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Susitna-Watana Hydroelectric Project Document
ARLIS Uniform Cover Page
Title:
Stream flow assessment
SuWa 13
Author(s) – Personal:
Author(s) – Corporate:
Prepared by Tetra Tech, Inc.
AEA-identified category, if specified:
March 01, 2013 Filing
AEA-identified series, if specified:
Series (ARLIS-assigned report number):
Susitna-Watana Hydroelectric Project document number 13
Existing numbers on document:
Published by:
[Anchorage, Alaska : Alaska Energy Authority, 2013]
Date published:
February 2013
Published for:
Prepared for Alaska Energy Authority
Date or date range of report:
Volume and/or Part numbers:
Attachment G
Final or Draft status, as indicated:
Document type:
2012 Study Report
Pagination:
Viii, 93, [171] p.
Related work(s):
Cover letter (SuWa 6), Attachments A-F, H-I (SuWa 7-12, 14-15)
Pages added/changed by ARLIS:
Added cover letter
Notes:
All reports in the Susitna-Watana Hydroelectric Project Document series include an ARLIS-
produced cover page and an ARLIS-assigned number for uniformity and citability. All reports
are posted online at http://www.arlis.org/resources/susitna-watana/
March 1, 2013
Ms. Kimberly D. Bose
Secretary
Federal Energy Regulatory Commission
888 First Street, NE
Washington, DC 20426
Re: Susitna-Watana Hydroelectric Project, FERC Project No. 14241-000;
Filing of 2012 Baseline Environmental and Resources Study Reports
Dear Secretary Bose:
As explained in its Pre-Application Document and Revised Study Plan (RSP) for
the proposed Susitna-Watana Hydroelectric Project, FERC Project No. 14241 (Project),
the Alaska Energy Authority (AEA) carried out numerous baseline environmental and
resources studies related to the proposed Project during the 2012 field season. Because
the 2012 studies occurred prior to the commencement of the study phase of the licensing
effort under the Federal Energy Regulatory Commission’s (Commission) Integrated
Licensing Process, AEA was not required to complete these baseline studies. However,
AEA voluntarily undertook these studies for purposes of taking advantage of the 2012
field season to gather environmental data related to the proposed Project, and to help
inform the scope and methods of the licensing studies during 2013-14, as set forth in
AEA’s RSP.
As AEA has completed the study reports associated with these 2012 baseline
environmental and resources studies, it has made the study reports publicly available by
uploading them to the “Documents” page of its licensing website, http://www.susitna-
watanahydro.org/type/documents/. The purpose of this filing is to submit these study
reports to the Commission’s record for the above-referenced Project.
In particular, the following study reports are attached, all of which are relevant to
the Commission’s study plan determination scheduled for April 1, 2013:
• Attachment A: Adult Salmon Distribution and Habitat Utilization Study
(January 2013)
• Attachment B: Synthesis of Existing Fish Population Data (February 2013)
• Attachment C: Mercury Assessment and Potential for Bioaccumulation
(February 2013)
2
• Attachment D: Technical Memorandum, Susitna River Large Woody Debris
Reconnaissance (March 2013)
• Attachment E: Riparian Vegetation Study Downstream of the Proposed
Susitna-Watana Dam (February 2013)
• Attachment F: Technical Memorandum, Reconnaissance Level Assessment of
Potential Channel Change in the Lower Susitna River Segment (February
2013)
• Attachment G: Stream Flow Assessment (February 2013)
• Attachment H: Development of Sediment-Transport Relationships and an
Initial Sediment Balance for the Middle and Lower Susitna River Segments
(February 2013)
• Attachment I: Technical Memorandum, Initial Geomorphic Reach
Delineation and Characterization, Middle and Lower Susitna River Segments
(February 2013)
As the remaining 2012 study reports are finalized, AEA will continue to update its
website and submit them to the record.
If you have questions concerning this submission, please contact me at
wdyok@aidea.org or (907) 771-3955.
Sincerely,
Wayne Dyok
Project Manager
Alaska Energy Authority
Attachments
cc: Distribution List (w/o Attachments)
Attachment G
Stream Flow Assessment (February 2013)
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech, Inc.
February 2013
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page i February 2013
TABLE OF CONTENTS
Summary ..................................................................................................................................... viii
1. Introduction ........................................................................................................................1
2. Study Objectives.................................................................................................................1
3. Study Area ..........................................................................................................................2
3.1. General .....................................................................................................................2
3.2. Specific Study Area .................................................................................................2
4. Assessment of pre-Project and Maximum Load Following OS-1 Stream Flows .........3
4.1. Objectives ................................................................................................................3
4.2. Available Data .........................................................................................................3
4.3. Methods....................................................................................................................4
4.3.1. Pre-Project................................................................................................... 4
4.3.2. Maximum Load Following Operation Scenario 1 ...................................... 4
4.4. Results ......................................................................................................................5
4.4.1. Pre-Project................................................................................................... 5
4.4.2. Maximum Load Following OS-1 ................................................................ 7
4.5. Discussion and Conclusions ....................................................................................8
4.5.1. Seasonal and Flow-duration Comparison ................................................... 9
4.5.2. Flood-frequency Comparison ..................................................................... 9
5. Stage-Exceedence Analysis ..............................................................................................10
5.1. Objectives ..............................................................................................................10
5.2. Methods..................................................................................................................10
5.2.1. Conversion of Mean Daily Flow Records to Stage Records .................... 10
5.2.2. Stage-Duration Analyses and Stage-Exceedence Analyses ...................... 11
5.3. Results ....................................................................................................................12
5.4. Discussion and Conclusions ..................................................................................13
6. Specific Gage Analysis .....................................................................................................15
6.1. Objectives ..............................................................................................................15
6.2. Methods..................................................................................................................15
6.3. Results ....................................................................................................................17
6.4. Discussion and Conclusions ..................................................................................17
7. Discharge Effects on Ice Elevation and Cross-sectional Flow Characteristics ..........18
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page ii February 2013
7.1. Objectives ..............................................................................................................19
7.2. Methods..................................................................................................................19
7.3. Results ....................................................................................................................20
7.4. Discussions and Conclusions .................................................................................20
8. References .........................................................................................................................20
9. Tables ................................................................................................................................22
10. Figures ...............................................................................................................................57
LIST OF TABLES
Table 4.2-1. List of streamflow gages. .......................................................................................23
Table 4.4-1. Average annual flows (cfs) for pre-Project conditions based on the USGS
extended record. .....................................................................................................24
Table 4.4-2. Average monthly flows (cfs) at USGS gages in the Susitna River watershed
for pre-Project conditions based on the USGS extended record............................28
Table 4.4-3. Annual flow exceedence ordinates (cfs) for pre-Project conditions based on
the USGS extended record. ....................................................................................29
Table 4.4-4. Mainstem Susitna River estimated return period peak flows (cfs) for
pre-Project conditions based on the USGS extended record. ................................30
Table 4.4-5. Susitna River Tributary estimated return period peak flows (cfs) for pre-Project
conditions based on the USGS extended record. ...................................................30
Table 4.4 6. Average monthly flows (cfs) at three USGS gages in the Susitna River
watershed for Maximum Load Following Scenario OS-1, based on the HEC-
ResSim model. .......................................................................................................31
Table 4.4-7. Average annual flows (cfs) for Maximum Load Following OS-1 conditions
based on the HEC-ResSim model. .........................................................................32
Table 4.4-8. Annual and monthly flow exceedence ordinates (cfs) for Maximum Load
Following OS-1 conditions at Susitna River at Gold Creek based on the HEC-
ResSim model. .......................................................................................................34
Table 4.4-9. Annual and monthly flow exceedence ordinates (cfs) for Maximum Load
Following OS-1 conditions at Susitna River at Sunshine based on the HEC-
ResSim model. .......................................................................................................35
Table 4.4-10. Annual and monthly flow exceedence ordinates (cfs) for Maximum Load
Following OS-1 conditions at Susitna River at Susitna Station based on the
HEC-ResSim model. ..............................................................................................36
Table 4.4-11. Susitna River estimated return period peak flows (cfs) for Maximum Load
Following OS-1 conditions based on the HEC-ResSim model. ............................37
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iii February 2013
Table 4.5-1. Average monthly flow (cfs) comparison for pre-Project and Maximum Load
Following OS-1 conditions. ...................................................................................38
Table 4.5-2. Average annual flow (cfs) comparison for pre-Project versus Maximum Load
Following OS-1 conditions. ...................................................................................39
Table 4.5-3. Annual flow exceedence ordinate (cfs) comparison for Pre-Project and
Maximum Load Following Scenario OS-1. ...........................................................42
Table 4.5-4. Susitna River estimated return period peak flow (cfs) comparison for
pre-Project and Maximum Load Following Scenario OS-1. .................................43
Table 4.5-5. Recurrence interval of annual peak flows for pre-Project and Maximum
Load Following Scenario OS-1. ............................................................................44
Table 5.2-1. USGS Measurements Used to Develop Representative Cross Section
Geometry................................................................................................................45
Table 5.3-1. Annual Stage-exceedence Ordinate (feet) Comparison for pre-Project and
Maximum Load Following OS-1 Hydrologic Conditions at Sunshine Gage
and Susitna Station Gage. ......................................................................................45
Table 5.3-2. Monthly (October through March) Stage-exceedence Ordinate (feet)
Comparison for pre-Project and Maximum Load Following OS-1 Hydrologic
Conditions at Sunshine Gage. ................................................................................46
Table 5.3-3. Monthly (April through September) Stage-exceedence Ordinate (feet)
Comparison for pre-Project and Maximum Load Following OS-1 Hydrologic
Conditions at Sunshine Gage. ................................................................................47
Table 5.3-4. Monthly (October through March) Stage-exceedence Ordinate (feet)
Comparison for pre-Project and Maximum Load Following OS-1 Hydrologic
Conditions at Susitna Station Gage........................................................................48
Table 5.3-5. Monthly (April through September) Stage-exceedence Ordinate (feet)
Comparison for pre-Project and Maximum Load Following OS-1 Hydrologic
Conditions at Susitna Station Gage........................................................................49
Table 5.3-6. Monthly Stage Statistics for pre-Project and Max Load Following OS-1
Hydrologic Conditions at Sunshine Gage. .............................................................50
Table 5.3-7. Monthly Stage Statistics for pre-Project and Max Load Following OS-1
Hydrologic Conditions at Susitna Station Gage. ...................................................51
Table 5.4-1. Annual Flow-exceedence and Stage-exceedence Comparison for the
pre-Project and Maximum Load Following OS-1 Hydrologic Conditions at
Sunshine Gage and Susitna Station Gage. .............................................................52
Table 6.2-1. USGS Ratings and Effective Dates at Sunshine Gage...........................................53
Table 6.2-2. USGS Ratings and Effective Dates at Susitna Station Gage. ................................53
Table 6.2-3. Flows Selected for Specific Gage Analysis, Susitna Station Gage. ......................54
Table 6.3-1. Stages at Selected Specific Discharges Calculated from USGS Published
Ratings for the Susitna Station Gage. ....................................................................54
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iv February 2013
Table 7.2-1. Ice Covered Discharge Measurement at USGS Susitna at Sunshine Gage .......... 55
Table 7.2-2. Ice Covered Discharge Measurement at USGS Susitna at Susitna Gage. .............56
LIST OF FIGURES
Figure 3.2-1. Susitna River study area and large-scale river segments. ..................................... 58
Figure 4.4-1. Average monthly flows (cfs) in the Susitna River and major tributaries
downstream from the Watana Dam site under pre-Project conditions based on
the USGS (2012) 61-year extended record. Solid bars are mainstem gages;
cross-hatched bars are tributaries. ......................................................................... 59
Figure 4.4-2. Annual flow-duration curves mainstem gages for pre-Project conditions
based on the USGS extended record. .................................................................... 60
Figure 4.4-3. Annual flow-duration curves tributary gages for pre-Project conditions based
on the USGS extended record. .............................................................................. 61
Figure 4.4-4. Monthly Flow-duration curves for January for mainstem gages for pre-Project
conditions based on the USGS extended record. .................................................. 62
Figure 4.4-5. Relationship between recorded annual instantaneous peak discharge and the
corresponding mean daily discharge at Gold Creek. Similar plots for other
gages are provided in Appendix D. ....................................................................... 63
Figure 4.4-6. Average monthly flows (cfs) in the Susitna River under Maximum Load
Following Scenario OS-1, based on the HEC-ResSim model results. Also
shown are major tributary inflows. ....................................................................... 64
Figure 4.4-7. Annual flow-duration curves for three mainstem gages for Maximum Load
Following OS-1 Conditions based on HEC-ResSim model. ................................ 65
Figure 4.4-8. Flood-frequency curve for Susitna River at Gold Creek for Maximum Load
Following OS-1 conditions based on the HEC-ResSim model. ........................... 66
Figure 4.4-9. Flood-frequency curve for Susitna River at Sunshine for Maximum Load
Following OS-1 conditions based on the HEC-ResSim model. ........................... 67
Figure 4.4-10. Flood-frequency curve for Susitna River at Susitna Station for Maximum
Load Following OS-1 conditions based on estimated HEC-ResSim model
output. ................................................................................................................... 68
Figure 4.5-1. Average monthly flows (cfs) in the Susitna River watershed for pre-Project
and Maximum Load Following OS-1 conditions. ................................................ 69
Figure 4.5-2. Annual flow-duration curve comparison for Pre-Project and Maximum Load
Following OS-1 conditions. .................................................................................. 70
Figure 4.5-3. Flood-frequency curve for Susitna River at the Watana Dam for Maximum
Load Following OS-1 conditions based on estimated HEC-ResSim model
output. ................................................................................................................... 71
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page v February 2013
Figure 4.5-4. Flood-frequency curve for Susitna River at Gold Creek (USGS Gage No.
