material mapping will be evaluated together with the bed-material sampling data to identify
roughness zones, which in turn, will be used to specify channel roughness for the 1-D and 2-D
Bed Evolution models. It will also be used to assist in specifying the bed-material gradation
throughout the 2-D model domain.
Acoustic Doppler Current Profiler (ADCP) measurements: ADCP data were collected at the
7 Focus Areas in 2013 (Study 8.5). The ADCP data provide discharge measurements in the main
channel and side channels that are being used to determine the flow distributions for model
calibration. The velocity data are being used for the 2-D model calibration and to evaluate the
roughness characteristics of the bed material. The 2-D model calibration is being conducted by
comparing the depth averaged direction and magnitude of the measured velocity data with the
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predicted model output. It is anticipated that the bed-material roughness (k) will be back
calculated using the measured vertical velocity profile data and the logarithmic vertical profile
equation. Preliminary testing of this method showed promising results.
Stage hydrographs: Stage hydrographs are available from the USGS National Water
Information System website (http://waterdata.usgs.gov/nwis) at the USGS gage stations.
Surface water stage measurements were collected as part of the Ground Water Modeling Study
(Study 7.5). In 2012, one surface water stage recorder was installed in the Lower River, eight
stage recorders were installed along the Middle River, and one stage recorder was installed in the
Upper River (Table 5.1-15). A summary of the data available is listed in Table 5.1-15. Complete
stage measurements for 2013 are available for the Lower and Upper River recorders, partial
records are available at three recorders in the Middle River, and no data are available at the
remaining five recorders in the Middle River.
Sediment transport measurements: Historically and in 2012 and 2013 the USGS collected
measurements of sediment transport at various locations along the Susitna River (ISR 6.5 Section
5.2). These data will support the calibration of the bed load and suspended bed-material load
transport simulated using the 1-D Bed Evolution Model.
5.1.9.5. LiDAR Verification and Acquisition
5.1.9.5.1. Su-Wa LiDAR
LiDAR data acquisition occurred between September 9, 2013 and November 8, 2013. A total of
11 flight days of acquisition were completed. Unfavorable weather prevented completion of the
total acquisition area. The 2013 collected airborne LiDAR point cloud dataset covers 107.7
square miles and is located over the confluence area of Susitna, Chulitna, and Talkeetna rivers as
well as a small section just south of the Three Rivers Confluence Area. The area covers priority
areas 01 South, 02 South, 03, 04, and 07 as shown in Figure 5.1-29.
As shown in Tables 5.1-16 and 5.1-17, the FVA of the LiDAR meets the target accuracy of
RMSEz < 9.25 cm (approximately 0.30 ft.). Including brush, low vegetation, and forested lands,
SVA (RMSEz) ranges from approximately 0.5 to 0.62 ft. The vertical accuracy at the 95 percent
confidence level is 1.96 times the RMSEz, which is approximately 0.5 ft. for open terrain and up
to 1.2 ft. for other terrain types. These values indicate that the FVA is 1-ft contour interval
equivalent and that the SVA is approximately 2-ft contour equivalent (previously presented
Table 4.1-8).
The verification process followed the ASPRS guidelines for vertical accuracy reporting for
LiDAR data (ASPRS 2004) which recommends,
• “A LiDAR dataset’s required ‘fundamental’ vertical accuracy, which is the vertical
accuracy in open terrain tested to 95% confidence (normally distributed error), shall be
specified, tested and reported.”
• “If information is required on the vertical accuracy achieved within other ground cover
categories outside open terrain, either to meet the same specification as the fundamental
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vertical accuracy or a more relaxed specification, then “supplemental” vertical
accuracies, that is vertical accuracy tested using the 95th percentile method (not
necessarily normally distributed) shall be specified, tested and reported for each land
cover class of interest”
5.1.9.5.2. Mat-Su LiDAR Verification
The 2011 Mat-Su LiDAR as originally delivered was not brought to true ground by shifting to
surveyed data (indexing), nor was a verification process conducted. The survey points collected
in 2013, however, can still be used to assess the vertical accuracy of the Mat-Su LiDAR. The
survey points were used to verify the 2011 Mat-Su LiDAR and the verification results are shown
in Table 5.1-18. The Mat-Su LiDAR was collected in 2011 and the survey was conducted in
2013. The verification results are, therefore, not a complete comparison because some open
areas, especially bank lines and bar heads, are prone to change due to deposition or scour. As
shown, the FVA RMSEz is approximately 5 times as high for the Mat-Su LiDAR than the Su-
Wa LiDAR with an approximate 4-ft contour equivalency. The SVA is approximately 1.5 times
the Su-Wa LiDAR with an approximate 3-ft contour equivalency.
5.1.9.5.3. 2011 Mat-Su LiDAR Indexing
The indexing process of the 2011 Mat-Su LiDAR was completely performed in
Terrascan/Microstation environment and it was corroborated using the LiDAR processing
software LP360. Table 5.1-19 shows a comparison of 525 open terrain points to the Mat-Su
LiDAR. The Mean difference was used to shift the LiDAR to true ground. After indexing, the
vertical accuracy was reevaluated. The results, presented in Table 5.1-20, show that the RMSEz
for FVA reduced to 0.92 and for SVA was largely unchanged. All the tests result in an
approximate 3-ft a contour equivalence.
5.1.10. Electronic Data
The following data produced in 2013 for Study Component 1 are available on the GINA website
at http://gis.suhydro.org/reports/isr:
• Subsurface Bed-material Sample Locations on the Middle and Lower Susitna Rivers
shapefile
File name: ISR_6_6_FGM_BedSamp_Subsurface
• Subsurface (SubS) Bed-material field and lab data excel spreadsheet [surface (Sur)
samples at same location are included in combined spreadsheet]
File name format: ISR_6.6_FGM_SuWa TtGeo Sur SubS + date collected + PRM +
location + DistChart QC3 + initials of QC performer + date of QC
File name example: ISR_6.6_FGM_SuWa TtGeo Sur SubS 20130714 PRM 103.9
DistChart QC3 LWZ 20140115
• Surface Bed-material Sample Locations on the Middle and Lower Susitna Rivers
shapefile
File name: ISR_6_6_FGM_BedSamp_Surface
• Surface Bed-material field and lab data excel spreadsheet
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File name format: ISR_6.6_FGM_SuWa TtGeo Sur + date collected + PRM +
location + DistChart QC3 + initials of QC performer + date of QC
File name example: ISR_6.6_FGM_SuWa TtGeo Sur 20130817 PRM 144.9A-FA144
DistChart QC3 MRM 20140115
• Bank Material Sample Locations within the Middle Susitna River Segment shapefile
File name: ISR_6_6_FGM_Bank_Samples
• Bank Material lab data
File name format: ISR_6.6_FGM_SuWa TtGeo Bank + sample number + date
collected + PRM location + LabResults QC3 + initials of QC perfomer + date of
QC3
File name example: ISR_6.6_FGM_SuWa TtGeo Bank1 20130907 PRM 145.7
LabResults QC3 LabResults QC3 ALS 20140114
• Cross-section Observations, Surveys and Level Loops Locations Shapefile
File name: ISR_6_6_FGM_XSec_Obs_Survey
• Cross-section Level Loops excel spreadsheet
File name: ISR_6.6_FGM_WSE_LevelLoops
• Cross-section Observations Summary excel spreadsheet
File name: ISR_6.6_FGM_XSec_Obs_Summary
• Tributary Survey excel spreadsheets
File name: ISR_6.6_FGM_WhiskersCreek_Survey
File name: ISR_6.6_FGM_UnnamedTrib113.7_Survey
File name: ISR_6.6_FGM_SlashCr_Survey
File name: ISR_6.6_FGM_GashCr_Survey
File name: ISR_6.6_FGM_LaneCr_Survey
File Name: ISR_6.6_FGM_SkullCr_Survey
File Name: ISR_6.6_FGM_GoldCr_Survey
File Name: ISR_6.6_FGM_IndianR_Survey
File Name: ISR_6.6_FGM_UnnamedTrib144.6_Survey
File Name: ISR_6.6_FGM_TrappersCr_Survey
• Geomorphic Surface Mapping Shapefile
File name: ISR_6_6_FGM_Surface_Mapping
5.2. File Name: Study Component: Model Existing and with-Project
Conditions
This section includes the current results of data collection and analysis for this study component.
The primary results from the 2013 effort involved identification of the long-term hydrologic
record, selection of representative hydrologic years and investigation of the influence of PDO.
The results are specific to the Fluvial Geomorphology Modeling below Watana Dam Study and
have been reviewed by other studies, primarily the Fish and Aquatics Instream Flow Study
(Study 8.5) and the Ice Processes in the Susitna River Study (Study 7.6). The initial results were
presented at the December 3, 2013 TWG meeting and will be coordinated with the stakeholders
before final selection of the various hydrologic conditions to be used in the modeling efforts.
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5.2.1. Existing Conditions – Base Case Modeling
As per the Study Plan, the existing conditions modeling has not commenced and will be
performed after the 1-D and 2-D Bed Evolution and Hydraulic models have been developed and
calibrated. The initial selection of the hydrology to represent the existing conditions has been
completed for Fluvial Geomorphology Modeling below Watana Dam. The selection has been
coordinated with Fish and Aquatics Instream Flow Study (Study 8.5) and Ice Processes in the
Susitna River Study (Study 7.6), and will be finalized based on input from the stakeholders. The
hydrologic input for the 1-D Bed Evolution Model includes a 50-year period from the 61 years of
available hydrologic record and the 2-D Bed Evolution Models include representative years. As
presented in Appendix E, the 50-years were selected to include the best quality data. This was
achieved by first eliminating five years (water years 1997 – 2001) when the USGS Susitna River
gage at Gold Creek (gage no. 15292000) and all but one other gage were synthesized (USGS
2012) from the USGS Talkeetna River gage near Talkeetna (gage no. 15292700) reducing the
number of years to 56. The USGS indicated that six water years (1954, 1956, 1958, and 1961-
1963) of flow records at the Susitna River at Gold Creek gage included likely estimated flows.
The annual flow hydrographs for these years include long periods of time (several weeks to
approximately one month) when discharge was recorded as constant during open water periods
(May through September). The six years were eliminated from the remaining 56 years to arrive
at the required 50 year flow record. As a final step in this evaluation the flow duration curves for
the 50-year record were compared with the complete (though partially estimated and partially
synthesized) 61-year record and these curves are nearly indistinguishable. Therefore the
recommended 50-year record for the 1-D Bed Evolution includes water years 1950-1953, 1955,
1957, 1959-1960, 1964-1996, and 2002-2010.
The Study Plan also indicates that up to six representative years will be used for the 2-D Bed
Evolution Models of the 10 Focus Areas in the Middle Susitna River. The representative years
will include wet, average and dry conditions and consider periods of warm and cool Pacific
Decadal Oscillation (PDO). To investigate the influence of PDO, the 50 selected years were
divided into warm and cool PDO conditions and ranked from lowest to highest by water year
average annual discharge, open water average discharge approximated by May through
September flows, and by maximum average daily flow. The higher-, median-, and lower-range
flow years were reviewed as candidate representative wet, average and dry years including warm
and cool PDO. The two most extreme flow years were excluded as candidates as they are not
representative of wet or dry conditions. Similarly, dry and average years that contain extremely
high peak flows were excluded and wet years that did not include high peak flows were
excluded. Two wet, average and dry years were selected for each PDO condition and the annual
hydrographs were compared. Appendix E Figures 5.10 (dry), 5.12 (average), and 5.14 (wet)
show the annual hydrographs for the candidate years and Figures 5.11, 5.13, and 5.15 are the
corresponding annual flow duration curves. There were no visually appreciable differences
related to PDO between the hydrographs or flow duration curves within each hydrologic
condition.
As described in detail in Appendix E, Wilcoxon Rank Sum test was used to evaluate differences
in between warm and cool PDO. The test indicated that there are no statistically significant
differences in mean annual flow, average open water and monthly flows (May to September),
and maximum daily flows (Appendix E Tables 5.2 and 5.3). There are statistically significant
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differences in minimum daily and average winter and monthly flows (October to April). Based
on these results, AEA recommends that the 2-D bed evolution modeling for open-water
conditions will be conducted for three representative years without additional consideration of
PDO. Three representative years were recommended from the original 12 candidate years of
four each for wet, average and dry conditions. The three years are 1981, 1985, and 1950 to
represent wet, average, and dry years. After additional analysis by the Fish and Aquatics
Instream Flow and Ice Processes in the Susitna River studies, it was agreed that 1970 should be
substituted as the representative dry year. These recommended years will be presented to the
TWG for feedback and these three years may be revised depending on input that is received.
5.2.2. Future Conditions – with-Project Scenarios
There are no results for 1-D or 2-D Bed Evolution and Hydraulic modeling efforts for the four
with-Project scenarios.