1529200) for Maximum Load Following OS-1 conditions based on estimated
HEC-ResSim model output................................................................................... 72
Figure 4.5-5. Flood-frequency curve for Susitna River at Sunshine (USGSG Gage No.
15292780) for Maximum Load Following OS-1 conditions based on estimated
HEC-ResSim model output................................................................................... 73
Figure 4.5-6. Flood-frequency curve for Susitna River at Susitna Station (USGS Gage No.
1524350) for Maximum Load Following OS-1 conditions based on estimated
HEC-ResSim model output................................................................................... 74
Figure 5.2-1. USGS Published and Extrapolated Stage-Discharge Rating for Susitna River
USGS Gage at Sunshine. ...................................................................................... 75
Figure 5.2-2. USGS Published and Extrapolated Stage-Discharge Ratings for Susitna River
USGS Gage at Susitna Station. ............................................................................. 76
Figure 5.3-1. Annual Stage-exceedence Relationships for pre-Project and Max LF OS-1
Conditions, Sunshine Gage. .................................................................................. 77
Figure 5.3-2. Annual Stage-exceedence Relationships for pre-Project and Max LF OS-1
Conditions, Susitna Station Gage. ........................................................................ 78
Figure 5.3-3. Monthly Stage-exceedence Relationships for May for pre-Project and
Max LF OS-1 Conditions, Sunshine Gage. .......................................................... 79
Figure 5.3-4. Monthly Stage-exceedence Relationships for May for pre-Project and
Max LF OS-1 Conditions, Susitna Station Gage. ................................................. 80
Figure 5.3-5. Select Annual Water-surface Elevation exceedence Values for pre-Project
and Max LF OS-1 Conditions, Sunshine Gage. .................................................... 81
Figure 5.3-6. Select Annual Water-surface Elevation exceedence Values for pre-Project and
Max LF OS-1 Conditions, Susitna Station Gage. ................................................. 82
Figure 5.4-1. Comparison of Stage-Discharge Ratings for Susitna Station and Sunshine
Gages..................................................................................................................... 83
Figure 5.4-2. Monthly 90 percent pre-Project and Max LF OS-1 Stage-exceedence Values,
Sunshine Gage. ..................................................................................................... 84
Figure 5.4-3. Monthly 90 percent pre-Project and Max LF OS-1 Stage-exceedence Values,
Susitna Station Gage. ............................................................................................ 84
Figure 5.4-4. Monthly 50 percent pre-Project and Max LF OS-1 Stage-Exceedence Values,
Sunshine Gage. ..................................................................................................... 85
Figure 5.4-5. Monthly 50 percent pre-Project and Max LF OS-1 Stage-exceedence Values,
Susitna Station Gage. ............................................................................................ 85
Figure 5.4-6. Monthly 10 percent pre-Project and Max LF OS-1 Stage-exceedence Values,
Sunshine Gage. ..................................................................................................... 86
Figure 5.4-7. Monthly 10 percent pre-Project and Max LF OS-1 exceedence Values,
Susitna Station Gage. ............................................................................................ 86
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page vi February 2013
Figure 6.2-1. Vicinity Map for Susitna River at Sunshine Gage. ............................................... 87
Figure 6.2-2. Vicinity Map for Susitna River at Susitna Station Gage. ..................................... 88
Figure 6.2-3. USGS Stage and Discharge Measurements at Susitna River at Sunshine Gage
(USGS 15292780). ................................................................................................ 89
Figure 6.2-4. USGS Stage and Discharge Measurements at Susitna River at Susitna Station
Gage (USGS 15294350). ...................................................................................... 89
Figure 6.2-5. Historical Stage-Discharge Ratings for Susitna River at Susitna Station Gage. .. 90
Figure 6.3-1. Specific Gage Curves for Susitna River at Susitna Station Gage. ........................ 91
Figure 7.3-1. Velocity versus discharge for ice-covered and open-water conditions based on
USGS measurements at the Susitna River at Sunshine gage .................................92
Figure 7.3-2. Hydraulic (i.e., average) depth versus discharge for ice-covered and open-water
conditions based on USGS measurements at the Susitna River at
Sunshine gage ........................................................................................................93
Figure 7.3-3. Cross-sectional area versus discharge for ice-covered and open-water
conditions based on USGS measurements at the Susitna River at
Sunshine gage. .......................................................................................................94
APPENDICES
Appendix A. Average Monthly Flow by Water Year for Pre-Project Conditions
Appendix B. Flow Duration Curves for Pre-Project Conditions
Appendix C. Flow Exceedence Summary Data for Pre-Project Conditions
Appendix D. Flood Frequency Regression Plots
Appendix E. Flood Frequency Curves for Pre-Project Conditions
Appendix F. Average Monthly Flow (cfs) by Water Year for Post-Project Conditions
Appendix G. Monthly Flow Duration Curves for Post-Project Conditions
Appendix H. Monthly Flow Duration Comparison for Pre-Project and Post-Project Conditions
Appendix I. Monthly Flow Exceedence Comparison (cfs) for Pre-Project and Post-Project
Conditions
Appendix J. Annual and Monthly Stage-exceedence Curves (Pre-Project and Maximum Load
Following OS-1 Conditions) for Sunshine Gage Location and Susitna Station
Gage Location
Appendix K. Plots of Select Water-surface Elevation Exceedence Values (Pre-Project and
Maximum Load Following OS-1 Conditions) for Sunshine Gage and Susitna
Station Gage Cross Section
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page vii February 2013
LIST OF ACRONYMS AND SCIENTIFIC LABELS
Abbreviation Definition
AEA Alaska Energy Authority
cfs cubic feet per second
FDC flow-duration curve
FERC Federal Energy Regulatory Commission
ILP Integrated Licensing Process
NAVD North American Vertical Datum
NEPA National Environmental Policy Act
NGVD National Geodetic Vertical Datum
OS Operation Scenario
Project Susitna-Watana Hydroelectric Project
PRM Project River Mile
RM River Mile
sq. mi. square mile
USGS U.S. Geological Survey
WY Water Year
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page viii February 2013
SUMMARY
The 2012 Stream Flow Assessment involved analysis of pre-Project and post-Project flows in the
Susitna River below Watana Dam. The pre-Project condition was based on the extended flow
record developed by the USGS. The post-Project condition was based on a hypothetical
operational scenario (OS) referred to as Maximum Load Following OS-1.
The purpose of the Stream Flow Assessment was to identify the potential Project related changes
in Susitna River flows and stage in the Lower River (the portion of the river downstream of the
Susitna, Chulitna and Talkeetna river confluence). The analysis performed was an initial
assessment to inform the study planning and early execution phases of the integrated licensing
process (ILP). Of primary interest was whether the results of the analysis indicate the need to
extend portions of Fluvial Geomorphology Modeling Study and other studies further
downstream in the Lower River.
The 2012 work involved four main areas of analysis: Assessment of pre-Project and Maximum
Load Following OS-1 stream flows, determination of stage exceedances at the Sunshine and
Susitna Station USGS gages, and analysis of the long-term stability of the USGS gages (specific
gage analysis) and evaluation of discharge effects on ice elevation an flow characteristics at the
USGS gages.
The study results were provided the hydrologic information to perform three other 2012 study
efforts, the Reconnaissance Level Assessment of Potential Channel Change in the Lower Susitna
River Segment, Development of Sediment-Transport Relationships and an Initial Sediment
Balance for the Middle and Lower Susitna River Segments, and Synthesis of the 1980s Lower
Susitna River Segment Aquatic Habitat Information. Updated and more detailed analysis of the
Susitna River hydrology under Project conditions will be investigated in the 2013 and 2014
studies, including other operating scenarios in addition to Maximum Load Following OS-1.
The most significant finding of the Stream Flow Assessment comes from the results of the
annual peak flow frequency analysis. Comparison of results between the existing conditions and
the Maximum Load Following Operations Scenario 1 indicates the potential for an appreciable
post-Project reduction in flows in the 1.5- to 5-year range of recurrence intervals in the Lower
River. Discharges in the range of the 1.5- to 5-year peaks are often representative of the channel
forming or effective discharge to which the bankfull channel capacity adjusts in streams such as
the Lower River Segment that have mobile bed material and a substantial sediment supply. For
the 2-year event, the reduction at Sunshine and Susitna Station were estimated at 24 and 17
percent, respectively. Relationships between channel size and discharge suggest that the level of
peak flow reduction could result narrowing of the channel width by in slightly greater than 10
percent in the portion of the Lower River below Sunshine, and less than 10 percent downstream
from the Yentna River confluence. These preliminary results have served as part of the decision
criteria to extend the Fluvial Geomorphology Modeling Study 50 miles further downstream in
the Lower River to the Susitna Station USGS Gage, or approximately 30 miles above the mouth
of the river in order to provide more detailed assessment of the potential Project effects in this
portion of the river.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 1 February 2013
1. INTRODUCTION
The Alaska Energy Authority (AEA) is preparing a License Application that will be submitted to
the Federal Energy Regulatory Commission (FERC) for the Susitna-Watana Hydroelectric
Project (Project) using the Integrated Licensing Process (ILP). The Project is located on the
Susitna River, an approximately 300-mile-long river in the Southcentral Alaska. The Project’s
dam site would be located at River Mile (RM) 184. The results of this study provided
information to inform the 2013–2014 licensing study program, Exhibit E of the License
Application, and FERC’s National Environmental Policy Act (NEPA) analysis for the Project
license.
This report provides the results of the Streamflow Assessment Task and the River Stage subtask
of the Riverine Habitat-Flow Relationship Assessment Task, both conducted as part of the
Geomorphology Study’s 2012 Reconnaissance Level Geomorphic and Aquatic Habitat
Assessment of the Project Effects on the Lower River Channel Study (AEA 2012). The report
includes the results of the hydrologic analysis which summarizes pre-Project hydrology and post-
Project hydrology under an operations scenario referred to as Maximum Load Following
Operation Scenario 1 (OS-1) conditions hydrology.
The pre-Project analysis was performed using 61-year extended hydrologic records developed by
the U.S. Geological Survey (USGS 2012) for the period from Water Year (WY) 1950 through
WY2010 for 11 streamflow gages located in the Susitna Basin. The Maximum Load Following
OS-1 analysis was performed using a simulated record developed with-Project conditions flow
routing model (MWH 2012) for the same period. The Maximum Load Following OS-1 is based
on the assumption that the entire load fluctuation of the entire Railbelt would be provided by the
Susitna-Watana Project, and that all other sources of electrical power in the Railbelt would be
running at base load. This assumed condition is not realistic for an entire year, and the results of
this condition should be conservative with respect to assessing downstream impacts of load
following.
The analysis included monthly flow summaries, flow-duration curves, flood frequencies curves,
and associated statistics the gages for which flow records are available. A comparison between
the pre-Project conditions and the Maximum Load Following OS-1 conditions was also
conducted for the Gold Creek, Sunshine and Susitna Station gages.
The analysis presented in this report is an initial assessment intended to help in the study
planning and early execution phases of the ILP. The routing model downstream of the Project
utilized the 1980s cross-sections and simplified routing techniques. The open water hydraulic
routing (R2 Resource Consultants et al. 2013) model being currently developed will replace
1980s-based routing model applied in this initial assessment. Analysis to be conducted in 2013
and 2014 will replace the initial assessment presented in this report.
2. STUDY OBJECTIVES
The overall objective of this memorandum is to evaluate the relative magnitude of changes to the
flow regime of the Susitna River pre- and post-Project and associated change in river stage. More
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 2 February 2013
specifically, the objectives are to characterize the existing streamflow regime in the Susitna
River and key tributaries, and to perform preliminary quantification of the anticipated changes
under Maximum Load Following OS-1 conditions, including assessments of the following,
interrelated topics:
Pre-Project and Maximum Load Following OS-1 streamflows
Pre-Project and Maximum Load Following OS-1 river stage duration at the Sunshine and
Susitna Station USGS gages
Analysis of specific gages to assess historic changes in the stage-discharge relationships at
the mainstem gages
Using available USGS data identify discharge effects on ice elevation and cross-sectional
flow characteristics, if feasible.
Throughout this report, the term “Available Record” refers to the data collected by the USGS at
each gage and varies in availability based on the years each gage was in operation. The term
“Extended Record” refers to the 61-year (WY1950 and WY2010) record of daily streamflows
developed by the USGS through correlation analysis for each of the 11 streamflow gages that
was considered in the pre-Project analysis.
3. STUDY AREA
3.1. General
The Susitna River, located in Southcentral Alaska, drains an area of approximately 20,010 square
miles and flows about 320 miles from its headwaters at the Susitna, West Fork Susitna, and East
Fork Susitna glaciers to the Cook Inlet (USGS 2012). The Susitna River basin is bounded on the
west and north by the Alaska Range, on the east by the Talkeetna Mountains and Copper River
Lowlands and on the south by Cook Inlet. The highest elevations in the basin are at Mt.
McKinley at 20,320 feet while its lowest elevations are at sea level where the river discharges
into Cook Inlet. Major tributaries to the Susitna River between the headwaters and Cook Inlet
include the Chulitna, Talkeetna and Yentna rivers that are also glacially fed in their respective
headwaters. The basin receives, on average, 35 inches of precipitation annually with average
annual air temperatures of approximately 29oF.
3.2. Specific Study Area
For the Susitna-Watana Hydro Project licensing effort the Susitna River from Cook Inlet to the
Maclaren River confluence at Project River Mile (PRM)261.3, the river has been subdivided into
three segments (Tetra Tech 2013) whose general characteristics are governed by the basin
geology as described by Wilson et al. (2009). The segments are referred to as the Upper, Middle
and Lower Susitna River segments (Figure 3.2-1):
Upper Susitna River Segment: Maclaren River confluence (PRM 261.3) downstream to the
proposed Watana Dam site (PRM 187.1)
Middle Susitna River Segment: Proposed Watana Dam site (PRM 187.1) downstream to the
Three Rivers Confluence (PRM 102.4)
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 3 February 2013
Lower Susitna River Segment: Three Rivers Confluence (PRM 102.4) downstream to Cook
Inlet (PRM 3.3)
In addition to the segment boundaries, Figure 3.2-1 also shows the locations of gaging stations
where flow, and in some cases, sediment measurements are available. The upstream-most
segment, referred to as the Upper River (UR), extends from PRM 261.3 to PRM 187.1 at the
Watana Dam site. The morphologic characteristics of this segment of the river are dominated by
the products of Quaternary-age glaciation. The Middle River (MR) segment extends from the
Watana Dam site to the Three Rivers Confluence at about PRM 102.4. The general
characteristics of the river in this segment are heavily influenced by bedrock outcrop as well as
Quaternary-age glaciations. The Lower River (LR) segment extends from the Three Rivers
Confluence (PRM 102.4) to the tidal flats at Cook Inlet (PRM 3.3). The morphologic
characteristics of the river in this segment are dominated by the sediment loading from the major
tributaries and variable resistance to erosion of the Pleistocene-age, glacially-derived materials
including tills (moraines), glacio-fluvial sediments in various elevation outwash-surfaces and
glacio-lacustrine sediments that control the width of the valley.
The study effort presented in this Technical Memorandum is concentrated on the Lower Susitna
River Segment. However, the study area also includes the Middle and Upper Susitna River
Segment since USGS gaging stations that helped form the basis for the hydrologic analysis are
located throughout the Susitna River Basin.
4. ASSESSMENT OF PRE-PROJECT AND MAXIMUM LOAD
FOLLOWING OS-1 STREAM FLOWS
4.1. Objectives
The overall purpose of this task is to develop hydrologic information for both the pre-Project and
Maximum Load Following OS-1 (post-Project scenario) conditions and use this information to
compare pre-Project and potential post-Project flows. Specific hydrologic indicators to be
developed include: monthly and annual flow duration curves, monthly flow statistics (mean,
median, maximum and minimum), and annual flood frequency analysis.
4.2. Available Data
There are 14 USGS streamflow gages in the Susitna River Basin plus one on the Little Susitna
River that was used as an index station (Table 4.2-1 and Figure 3.2-1). The period of record for
these gages ranges from 58 years at the Gold Creek gage to less than 10 years at the Yentna
River at Susitna Station and the Susitna River at Sunshine gages. The available data from many
of these gages “…might not adequately represent long-term streamflow conditions” in the
Susitna River Basin because of the short period of record and the distribution of years during
which data were collected (USGS 2012). To provide a consistent long-term record, the USGS
extended the record of 11 of these gages to 61 years (WY1950 – WY2010). WY1950 was
selected for the start of the record because this was the first full water year of data collection for
the primary index station at Gold Creek. The Montana Creek (Mont), Deception Creek (Decep),
and the Deshka River (Desh) gages were not included in the extended record analysis because
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they could not be adequately correlated to any long-term index station for the entire study period
(USGS 2012).
4.3. Methods
This section describes the methods used to develop the monthly flows and summary statistics,
the flow duration analysis, and the flood frequency analysis for both the pre-Project and
Maximum Load Following OS-1 conditions.
4.3.1. Pre-Project
Monthly flow summaries were developed from the USGS (2012) extended records (downloaded
from the USGS website at http://pubs.usgs.gov/sir/2012/5210) by calculating the average,
maximum, minimum and median flow by month across all 61 years of the extended record, with
all results rounded three significant figures. Flow-duration curves (FDCs) that represent the
percentage of time each discharge is equaled or exceeded during the period of analysis were then
developed using the mean daily data from the extended records. The FDCs were developed for
each month and on an annual basis for each gage.
Flood frequency curve were also developed for each of the gages using the U.S. Army Corps of
Engineers Hydraulic Engineering Center Statistical Software Package (HEC-SSP) that applies
standard methods outlined in Bulletin 17B (IACWD 1982). These methods involve fitting a log-
Pearson Type III (LPIII) frequency distribution to the annual peak flow. Recorded annual peak
flow data for the available record were downloaded from the USGS water data website
(http://waterdata.usgs.gov) for each gage. As noted above, the period of available record at these
gages ranges between 10 and 58 years. The records were, therefore, extended to 61 years by
developing a correlation relationship between instantaneous peak flow and the corresponding
mean daily flow, and applying that relationship to the annual maximum mean daily flow in the
extended portion of the record. The LPIII distribution was fit to the extended data using the
weighted-skew method with a regional skew coefficient of 0.70 from the map of Generalized
Skew Coefficients in IACWD (1982), the station skew that is a function of the measured data,
and the recommended value of 0.302 for the mean square error of the generalized skew
coefficient. HEC-SSP conducts high and low outlier tests to remove data that departs
significantly from the trend of the annual series before fitting the distribution to the data.
To provide a basis for directly comparing modeled flows under Maximum Load Following
Operation Scenario 1 (OS-1), MWH (2012) performed HEC-ResSim modeling for the pre-
Project condition using the USGS gage records as model input. The HEC-ResSim model used
the 1980s cross sections and the Muskingum-Cunge hydrologic routing procedure to route the
flows downstream of the Watana Dam site to Sunshine Station. Flood frequency analyses were
conducted using the annual hourly maximum flows as a surrogate for the 15-minute
“instantaneous” measurements that are typically used for this purpose.