5.2.3. Uncertainty
There are no results for the evaluation of uncertainty in the 1-D and 2-D Bed Evolution and
Hydraulic modeling.
5.2.4. Synthesis of Reach-Scale and Local-Scale Analyses
There are no results for the synthesis of reach-scale and local-scale analyses.
5.2.5. Electronic Data
No electronic data are presented for Study Component 2 on the GINA website.
5.3. Study Component: Coordination and Interpretation of Model
Results
As identified below, the effort conducted in 2013 was primarily in the area of internal
coordination and integration between the Fluvial Geomorphology Modeling below Watana Dam
Study and the Geomorphology Study (Study 6.5) and external coordination with the Fish and
Aquatics Instream Flow Study (Study 8.5), Riparian Instream Flow Study (Study 8.6), Ice
Processes in the Susitna River Study (Study 7.6), Groundwater Study (Study 7.5), Water Quality
Modeling Study (Study 5.6), and Characterization and Mapping of Aquatic Habitats (Study 9.9).
A wide variety of products has been developed by the Geomorphology Study (Study 6.5) that has
aided the guidance of the development of the Fluvial Geomorphology Modeling below Watana
Dam Study (Section 5.3.1). Coordination and integration with the other studies mentioned has
centered on integration of the modeling efforts and in particular transfer of information between
the various studies in terms of results from one study becoming input to another study. The
modeling studies are jointly working on the Proof of Concept to develop the linkages between
the various models and refine the development of the suite of results that will form a large part of
the metrics that Project effects will be evaluated.
This effort has been progressing well. The Geomorphology Study has provided the information
needed by the Fluvial Geomorphology Study to help guide the development of the 1-D and 2-D
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Bed Evolution model. The coordination with the other modeling studies is also proceeding well
through the efforts identified below (Section 5.3.2).
5.3.1. Integration of Geomorphology and Fluvial Geomorphology Modeling
Study
Components of the Geomorphology Study directly contribute key information and data to the
Fluvial Geomorphology Modeling below Watana Dam Study, and vice versa. Study components
of the Geomorphology Study (Study 6.5) have and will continue to provide required information
to the Fluvial Geomorphology Modeling below Watana Dam Study.
Results from the Geomorphology Study (Tetra Tech 2013b) were used to establish reach
boundaries within the Middle and Lower River Segments, cross section locations and reach
boundaries for the 1-D Bed Evolution Model and roughness boundaries for the channel and
overbank surfaces for both 1-D and 2-D Bed Evolution models. Geomorphic process models
that describe the formation and maintenance of lateral geomorphic features and habitats and
floodplain features (Study 6.5 ISR Section 5.1.3.3) provide starting points for assessing the
reasonableness of the 1-D and 2-D Bed Evolution model results and whether adjustments to the
numerical or conceptual models are required. Integration of field observations and hydrologic
analyses to understand the potential role of ice processes in the evolution of floodplain surfaces
(ISR Study 6.5 Section 5.1.3.5.5). Sediment input to the 1-D and 2-D Bed Evolution models are
directly derived from components of the Geomorphology Study (Tetra Tech 2013a).
Geomorphic change over time and space resulting from the comparative aerial photo analysis
(1980s and 2012 completed with 1950s underway) established the rates and locations of
geomorphic change in the Middle and Lower River segments that will be used to assess model
results and provide reality checks to the model output (ISR 6.5 Section 5.4 and Tetra Tech
2013g). The areas of various macrohabitat types for a specific flow represented on aerial
photography provides a measure of habitat connectivity that will be used to verify model results
(ISR 6.5 Sections 5.5 and 5.7, Tetra Tech 2013f). Preliminary assessments of the project effects
on the Middle and Lower River Segments provide direct input for assessing the range of flows
that are required to be modeled to represent geomorphic processes and channel geometries and
the relative sensitivities of the identified reaches to changes in driving variables (Tetra Tech
2013c and Tetra Tech 2013d). Sediment loading to the reservoir and preliminary estimates of
reservoir trap efficiency feed directly into both the 1-D and 2-D Bed Evolution modeling (ISR
Section 5.8.1). Quantification of the sources, volumes and spatial distributions of large woody
debris provide direct input to the models with respect to estimation of Manning’s n values and a
check on model estimates of bank erodibility (ISR 6.5 Section 5.9).
5.3.2. Coordination of Results with Other Resource Studies
To-date, the fluvial geomorphology models have not been fully developed and thus extensive
results are not yet available. However, preliminary results for the hydraulic component of the 2-
D bed evolution model have been developed for FA-104 (Whiskers Slough) and provided to the
Fish and Aquatics Instream Flow Study to develop the linkages to transfer data between the
models. The results of this effort were presented at the November 2013 IFS Technical Team
meeting. There has been considerable coordination and discussions with other study teams at
Technical Working Group meetings, the November 2013 IFS Technical Team meeting, joint
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field trips in 2012 and 2013, and through informal communications on the outputs required by
the other study teams including; Open-water Flow Routing Model (ISR Study 8.5 Section 5.3.1),
Fish and Aquatics Instream Flow (Study 8.5), Riparian Instream Flow (Study 8.6), Ice Processes
in the Susitna River (Study 7.6), Water Quality Modeling (Study 5.6), Groundwater (Study 7.5)
and Characterization and Mapping of Aquatic Habitats (Study 9.9) studies.
5.3.3. Electronic Data
No electronic data are presented for Study Component 3 on the GINA website.
6. DISCUSSION
6.1. Study Component: Bed Evolution Model Development,
Coordination, and Calibration
6.1.1. Development of Bed Evolution Model Approach and Model Selection
The development of the initial 1-D and 2-D Bed Evolution models is progressing based on
available surveys and data. The data appear to be sufficient but final determination of data
adequacy will be made in the next year of study as the models are calibrated and run for a range
of conditions.
6.1.1.1. One-Dimensional (1-D) Bed Evolution Model
Based on the information provided in Section 4.1.2.1.1 and in Tetra Tech (2013h), the
Geomorphology Study team had tentatively proposed to use HEC-6T for the reach-scale 1-D
sediment transport analysis. This proposal was based on confidence gained that HEC-6T is
capable of effectively and efficiently modeling the processes that are important for this scale of
geomorphic analysis. The key advantages of HEC-6T are (1) its wide application experience; (2)
looped network capability; and (3) large number of sediment transport equations (including both
Parker (1990) and Wilcock and Crowe (2003)), sediment sizes, and hydrograph ordinates (Tetra
Tech 2013h). However, subsequent to the issuance of Tetra Tech (2013h), the Geomorphology
Study team was presented with new information that necessitated reconsiderations of the
recommendation to select HEC-6T. The USACE Hydrologic Engineering Center (HEC) is
enhancing the sediment routing algorithms in the HEC-RAS modeling software; Tetra Tech staff
have been working closely with HEC staff to test the enhanced sediment routing functionality.
In fall 2013, HEC staff offered to the Geomorphology Study team a previously tested beta
release of the software (HEC-RAS 4.2.0). This version of the software includes the following
enhancements that are relevant to the 1-D Bed Evolution modeling:
• Sediment routing for fully-unsteady hydraulics
• Sediment routing through split flows
• The Exner 7 bed sorting algorithm (Copeland 1993)
• A coupled Meyer-Peter-Müller (1948) and Toffaleti (1968) transport function
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• Capabilities to calibrate selected sediment transport functions by adjusting coefficients
and exponents. For example, the Wong and Parker (2006) correction can be applied to
the Meyer-Peter-Müller (1948) bed load function.
Other benefits of the HEC-RAS software include widespread industry acceptance, public
availability, ease of use, and a graphical user interfaces that facilitate data input and review of
results. While HEC-RAS Version 4.2.0 was not available at the time the initial model selection
was occurring (Tetra Tech 2013h), it is now believed that this software is most appropriate given
the benefits identified above and given that it will allow for better integration with the Open
Water Flow Routing Model (ISR Study 8.5 Section 4.3) which is also using the HEC-RAS
modeling software for hydraulic analysis of the Middle and Lower Susitna River segments. If at
any point in the model development and testing it is found that the upgraded version of HEC-
RAS will not allow for successful bed evolution modeling of the Susitna River, the modeling
approach will revert to using the previously selected HEC-6T software. Conversion of the HEC-
RAS model inputs to HEC-6T model format can be easily accomplished requiring only minimal
effort.
6.1.1.2. Two-Dimensional (2-D) Bed Evolution Model
During the model selection process, it was thought that SRH-2D may not be appropriate for the
bed evolution modeling due to the limitation of 16,000 elements. The initial SRH-2D mesh
developed for FA-104 (Whiskers Slough) has approximately 10,000 elements. FA-104
(Whiskers Slough) is a reasonably complex site with multiple side channels and the main
channel has been extended approximately 2 miles upstream of the FA boundary. Given, the
number of elements in the SRH-2D mesh is significantly less than 16,000 and the model has
sufficient resolution, it is very likely mesh size will not be a limiting factor and SRH-2D remains
a viable model for the study.
Initial indications of the 2-D Bed Evolution Model development indicate the quality and
resolution of the survey data is good and is resulting in high quality 2-D models. In developing
the TINS for the 7 Focus Areas that have been surveyed, the extents of the surveys will be
reviewed to determine if there is need to extend the surveys upstream or downstream to provide
better mesh resolution and better prediction of the hydraulic conditions in the vicinity of the FA
boundaries. The TINS will also be reviewed to determine if there are any areas in which
additional points need to be collected to adequately represent the geometry of the Focus Area.
6.1.2. Coordination with other Studies
Coordination with others studies in 2013 was ongoing and extensive involving primarily data
collection and model development. The3 effort included internal coordination between the
Fluvial Geomorphology Modeling below Watana Dam Study and the Geomorphology Study
(Study 6.5) and external coordination with the Fish and Aquatics Instream Flow Study (Study
8.5), Riparian Instream Flow Study (Study 8.6), Ice Processes in the Susitna River (Study 7.6),
Groundwater Study (Study 7.5), Water Quality Modeling Study (Study 5.6), and
Characterization and Mapping of Aquatic Habitats (Study 9.9). The success of the coordination
effort between the studies will be demonstrated by the Proof of Concept to be reported on in
2014. Additional discussion of coordination efforts is provided in Section 6.3.
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6.1.3. Model Resolution and Mesh Size Considerations
Areas identified by the aquatic habitat team members are modeled at element resolution of
approximately 6.5 feet (2 m), which resulted in meshes with a very large number of elements and
in longer development times than is typical for the areal extent of the Focus Areas. During the
development of the initial SRH-2D habitat mesh, different methods for constructing the meshes
were tested, which has resulted in an efficient methodology for constructing the subsequent
meshes.
No significant or unanticipated issues arose during the development of the initial SRH-2D
habitat mesh. Development of the mesh size and extents has been coordinated with the Fish and
Aquatics Instream Flow Study (Study 8.5) to ensure that the proper resolution is being obtained
throughout the each Focus Area to meet fish and aquatic habitat modeling needs.
6.1.4. Focus Area Selection
The selected Focus Areas are adequate to represent the more complex (e.g. split flows, mid-
channel bars, and continuous bank-attached floodplain segments) geomorphic regions within the
Middle River. The simpler geomorphic regions, identified by a single laterally confined channel
with limited sediment storage in mid-channel bars and non-continuous bank-attached floodplain
segments, are adequately represented within the selected 1-D Bed Evolution model and do not
require the 2-D Bed Evolution modeling being performed in the Focus Areas.
The Geomorphic Assessment Areas (GAAs) were developed in the Geomorphology Study
(Study 6.5) because it was necessary to identify governing geologic controls in order to explain
the genesis and spatial distribution of geomorphic features within Focus Areas. The GAAs have
limits that extend beyond the limits of the Focus Areas. This expanded area is intended to
include all geomorphic surfaces encompassed between upstream and downstream lateral
constrictions such as bedrock, moraines, terraces and alluvial fans. The 2-D Bed Evolution
model mesh extents may be expanded to align with the defined GAA boundaries. This may be
performed if the expanded boundaries are required to adequately predict flow distribution at
either the upstream or downstream boundary of the model.
6.1.5. Model Calibration and Validation
6.1.5.1. One-Dimensional (1-D) Bed Evolution Model
The development of the 1-D Bed Evolution Model is still underway, so calibration and validation
of the hydraulics and sediment transport routines has not yet been completed. Results of initial
calibration will be presented in the Proof of Concept effort being completed and reported on in
2014. The adequacy of data collected to support the calibration is discussed in Section 6.1.9.1.
6.1.5.2. Two-Dimensional (2-D) Bed Evolution Model
The compilation and review of calibration data is being finalized from the 2013 data collection
effort; therefore model calibration and validation have not yet been performed. The initial SRH-
2D simulations were computationally stable with excellent flow conservation, which supports the
selection of SRH-2D for further model evaluation. No River2D runs have been conducted, and
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therefore, there are no observations to discuss. Results of initial calibration and model
comparison will be presented in the Proof of Concept effort being completed and reported in
2014.