4.3.2. Maximum Load Following Operation Scenario 1
Flow-duration and flood frequency analyses were performed for a post-Project scenario, referred
to as Maximum Load Following Operation Scenario 1 (OS-1), were performed for the three
mainstem Susitna River gages (Gold Creek PRM 140, Sunshine PRM 88 and Susitna Station
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PRM 30) below the Watana Dam site (PRM 187) using the same methods that were described in
the previous section for the pre-Project analysis. Data used in the analysis were developed by
MWH (2012) using the HEC-ResSim operations model of the Project that uses the USGS 61-
year extended record of mean daily flows as a long-term reservoir inflow time series. The model
run on which these data are based represents a preliminary operation scenario that was developed
by placing the entire variability of the Railbelt electricity load on Susitna-Watana; thus, it
represents a maximum (or worst-case) load-following scenario (John Haapala, personal
communication, January 24, 2013). The model was used to route the reservoir outflows
downstream through the Susitna River to the Sunshine Gage at PRM 88, providing a 61-year
period of simulated flows for Maximum Load Following OS-1 at Gold Creek and Sunshine. A
61-year flow record for the Susitna Station gage was estimated by adding the difference between
the flows at the Sunshine and Susitna Station gages from the USGS (2012) extended record to
the routed flows at Sunshine. Annual hourly maximum hourly flows from the HEC-ResSim
routings were used for the peak flood frequency analysis at Gold Creek and Sunshine as a
surrogate for the instantaneous (15-minute) gage data that is typically used for this type of
analysis, since the maximum temporal resolution of the model output is 1 hour. This approach is
not considered to be a significant limitation in the analysis, since Susitna River is relatively
large, and the difference between the peak 15-minute and maximum hourly flows is typically
quite small. The frequency analysis for Susitna Station was performed based on the annual
maximum mean daily flows because sufficient information is not available at this time to reliably
estimate maximum flows at a higher temporal resolution. As will be shown in the analysis, this
is also not a significant limitation at this location on the river.
4.4. Results
This section details the monthly flows and summary statistics, the flow duration analysis, and the
flood frequency analysis for both the pre-Project and Maximum Load Following OS-1
conditions.
4.4.1. Pre-Project
The pre-Project condition is based on the 61-year extended flow record developed by the USGS
(2012). It represents flow conditions without the Project in place.
4.4.1.1. Average Annual and Monthly Flow Summary
The average annual discharge from the USGS (2012) extended record at Gold Creek is about
9,700 cfs (average annual volume of ~7M ac-ft), and it is between 8,100 and 11,200 cfs in 80
percent of the years (Tables 4.4-1 and 4.4-2). Due, primarily, to inflows from the Chulitna and
Talkeetna rivers that contribute 36 and 17 percent of the total, respectively, the average annual
flow increases to about 24,000 cfs (~17.4M ac-ft) at the Sunshine gage, and is between 20,400
and 26,900 cfs in 80 percent of the years. At the Susitna Station gage, the average annual
discharge is about 48,600 cfs (~35.2M ac-ft) and is between 42,500 and 55,600 cfs in 80 percent
of the years. The Yentna and Skwentna River contribute 40 percent and 14 percent of the total
flow at Susitna Station, respectively.
The Susitna River and its tributaries are located at varying elevations and the seasonal variability
in flow is, in large part, driven by seasonal snow melt in June and July, and also by the relative
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timing and magnitude of glacial melt and rainstorm outside this period. Under pre-Project
conditions, the highest flows occur in June, the low-flow period occurs between November and
April, and flows are typically elevated above baseflow from May through October (Figure 4.4-1
and Table 4.4-2). Monthly flow summaries for each year in the extended record on which these
averages are based are provided in Appendix A.
4.4.1.2. Flow-duration Analysis
The annual flow-duration curves indicate the expected increase in discharge from upstream to
downstream, consistent with the average annual flows discussed in the previous section (Figures
4.4-2 and 4.4-3, Table 4.4-3). For example, the median annual flow (flow that is equaled or
exceeded 50 percent of the time) increases from about 2,050 cfs at Cantwell to about 3,400 cfs at
Gold Creek, 8,220 cfs at Sunshine and 19,000 cfs at Susitna Station. Similarly, the 90-percent
exceedence flow increases from about 690 cfs at Cantwell, to about 1,200 cfs at Gold Creek,
2,830 cfs at Sunshine and 6,400 cfs at Susitna Station, and the 10-percent exceedence flow
increases from 16,500 cfs at Cantwell to about 25,300 cfs at Gold Creek, 64,000 cfs at Sunshine,
and 124,000 cfs at Susitna Station. Similar flow-duration curves were developed for each month
at each of the stations, including the tributaries (Appendix B), and the values for specific
exceedence durations are tabulated in Appendix C. An example of a monthly flow duration curve
is provided in Figure 4.4-4.
4.4.1.3. Flood-Frequency Analysis
The pre-Project flood-frequency analysis was performed for each of the gages using a
combination of the recorded instantaneous peak flow data and the USGS extended record. This
was accomplished by first correlating the recorded peak discharges for the period of record with
the mean daily discharges on the day of the peak discharge (Figure 4.4-5). The instantaneous
peak discharges for the years in the extended record for which measured data are not available
were then estimated by applying the resulting regression relationship to the maximum mean
daily discharge. As seen in Figure 4.4-5, the relationship for the Gold Creek gage that is being
used here as an example fits the recorded data very well (R2=0.98). This relationship indicates
that the instantaneous peak flows at Gold Creek are typically about 4 percent greater than the
corresponding mean daily flow at discharges in the 20,000-cfs range, increasing to about 7
percent at flows in the 90,000-cfs range. Similar relationships for the other gages are provided in
Appendix D. A potential source of error in this method results from the fact that the
instantaneous peak discharge does not always occur on the same day as the maximum mean
daily discharge. This is not believed to be a significant limitation, however, because this occurs
in less than 20 percent of the years, and the difference between the maximum mean daily flow
and the mean daily flow on the day of the peak was not significant during those years.
Flood frequency curves developed using the HEC-SSP program with the resulting extended
record of peak discharges indicates that the 2-year recurrence interval peak discharge is about
27,300 cfs at the Cantwell gage and about 43,500 cfs at Gold Creek (Table 4.4-4). The 2-year
peak discharges at Sunshine and Susitna Station are substantially higher (106,000 and 170,000
cfs, respectively). The 2-year peak discharges in the Chulitna and Yentna River are 35,200 and
23,200 cfs, respectively (Table 4.4-5). The peak discharges for other events from the 1.25-year
through the 100-year recurrence interval flows are also provided in Tables 4.4-4 and 4.4-5, and
the plotted flood-frequency curves with the data points from the extended record and upper and
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lower 90-percent confidence bands and the computed frequency curve at each of the gages being
considered in this analysis are provided Appendix E.
4.4.2. Maximum Load Following OS-1
The presence of the Watana Dam at PRM 187 will affect flows in the mainstem of the Susitna
River downstream of the project site, but flows in the tributaries and the mainstem upstream
from the reservoir will not be affected by the dam. The Maximum Load Following OS-1
analysis, therefore, only considered the three gages along the mainstem downstream from PRM
187 (i.e., Gold Creek, Sunshine, and Susitna Station). As discussed above, the flow records used
for the Maximum Load Following Scenarios OS-1 analysis were developed by MWH (2012)
using a HEC-ResSIM model that represents a preliminary operation scenario that was developed
by placing the entire variability of the Railbelt electricity load on Susitna-Watana; thus, it
represents a maximum (or worst-case) load-following scenario (John Haapala, personal
communication, January 24, 2013). The HEC-ResSim model only considered flows in the reach
between Watana Dam and the Sunshine gage. To estimate the Susitna Station Maximum Load
Following OS-1 flows, the pre-Project difference between the mean daily flow at the Sunshine
and Susitna Station gages was added to the Maximum Load Following OS-1 Sunshine mean
daily flows, under the assumption that flow changes in that part of the reach would be the same
under both pre-Project and Maximum Load Following OS-1 conditions. The HEC-ResSim
model was also run for pre-Project (i.e., unregulated) conditions. Results from this run were
used as the basis for comparing pre- and Maximum Load Following OS-1 conditions since the
purpose of the comparison is to assess the differences between the two conditions, and there are
minor differences between the measured and simulated flow record that could potentially
confound the analysis. This comparison described in Section 6.
4.4.2.1. Monthly and Annual Flow Summary
The Project does not permanently add to or divert flows from the river. As a result, the
simulated average annual discharge at the three gages under the Maximum Load Following
Scenario OS-1 is essentially the same as under pre-Project conditions, ranging from about 9,700
cfs at Gold Creek to about 24,000 cfs at Sunshine and 48,500 cfs at Susitna Station, and the
variability from year to year is also approximately the same (Tables 4.4-6 and 4.4-7). Average
monthly flow releases under Maximum Load Following Scenario OS-1 are; however, more
uniformly distributed throughout the year than under pre-Project conditions (Figure 4.4-6).
Tributary inflows between the dam and the Three Rivers Confluence are relatively small
compared to the mainstem flows; thus, the distribution of average monthly flows at the Gold
Creek gage is also relatively uniform. Unlike the upstream, smaller tributaries, inflows from the
Chulitna and Talkeetna Rivers are significant compared to the upstream mainstem flows, and
there is, therefore, significant seasonal variability in the downstream river, even under the
Maximum Load Following Scenario OS-1. Monthly flow summaries for the individual gages for
each year in the extended record are provided in Appendix F.
4.4.2.2. Flow-duration Analysis
The annual and monthly flow-duration curves also reflect the more uniform distribution of flows
throughout the year under Maximum Load Following Scenario OS-1 (Figure 4.4-7 and Tables 4.4-8
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through 4.4-10). The median flow at the Gold Creek gage, for example, increases from about
3,400 cfs under pre-Project conditions to about 8,800 cfs under Maximum Load Following Scenario
OS-1, and the 10-percent (low) exceedence flow increases from about 1,200 to 7,200 cfs, while
the 90-percent (high) exceedence flow decreases from about 25,300 to 12,300 cfs. Similar
changes occur at the two downstream gages, but the relative magnitude of the change is smaller
because of the influence of the tributary inflows. For example, the median flow at Sunshine for
Maximum Load Following Scenario OS-1 (13,200 cfs) is about 60 percent larger than the pre-
Project median flow (8,200 cfs) and the Maximum Load Following Scenario OS-1 median flow
at Susitna Station (23,100 cfs) is about 20-percent larger than the pre-Project median flow
(19,000 cfs). A duration analysis of monthly flows was also conducted, and the resulting
duration curves for each of the gages are provided in Appendix G.
4.4.2.3. Flood-frequency Analysis
As noted above, the flood frequency analysis for Maximum Load Following Scenario OS-1 was
conducted using the simulated annual maximum hourly flows from the HEC-ResSim model.
Based on the analysis, the 2-year peak discharge at Gold Creek will decrease to about 23,900 cfs
under Maximum Load Following Scenario OS-1, and the 100-year peak discharge will decrease
to about 66,400 cfs, reductions of 45 and 28 percent, respectively (Table 4.4-11, Figure 4.4-8).
Consistent with the mean daily flows, the reduction at the two downstream gages is less
significant. At Sunshine, for example, the 2-year peak will decrease by about 24 percent to
72,000 cfs and the 100-year peak will decrease by about 23 percent to 137,000 cfs (Figure 4.4-9).
The estimated 2- and 100-year peaks at Susitna Station will decrease by only about 18 percent to
142,000 cfs and 5 percent to 261,000 cfs, respectively (Figure 4.4-10).
4.5. Discussion
The pre-Project hydrology analysis was conducted based on the USGS extended record data at
the five mainstem gages and six tributary gages for which the data were available. Unregulated
flows at the Watana Dam-site were also developed using the HEC-ResSim model to provide a
basis for directly comparing pre-Project and Maximum Load Following Scenario OS-1 flows at
that location.
The specific effects of the proposed Watana Dam on the downstream flow regime will, of
course, depend on the manner in which the reservoir is operated. The HEC-ResSim model on
which the Maximum Load Following Scenario OS-1 analysis is based represents a preliminary
operation scenario that was developed by placing the entire variability of the Railbelt electricity
load on the Susitna-Watana Project; thus, it represents a maximum (or worst-case) load-
following scenario (John Haapala, personal communication, January 24, 2013).
Because the Project will not affect mainstem flows upstream from the reservoir or inflows from
the downstream tributaries, the Maximum Load Following OS-1 analyses only considered the
Gold Creek, Sunshine, and Susitna Station gages. Output from the HEC-ResSim model was
used directly for the analysis at Gold Creek and Sunshine. Since the model domain only extends
downstream to PRM 88, it was necessary to estimate Maximum Load Following Scenario OS-1
flows at Susitna Station using the simulated Sunshine flows, adjusted for the difference between
the Sunshine and Susitna Station flows from the USGS extended record.
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4.5.1. Seasonal and Flow-duration Comparison
The Project will change the seasonal flow patterns by increasing flow during the typical low-
flow season that occurs in late-fall, winter and early-spring under pre-Project conditions, and
decreasing the flows during the pre-Project high-flow period between May and September (Table
4.5-1 and Figure 4.5-1). These changes also affect the annual mean daily flow duration curves
by reducing the magnitude of flows in the high-flow range that occur 30 to 40 percent of the
time, and increasing flows in the low flow (60 to 70 percent) range (Table 4.5-2 and Figure 4.5-
2). In all cases, the relative magnitude of the changes is much greater in the Middle River above
the Three Rivers Confluence, and they decrease in the downstream direction because of the
influence of the major tributary inflows.
4.5.2. Flood-frequency Comparison
Comparison of the flood frequency curves developed from the 61-year record of flows from the
HEC-ResSim model results indicates that the annual peak flows for equivalent recurrence
intervals at the Watana Dam site will decrease by about 50 percent for frequent events in the
1.25- to 1.5-year range under Maximum Load Following Operation Scenario OS-1, with the
relative change decreasing to approximately 27 percent at the 100-year peak discharge (Table
4.5-4 and Figure 4.5-3). The relative change at Gold Creek is similar, decreasing from 50 percent
to 59 percent for frequent events to about 28 percent at the 100-year peak (Figure 4.5-4). At
Sunshine, the relative magnitude of the change is somewhat smaller, ranging from about 25
percent for frequent events to about 23 percent at the 100-year peak, due primarily to inflows
from the Chulitna and Yentna Rivers (Figure 4.5-5). Tributaries downstream from Sunshine,
including the Yentna and Skwentna, cause a further decrease in the relative change at Susitna
Station (17 to 18 percent for the frequent event to only about 5 percent at the 100-year peak)
(Figure 4.5-6).
These results can also be assessed by comparing the recurrence intervals of equivalent discharges
under pre-Project and Maximum Load Following Operation Scenario OS-1 (Table 4.5-5). For
example, the 2-year peak discharge of 34,200 cfs at the Watana Dam site under pre-Project
conditions would occur only about once in 10 years, on average, and the 20-year flow of 57,600
cfs would occur only about once in 140 years, on average, with Maximum Load Following
Operation Scenario OS-1. At Gold Creek, the 2-year peak discharge of 43,700 cfs would occur
about once in 12 years on average and the 20-year flow of 72,300 cfs could occur very rarely
(once in about 166 years, on average) under Maximum Load Following Operation Scenario OS-
1. The 2-year peak discharge at Sunshine of 94,700 cfs would occur about once every 7 to 8
years, and the 20 year flow of 143,600 cfs would occur about once in 150 years, on average. The
changes are less significant at Susitna Station, with the pre-Project 2-year flow of 170,300 cfs
occurring about once in 5.2 years and the 20-year flow of 233,500 cfs occurring about one in 43
years, on average, with Maximum Load Following Operation Scenario OS-1.
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5. STAGE-EXCEEDENCE ANALYSIS
This section documents the analysis that was conducted to evaluate the relative difference in
stage associated with the two hydrologic conditions: pre-Project and Maximum Load Following
OS-1. This analysis built on the results of the flow duration analysis. The stage exceedence
analysis was conducted at two locations along the Lower Susitna River Segment: the Sunshine
Gage (USGS 15292780) and the Susitna Station Gage (USGS 15294350).
This stage exceedence analysis was conducted as part of the overall 2012 Lower River
Geomorphology Study, specifically as part of the “Riverine Habitat-Flow Relationship
Assessment” task.
5.1. Objectives
The objective of this analysis is to quantify the relative change in river stage at two locations in
the Lower Susitna River Segment between the pre-Project hydrologic condition and the
Maximum Load Following OS-1 hydrologic condition. The results of the analysis provide a
preliminary assessment of the change in hydraulic conditions in the Lower Susitna River
Segment. The results will also provide a basis for interpreting how hydraulic responses to
changes in hydrologic conditions can affect habitats and access to tributaries in the Lower River
(described in a separate technical memorandum).
5.2. Methods
The primary sources of information used to conduct the stage exceedence analysis at each gage
location were (1) the most recent USGS stage-discharge ratings at each site, and (2) the results of
the flow-duration analyses for the pre-Project and the Maximum Load Following OS-1
hydrologic conditions. The mean daily flow record (WY1950 through WY2010) for each
hydrologic condition was converted to values of stage, in feet, using the most recent USGS
stage-discharge ratings. It is noted that the ratings developed for both gages do not account for
the effects of ice on river stage. Each computed stage for the WY1950 through WY2010 period
of record therefore represents the stage corresponding to the mean daily flow; it does not
necessarily represent the mean daily stage.
5.2.1. Conversion of Mean Daily Flow Records to Stage Records
At the Sunshine Gage, the most recent rating published by the USGS is Rating ID 6.0 (the red
line in Figure 5.2-1). Rating ID 6.0 is based on measurements conducted by the USGS through
September 2012. According to USGS staff, at this gage there have not been any open water
measurements for discharges less than 35,000 cfs, so the rating is not defined for flows less than
this threshold (Josh Morse, personal communication, January 31, 2013).
The USGS is not currently maintaining the Susitna Station Gage. Rating ID 4.0 is the most
current, with an apparent inflection in the rating at a stage of 10 feet (Figure 5.2-2). This rating
and is based on flow measurements conducted through October 2003.
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The lowest measured flow used to develop the Sunshine stage-discharge rating is 2,940 cfs and
the lowest measured flow used to develop the Susitna Station stage-discharge rating is 28,000
cfs. Since the mean daily flow record at both sites includes flows less than these minima, the
published ratings at both gages were extrapolated by fitting trend lines to the published
relationships (Figures 5.2-1 and 5.2-2). For the Susitna Station Gage, the extrapolation was based
only the stage-discharge relationship for stages less than 10 feet.
In converting the mean daily flow series to corresponding series of stage, the lookup function in
Microsoft Excel was used. For flows greater than the minimum value on the published ratings,
the published ratings were used to calculated stage; for flows less than these minimum values,
stages were estimated using the trend lines extrapolated from the published datasets. This method
produced a complete record of stages corresponding to the each value of mean daily flow at each
of the two USGS locations for the pre-Project and Maximum Load Following OS-1 conditions.
5.2.2. Stage-Duration Analyses and Stage-Exceedence Analyses
A stage-duration analysis was conducted at each gage location, using the two complete stage
records (WY1950 through WY2010) for both the pre-Project and Maximum Load Following
OS-1 hydrologic conditions. An annual stage-duration analysis was based on the stage values for
the entire period of record, and monthly stage-duration analyses were based on the stage values
for each of the twelve months throughout the entire period of record. The results of these
analyses were used to identify stage-exceedence relationships on annual and monthly bases. The
stage-exceedence relationships corresponding to the pre-Project hydrologic conditions and the
Maximum Load Following OS-1 hydrologic conditions were plotted together to compare the
relative changes in stage across the range of exceedence values. A statistical analysis was also
conducted to quantify the maximum, minimum, average and median stages by month.
To better illustrate how the changes in stage relate to the channel/floodplain morphology at each
site, selected stage-exceedence ordinates were converted to water surface elevations and overlaid
on plots of cross section geometry. The 10-, 50- and 90-percent exceedence values were selected
for this graphical representation. Representative cross section geometry was first developed at
each gaging station location using USGS discharge measurement notes for a recent high flow
measurement. Table 5.2-1 summarizes the specific USGS flow measurements that were used to
develop the representative cross section geometry at each location.
Cross-section geometry was developed by converting each incremental depth measurement (feet)
corresponding to the information in Table 5.2-1 to a bed elevation (feet, NAVD88) using
Equation 5.2-1.
[ ] (5.2-1)
where
Elevbed = elevation of bed at each horizontal increment (feet, NAVD88)
Gage = gage reading at time of USGS flow measurement (feet), see Table 5.2-1
Datum = assumed gage datum relative to NGVD29 (40 feet for Susitna Station;
242 feet for Sunshine)
Conversion = conversion from NGVD29 to NAVD88 (6 feet used at both locations)
Depth = USGS measured depth at each horizontal increment (feet)
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There is no published conversion factor available in the vicinity of the two gaging stations to
transform elevations between the NGVD29 geodetic datum and the NAVD88 geodetic datum.
However, several National Geodetic Survey control points were found in the vicinity of the
Susitna River. A number of these control points reported elevations relative to both NGVD29
and NAVD88. A review of a number of these control points found that the average difference in
elevations expressed in NGVD29 and elevations expressed in NAVD88 was approximately 6
feet. This vertical transformation was therefore assumed at both gage locations.
The stages associated with the 10-, 50 and 90-percent exceedences were converted to water
surface elevations using Equation 5.2-2.
(5.2-2)
where
WSEL = water surface elevation corresponding to specified stage (feet, NAVD88)
Stage = stage selected from stage-exceedence relationship (feet)
Datum = assumed gage datum relative to NGVD29 (40 feet for Susitna Station;
242 feet for Sunshine)
Conversion = conversion from NGVD29 to NAVD88 (6 feet used at both locations)
5.3. Results
This section presents the results of the comparative stage-exceedence analysis for the pre-Project
and the Maximum Load Following OS-1 hydrologic conditions at both the Sunshine Gage and
the Susitna Station Gage. Specific conclusions drawn from this analysis are presented in Section
5.4. Note that the stage values presented in the graphs and tables in this section are unique to
each gage location. In other words, a five-foot stage at the Sunshine Gage is not equivalent to a
five-foot stage at the Susitna Station Gage.
Tables 5.3-1 through 5.3-5 present the results of the stage-exceedence analyses of the pre-Project
hydrologic condition as compared to those for the Maximum Load Following OS-1 hydrologic
condition. Table 5.3-1 includes specific annual stage-exceedence ordinates for both gage
locations. Tables 5.3-2 and 5.3-3 include monthly stage-exceedence ordinates for the Sunshine
Gage; Tables 5.3-4 and 5.3-5 include monthly stage-exceedence ordinates for the Susitna Station
Gage. In each of these tables, the relative change in stage (either positive or negative) for each
exceedence percentile is indicated.