6.1.6. Tributary Delta Modeling
Of the 20 tributaries selected for modeling, reconnaissance was planned for 13 tributary deltas
during the 2013 field season, three in the Lower River and 10 in the Middle River. Since the
reconnaissance at Birch Creek could not be carried out due access not being granted by a private
landowner, attempts for access are planned in a next year of study. Of the remaining 12
tributaries with efforts planned for 2013, only the unnamed tributary (PRM 115.4) was removed
from the list of candidates based on observations made during the 2013 reconnaissance of low
sediment production and an absence of a delta. This decision was agreed upon in conjunction
with the Study of Fish Passage Barriers in the Middle and Upper Susitna River and Susitna
Tributaries (Study 9.12).
6.1.7. Large Woody Debris Modeling
There is extensive data now available from the 2013 field season on large woody debris
quantities and characteristics (ISR Study 6.5 Section 5.9). This data includes conditions before
and after high September 2012 flows, which will be used in the next year of study to help
quantify the variability of debris loading over a range of flow conditions.
6.1.8. Wintertime Modeling and Load-Following Operations
There are numerous observations of ice cover and breakup conditions made by the Ice Processes
in the Susitna River Study (ISR Study 7.6) from the winter periods of 2010-2011 and 2012-2013
and anticipate additional useful information from the 2013-2014 winter. Observations of ice
effects were also made by the Geomorphology (Study 6.5) and Riparian Instream Flow (Study
8.6) studies during the 2013 field season. These data will be used to further develop winter
conditions models, especially as they relate to ice jam breakup conditions.
6.1.9. Field Data Collection Efforts
The field data collection efforts in 2013 were carried out to support various components of this
study, as well as the Geomorphology Study (ISR Study 6.5). A significant amount of the data to
be used by the Fluvial Geomorphology Study was collected by the Fish and Aquatics Instream
Flow Study (Study 8.5).
6.1.9.1. 1-D Bed Evolution Model
The development and calibration of the 1-D Bed Evolution Model rely on various types of field
data (Section 5.1.9.1). Field data collected in 2013 are largely adequate to support development
and preliminary calibration of the model, but final determination of data adequacy will be made
in the next year of study as the hydraulic and sediment transport/bed evolution models are
calibrated.
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Hydraulic Observations: It is expected that the characterizations of hydraulic roughness will be
adequate for setting initial energy loss parameters (Manning’s n-values). Categories of
roughness based on observations generally followed surfaces delineated in the geomorphic
mapping (ISR Study 6.5 Section 5.1.3.5.1) along the Middle River. Based on these observations,
representative overbank roughness values (Table 5.1-3) were assigned to each geomorphic
mapping unit, which are being used to assign preliminary roughness values to the 1-D and 2-D
Bed Evolution models. These values are a primary calibration parameter, so the initial values
will be adjusted as needed to achieve model calibration.
The water-surface measurements, particularly those collected during the mid-August high-flow
event, provide valuable data for calibration of the 1-D and 2-D Bed Evolution models. The
water-surface elevation measurements, together with those collected by the Fish and Aquatics
Instream Flow Study (Study 8.5), provide very good coverage along the Middle River
downstream of PRM 146.6. Further discussion of the water-surface measurements is provided
with water-surface measurements compiled from other studies in Section 6.1.9.4. Appendix D
summarizes the water-surface elevations measured as part of Studies 6.5 and 6.6. It is
recommended to continue collecting water-surface elevation measurements using the same
methodology and, when possible (and safe), to collect water-surface elevations during high flow
events of primary interest to the Geomorphology Studies as well as lower flows of primary
interest to habitat modeling. Above certain levels, safety issues limit access to the river and the
stage recorders become the primary means of collecting high flow water surfaces elevations.
Sediment Sampling:
Surface and subsurface sampling: Review of the surface and subsurface sediment sampling
results presented in Appendix A indicates that it is sufficient for initial development of the 1-D
and 2-D Bed Evolution models. The spacing and extent of the samples provides good coverage
throughout the Lower Susitna River Segment and good coverage in the Middle Susitna River
Segment to PRM 146.6. The results show consistent trends within the Segments that will
provide data for the bed evolution models and for interpretation of physical processes.
Bank material sampling: The bank material sampling was mostly conducted in the Focus Areas
in 2013 with 59 samples collected in the Focus Areas and 6 samples collected in the Middle
River outside of the Focus Areas (Table 5.1-10, Appendix C). A full analysis of the bank
samples has not been conducted; however, a preliminary review indicates that the bank materials
are relatively consistent along Middle River with a median size (D50) of about 0.1 mm, which
corresponds to the very fine sand category. In addition, the preliminary review of the spatial
distribution of the bank samples and the uniformity of the bank materials indicates the sampling
method was more than sufficient to characterize the bank materials.
Pebble counts were conducted along the base of the banks to determine the gradation of the
materials that composed the base core of the islands. A comparison of the base of bank materials
with the bar head materials indicated that both had very similar gradations. It is therefore
recommended that base of bank samples continue to be collected in a next year of study at about
the same frequency as in 2013 or in locations where the gradation appears to be significantly
different compared to nearby bar head samples.
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In a next year of study, bank sampling will be conducted at the remaining 3 Focus Areas using
the same techniques that were applied in 2013. Where necessary, additional bank material
samples will be collected in areas outside of the focus areas to characterize any substantial
changes in bank materials.
Winter sediment sampling: Underwater camera equipment was tested during the ice-covered
period to determine: (1) if it is possible to obtain video of the channel bed, (2) the best
combination of equipment, and (3) whether it is possible to develop a sediment gradation of the
channel bed from the video images. The underwater camera techniques provided images that can
be used to determine main channel streambed gradation, and these techniques will be used for
application to a full scale field data collection campaign. Underwater video analysis is not
possible during the open-water period due to poor visibility caused by fine sediment from glacial
melt. During the underwater camera testing, water clarity was good and did not negatively
impact the ability to acquire streambed images. Additionally, frazil ice and other moving
material did not negatively impact the performance of this test work and resulting image quality.
Main channel velocities were high, but did not prevent the submergence and operation of the
underwater camera equipment. The 2013 effort indicated that it will be possible to develop bed-
material gradation in the deeper portions of the channel during the winter period. It took
approximately 1 day, including travel time to and from the site, to collect the video data at each
transect.
Comparison of current and historical surface samples: The sediment samples collected during
2013 were compared to sediment samples collected in the 1980s. R&M Consultants (1985)
presents gradations of bed-material samples collected to evaluate with-Project aggradation
downstream of the Three Rivers Confluence. Armor layer and subsurface bed-material samples
were collected during October 1984 at seven cross sections between the Three Rivers
Confluence and the USGS gaging station at Sunshine (Table 6.1-1). R&M Consultants (1985)
indicates five samples were biased toward the larger particle sizes because the sediment was
chipped out of the frozen bed; the remaining two samples were considered representative
because the armor layer was not frozen. The armor layer was reported as marginally developed
at RM 87.7 (PRM 91.1), so it was not included in the comparison presented below.
Harza-Ebasco (1984) provides results of bed-material sampling from 46 mainstem and side
channel locations along the Susitna River. Samples from submerged locations were collected
with a 6-inch-diameter pipe dredge; samples located in less than about 1.5 feet of water were
collected with a shovel. Size distributions were determined by sieve analyses. Table 6.1-2
provides the median bed-material size for the 18 surface/pavement samples collected from the
mainstem Susitna River.
Appendix A provides the D50 values calculated for the surface samples collected in 2013. These
samples were screened to remove locations not along the main channel of the Middle or Lower
Susitna River Segments and plotted along with the D50 values from the 1980s sampling (Figure
6.1-1 and Figure 6.1-2).
In the Lower Susitna River Segment, the 1980s sampling was limited to the area upstream of the
USGS gaging station at Sunshine. In this reach, the median D50 from the 1980s samples is about
50 mm and the median D50 from the 2013 samples is about 45 mm (Figure 6.1-1). This
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similarity indicates a general consistency in the median surficial bed material. Downstream of
PRM 92, the 2013 samples have a median D50 of 33 mm, indicating a relatively consistent
median surface sediment size downstream of the approximate location of the USGS gage at
Sunshine. The median bed surface size, based only on the 2013 samples, is slightly finer
downstream of PRM 92 than between PRM 92 and PRM 102.4. The general consistency of the
1980s and 2013 D50 values of the surface sediment samples from the mainstem channel provides
support to the preliminary assessment of vertical stability based on comparisons of 1982 and
2013 thalweg profiles (ISR 6.5, Figure 5.1-2).
In the Middle Susitna River Segment, the median D50 of the 1980s samples is 53 mm and the
median D50 of the 2013 samples is 59 mm (Figure 6.1-2). As with the Lower Susitna River
Segment, this similarity indicates the potential for general consistency in the median surficial bed
material over the 30 years between sampling periods.
6.1.9.2. Focus Areas
The data collected in the Focus Areas was conducted as part of the overall data collection effort
in ISR Study 6.5 and 6.6 and has been described elsewhere in this report. The Geomorphology of
the Focus Areas was mapped and characterized in Study 6.5 (ISR section 6.1.3). The bed-
material sampling conducted has been described under the 1-D modeling effort (Section 6.1.9.1).
Additional mapping of bed material performed in the Fish and Aquatics Instream Flow Study
(Study 8.5) is discussed in Section 6.1.9.4). The bathymetric and topographic survey information
(collected under Study 8.5) along with LiDAR to develop the geometry of the Focus Areas is
discussed under Section 6.1.9.4 and 6.9.1.5, respectively. Water surface elevation measurements
collected in this study to calibrate the hydraulics models are discussed in section 6.1.9.1. Model
calibration information collected by the Fish and Aquatics Instream Flow Study, including water
surface elevations and ADCP measurements of velocity and depth are discussed in Section
6.1.9.4 (Water surface elevations and ADCP measurements).
The data collected in the Focus Areas, including the bathymetric and topographic mapping,
velocity, water surface elevations and sediment sampling, and bank observations has been high
quality in terms of amount and spatial distribution of sampling, and appears to be sufficient for
model development. The same data collection methodologies and techniques will be used at the
3 remaining Focus Areas in a next year of study. As the 2-D Bed Evolution Model development
and calibration proceeds in 2014 as part of the Proof of Concept, any data gaps in the 2013 data
collected at the 7 Focus Areas in 2013 will be identified and the data gaps filled by information
collected in a next year of study.
6.1.9.3. Tributary Deltas
The channel geometry surveys and bed-material samples collected in 2013 from the 11
tributaries appear adequate to quantify the sediment loading delivered to the tributary deltas.
These data have been used develop preliminary hydraulic models that will be used to calculate
sediment loads. No data were collected at the unnamed tributary (PRM 115.4) based on the lack
of an observed delta and the low sediment production potential from the contributing watershed.
Since access across private lands to Birch Creek was not granted in 2013, no data could be
collected; if access is not granted for future data collection, the sediment loading to the tributary
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delta will need to be estimated. As the tributary model development proceeds in 2014 as part of
the Proof of Concept, any data gaps in the 2013 data collected at the 11 tributaries in 2013 will
be identified and the data gaps filled by information collected in a next year of study.
6.1.9.4. Field Data from Other Studies
The development and calibration of the 1-D and 2-D Bed Evolution models rely heavily on field
data collected from other studies. Both models will use surveyed water-surface elevations and
measured flows to calibrate steady-state hydraulics (estimated flows will be used where
measurement flows are unavailable). Measured flows in split channel reaches are useful in
calibrating simulated split flows. Recorded flow and stage hydrographs will support properly
representing the translation and attenuation of flow. Further calibration of the 2-D Bed
Evolution and Hydraulic models will be based on measured velocities from ADCP data collected
specifically for this purpose in the seven Focus Areas.
Cross section surveys: To date, a total of 179 cross sections have been surveyed along the
Lower and Middle Susitna River Segments, the Chulitna River, and the Talkeetna River. Of this
total, 63 sections have been surveyed along the Lower River between PRM 29.9 and PRM 102.4,
which corresponds to an average spacing of approximately 1.1 miles. While this spacing appears
adequate for development and calibration of the 1-D Bed Evolution Model, 13 cross sections
have been identified as candidates for future survey should the need arise (Table 6.1-3); further,
if additional locations arise as a result of unsuccessful model calibration, additional candidates
may be identified. Along the Middle River, between PRM 102.7 and PRM 187.2 (excluding
Devils Canyon, geomorphic reach MR-4: PRM 166.1 to PRM 153.9), 104 cross sections have
been surveyed, corresponding to an average spacing of approximately 0.7 miles. Similar to the
method described for the Lower River, 17 candidate cross sections have been identified for
future surveying should the need arise, or additional cross section survey needs may be
identified. Due to lack of access upstream of PRM 146.1 during the 2013 field season, 15
Middle River cross sections planned for survey could not be surveyed. While only two cross
sections were surveyed along the Chulitna River, no further surveys are planned because it is
expected that geometry can reasonably be represented using LiDAR topography and estimated
bathymetry (Tetra Tech 2013h). Four additional cross sections may be surveyed in the next year
of study along the Talkeetna River if the 10 sections already surveyed are not adequate for model
calibration.