Table 5.3-6 (Sunshine Gage) and Table 5.3-7 (Susitna Station Gage) provide results of statistical
analyses of monthly stages calculated for both the pre-Project hydrologic conditions and the
Maximum Load Following OS-1 hydrologic conditions. In each table, the relative change in
stage (either positive or negative) for each statistic is indicated.
At the two gage locations, annual stage-exceedence relationships and monthly stage-exceedence
relationships were developed for both the pre-Project and the Maximum Load Following OS-1
conditions. To allow a direct comparison between the results for the two hydrologic conditions,
the stage-exceedence relationships were plotted together. Annual stage-exceedence relationships
for the Sunshine Gage are provided in Figure 5.3-1; the annual relationships for the Susitna
Station Gage are shown in Figure 5.3-2. As seen in these two figures, the line representing the
pre-Project conditions is solid whereas the line representing the Maximum Load Following OS-1
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conditions is dashed. Figure 5.3-3 (Sunshine Gage) and Figure 5.3-4 (Susitna Station Gage)
illustrate the monthly stage-exceedence relationships for the month of May. Appendix J includes
plots of the pre-Project and the Maximum Load Following OS-1 annual and monthly stage-
exceedence relationships for the two locations.
The results of the stage-exceedence analysis are alternatively presented on representative cross
section plots at each gage location, after converting the stages (feet) to water surface elevations
(feet, NAVD88). For this presentation, the 90-, 50- and 10-percent pre-Project and Maximum
Load Following OS-1 stage-exceedence values were converted to water surface elevations (see
Equation 5.2-2) and overlaid on the representative cross section geometry (Figures 5.3-5 and 5.3-
6). Appendix K includes identical figures showing the results of the monthly stage-exceedence
analyses at both gages. This method of presentation provides a visual assessment of the relative
changes in water surface elevation between the pre-Project and the Maximum Load Following
OS-1 hydrologic conditions. It also provides a visual assessment of the relationship between the
water-surface elevations associated with the range of flows between the 10- and 90-percent
stage-exceedences.
5.4. Discussion
The stage-discharge ratings published by the USGS do not include the effect that ice has on river
stage. For this reason, the results of the stage-exceedence analyses through the winter months
should consider this limitation.
The tables and figures presented in the Section 5.3, Appendices A and B indicate that the
magnitude of change in stage (or water-surface elevation) from the pre-Project condition to the
Maximum Load Following OS-1 condition varies somewhat between the two gage locations.
The results also indicate that the changes in stage vary considerably by season (i.e., month).
Regarding the sensitivity to location, it was found that for a given exceedence percentile and a
given month, the magnitude of change in stage from the pre-Project hydrologic condition to the
Maximum Load Following OS-1 hydrologic condition was often quite different between the two
gage locations (Table 5.4-1). As seen in Table 5.4-1, the relative change in flow from the pre-
Project hydrologic condition to the Maximum Load Following OS-1 hydrologic condition for a
given exceedence percentile is roughly equivalent between the Sunshine Gage and the Susitna
Station Gage. However, the change in stage from the pre-Project hydrologic condition to the
Maximum Load Following OS-1 hydrologic condition for this same exceedence percentile
varies. For stages less than the 50-percent exceedence, the change is slightly greater at the
Susitna Station Gage than at the Sunshine Gage; when the stage is greater than the 50-percent
exceedence value; the change at the Sunshine Gage is greater than at the Susitna Station Gage.
Since the change in flows is approximately the same for each exceedence probability, the
explanation is due to the differences in the slope of the published stage-discharge ratings at the
two sites. For higher flow conditions, an equivalent change in flow rate at the two locations is
associated with a larger change in stage at the Sunshine Gage than at the Susitna Station Gage
(Figure 5.4-1).
Regarding the sensitivity to seasonality, it was found that for a given exceedence percentile and a
given month, the magnitude of change in stage from the pre-Project hydrologic condition to the
Maximum Load Following OS-1 hydrologic condition was often quite different between the two
gage locations. For high-flow conditions (i.e. during the months of May through August,
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inclusive), the changes in stage at the Sunshine Gage were higher than at the Susitna Station
Gage for all exceedence probabilities.
The magnitude of the change in flow in the Susitna River from the pre-Project to the Maximum
Load Following OS-1 condition varies by month, as illustrated in the monthly flow-duration
curves provided in Appendix G. This monthly variability is a product of the assumptions that
were made for Watana Dam operating under the Maximum Load Following OS-1 hydrologic
condition. Correspondingly, the magnitude of the change in stage also varies by month. This
monthly variability was shown in the tables in the previous section and is further illustrated in
monthly bar charts (Figures 5.4-2 through 5.4-7). These bar charts illustrate the change in stage,
by month, at a specific location (either the Sunshine Gage or the Susitna Station Gage) for a
specific stage-exceedence value. For instance, Figure 5.4-2 is for the Sunshine Gage location,
illustrating the change in magnitude for the 90-percent stage exceedence value for each of the
twelve months. Similar figures were developed for the 50- and 10-percent exceedence values at
both gage locations.
The months that exhibited the least pronounced absolute change in hydrologic conditions were
the months of August and September. This same observation was identified for the absolute
change in stage at both gage locations. At the Sunshine Gage, the change in stage for the
exceedence percentiles summarized in Table 5.3-3 ranged from -1.00 to +0.27 feet. At the
Susitna Station Gage, the change in stage for the exceedence percentiles summarized in Table
5.3-5 ranged from -0.45 to +0.22 feet.
During the months of June and July, the entire flow-exceedence relationship for the Maximum
Load Following OS-1 hydrologic condition was lower than for the pre-Project condition at both
gage locations. Therefore, stage values for the entire range of flows for these months were also
reduced. For instance, the median value of stage (50-percent exceedence) at the Sunshine Gage
was reduced by 1.43 feet (June) and 1.21 feet (July). At the Susitna Station Gage, the reduction
in the median value of stage was 0.87 feet (June) and 0.77 feet (July). The months of June and
July exhibited the largest reduction in stage values, using the median value as the measure.
Overall, the largest changes in stage occurred during the winter/spring months of November
through April. For each of these months, the median value of stage was increased by more than
one foot at both of the gage locations (see Tables 5.3-6 and 5.3-7). This observation is attributed
to the lowest magnitude flows during these months of the year, and incremental changes in lower
flows producing relatively larger changes in stage due to the steepness of the lower part of the
stage-discharge ratings. However, as previously stated, it is noted that the stage-discharge ratings
published by the USGS do not include the effect that ice has on river stage. Thus, interpretation
of the calculated stages should consider this limitation.
In summary, the months of October through April exhibit increased stages at both gage locations
for the entire range of exceedence probabilities that were included in Tables 5.3-2 through 5.3-5.
The month of May exhibits increased stages for the lower flow conditions and reduced stages for
the higher flow conditions. The months of June and July show reduced stages at both gage
locations for all flow conditions. The months of August and September showed increased stages
for the lower flow conditions and reduced stages for the higher flow conditions.
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6. SPECIFIC GAGE ANALYSIS
This section documents the specific gage analysis that was conducted to characterize the relative
vertical stability of the Susitna River channel. The analysis requires comparisons of stage-
discharge ratings over time, so analyses were planned for the two USGS gaging stations that are
located in the Lower River Segment. The analysis was to be conducted at the Susitna River at
Sunshine Gage (USGS Gage 15292780) and the Susitna River at Susitna Station Gage (USGS
Gage 15294350); however, as further described in Section 6.2, the analyses were completed only
for the Susitna Station Gage.
This specific gage analysis was conducted as part of the overall 2012 Lower River
Geomorphology Study, specifically as part of the “Riverine Habitat-Flow Relationship
Assessment” task (AEA 2012).
6.1. Objectives
The objective of this analysis is to assess the relative vertical stability of the Susitna River
channel in the immediate vicinity of the two USGS gaging stations in the Lower River Segment.
6.2. Methods
A specific gage analysis involves the development of a graph of stage for a specific discharge at
a particular location plotted over time. When such an analysis is made for a family of specific
discharges, a family of graphs can be plotted. The resulting family of curves illustrates the
changes in stage for each specific discharge, so the curves can be used to interpret if the channel
in the vicinity of the gaging station is considered to be in equilibrium. If the family of curves
neither progressively rise nor fall over time, the channel may be considered to be in a state of
dynamic equilibrium. If the family of curves exhibits a progressive pattern of rising (falling), this
may be interpreted to indicate bed aggradation (degradation).
Specific gage analyses are ideally conducted using direct measurements of stage and discharge.
However, an adequate number of measurements are required for each specific discharge of
interest over the period of analysis for meaningful interpretation of the results. In this study,
insufficient measurement data were available, so the analyses were conducted using an
adaptation of the “specific gage” technique described by Blench (1969) and Klingeman (1973).
The adaptation relied on published stage-discharge ratings developed by the USGS for the
gaging stations instead of directly measured stages and discharges. There are six such ratings
available for the Sunshine Gage and four ratings available for the Susitna Station Gage.
Information regarding each of the ratings is summarized in Tables 6.2-1 and 6.2-2, along with
relevant station notes from the USGS station description.
The current location of the Susitna River at Sunshine Gage is on the left bank, approximately
fifty feet downstream of the George Parks Highway Bridge near PRM 88 (Figure 6.2-1). The
flow in the 2012 aerial photo (Figure 6.2-1) is 38,000 cfs, as measured at the Sunshine Gage. The
channel is straight for about 2,500 feet downstream of the gage and for about 1,500 feet
upstream. Further upstream, the channel is braided. According to the USGS station notes, at low
and medium stages, a side channel can form along the right bank upstream of and under the
bridge, and at medium to high stages, this channel can flow back into the main channel
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downstream of the gage. Since its original installation, the gage has been moved twice. Each
time the gage was moved, the USGS revised the reference datum. According to the USGS station
notes, the datum was “lowered by 5.0 feet on May 28, 1982”. However, the stage values in the
rating table for Rating No. 1 were subsequently adjusted so that this rating, as currently
published, is relative to the lowered datum (Josh Morse, personal communication, January 31,
2013). When the gage was re-established on October 6, 2011 at its new location downstream of
the bridge, the USGS station notes indicate that 10 feet was added to the datum to prevent
negative gage height values. It is not certain whether this adjustment of 10 feet reflects the actual
difference in elevation between the datums at the two locations.
The location of the Susitna River at Susitna Station Gage is on the left bank, approximately 1.5
miles downstream of the confluence with the Yenta River, near Project River Mile (PRM) 30
(Figure 6.2-2). The gage is located at the mid-point of a one-mile long straight section of the
river. According to the USGS station notes for this gage, the hydraulic control at the site is the
downstream channel for all but extreme stages, when the island 2,000 feet downstream may
become the control. The station notes go on to state that while at higher flows there is one
channel, at mid- to low-flows, a sand bar is exposed approximately 1,000 feet from the left bank
which divides the river into two channels. This sand bar can be seen in Figure 6.2-2. The aerial
photo used in this figure was flown on September 30, 2012 when the recorded discharge at the
USGS gage at Sunshine was 48,000 cfs. This flow corresponds approximately to a 25 percent
pre-Project annual exceedence flow.
The Susitna River at Sunshine Gage was in continuous operation from May 1981 through June
1986 and was subsequently re-established in October 2011. To date, a total of fifty-six flow
measurements have been made at the site, with only two measurements made during the 25 year
period between June 1986 and October 2011. Figure 6.2-3 graphically illustrates the time of
survey and the magnitude of the USGS discharge measurements. Measurements that were rated
as “Poor” by the USGS are distinguished since these were generally made during periods of ice
cover. Rating No. 6 is the current rating for this station.
The Susitna River at Susitna Station Gage was in continuous operation from May 1975 through
September 1993 and is now considered inactive. For the entire period of record, the gage
remained in the same location and was never moved. To date, a total of 130 flow measurements
have been made at the site, with six of them having been made subsequent to when the gage
became inactive. Figure 6.2-4 graphically illustrates the time of survey and the magnitude of the
USGS discharge measurements. Measurements that were rated as “Poor” by the USGS are
distinguished since these were generally made during periods of ice cover. Rating No. 4 was the
last published rating for this station.
The specific gage analysis was not completed for the Sunshine Gage location for several reasons.
The gage has been moved on two occasions, with changes made to the recording datum after
each move. More importantly, however, the gage was discontinued in 1986 so there is only a
short five year period of gage operation and discharge measurement data. There was nearly a
twenty-five year gap in time between when the gage was discontinued in 1986 and re-established
in 2011 (at the new location downstream of the George Parks Highway Bridge), and although
there have been eight flow measurements conducted since the gage was re-established, there is
some uncertainty that the gage datum at the new location is correctly tied to the previous datum.
Therefore, the specific gage analysis was only conducted for the Susitna Station Gage.
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The first step for conducting a specific gage analysis is to confirm that measured stages reference
the same datum over the entire period of the analysis. If different datums are referenced,
conversions to a consistent reference are required. No adjustments were needed for the Susitna
Station Gage because the gage was never moved and the USGS never changed the reporting
datum. Figure 6.2-5 shows the four ratings published by the USGS for this gaging station.
The next step was to select specific discharges for analysis. The flow magnitudes that were
selected for the Susitna Station Gage analysis were obtained from the pre-Project flow-duration
analysis and the pre-Project flood-frequency analysis. The magnitudes that were selected were
intended to cover a wide range of flow rates, and to include flows that had geomorphological
significance. For instance, the 1.01- and 2-year return period flows were selected because they
bracket the return period of bankfull discharge (Leopold et al. 1964). Table 6.2-3 summarizes the
flow rates that were selected to develop the family of curves for the Susitna Station specific gage
analysis. As indicated in this table, the minimum flow rate common to all of the published
ratings is 30,000 cfs, so this selected as the minimum flow of interest. It is noted that 30,000 cfs
is approximately equal to the pre-Project 45 percent annual exceedence flow. The maximum
flow common to all of the published rating curves was 201,000 cfs. The pre-Project 5-year return
period flow of 197,000 cfs was selected as the maximum flow for analysis because it was
reasonably close to the maximum value on the published ratings.
The final step was to calculate the stage for each selected flow in Table 6.2-3 from each of the
four USGS rating curves representing different periods in time. The results were plotted to
develop the specific gage graphs.
6.3. Results
The tabular results of the specific gage analysis conducted at the Susitna Station Gage are
summarized in Table 6.3-1. The stages in this table were calculated using the four ratings
published by the USGS. The results shown in Table 6.3-1 were plotted to develop a family of
nine specific gage curves (Figure 6.3-1). In developing the figure, the stage values for each flow
rate were assumed constant throughout the range of effective dates for each rating, thus giving
the curves a stair-step appearance. Each curve illustrates the changing conditions in river stage
for the indicated flow rate over the period of record for the gaging station.
6.4. Discussion
A specific gage analysis was conducted for the Susitna River at Susitna Station Gage. A similar
analysis was not conducted for the Susitna River at Sunshine Gage, in part because the period of
time when the gage was in operation and when discharge data was collected was only five years
(May 1981 through June 1986). Although the Sunshine Gage was re-established in 2011, and
flow measurements have been conducted since this time, there is some uncertainty as to whether
the gage datum at the new location is tied to the previous datum.
The analysis of the Susitna River at Susitna Station encompassed four periods (each defined by a
published USGS rating) over the course of approximately 18 years, from 1975 through 1993.
During this period, the USGS conducted 69 discharge measurements, ranging from 5,380 to
221,000 cfs, rated as either “Good” or “Fair”. The fact that the USGS only developed four
ratings for this 18-year period is indicative of a fairly stable channel section over this time.
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This observation is substantiated by the graphical results of the specific gage analysis. The
family of specific gage curves shows evidence that for the range of flows selected, there has been
only minor changes in stage, with no more than 0.5 feet of change for a given flow rate between
any two rating periods. If net stage change for a given flow rate is defined as the change in stage
between Rating 1 and Rating 4, then the flows associated with the largest net increase in stage
are 80,000 and 94,000 cfs, each showing a net increase of 0.3 feet. The flow rate with the largest
net decrease in stage (i.e., 0.5 feet) was 197,000 cfs.
Overall, the trend in stage change was for a net decrease of no more than 0.5 feet for flows
greater than or equal to 152,000 cfs (1.25-year return period), and a net increase of no more than
0.3 feet for flows between 60,000 and 132,000 cfs. For flows less than 60,000 cfs, the results
indicated a net decrease in stage of no more than 0.3 feet.
The flow rates with the least amount of net change in stage were 132,000 cfs (1.01-yr return
period) and 152,000 cfs (1.25-year return period), each with a net change of only 0.1 feet.
The small observed net decrease of specific gage for flows greater than 152,000 cfs may indicate
a minor change in the downstream channel control during high flows. This might be due to
changes in the planform of the downstream island that the USGS indicated may function as a
high flow control, or it might be due to widening of the channel downstream of the gage. The
variation in specific gage for flows less than 152,000 cfs might simply be a result of the changing
influence of the adjacent sandbar over time. However, given the small magnitudes of change in
stage as summarized above and as seen in Figure 6.3-1, and the apparent absence of any
substantial progressive changes in stage for specific discharges over and 18-year period, the
Susitna River channel section in the vicinity of the Susitna Station Gage can be considered to be
in equilibrium.
7. DISCHARGE EFFECTS ON ICE ELEVATION AND CROSS-
SECTIONAL FLOW CHARACTERISTICS
The available data from the USGS Susitna River at Sunshine and Susitna River at Susitna Station
mainstem gages were evaluated to assess potential discharge effects on ice elevation and cross
sectional flow characteristics (depth and velocity) at the gage locations, as part of the Riverine
Habitat-Flow Relationship Assessment.
Ice cover over a river channel increases resistance to flow in several ways, including the
following (Beltaos 1995):
Increases in the wetted perimeter on which shear stress operates, causing a significant
reduction in the hydraulic radius for the same flow depth, compared to open-water
conditions,
Increases in the total channel resistance due to the roughness of the undersurface of the ice
cover, and
Potentially significant reductions in cross-sectional area due to large, undersurface ice
protrusions.
Resistance to flow and the conveyance capacity in an ice-covered channel are often difficult to
estimate precisely due to the following complicating factors (Beltaos 1995):
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The increase in roughness of the undersurface of the ice cover is difficult to measure directly
or estimate indirectly from velocity profiles,
The unobstructed waterway under the ice cover varies with large deposits of loose slush in a
manner that is difficult to estimate,
With an ice cover, the slope of the energy grade line is assumed to be parallel to that for
uniform, steady, open channel flow conditions, an assumption that may be invalid,
particularly with heavy frazil loads or rapid flow variation,
The bed roughness can be significantly different under ice cover than for open channel
conditions
7.1. Objectives
The objective of this analysis was to determine whether discharge effects on ice elevation and
flow characteristics could be detected from the available data at the USGS gages, and if so, to
approximate the magnitude of these effects.
7.2. Methods
Winter gage data are available from 13 measurements taken between 1981 and 1986 at the
Sunshine gage and 23 measurements taken between 1982 and 1993 at the Susitna Station gage.
These measurements were recorded by hand, and the hand-written notes were entered into an
Excel spreadsheet to analyze the relationships between discharge, ice thickness, and cross
sectional flow characteristics (Tables 7.2-1 and 7.2-2).
The data were reviewed to determine discharge effects on ice elevation and flow characteristics.
Unfortunately, neither the stage nor the water-surface elevation were surveyed during the field
discharge measurements, thus comparisons to ice elevation were not possible. In addition, the
hydraulic condition of the flow and the interface of the ice cover were not noted. It is, therefore,
not possible to evaluate whether the flow was under pressure, and if so, by how much. As a
result, the effects of the pressure head on the hydraulic properties cannot be assessed with the
available data.
Further analysis could not be performed for the Susitna Station gage site, because the hydraulic
(i.e., area, width and velocity) data from the open-water field measurements were not reported.
The USGS NWIS site contains field measurement data for the Sunshine gage for 48
measurements from 1981 through 2012, including 15 ice measurements. The 13 measurements
for which hand written notes were obtained, and additional measurements taken on January 31,
2012, and March 19, 2012, are included (Table 7.2-1). There are 35 measurements reported for
open water conditions.
Reported data for the field measurements include channel discharge, channel width, channel area
and channel velocity (hydraulic depth was calculated by dividing the channel area by the channel
width). The data for the 48 measurements were used to compare trends of velocity, hydraulic
depth and flow area with discharge between ice covered and open channel flow conditions.
The available data at the Susitna Station gage site does not include the hydraulic (i.e., area, width
and velocity) data from the field measurements.
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7.3. Results
Independent regression lines through the velocity versus discharge data at the Sunshine gage
indicates that there may be difference in the relationship for ice-covered conditions compared to
open-water conditions (Figure 7.3-1). The ice cover line is steeper and appears to be shifted to
somewhat higher velocities than the open-water line, which is reasonable based on the expected
relationships for pressure flow and open-water flow at equivalent discharges. However, since
the range of discharges for the ice-cover data is relatively small and all of the points were
collected at discharges less than the range of discharges from the open-water data, drawing this
conclusion from the data, alone, is tenuous. In fact, a regression line through the combined data
set appears to fit reasonably well, with the exception of a few points at the lower end of each data
set that had unusually low velocities compared to the remainder of the data sets. The hydraulic
(i.e., average) depth and cross sectional relationships (Figures 7.3-2 and 7.3-3) lead to the same
conclusions.
7.4. Discussions
The available data at the Sunshine and Susitna Station gages, that represent pre-Project
conditions, do not provide sufficient information with which to draw defensible conclusions
about the differences in hydraulic conditions between ice-covered and open-water conditions,
particularly those that will occur under Project conditions. Future discharge measurements under
ice-cover conditions should include the elevation of the top of the ice and the static water-level to
provide a basis for assessing the degree of pressure flow.
8. REFERENCES
AEA (Alaska Energy Authority). 2012. Revised Study Plan: Susitna-Watana Hydroelectric
Project FERC Project No. 14241. December 2012. Prepared for the Federal Energy
Regulatory Commission by the Alaska Energy Authority, Anchorage, Alaska.
http://www.susitna-watanahydro.org/study-plan.
Ashton, G.D. 1986. River and Lake Ice Engineering. Water Resources Publications, Littleton,
Colorado.
Beltaos, S. 1995. River Ice Jams. Water Resources Publications, LLC.
Blench, T. 1969. Mobile-Bed Fluviology. 2nd edition. Univ. of Alberta Press. Edmonton. 28 p.