Topographic and bathymetric surveys within Focus Areas: The bathymetric data collected as
part of Study 8.5 was used to assign elevations to the FA-104 (Whiskers Creek) 2-D Bed
Evolution Model. The bathymetric and topographic data were collected mostly along transects
set perpendicular to the flow and at a spacing of approximately 200 feet. The combination of
bathymetric and topographic data survey, together with the overbank LiDAR provides adequate
resolution to develop the 2-D models.
A TIN developed from the bathymetric, land, and LiDAR survey data at FA-128 (Slough 8A)
provides a good representation of the main channel bed, side channels, other lateral features,
bars, islands, and floodplain. The TIN includes sufficient resolution to define the breaching
elevations between the main channel and side channels.
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As the 2-D Bed Evolution Model development and calibration proceeds in the next year of study,
any data gaps in the topographic and bathymetric survey data collected at the 7 Focus Areas in
2013 will be identified and the data gaps filled by information collected in a next year of Study.
Water-surface elevation (WSE) measurements: Coupled measurements of WSE and flow
provide the basis for calibrating steady-state hydraulics for the bed evolution models; these
measurements are also used within the Fish and Aquatics Instream Flow Study to calibrate the
Open-Water Flow Routing Model (ISR 8.5 Section 4.3). The method for calibrating the Open-
Water Flow Routing Model uses coupled measurements of WSE and flow for categories of high,
medium, and low flow. The thresholds between categories were calculated using the 61-year
period of record for the months of June through September at the UGSG gaging stations at Gold
Creek (Middle River) and at Sunshine (Lower River). Annual flow duration curves were
developed for each gage, and the flows corresponding to the 33 percent exceedance (i.e., the
threshold between high and medium flows) and the 67 percent exceedance (i.e., the threshold
between the medium and low flows) were identified (Table 6.1-4). These thresholds were
compared to estimates of the effective discharge and flows required to mobilize bed material as
presented in ISR 6.5 Section 5.3.4 and Section 5.3.3, respectively (Table 6.1-4). The threshold
flows developed for the Fish and Aquatics instream Flow Study are less applicable for
calibration of the bed evolution models; what is more important is whether the coupled
measurements are adequate to calibrate the simulated hydraulics under conditions when the bed
is mobile and substantial sediment is in transport. Additional measurements of flow and WSE
collected along the Middle River during high flows occurring between late August and early
September 2013 were considered. All available coupled measurements of WSE and flow were
screened using threshold conditions of bed mobilization and effective discharge (using
calculations at the gaging stations as indicators for the whole river segments); illustrations of the
screening are presented for the Lower Susitna River Segment in Figure 6.1-3 and for the Middle
Susitna River Segment in Figure 6.1-4.
Based on the screening of the coupled WSE and flow measurements, it appears that the available
measurements are adequate for calibrating the bed evolution models in the Middle River
(downstream of PRM 146.6) for conditions when the bed is mobile and substantial sediment is in
transport; however, in the Middle River upstream of PRM 146.6 and in the Lower River,
additional measurements are recommended. These additional measurements should be targeted
to flows as measured, respectively at the Gold Creek gage in excess of about 27,000 cfs and at
the Sunshine gage in excess of about 70,000 cfs. Ideally these measurements can be coordinated
with the needs of the Fish and Aquatics Instream Flow Study to obtain high-flow measurements
in the Middle River (i.e., in excess of 24,000 cfs as measured at Gold Creek) and in the Lower
River (i.e., in excess of 60,600 cfs as measured at the USGS gage at Sunshine).
Bed-material mapping: The bed-material (substrate) mapping data have not yet been reviewed,
so no assessment of the data adequacy can be made. These data are supplemental to the bed-
material sampling conducted in the Focus Areas as part of Studies 6.5 and 6.6. It is expected that
these data, even though categorical in nature, will prove useful in characterizing grain roughness
to specify roughness values the 1-D and 2-D Bed Evolution models.
Acoustic Doppler Current Profiler (ADCP) measurements: ADCP measurements were
collected in 2013 at all 7 Focus Areas both lateral and longitudinal to flow paths. These
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measurements provide velocity and depths at points throughout the Focus Areas as well as a
means to determine the flow within individual channel features within the Focus Areas. The
ADCP flow measurements collected as part of ISR Study 8.5 are sufficiently accurate and
spatially distributed to quantify the flows in the main channel and side channels at all of the
Focus Areas. The discharge measurements will be used to calibrate the 1-D and 2-D Bed
Evolution models by comparing the simulated flows to the measured data. The combination of
longitudinal and lateral velocity profiles provide a large set of measurements to calibrate cell
velocities in the 2-D Bed Evolution models at each Focus Area.
The raw ADCP measurements have not yet been processed to create depth-averaged ADCP data,
which will include magnitude and direction, and will be used in the 2-D Bed Evolution and
Hydraulic models calibration process. Table 6.1-5 summarizes the number of ADCP
measurements and corresponding discharges collected in 2013 at the Focus Areas; Figure 6.1-5
is an example that illustrates the locations and extents of the ADCP measurements collected at
FA-104 (Whiskers Slough).
Stage hydrographs: The stage hydrographs recorded at the USGS gaging stations at Tsusena
Creek, Gold Creek, Sunshine, and Susitna Station will provide valuable calibration data for 1-D
and 2-D Bed Evolution models. After calibrating the steady state hydraulics, the stage
hydrographs will serve as a primary reference for calibrating the unsteady hydraulics.
Surface-water stage measurements were collected during 2013 at various locations along the
Susitna River (ISR Study 8.5 Sections 4.3.1.1 and 4.4.1.1). Water levels and flows were
measured at Curry (Gage ESS50 at PRM 124.1), below Lane Creek (Gage ESS45 at PRM
116.6), above Whiskers Creek (Gage ESS40 at PRM 107.2), below Twister Creek (Gage ESS30
at PRM 98.4), and at Susitna Station (ESS20 at PRM 29.9). When coupled with the USGS stage
hydrographs, these surface-water stage measurements are expected to be adequate to calibrate
the unsteady hydraulics simulated using the 1-D and 2-D Bed Evolution models; however,
calibration of the preliminary models in early 2014 as part of the Proof of Concept will
determine whether additional calibration data are recommended.
Sediment transport measurements: The sediment transport measurements collected by the
USGS at gaging stations provide key information for calibrating and validating the simulated
sediment transport and bed evolution. These data are summarized in Tetra Tech (2013a) and the
Geomorphology Study (ISR Study 6.5 Section 5.2). These data when combined with the 1980s
data collected by the USGS form an extensive data base that is sufficient to develop relationships
for the sediment supply from the Susitna River upstream of the Watana Dam site and the major
tributaries represented by the Chulitna, Talkeetna and Yentna rivers within the Study area.
Further discussion of the adequacy of these data is provided in ISR Study 6.5 Section 6.2. It is
noted that the USGS will continue to collect another year of sediment transport information in a
next year of study.
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6.1.9.5. LiDAR Verification and Acquisition
6.1.9.5.1. Su-Wa LiDAR Verification
The 2013 Su-Wa LiDAR meets 1-ft contour equivalence in open terrain (FVA) and 2-ft contour
equivalence in brush and forested land areas (SVA). The RMSEz and 95% confidence levels of
these data are approximately 0.25 and 0.5 ft for FVA, and 0.5 and 1.1 ft for SVA. These results
indicate that the Su-Wa LiDAR meets project specifications for LiDAR acquisition. Due to
unfavorable weather conditions, not all of the desired LiDAR was acquired. Therefore, the 2011
Mat-Su LiDAR was evaluated for suitability.
6.1.9.5.2. 2011 Mat-Su LiDAR Verification
The Matanuska-Susitna Borough 2011 LiDAR data acquisition was completed without the
collection of ground survey points and the 2011 LiDAR point cloud was not ground-truthed
(verified or indexed). For this study, the Mat-Su LiDAR verification was performed using
available data from PRM 31 to PRM 147.The Lower and Middle Susitna River areas are
undeveloped, which makes the identification of clear and open areas difficult. Most of the points
identified and used for the Fundamental Vertical Accuracy test (FVA) are located on types of
terrain (e.g. sandbars) that might not be considered for use in verification in normal conditions.
The result of the 2011 Matanuska-Susitna LiDAR verification shows that the FVA at the 95%
confidence level is 2.4 ft and for SVA is approximately 1.6 ft.
6.1.9.5.3. 2011 Mat-Su LiDAR Indexing
Indexing (vertical datum adjustment) is common practice to adjust a LiDAR dataset to a vertical
datum defined by survey points. The fundamental vertical accuracy of the LiDAR dataset after
indexing is 1.8ft at a 95% confidence level. This is significantly higher than for the 2013 Su-Wa
and would not meet Project specifications for new LiDAR acquisition. The fundamental vertical
accuracy is determined through check points in open terrain. Supplemental vertical accuracy is
approximately 1.7 ft at the 95% confidence interval.
For areas in vegetated terrain, the 95% confidence interval for vertical accuracy increases from
1.1 to 1.7 ft, and for open terrain it increases from 0.5 to 1.8 ft. This illustrates the more dynamic
nature of in-channel features including bars, heads of islands, and bank lines, as compared with
overbank areas including floodplains and terraces. The primary use of LiDAR was to extend
cross sections outside the channel banks. Given the approximate 0.6 ft of potential accuracy
improvement at the 95% confidence level, it may not be warranted to acquire additional LiDAR
in vegetated areas. One in-channel area that required high density LiDAR was in the Chulitna
River, where LiDAR was to be the primary source of in-channel data (Tetra Teach 2013h).
LiDAR for this area was acquired in 2013.
Although improvements can be made in overbank and in-channel areas, in-channel areas can be
surveyed efficiently using standard survey approaches. Therefore, in 2014, decisions will need
to be made whether the existing LiDAR is adequate for Project use by the various study
components. If the existing LiDAR is not deemed to be adequate then alternative methods will
be considered in various study areas.
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6.2. Study Component: Model Existing and with-Project Conditions
This section includes discussion of the current status of this study component. RSP Section 6.6.7
lists the primary studies that will provide information to the Fluvial Geomorphology Modeling
below Watana Dam Study including a summary of the type of information. Based on numerous
discussions with study leads and senior technical staff, information presented at TWG and other
meetings, and review of study reports and technical memorandums, it appears that each study is
on track to provide desired information.
6.2.1. Existing Conditions – Base Case Modeling
Reach-scale 1-D and local-scale 2-D Bed Evolution models are currently being developed for the
Middle and Lower Susitna River segments and Focus Areas. The adequacy of the input data will
be evaluated as part of the model development and calibrations, but no deficiencies are currently
evident other than the inability to collect data upstream of PRM 146.1 during the 2013 field
season. Data collection for the Middle Susitna River between PRM 146.1 and the Watana Dam
site are planned for in a next year of study. The reach-scale modeling will include a 50-year
periods of open water conditions comprised of a sequence of approximate 5 month periods
(approximately May through September of each year). The actual start and end dates of each
year will be evaluated based on the onset of ice cover conditions and breakup. For the 2-D Bed
Evolution modeling, three representative years have been recommended and information on the
selection of these years is included in Appendix E. Should other factors be identified
adjustments to the recommended years can be made in 2014.
6.2.2. Future Conditions – with-Project Scenarios
The with-Project scenarios include maximum load-following, intermediate load-following, base-
load, and a run-of-river. The Reservoir Operation Model (ISR Study 8.5 Section 4.3) will
provide reservoir outflows for each of these scenarios to provide a upstream flow boundary to
the 1-D Bed Evolution Model.
6.2.3. Uncertainty
The RSP Section 6.6.4.2.2.3 indicates that here is a wide range of information that can be used to
identify and understand uncertainty related to the fluvial geomorphology modeling. In addition
to sensitivity analysis, significant hydrologic variability is included in the 50-year flow record for
1-D Bed Evolution Model and in the representative years selected for the 2-D Bed Evolution
models. The range of operational scenarios, including a range of load conditions and run-of-
river, will also introduce significant hydrologic variability in the with-Project Scenarios.
The sensitivity analysis discussed in the RSP identified hydraulic roughness coefficients,
magnitude and gradation of inflowing sediment loads, substrate size gradation, and
dimensionless critical shear values as parameters to be varied. Hydraulic roughness is directly
associated with flow velocity, which is the primary hydraulic variable related to sediment
mobilization and transport. Base on the calibration results there will be sufficient information to
evaluate the range of roughness values to include in the sensitivity analysis. There will also be
sufficient information based on the number of bed-material samples to evaluate the degree
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sediment gradation needs to be included in the sensitivity analysis. Critical shear is intrinsic to
the sediment transport equations being considered for this study component and will be
evaluated during model calibration. Therefore, this variable may not be available for inclusion
as part of the sensitivity analysis. Incoming sediment loads often have significant uncertainty
and may impact the interpretation of results. Therefore, input sediment loads and roughness
values are likely to be the primary parameters for the sensitivity analysis.
6.2.4. Synthesis of Reach-Scale and Local-Scale Analyses
As shown in Figure 5.2-1, the reach-scale 1-D Bed Evolution Model provides information to the
local-scale 2-D Bed Evolution Models. The information includes sediment loads and boundary
conditions required by the 2-D Bed Evolution Models. Should the 1-D Bed Evolution Model
show appreciable change at years 25 or 50, the downstream boundary conditions and the
geometry of the 2-D Bed Evolution Models would need to reflect these changes. The synthesis
is not only between the reach- and local-scale models, but also among the morphology modeling
and other studies. As discussed in Section 4.3, the primary interdependencies include the
Geomorphology, Ice Processes in the Susitna River, Riparian Instream Flow, and Fish and
Aquatics Instream Flow (Open-water Flow Routing Model study component) studies.
6.3. Study Component: Coordination and Interpretation of Model
Results
The effort conducted in 2013 was primary in the area of internal coordination and integration
between the Fluvial Geomorphology Modeling below Watana Dam Study and the
Geomorphology Study (Study 6.5) and external coordination with the Fish and Aquatics
Instream Flow Study (Study 8.5), Riparian Instream Flow Study (Study 8.6), Ice Processes in the
Susitna River Study (Study 7.6), Groundwater Study (Study 7.5), Water Quality Modeling Study
(Study 5.6), and Characterization and Mapping of Aquatic Habitats (Study 9.9).
6.3.1. Integration of Geomorphology and Fluvial Geomorphology Modeling
Study
This effort has been progressing well and the Geomorphology Study (Study 6.5) has provided
the information needed by the Fluvial Geomorphology Modeling below Watana Dam Study to
help guide the development of the 1-D and 2-D Bed Evolution models (Section 5.3.1). The bed
evolution models are being developed incorporating the results of the Geomorphology Study,
including geomorphic reach delineation (Tetra Tech 2013b), tributary and mainstem sediment
supply (ISR Study 6.5 Section 4.3 and Tetra Tech 2013a), sediment-load analyses (Tetra Tech
2013a, Tetra Tech 2013c), effective discharge analyses (ISR 6.5 Section 4.3.2.4), preliminary
system equilibrium and sensitivity analyses (ISR 6.5 Section 4.6.2.3 and Tetra Tech 2013c),
LWD loading and distribution and reservoir sediment supply and trap efficiency (ISR Study 6.5
Section 4.8.2.1). Model results will be evaluated in terms of geomorphic processes as identified
in geomorphic process models (Study 6.5 ISR Section 4.1.2.3.3) as well as spatial distribution of
predicted changes and likely magnitude of geomorphic changes. Continuous coordination
between the Fluvial Geomorphology Modeling below Watana Dam and Geomorphology studies
ensures that the two studies are fully integrated.
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 91 February 2014 Draft
6.3.2. Coordination of Results with Other Resource Studies
The coordination with the other modeling studies is also proceeding well through the efforts
identified in Section 5.3.2. Coordination and integration with the other resource studies
mentioned has centered on integration of the modeling efforts and in particular transfer of
information between the various studies in terms of results from one study becoming input to
another study. The modeling studies are jointly working on the Proof of Concept to develop the
linkages between the various models and refine the development of the suite of results that will
form a large part of the metrics that Project effects will be evaluated.
7. COMPLETING THE STUDY
[As explained in the cover letter to this draft ISR, AEA’s plan for completing this study will be
included in the final ISR filed with FERC on June 3, 2014.]
8. LITERATURE CITED
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debris. Geomorphology 51. pp 175-185.
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Mussetter Engineering, Inc. 2008. Flood Inundation Mapping, Flood Hazard Evaluation, and
Downstream Impact Analysis of the Carmel River Reroute and Removal Option for the
San Clemente Dam Seismic Retrofit Project, California. Prepared for California Coastal
Conservancy and MWH Americas, Inc. February.
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Mussetter, R.A., Harvey, M.D. and Sing, E.F. 1995. Assessment of dam impacts on downstream
channel morphology. In Lecture Series, U.S. Committee on Large Dams, San Francisco,
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Mussetter, R.A. and Harvey, M.D. 1996. Geomorphic and hydraulic characteristics of the
Colorado River, Moab, Utah: Potential impacts on a uranium tailings disposal site. Proc.
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Balkema, Rotterdam. pp 405-414.
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interface cooperative: public domain software for river modeling. 2nd Joint Federal
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gravel rivers. University of Minnesota, St. Anthony Falls Hydraulic Laboratory, External
Memorandum No. M-220.
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Resources, University of California at Davis, 158 pp.
R2 Resource Consultants, Inc. (R2) 2013a. Selection of Focus Areas and Study Sites in the
Middle and Lower Susitna River for Instream Flow and Joint Resource Studies—2013
and 2014. Technical Memorandum for Alaska Energy Authority Susitna-Watana
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R2 2013b. Technical Memorandum: Adjustments to the Middle River Focus Areas. Susitna-
Watana Hydroelectric Project Prepared for the Alaska Energy Authority. Anchorage,
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R&M Consultants, Inc. 1982a. Alaska Power Authority Susitna Hydroelectric Project, Task 3 –
Hydrology, Tributary Stability Analysis. Prepared for Acreas American, Inc.
Anchorage, Alaska.
R&M Consultants, Inc. 1982b. Alaska Power Authority Susitna Hydroelectric Project, Task 3 –
Hydrology, Reservoir Sedimentation. Prepared for Acres American, Inc. Anchorage,
Alaska.
R&M Consultants, Inc. 1982c. Alaska Power Authority Susitna Hydroelectric Project, Task 3 –
Hydrology, Hydraulic and Ice Studies. Prepared for Acres American, Inc. Anchorage,
Alaska.
R&M Consultants, Inc. 1985. Susitna Hydroelectric Project Lower Susitna River Aggradation
Study: Field Data. Final Report. Document No. 2719. Prepared for Harza-Ebasco
Susitna Joint Venture. Anchorage, Alaska.
Rosgen, D.L. 1996. Applied River Morphology. Wildland Hydrology. Pagosa Springs.
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Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 95 February 2014 Draft
Ruark, M., Niemann, J., Greimann, B., and Arabi. 2011. Method for Assessing Impacts of
Parameter Uncertainty in Sediment Transport Modeling Applications. Journal of
Hydraulic Engineering, ASCE, v 137. no. 6. pp 623-636.
Shields, F.D. and Gippel, C.J. 1995. Prediction of effects of woody debris removal on flow
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Columbia.
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woody debris on the channel morphology of a forest, gravel-bed stream. Journal of
Hydrology 151. pp 153-178.
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Sediment Augmentation Feasibility Study, Nebraska. Prepared for the Platte River
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AEA.http://www.susitnaWatanahydro.org/documents/AEA_SuWa_FluvialModelingTech
Memo20120518_Draft.pdf
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Balance for the Middle and Lower Susitna River Segments. Susitna-Watana
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Energy Authority. Anchorage, Alaska.
Tetra Tech. 2013b. Initial Geomorphic Reach Delineation and Characterization, Middle and
Lower Susitna River Segments. Susitna-Watana Hydroelectric Project. 2012 Study
Technical Memorandum. Prepared for the Alaska Energy Authority. Anchorage, Alaska.
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Susitna River Segment. Susitna-Watana Hydroelectric Project. 2012 Study Technical
Memorandum. Prepared for the Alaska Energy Authority. Anchorage, Alaska.
Tetra Tech. 2013d. Stream Flow Assessment. Susitna-Watana Hydroelectric Project. 2012 Study
Technical Memorandum. Prepared for the Alaska Energy Authority. Anchorage, Alaska.
Tetra Tech. 2013e. Synthesis of 1980s Aquatic Habitat Information. Susitna-Watana
Hydroelectric Project. 2012 Study Technical Memorandum. Prepared for the Alaska
Energy Authority. Anchorage, Alaska.
Tetra Tech. 2013f. Mapping of Aquatic Macrohabitat Types at Selected Sites in the Middle and
Lower Susitna River Segments from 1980s and 2012 Aerials. Susitna-Watana
Hydroelectric Project. 2012 Study Technical Memorandum. Prepared for the Alaska
Energy Authority. Anchorage, Alaska.
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 96 February 2014 Draft
Tetra Tech. 2013g. Mapping of Geomorphic Features and Assessment of Channel Change in the
Middle and Lower Susitna River Segments from 1980s and 2012 Aerials. Susitna-Watana
Hydroelectric Project. 2012 Study Technical Memorandum. Prepared for the Alaska
Energy Authority. Anchorage, Alaska.
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Revised June 30, 2013. Susitna-Watana Hydroelectric Project. Prepared for the Alaska
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Distribution. Field Report. Review Draft: June 30. Susitna-Watana Hydroelectric Project.
Prepared for the Alaska Energy Authority. Anchorage, Alaska.
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Version 5.0. July
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Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 97 February 2014 Draft
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INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
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9. TABLES
Table 3.1-1. Schedule for the downstream study limit determination process for the Fluvial Geomorphology Modeling
below Watana Dam Study.
Step in Downstream Geomorphology Study Limit Determination Date
RM 75 downstream geomorphology modeling limit proposal in RSP December 2012
Recon. level assess. of Project effects in the L. Susitna River Segment and flow routing model results January 2013
Tech. memorandum on recon. level assessment of Project effects in the Lower Susitna River
Segment February 2013
TWG meeting for confirmation or adjustment of downstream geomorphology modeling limit –
downstream study limit extended to PRM 29.9 February 2013
1-D Bed Evolution modeling and 2013 Geomorphology Study results and tech memo 2014
TWG meeting to reevaluate and confirm or adjust downstream modeling limit of PRM 29.9 2014
Collect additional data if need identified (Second Study Season) Summer 2nd Study
Season
Table 4.1-2. Average Annual Sediment Loading at USGS Gaging Stations (R&M Consultants, Inc. 1982b).
USGS Gaging Station Average Annual Sediment Load (tons)
Suspended Sediment Bed load1 Total Load
Susitna River near Cantwell 6,898,000 207,000 7,105,000
Susitna River at Gold Creek 7,731,000 232,000 7,963,000
Note:
1 Estimated as 3 percent of suspended sediment load
Table 4.1-2. Average Annual Sediment Loading at USGS Gaging Stations and Watana Dam (Harza-Ebasco 1984).
Location Average Annual Sediment Load (tons)
Suspended Sediment Bed load1 Total Load
Susitna River near Cantwell 5,660,000 170,000 5,830,000
Susitna River at Gold Creek 7,260,000 218,000 7,478,000
Watana Dam 6,530,000 196,000 6,726,000
Note:
1 Estimated as 3 percent of suspended-sediment load.
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FERC Project No. 14241 Page 99 February 2014 Draft
Table 4.1-3 Model input and results interactions among various Studies and study components.
Modeling Task Input and Results Hydrology Sediment Hydraulics Channel & Floodplain Geometry
1-D Tributary
Sediment
Modeling
Input Site speific1 bed material from site samples site specific D/S stage-discharge Existing at T = 0 (yr-0)3
Results for: Results for range of steady flows to develop sediment-rating curves at mouth of each tributary
1-/2-D Morph. n/a trib. Sediment-rating curves n/a n/a
Aquatic Habitat (8.5) n/a n/a V, D, WSE some trib. mouths barrier/delta change some tribs.
Fish Access(9.12) n/a n/a V, D, WSE some trib. mouths barrier/delta change some tribs.
1-D Bed Evolution
Modeling
(Reach-Scale)
Input 50-yrs Existing & 3 OS1 Existing & 3 OS2 stage-discharge at Susitna Sta. Existing at T = 0 (yr-0)3
Results for: Results for continuous 50-year simulations throughout 1-D modeling domain
2-D Morphology n/a U/S sed. rating curves at FAs D/S stage-discharge at FAs main channel change
1-D Ice(7.6) n/a n/a stage-discharge at 3-Rivers main channel change4
Flow Routing(8.5) n/a n/a n/a main channel change4
Aquatic Habitat(8.5) n/a substrate change4 stage-discharge relationships main channel change4
Riparian Habitat(8.6) n/a sediment supply to overbanks stage-discharge relationships bar/island/floodplain change
2-D
Bed Evolution
Modeling
(Local-Scale)
Input <1-yr wet, avg., dry with
PDO, Existing & 3 OS1
U/S sed. rating curves at FAs for
yrs-0,25,50 for Existing & 3 OS5 D/S stage-discharge at FAs for
yrs-0,25,50 for Existing & 3 OS5 Existing (yr-0)3, yrs-25,505
in main channel
Results for: Results for range of <1-yr simulations throughout FA modeling domain
2-D Hydraulic n/a Bed-material gradation change4 n/a lateral feature trends
2-D Ice(7.6) n/a n/a n/a lateral feature trends4
Flow Routing(8.5) n/a n/a n/a n/a
Aquatic Habitat(8.5) n/a substrate change4 n/a barrier/delta change
Riparian Habitat(8.6) n/a sediment supply to overbanks n/a bar/island/floodplain change
2-D
Hydraulic
Modeling
(Local-Scale)
Input Range of steady flows6 Bed-material gradation change7 D/S stage-discharge at FAs for
yrs-0,25,50 for Existing & 3 OS5 Existing (yr-0)3, yrs-25,50 main
channel5 and lateral features7
Results for: Results for range of steady flows throughout FA modeling domain
Ice, Flow Routing n/a n/a n/a n/a
Aquatic Habitat(8.5) n/a n/a V, D, WSE, etc. throughout FAs n/a
Riparian Habitat(8.6) n/a n/a V, D, WSE, etc. throughout FAs n/a
Notes: 1 From Open-Water Flow Routing Model development effort (Study 8.5 Section 4.3). 2 From gage data (USGS), sediment transport study (ISR Study 6.5 Section 4.2 and Tetra Tech 2013a). 3 From hydrographic survey, land-based survey, and LiDAR. (Studies 8.5 and 6.6, survey by Tetra Tech for some tributaries.) 4 Only if magnitude of change is sufficiently large to warrant inclusion in other study aspects.
5 From 1-D Bed Evolution Models (Reach-Scale). 6 From habitat study requirements. 7 From 2-D Bed Evolution Modeling trends (Local-Scale).
This table does not include all interactions involving Ice Processes and Large Woody Debris conditions related to bed evolution modeling.
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 100 February 2014 Draft
Table 4.1-4. Summary of model parameter precedencies for water resources models to be applied in the Susitna-Watana licensing effort.
Model Study Section Software Program Precedence (Parameters that the model results will be adopted for as the governing values)
Reservoir Operation Model Engineering HEC ResSim
Project releases (discharge from the dam including spills) and reservoir pool elevations. The model will be refined
throughout the study period to reflect any changes in project configuration and as operations scenarios are
developed. (Available Q4 2012 )
Initial Flow Routing Model
(Hydrologic Routing) Engineering HEC ResSim Discharge, stage and other hydraulic parameters such as velocity and depth from RM 184 to RM 84 until the Open-
water Flow Routing Model is developed (Q1 2013)
Open-water Flow Routing
Model (Hydraulic Routing) 8.5 HEC-RAS
Discharge, stage and other 1-D hydraulic parameters such as velocity and depth from RM 184 downstream to RM 74
once the model is developed (Q1 2013 version 1) during open water periods. Model will be updated with additional
cross section from 2013 field work (Q4 2013 ver. 2) and finalized (Q4 2nd Study year, ver. 3). Provides boundary
conditions to 2-D Bed Evolution Model.
River1D Ice Processes
Model 7.6 River 1D
Discharge, stage, and other 1-D hydraulic parameters such as velocity and depth from RM 184 to RM 100 during
periods of ice formation, ice cover and ice break-up once model is developed (Q4 2013 ver. 1, Q4 2nd Study year, ver.
2). The model will also provide water temperature, ice extents and ice thickness for the same period.
River1D Ice Processes
Model
River2D Focus Area Ice
Models
7.6 River 1D
River 2D
Hydraulic conditions, water temperature, ice extents and ice thickness within the focus areas during periods of ice
formation, ice cover and ice break-up.
2-D River Water Quality
Model 5.6 EFDC Water temperature during the open water period and other water quality parameters year round from RM 184 to RM
26
1-D Bed Evolution Model
(Hydraulics and Sediment
Transport)
6.6 HEC-6T1
(Q2 2013)
One-dimensional sediment transport characteristics, bed aggradation/degradation and substrate gradation in the
main channel from RM 184 to RM 74. May be used to determine these parameters for localized off-channel habitat
within focus areas. Open-water Flow Routing Model will take precedence for 1-D hydraulics.
2-D Bed Evolution Model
(Hydraulics and Sediment
Transport)
6.6 TBD2
(2014)
Detailed two-dimensional hydraulic and sediment transport characteristics, bed aggradation/degradation and
substrate gradation within the focus areas. Will provide two-dimensional velocity and depth for FA-IFS within focus
area where applied during the open water period. Boundary condition of downstream water surface elevation and
upstream inflow supplied by Open-water Flow Routing Model
Notes:
1 HEC-6T was selected. However, HEC-RAS version 4.2 has become available and is being evaluated for suitability on this project.
2 Candidate Models: SRH-2D and River-2D are being evaluated to determine which model is most suitable for this project.
INITIAL STUDY REPORT FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY (6.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 101 February 2014 Draft
Table 4.1-5. Calibration Datasets for 1-D and 2-D Bed Evolution Models.
Source Type of data
Tetra Tech Inc. water-surface elevations, high-water marks
Brailey Hydrologic
Consultants
Water-surface elevations, ADCP velocity measurements
Geovera, LLC. Water-surface elevations
U.S.G.S. Flow data, stage data, sediment transport measurements, sediment gradations
R2 Resources, Inc. Water-level loggers and stage
Table 4.1-6. Sieve bulk sample area dimensions.
Dmax (mm) Weight (lb) Depth (ft) Depth (in) Square (ft) Diameter (ft)
2 0.024 0.01 0.2 0.1 0.1
4 0.189 0.03 0.3 0.2 0.3
8 1.51 0.05 0.7 0.5 0.6
11.3 4.23 0.08 0.9 0.7 0.8
16 12.0 0.11 1.3 1.0 1.1
22.6 33.6 0.15 1.8 1.4 1.6
32 101 0.22 2.6 2.0 2.3
45 185 0.31 3.7 2.3 2.6
64 307 0.44 5.2 2.5 2.8
90 400 0.61 7.3 2.4 2.7
128 400 0.87 10.4 2.0 2.2
180 400 1.22 14.7 1.7 1.9
256 400 1.74 20.9 1.4 1.6
360 400 2.45 29.4 1.2 1.3
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Table 4.1-7. 2013 Susitna-Watana airborne LiDAR data specifications.
Data Specification Description
Point density Minimum 8 points per square meter
Nominal point spacing 0.45 meter
Field of view 30° angle
Returns per pulse 4
Horizontal projection NAD 1983 State Plane Alaska 4 FIPS 5004
Vertical projection NAVD 88 – GEOID09
Horizontal accuracy (RMSEr) ≤ 17 cm (~0.56 ft)
Vertical accuracy (RMSEz) ≤ 9.25 cm (~0.30 ft)
LiDAR intensity values 0 to 255 (8 bits)
LiDAR files version ASPRS LAS files version 1.2
Vertical and horizontal units U.S. Survey Feet
Table 4.1-8. Comparison of NMAS/NSSDA Vertical Accuracy (ASPRS 2004).
NMAS Equivalent Contour Interval (ft) NSSDA RMSEz (ft) NSSDA Vertical Accuracy at 95% confidence level (ft) Required Accuracy for Reference Data for “Tested to Meet” (ft)
0.5 0.15 0.30 0.10
1 0.30 0.60 0.20
2 0.61 1.19 0.40
3* 0.92* 1.79* 0.60*
4 1.22 2.38 0.79
5 1.52 2.98 0.99
10 3.04 5.96 1.98
Notes:
* Average of 2 and 4 ft equivalent contour interval rows in ASPRS 2004.
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Table 4.3-1: Primary output variables for which values are taken directly from the 1-D and 2-D Bed Evolution models and relevance to other studies.
Variable Description of Model Output Spatial Resolution Relevance to Other Studies
1-D Bed Evolution Model
Water-surface profiles Steady-state water-surface profiles for all discharges Cross section Geomorphology
Cross-sectionally averaged hydraulic
conditions
Flow depth, velocity, bed shear stress, channel top
width Cross section FA-IFS, R-IFS, Geomorphology
Bed-material load transport rates Transport rates by grain size fraction Cross section Geomorphology
Bed-material (i.e., substrate) gradations Change in surface layer bed gradations by cross
section over time (0, 25, 50 years) Cross section FA-IFS, Geomorphology
Bed elevation Changes in bed elevation with time Cross section, longitudinal profile FA-IFS, R-IFS, Geomorphology,
GW
2-D Bed Evolution Model
Water-surface elevations Steady and unsteady water-surface elevations Grid element FA-IFS, R-IFS, Geomorphology,
GW
Depth-averaged hydraulic conditions Flow depth , velocity (magnitude and direction), bed
shear stress Grid element FA-IFS, R-IFS, Geomorphology,
GW
Flow distribution among multiple channels
(including side channels)
Discharge in each branch (including side channels)
over range of flows; changes associated with bed
evolution model results
Channel width FA-IFS, R-IFS, Geomorphology,
GW
Bed-material load transport rates Transport rates by grain size fraction, including supply
to and transport through side channels Grid element FA-IFS, R-IFS, Geomorphology,
GW
Bed-material (i.e., substrate) gradations Change in substrate gradations by grid element over
time, including side channels and side sloughs Grid element FA-IFS, R-IFS, Geomorphology,
GW
Bed elevation
Changes in bed elevation with time, including side
channels and side sloughs. Evolution of mouths and
spawning areas of particular interest
Grid element FA-IFS, R-IFS, Geomorphology,
GW
Breaching flows Magnitude, frequency and duration of flows overtopping
control at the head of side channels Grid element →side channel width FA-IFS, Geomorphology
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Table 4.3-2: Key variables needed for the impact assessments for which results are obtained through additional analysis of predictions taken directly from the 1-D and
2-D Bed Evolution models.
Variable Description Spatial Resolution Relevance to Other Studies
1-D Bed Evolution Model
Wash load transport rates Correlations between wash load transport rates and
discharge Gage locations WQ, R-IFS
Overbank sedimentation rates Rate of sediment delivery into overbanks and vertical
accretion rates Reach-averaged R-IFS, Geomorphology
Breaching flows Magnitude, frequency and duration of flows overtopping
control at the head of side channels Site R-IFS, Geomorphology
Side channel connectivity Frequency, duration and inundation extent of backwater
flows into side channels Site R-IFS
Bed-Material Motion Thresholds (aka
Incipient Motion Analysis)
Frequency and duration of flows sufficient to cause
general mobilization of bed material
Cross section and/or reach-
averaged FA-IFS, Geomorphology
Bed-material transport capacity rating
curves
Bed-material transport capacity (total and by-size
fraction) as a function of discharge
Cross section and/or reach-
averaged Geomorphology
Effective Discharge Magnitude and frequency of flows that transport the
most sediment over defined period of time Reach-averaged Geomorphology
Bank erosion rates Estimated rate of erosion into main and side channel
banks
Cross section and/or reach-
averaged R-IFS, Geomorphology
LWD recruitment Quantities of LWD delivered to mainstem and side
channels due to bank erosion Reach R-IFS, Geomorphology
Deposition rates at tributary mouths Evolution of tributary mouth fans/bars over time Geomorphology unit FA-IFS, Geomorphology
Hydraulic conditions at tributary mouths Potential effect of changes in tributary mouths and
effects on fish passage into tributaries Geomorphology unit FA-IFS, Geomorphology
2-D Bed Evolution Model
Weighted-useable-area versus discharge
curves
Hydraulic conditions (velocity, depth, substrate size)
provided to FA-IFS for WUA estimates Grid element→ Habitat unit FA-IFS, Geomorphology
Overbank sedimentation rates Rate of sediment delivery into overbanks and vertical
accretion rates Grid element R-IFS, Geomorphology
Bed-Material Motion Thresholds (aka
Incipient Motion Analysis)
Frequency and duration of flows sufficient to cause
general mobilization of bed material Grid element→ Habitat unit FA-IFS, Geomorphology
Bank erosion rates Changes in bank shear stress and bank energy index
(BEI) Model reach R-IFS, Geomorphology
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Variable Description Spatial Resolution Relevance to Other Studies
Changes in side channel, side slough and
upland slough geometry Evolution of channel width and depth Grid element →side channel width FA-IFS, R-IFS,
Geomorphology
Fine sediment interactions in spawning
areas
Potential for infiltration and flushing of fines from
spawning substrate, including side channels and side
sloughs Grid element→ Habitat unit FA-IFS, R-IFS,
Geomorphology
LWD recruitment Changes in bank erosion rates that could affect LWD
recruitment Grid element FA-IFS, R-IFS,
Geomorphology
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Table 5.1-1 Potential 1-D Bed Evolution Models.
Characteristics & Evaluation Criteria
Software
HEC-RAS
Ver. 4.1.0
HEC-RAS
Ver. 4.2.0 SRH-1D MIKE 11 HEC-6T
General
Commercial/cost (if applicable) ○ ○ ○ ● / $8,000 ● / $3,000
Full or quasi-unsteady for sediment
transport simulation Quasi Both Both Full Quasi
Ice for fixed bed ● ● ○ ○ ○
Ice for moveable bed ● ● ○ ○ ○
Number of transport equations supported 7 8 13 10 18
Supports user-defined transport equation ○ ●1 ○ ○ ●
Closed-loop capability ○ ● ● ● ●
Experience with model H H L M H
Model Size Limitations
Number of cross sections NL NL NL NL 5,000
Number of hydrograph ordinates 40,000 40,000 NL NL 5,000
Number of sediment sizes 20 20 NL NL 20
Sediment Sizes Supported
Wash load (silt and clay) ● ● ● ● ●
Considers settling and resuspension ● ● ● ● ●
Sand ● ● ● ● ●
Gravel and cobble ●W ●W ●P,W ● ●P,W
● = Yes; ○ = No; H = High; M = Moderate; L = Low; NL = No Limit
P = Parker (1990), W = Wilcock & Crowe (2003) sediment transport functions
1 The user can calibrate coefficients and exponents of certain transport functions, thereby creating user-defined equations
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Table 5.1-2 Potential 2-D Bed Evolution Models Selected for Final Evaluation.
Evaluation Criteria Model
SRH-2D River2D
Proprietary/cost (if applicable) ○ ○
Unsteady flow capability ● ●
Ice for fixed bed ○ ●
Ice for moveable bed ○ ●
Number of transport equations supported 6 2
Supports user defined transport equation ○ ○
Relative execution speed M S
Model stability H H
Experience with model H M
Moveable boundary simulation ● ●
Finite element (FE) / Finite Volume (FV) FV FE
Grid structure: Flexible Mesh (FM) ● ●
# of mesh elements Hydrodynamic>200,000, Sed.
Transport <16,000
Hydrodynamic>100,000, Sed.
Transport >100,000
Wash load (silts, clays) ○ ○
Suspended Load ● ○
Considers settling ● ○
Sand ● ●
Gravel and cobble ● ●
Notes: ● = Yes; ○ = No; F = Fast; M = Moderate; S = Slow; L = Low
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Table 5.1-3 Tributary Modeling.
Tributary Name PRM Entering
Bank
Geomorphic
Reach
Focus
Area
Sediment
Input only 1-D or 2-D
Tsusena Creek 184.6 RB MR-2 n/a X 1-D
Fog Creek 179.3 LB MR-2 n/a X 1-D
Unnamed 174.3 LB MR-2 FA173 n/a 2-D
Unnamed 173.8 RB MR-2 FA173 n/a 2-D
Portage Creek 152.3 RB MR-5 FA151 n/a 2-D
Unnamed* 144.6 LB MR-6 FA144 n/a 2-D
Indian River* 142.1 RB MR-6 FA141 n/a 2-D
Gold Creek* 140.1 LB MR-6 n/a X 1-D
Skull Creek* 128.1 LB MR-6 FA128 n/a 2-D
Lane Creek* 117.2 LB MR-7 n/a X 1-D
Unnamed* 115.4 RB MR-7 FA115 n/a 2-D
Gash Creek* 115.0 LB MR-7 FA113 n/a 2-D
Slash Creek* 114.9 LB MR-7 FA113 n/a 2-D
Unnamed* 113.7 LB MR-7 FA113 n/a 2-D
Whiskers Creek* 105.1 RB MR-8 FA104 n/a 2-D
Trapper Creek* 94.5 RB LR-1 n/a n/a 1-D
Birch Creek* 92.5 LB LR-1 n/a n/a 1-D
Sheep Creek 69.5 LB LR-2 n/a n/a 1-D
Caswell Creek 67.0 LB LR-2 n/a n/a 1-D
Deshka River* 45.0 RB LR-3 n/a n/a 1-D
*Tributaries that will be analyzed in 2013.
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Table 5.1-4 Initial Manning’s Roughness Coefficients for 1-D and 2-D Bed Evolution Models.
Description* Abbreviation Initial Manning’s Roughness Coefficient
Bed Rock KF 0.05
Channel FAN 0.04
Fan MCGB & SCGB 0.08
Gravel Bar GD 0.05
Grano Diorite MC 0.15
Main Channel MFP 0.03
Mature Floodplain MORAINE 0.17
Moraine OCH 0.17
Overbank Channel OFP 0.12
Overbank Floodplain OUTWASH TCE 0.15
Outwash Terrace PC 0.17
Paleo Channel RRRR 0.12
Rail Road Riprap SC 0.05
Side Channel SS 0.03
Side Slough TCE 0.03
Terrace TR 0.17
Tributary US 0.035
Upland Slough VB 0.04
Vegetated Bar YFP 0.12
Young Floodplain KF 0.15
*Descriptions correspond to geomorphic mapping
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Table 5.1-5. Sources and Types of Data Used to Develop the 2-D Models.
Source Type of data
Tetra Tech Inc. water-surface elevation, high-water mark, bed-material gradations (surface + subsurface),
tributary sediment loads
Brailey Hydrologic
Consultants
Bathymetry, water-surface elevation, high-water mark, velocity measurements
Keystone Aerial Surveys,
Inc.
LiDAR Survey
Geovera, LLC. Overbank topography and channel surveys
U.S.G.S. Flow data, stage data, sediment transport measurements, sediment gradations
Bill Miller Ecological Channel substrate mapping
R2 Resources, Inc. HEC-RAS model
Fish and Aquatics IFS
Team
Mapping showing the fine mesh areas for the 2-D model development
Table 5.1-6: Focus Areas in the Middle Susitna River Segment.
Focus Area ID Common Name Downstream PRM Upstream PRM Geomorphic Reach Reach Type
FA-184 Watana Dam 184.7 185.7 MR-1 SC2
FA-173 Stephan Lake Complex 173.6 175.4 MR-2 SC2
FA-151 Portage Creek 151.8 152.3 MR-5 SC2
FA-144 Slough 21 144.4 145.7 MR-6 SC3
FA-141 Indian River 141.8 143.4 MR-6 SC3
FA-138 Gold Creek 138.5 140.0 MR-6 SC3
FA-128 Slough 8A 128.1 129.7 MR-6 SC3
FA-115 Slough 6A 115.3 116.5 MR-7 SC2
FA-113 Oxbow I 113.6 115.3 MR-7 SC2
FA-104 Whiskers Slough 104.8 106.0 MR-8 MC1/SC3
Table 5.1-7: Upstream and Downstream PRM boundaries for Geomorphic Assessment Areas.
Geomorphic Assessment Area PRM Length
Downstream Upstream mile
GAA-Whiskers Slough 104.2 107.4 3.2
GAA-Oxbow I 113.6 115.3 1.7
GAA-Slough 6A 115.3 117.3 2.0
GAA-Slough 8A 128.1 130.4 2.3
GAA-Gold Creek 137 140.1 3.1
GAA-Indian River 140.1 143.6 3.5
GAA-Slough 21 143.6 146.1 2.5
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Table 5.1-8 Tributary Modeling Results.
Tributary Name PRM Reconnaissance Conducted/
Planned
Model Developed
No.
Cross Sections
Modeled Channel Length (ft)
Average Channel Width (ft)
Average Channel Slope (ft/ft)
Tsusena Creek 184.6 Next Study
Season
n/a n/a n/a n/a n/a
Fog Creek 179.3 Next Study
Season
n/a n/a n/a n/a n/a
Unnamed 174.3 Next Study
Season
n/a n/a n/a n/a n/a
Unnamed 173.8 Next Study
Season
n/a n/a n/a n/a n/a
Portage Creek 152.3 Next Study
Season
n/a n/a n/a n/a n/a
Unnamed* 144.6 2013 HEC-RAS 4 151 31 0.038
Indian River* 142.1 2013 HEC-RAS 5 511 120 0.010
Gold Creek* 140.1 2013 HEC-RAS 4 194 37 0.022
Skull Creek* 128.1 2013 HEC-RAS 5 143 53 0.030
Lane Creek* 117.2 2013 HEC-RAS 5 167 32 0.009
Unnamed* 115.4 2013 No2 n/a n/a n/a n/a
Gash Creek* 115.0 2013 HEC-RAS 5 112 8 0.013
Slash Creek* 114.9 2013 HEC-RAS 5 67 8 0.018
Unnamed* 113.7 2013 HEC-RAS 6 66 26 0.044
Whiskers Creek* 105.1 2013 HEC-RAS 5 90 30 0.002
Trapper Creek* 94.5 2013 HEC-RAS 10 n/a3 n/a3 n/a3
Birch Creek* 92.5 Next Study
Season1
n/a n/a n/a n/a n/a
Sheep Creek 69.5 Next Study
Season
n/a n/a n/a n/a n/a
Caswell Creek 67.0 Next Study
Season
n/a n/a n/a n/a n/a
Deshka River* 45.0 2013 HEC-RAS 10 30,500 220 0.0005
Notes:
* Tributaries that will be analyzed in 2013.
1 Private landowner did not allow access in 2013, will try for access again in the next study season.
2 Excluded from modeling based on observations during 2013 reconnaissance of low sediment production and
absence of a delta.
3 Modeling is in development, so these results are not yet available.
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Table 5.1-9. Summary of the number of bank observations along the Susitna River and tributaries in 2013.
Location Cross Section Roughness Observations
Water-Surface Elevation Measurements Bank Profiles
Susitna River 20 20 30
Focus Areas 8 8 6
Table 5.1-10. Summary of the number of sediment samples collected along the Susitna River and tributaries in 2013.
Location
Susitna River
Pebble
Counts
Pebble
Count/Sub-Surface Sample Bulk Samples Bank Samples
Lower River 0 16 0 0
Middle River
(Excluding FA's) 5 22 1 6
FA104 9 5 2 14
FA113 4 8 0 9
FA115 8 4 0 5
FA128 5 1 0 8
FA138 6 5 0 10
FA141 7 3 0 5
FA144 12 6 0 6
Location
Tributaries
Pebble
Counts
Pebble Count/Sub-
Surface Sample
Bulk Samples Bank Samples
Trappers Creek 7 0 1 0
Indian River 2 1 0 0
Yentna River 1 2 0 0
Chulitna River 0 5 0 0
Deshka River 1 0 8 0
Talkeetna River 0 5 0 0
Slash Creek 0 0 1 0
Gash Creek 1 0 1 0
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Table 5.1-11. Sediment sampling conducted at the Tributary Delta study sites.
Tributary PRM
Surface Sample/ Pebble Count Subsurface Sample
Size (mm) Sand
Cover1 Size (mm) Less Than 2mm2
D16 D50 D84 % D16 D50 D84 %
Whiskers Creek 105.1 19 34 54 0 0.45 12 24 33
UNT 113.7 113.7 27 90 457 0 0.10 3 103 48
Slash Creek 114.9 n/a n/a n/a n/a 2 12 27 17
Gash Creek 115.2 12 24 46 2 2 19 102 18
Lane Creek 117.2 25 57 116 0 3 31 117 14
Skull Creek 128.1 23 69 223 0 2 23 80 16
Gold Creek 140.1 31 85 177 1 2 21 59 18
Indian River 142.1 35 75 162 0 0.6 19 49 27
UNT 144.6 144.6 27 83 179 0 2 24 59 15
1 Value is the percent of the surface that was covered with a layer of sand and finer material.
2 Value represents the percent of the subsurface sample that was less than 2 mm which is the upper limit of sand.
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Table 5.1-12. Cross Sections Surveyed through 2013 Field Season.
Lower Susitna River Segment Middle Susitna River Segment
PRM Date1 PRM Date1 PRM Date1 PRM Date1 PRM Date1 PRM Date1 PRM Date1
29.9 C 69.2 C 94.0 C 102.7 A 120.3 C 134.3 A,B 146.2 C
31.6 C 71.0 C 94.8 C 103.5 A 120.7 A 134.7 C 146.6 A
32.4 C 73.1 C 96.2 C 104.1 A 121.4 C 135.0 A 148.3 A
33.7 C 74.1 C 97.0 A 104.7 A 122.1 C 135.7 C 151.1 A
34.8 C 75.0 C 98.4 A,B 105.3 A 122.7 A 136.2 A 152.1 A,B
36.4 C 75.9 C 99.9 C 106.1 A 122.8 A 136.7 A 152.9 A
38.3 C 77.0 C 100.7 C 106.6 C 123.2 C 137.2 C 153.7 A
39.5 C 78.0 C 101.4 A,B 107.1 A 123.7 A 137.6 A,B 168.1 A
40.4 C 79.0 C 102.1 C 107.8 C 124.1 A,B 138.1 A 170.1 A
41.3 C 80.0 A n/a n/a 108.3 A 124.5 C 138.4 C 173.1 A
44.5 C 80.7 C n/a n/a 109.0 C 125.0 C 138.7 A 174.9 A
45.6 C 81.4 C n/a n/a 110.5 A,B 125.4 A 139.0 A 176.5 A
46.3 C 82.3 A n/a n/a 111.9 A 125.8 C 139.8 A 178.5 A
47.1 C 83.0 A n/a n/a 112.5 C 126.1 A 140.0 A,B 179.5 A
47.9 C 84.4 A n/a n/a 113.1 C 126.5 C 140.5 C 181.6 A
49.0 C 85.4 A n/a n/a 113.6 A,B 126.8 A,B 140.8 C 182.9 A
52.1 C 86.3 A n/a n/a 114.4 A 127.8 C 141.2 C 183.3 A
54.2 C 87.1 A n/a n/a 115.4 A 128.1 A 141.7 A 184.4 A
55.4 C 87.6 C n/a n/a 115.7 A 129.7 A,B 141.9 A 184.9 A
57.8 C 88.0 C n/a n/a 116.3 A 130.5 C 142.2 A,B 185.2 A
59.1 C 88.4 A n/a n/a 116.6 A 130.9 C 143.0 A 185.5 A
60.3 C 89.5 C n/a n/a 117.1 C 131.4 A 143.5 A 186.2 A
62.7 C 90.2 C n/a n/a 117.4 A 132.1 C 143.9 C 187.2 A
64.6 C 91.0 A n/a n/a 117.9 C 132.6 A 144.3 A n/a n/a
66.1 C 91.6 A n/a n/a 118.4 A 133.3 A 144.9 A n/a n/a
67.2 C 92.3 C n/a n/a 119.0 C 133.8 A 145.5 A n/a n/a
68.2 C 93.2 C n/a n/a 119.9 A,B 134.1 A 145.7 A,B n/a n/a
Note:
A = 2012field season; B = 2012 post-flood (end of September through early October); C = 2013 field season
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Table 5.1-13. Water-Surface Elevation (WSE) measurements collected during the Focus Area topographic surveys by
Fish and Aquatics Instream Flow (ISR Section 8.5).
Location No. of WSE measurements Comment
FA-104 846
WSE's collected along main-channel, side channels and
upland sloughs. Date of surveys and corresponding
discharges need to be determined
FA-113 358
FA-115 439
FA-138 759
FA-128 899
FA-141 578
FA-144 377
Table 5.1-14. Water surface elevations measurements collected for model calibration as part of the ADCP survey by Fish
and Aquatics Instream Flow (ISR Section 8.5).
Location No. of WSE measurements Date Approximate flow at time of measurements, cfs
FA-104 24 12-July-2013 17,500
FA-113 28 10-11 July, 2013 20,040
FA-115 19 10-July-2013 21,690
FA-128 64 2-July-2013 24,710
FA-138 21 1-July-2013 25,000
FA-141 19 30-June-2013 24,750
FA-144 20 29-June-2013 26,020
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Table 5.1-15. Summary of 2012-2013 data collected at ESS stationsa.
Station PRM Water
Level
Water
Temperature
Air
Temperature
Camera
Images
Land Access Granted Priority Studies Using Data
ESS80 225.0 Complete Complete Complete Yes Yes B Engineering, Upper Basin DGGS
ESS70 187.1 Missing
2013
Missing 2013 Complete Yes No A IFS, Ice Processes, Geomorphology, Water quality,
Engineering, Upper Basin DGGS, Groundwater
ESS65 176.5 Missing
2013
Missing 2013 Complete Yes No A IFS, Ice Processes, Geomorphology, Water Quality
ESS60 168.1 Missing
2013
Missing 2013 Complete Yes No A IFS, Ice Processes, Geomorphology, Water Quality
ESS55 152.2 Missing
2013
Missing 2013 Complete Yes No A IFS, Ice Processes, Geomorphology, Water quality,
Groundwater
ESS50 124.1 Partial 2013 Partial 2013 Complete Yes Yes A IFS, Ice Processes, Geomorphology, Water quality,
Groundwater
ESS45 116.6 Partial 2013 Partial 2013 Complete Yes Yes A IFS, Ice Processes, Geomorphology, Water quality,
Groundwater
ESS40 107.2 Partial 2013 Partial 2013 Complete Yes Yes A IFS, Ice Processes, Geomorphology, Water quality,
Groundwater
ESS35 102.1 Missing
2013
Partial 2013 Complete Yes Yes C IFS, Ice Processes, Geomorphology, Water quality,
Groundwater
ESS30 98.4 Complete Complete Complete Yes Yes B IFS, Ice Processes, Geomorphology, Water quality,
Groundwater
Notes:
a Table copied from ISR Study 8.5
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Table 5.1-16. Priority Area 01 South vertical accuracy tests results for 2013 LiDAR.
LiDAR Vertical Accuracy Test Cover type # Survey
points
Max
(US
Feet)
Min
(US
Feet)
Mean
(US
Feet)
STD
(US
Feet)
RMSEz
(US
Feet)
Vertical
accuracy at 95% confidence level
(US Feet)
# Outlier
s
Fundamental Vertical Accuracy Test Open terrain 39 0.545 -0.728 -0.015 0.275 0.272 0.533 0
Supplemental
Vertical
Accuracy Test
Brush
land/Low
vegetation
24 1.048 -1.100 -0.316 0.546 0.619 1.213 1
Forest land 23 0.500 -1.141 -0.344 0.429 0.542 1.062 0
Consolidated Vertical Accuracy Test
All land cover
types 86 1.048 -1.141 -0.191 0.427 0.465 0.911 1
Table 5.1-17. Priority Area 02 South, 03 and 04 vertical accuracy tests results for 2013 LiDAR.
LiDAR Vertical Accuracy Test Cover type # Survey points
Max (US
Feet)
Min (US Feet)
Mean (US
Feet)
STD (US
Feet)
RMSEz (US
Feet)
Vertical accuracy at 95% confidence
level (US Feet)
# Outliers
Fundamental Vertical Accuracy Test Open terrain 21 0.432 -0.473 0.004 0.215 0.209 0.410 0
Supplemental Vertical
Accuracy Test
Brush
land/Low
vegetation
21 1.071 -0.601 0.189 0.473 0.499 0.978 0
Forest land 19 1.640 -0.918 0.041 0.571 0.557 1.091 0
Consolidated
Vertical
Accuracy Test
All land
cover types 61 1.071 -0.918 0.053 0.391 0.391 0.766 1
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Table 5.1-18. 2011 Matanuska-Susitna LiDAR vertical accuracy verification results.
LiDAR Vertical Accuracy Test Cover type # Survey points Max (US Feet) Min (US Feet)
Mean (US
Feet)
STD (US
Feet)
RMSEz (US
Feet)
Vertical accuracy at 95% confidence
level (US Feet)
# Outlier
s
Fundamental Vertical Accuracy Test Open terrain 174 3.830 -2.840 0.728 0.991 1.227 2.405 2
Supplemental Vertical
Accuracy Test
Brush
land/Low
vegetation
174 2.256 -1.709 0.368 0.703 0.791 1.550 3
Forest land 174 3.504 -3.101 0.029 0.830 0.828 1.623 2
Consolidated
Vertical
Accuracy Test
All land cover
types 522 2.822 -2.840 0.361 0.844 0.917 1.797 10
Table 5.1-19. 2011 Matanuska-Susitna LiDAR comparison to obtain average elevation difference.
Cover type # Survey
points
Max (US
Feet)
Min (US
Feet)
Mean (US
Feet)
STD (US
Feet)
RMSEz
(US Feet)
Vertical accuracy at
95%
confidence
level
(US Feet)
# Outliers
Open terrain 525 3.291 -2.559 0.673 0.952 1.165 2.283 16
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Table 5.1-20. 2011 Matanuska-Susitna LiDAR vertical accuracy verification results after indexing.
LiDAR Vertical Accuracy Test Cover type # Survey points Max (US Feet) Min (US Feet)
Mean (US
Feet)
STD (US
Feet)
RMSEz (US
Feet)
Vertical accuracy at 95% confidence
level (US Feet)
# Outlier
s
Fundamental Vertical Accuracy Test Open terrain 174 2.668 -2.754 0.095 0.916 0.918 1.799 4
Supplemental Vertical
Accuracy Test
Brush
land/Low
vegetation
174 1.701 -2.038 -0.268 0.714 0.761 1.492 2
Forest land 174 2.577 -2.682 -0.615 0.710 0.937 1.837 6
Consolidated
Vertical
Accuracy Test
All land cover
types 522 2.836 -2.754 -0.254 0.858 0.894 1.752 9
Table 6.1-1. Lower Susitna River Bed-material Samples Collected in 1984 (R&M Consultants 1985).
1984 RM 2013 PRM Armor Layer Sample Number D50 (mm)1
97.1 100.4 6 38
95.9 99.3 7 46
93.1 96.3 3 32
91.8 95.4 6 55
90.6 93.3 5 55
87.7 91.1 6 11
86.3 90.3 5 55
Note:
1 Visually interpolated from gradation curves presented in R&M Consultants (1985)
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Table 6.1-2. Middle Susitna River Bed-material Samples Collected in 1983 (Harza-Ebasco 1984).
Table 6.1-3. Candidate Cross Sections Surveys for the Next Study Season.
Lower Susitna
River Segment
Middle Susitna
River Segment
PRM PRM PRM PRM
30.8 88.9 109.7 170.8
33.0 95.3 111.2 172.2
42.5 97.8 119.5 175.9
51.1 99.1 127.4 177.3
56.8 n/a 140.2 179.0
61.7 n/a 141.5 180.1
63.7 n/a 148.8 183.8
70.1 n/a 153.3 186.7
83.5 n/a 167.4 n/a
Location 2013 PRM D50 (mm)
LRX-1.0, left channel, center1 100.6 70
LRX-1.0, right channel, center1 100.6 50
LRX-2.3, near left bank 102.1 24
LRX-3.3, near left bank 102.8 58
LRX-3.3, near right bank 102.8 64
LRX-4, East bank, pavement 103.2 30
LRX-4, site 1, pavement 103.2 30
LRX-4, site 2, pavement 103.2 20
LRX-7.0, right channel 105.4 50
Near RM 109.3, pavement 113.0 65
Upstream of Lane Creek, pavement 117.3 58
Near LRX-18.2, Site 1, pavement 118.2 54
Near LRX-18.2, Site 2, pavement 118.8 10
Near Slough 10, pavement 137.0 20
LRX-42, center 138.6 52
Right channel Slough 11, pavement 139.0 60
LRX-45, center 140.0 65
LRX-51, center 142.3 70
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Table 6.1-4. Flow thresholds for evaluating coupled measurements of flow and WSE.
USGS Gaging Station
Fish and Aquatics Instream Flow Study
(ISR 8.5)
Geomorphology Study
(ISR 6.5)
Low/Medium Flow Threshold
(cfs)
Medium/High
Flow Threshold
(cfs)
Flow Required for
Bed Mobilization
(cfs)
Effective
Discharge
(cfs)
Susitna River at Sunshine
(Lower River) 45,500 60,600 16,000 66,000
Susitna River at Gold Creek
(Middle River) 17,700 24,000 25,000 27,000
Table 6.1-5. ADCP Discharge Measurements Collected at the Focus Areas in 2013.
Focus Area
Number of
Transects Date
Discharge
cfs)1 Date
Discharge
(cfs)1
FA-144 5 6/29/2013 ~26,000 9/7/2013 ~26,500
FA-141 5 6/30/2013 ~25,000 9/8/2013 ~29,500
FA-138 5 7/1/2013 ~25,000 9/6/2013 ~29,000
FA-128 5 7/2/2013 ~24,750 9/10/2013 ~26,200
FA-115 5 7/10/2013 ~21,750 9/13/2013 ~30,750
FA-113 7 7/11/2013 ~19,750 9/14/2013 ~25,500
FA-104 4 7/12/2013 ~17,500 9/15/2013 ~21,500
Note:
1 The discharges varied over the survey period. Representative discharges for the survey period were developed
from ISR Study Plan Section 8.5.4.4.1.1 (Figures 5.1-5a to 5.1-5g & 5.1-6a to 5.1-6g).
Note:
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10. FIGURES
[See separate file for figures.]
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APPENDIX A: BED-MATERIAL SAMPLES
[See separate file for appendix.]
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APPENDIX B: BED-MATERIAL SAMPLE LOCATIONS IN FOCUS AREAS
[See separate file for appendix.]
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APPENDIX C: BANK-MATERIAL SAMPLES
[See separate file for appendix.]
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APPENDIX D: WATER SURFACE MEASUREMENTS
[See separate file for appendix.]
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APPENDIX E: EVALUATION OF 50-YEAR SIMULATION PERIOD,
PACIFIC DECADAL OSCILLATION, AND SELECTION OF
REPRESENTATIVE ANNUAL HYDROGRAPHS
[See separate file for appendix.]
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ATTACHMENT A: FIELD REPORT, FIELD ASSESSMENT OF
UNDERWATER CAMERA PILOT TEST FOR SEDIMENT GRAIN SIZE
DISTRIBUTION
[See separate file for attachment.]