Hayse, J.W., S.F. Daly, A. Tuthill, RA. Valdez, B. Cowdell, and G. Burton. 2000. Effect of
Daily Fluctuations from Flaming Gorge Dam on Ice Processes in the Green River. All
U.S. Government Documents (Utah Regional Depository). Paper 87.
http://digitalcommons.usu.edu/govdocs/87
http://cripe.civil.ualberta.ca/Downloads/10th_Workshop/Ye_Zhu_1999.pdf
http://cripe.civil.ualberta.ca/Downloads/09th_Workshop/Kerr_et_al_1997.pdf
Interagency Advisory Committee on Water Data (IACWD), 1982. Guidelines for determining
flow frequency, Reston, Va., U.S. Geological Survey, Office of Water Data
Coordination, Hydrology Subcommittee Bulletin 17B.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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Klingeman, P.C. 1973, Indications of streambed degradation in the Willamette Valley. WRRI–
21, Water Resources Research Institute Report WRRI–21. Corvallis Department of Civil
Engineering. Oregon State University. 99 p.
Leopold, L.B., Wolman, M.G., and Miller, J.P., 1964. Fluvial Processes in Geomorphology.
Freeman Co., San Francisco, California, and London, 522 p.
MWH. 2012. Susitna-Watana Hydroelectric Project, Preliminary Susitna River Pre-Project and
Post-Project Flow Stages, presented at Technical Work Group Meetings, October 23-25.
R2 Resource Consultants, GW Scientific, Brailey Hydrologic and Geovera. 2013. Open Water
HEC-RAS Flow Routing Model. Prepared for Alaska Energy Authority. 69p.
Tetra Tech, Inc. 2013. 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.
U.S. Geological Survey. 2012. Streamflow Record Extension for Selected Streams in the Susitna
River Basin, Alaska, Scientific Investigations Report 2012–5210. 46 p.
Wilson, F.H., C.P. Hults, H.R. Schmoll, P.J. Haeussler, J M. Schmidt, L.A. Yehle, and K.A.
Labay. 2009. Preliminary Mapping of the Cook Inlet Region Alaska Including Parts of
the Talkeetna, Talkeetna Mountains, Tyonek, Anchorage, Lake Clark, Seward, Iliamna,
Seldovia, Mount Katmai, and Afognak 1:250,000 Scale Quadrangles. USGS Open-File
Report 2009-1108. 54p plus maps.
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9. TABLES
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Table 4.2-1. List of streamflow gages.
Gage
Number Gage Name
Drainage
Area
(sq. mi.)
Gage
Datum
(NGVD
29,ft)
Latitude Longitude Available Record Extended
Record
Main
Stem
River
Mile
15290000 Little Susitna River near Palmer 63 917 61o 42' 37" 149o 13' 47" 1948 - 2011 -
15291000 Susitna River near Denali 950 2,440 63o 06' 14" 147o 30' 57" 1957 - 1966; 1968 - 1986 Yes 291
15291200 Maclaren River near Paxson 280 2,866 63o 07' 10" 146o 31' 45" 1958 - 1986 Yes -
15291500 Susitna River near Cantwell 4,140 1,900 62o 41' 55" 147o 32' 42" 1961 - 1972; 1980 - 1986 Yes 223
15292000 Susitna River at Gold Creek 6,160 677 62o 46' 04" 149o 41' 28" 1949 - 1996; 2001 - 2011 Yes 136
15292400 Chulitna River near Talkeetna 2,570 520 62o 33' 31" 150o 14' 02" 1958 - 1972; 1980 - 1986 Yes -
15292700 Talkeetna River near Talkeetna 1,996 400 62o 20' 49" 150o 01' 01" 1964 - 2011 Yes -
15292780 Susitna River at Sunshine 11,100 270 62o 10' 31.3" 150o 10' 13.5" 1981 - 1986 Yes 84
15292800 Montana Creek near Montana 164 250 62o 06' 19" 150o 03' 27" 2005 - 2006; 2008 - 2011 -
15294005 Willow Creek near Willow 166 350 61o 46' 51" 149o 53' 04" 1978 - 1993; 2001 - 2011 Yes -
15294010 Deception Creek near Willow 48 250 61o 44' 52" 149o 56' 14" 1978 - 1985 -
15294100 Deshka River near Willow 591 80 61o 46' 05" 150 20' 13" 1978 - 1986; 1998 - 2001 -
15294300 Skwentna River near Skwentna 2,250 200 61o 52' 23" 151 22' 01" 1959 - 1982 Yes -
15294345 Yentna River near Susitna Station 6,180 80 61o 41' 55" 150 39' 02 1980 - 1986 Yes -
15294350 Susitna River at Susitna Station 19,400 40 61o 32' 41" 150 30' 45 1974 - 1993 Yes 28
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 24 February 2013
Table 4.4-1. Average annual flows (cfs) for pre-Project conditions based on the USGS extended record.
Water
Year
Average Annual Flow, Q (cfs), for Pre-Project Conditions
Susitna River
near Denali
Maclaren
River near
Paxson
Susitna
River near
Cantwell
Susitna
River at
Gold Creek
Chulitna
River near
Talkeetna
Talkeetna
River near
Talkeetna
Susitna River
at Sunshine
Willow
Creek near
Willow
Skwentna
River near
Skwentna
Yentna
River near
Susitna
Station
Susitna
River at
Susitna
Station
1950 2,200 816 5,080 8,030 7,410 3,390 19,600 277 5,520 16,300 42,400
1951 2,620 978 5,790 9,110 8,470 3,860 22,300 394 6,190 18,500 47,300
1952 2,570 962 6,060 9,530 8,190 4,030 22,900 423 6,280 18,300 46,800
1953 2,830 1,070 6,410 10,100 9,240 4,260 24,700 351 6,830 20,400 52,200
1954 2,810 1,040 6,150 9,680 8,890 4,090 23,700 308 6,560 19,600 49,700
1955 2,730 1,030 6,520 10,300 8,730 4,320 24,600 391 6,730 19,700 50,300
1956 3,180 1,190 7,310 11,400 9,790 4,880 27,600 343 7,420 21,800 55,200
1957 3,650 1,100 6,610 10,400 9,240 4,360 25,300 361 6,950 20,600 52,300
1958 2,510 1,110 5,990 9,480 8,770 3,970 23,000 271 6,420 18,900 48,700
1959 2,610 843 6,710 10,600 8,380 4,070 25,500 404 6,910 20,400 51,700
1960 2,900 1,180 6,140 9,690 8,360 3,920 23,600 340 6,390 17,900 47,700
1961 2,660 1,110 6,460 10,800 9,450 4,350 26,300 381 7,250 20,300 52,200
1962 3,190 1,010 7,990 11,600 8,820 4,370 27,500 431 5,700 16,000 47,900
1963 3,150 1,290 7,370 11,100 8,270 4,150 26,700 500 5,850 16,400 47,100
1964 2,600 960 6,610 9,770 9,310 3,950 22,600 351 6,270 17,500 42,700
1965 2,510 985 6,630 10,200 9,360 4,750 25,800 385 6,630 18,600 49,300
1966 2,410 816 5,190 9,430 8,650 4,220 23,600 327 6,430 18,000 46,300
1967 2,970 1,150 6,840 11,200 11,100 4,470 26,900 423 5,610 15,700 45,200
1968 3,430 896 6,130 9,790 9,170 4,470 24,600 379 6,440 18,000 46,800
1969 2,290 697 4,190 5,600 6,110 2,250 14,000 204 5,200 14,600 33,400
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 25 February 2013
Water
Year
Average Annual Flow, Q (cfs), for Pre-Project Conditions
Susitna River
near Denali
Maclaren
River near
Paxson
Susitna
River near
Cantwell
Susitna
River at
Gold Creek
Chulitna
River near
Talkeetna
Talkeetna
River near
Talkeetna
Susitna River
at Sunshine
Willow
Creek near
Willow
Skwentna
River near
Skwentna
Yentna
River near
Susitna
Station
Susitna
River at
Susitna
Station
1970 2,240 735 4,550 7,590 8,740 3,500 19,700 308 7,240 20,300 46,600
1971 2,900 1,090 6,820 10,300 8,410 5,300 25,400 399 6,940 19,400 47,800
1972 2,940 1,060 6,910 10,900 8,340 4,480 26,500 402 6,000 16,800 46,700
1973 2,240 890 5,110 8,090 7,590 3,850 20,800 350 5,240 14,700 41,400
1974 2,960 846 4,820 7,630 7,910 3,320 19,500 337 5,160 14,500 40,000
1975 3,000 1,030 6,550 10,300 8,970 4,340 25,400 410 6,490 18,900 46,100
1976 2,580 920 5,170 8,170 7,590 3,400 20,500 311 5,820 17,200 43,000
1977 3,050 1,160 6,410 10,100 8,740 4,360 24,700 434 10,100 26,300 56,000
1978 2,680 925 5,150 8,190 7,660 3,300 20,400 256 6,370 17,800 42,000
1979 3,040 886 6,030 9,490 8,940 4,450 24,000 433 6,630 20,700 53,700
1980 2,910 1,020 6,770 10,700 9,650 4,350 26,100 511 9,050 26,000 61,900
1981 3,400 1,170 7,890 12,000 10,400 4,420 28,400 367 9,050 24,900 55,700
1982 2,620 806 6,020 9,670 8,450 4,200 24,100 427 6,130 18,600 47,100
1983 2,830 994 6,510 9,920 8,220 3,640 23,600 349 6,390 18,300 43,800
1984 2,930 938 6,650 9,580 8,460 3,640 23,500 331 6,950 20,000 45,400
1985 3,000 1,070 5,930 9,880 8,460 4,260 24,300 468 6,840 19,700 47,300
1986 2,970 1,060 5,770 8,530 7,470 3,350 20,600 320 6,480 19,700 46,300
1987 3,060 1,070 6,710 10,600 9,860 4,810 26,700 416 7,750 23,600 54,900
1988 3,050 983 6,500 10,200 8,080 3,740 24,800 349 7,520 22,900 53,600
1989 3,210 1,030 6,500 10,300 8,960 4,240 25,500 413 7,980 24,400 56,500
1990 3,700 1,290 8,310 13,000 10,900 5,390 31,800 536 8,610 26,400 61,200
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 26 February 2013
Water
Year
Average Annual Flow, Q (cfs), for Pre-Project Conditions
Susitna River
near Denali
Maclaren
River near
Paxson
Susitna
River near
Cantwell
Susitna
River at
Gold Creek
Chulitna
River near
Talkeetna
Talkeetna
River near
Talkeetna
Susitna River
at Sunshine
Willow
Creek near
Willow
Skwentna
River near
Skwentna
Yentna
River near
Susitna
Station
Susitna
River at
Susitna
Station
1991 2,600 855 5,390 8,530 7,940 3,780 21,600 383 6,740 20,600 48,200
1992 2,430 863 5,510 8,720 7,510 3,530 21,600 335 6,080 18,400 43,900
1993 3,040 1,090 6,410 10,100 10,000 4,840 26,000 383 6,830 20,400 53,100
1994 2,770 990 6,300 9,960 9,170 4,340 25,100 413 6,710 19,800 51,800
1995 2,850 1,020 6,540 10,300 8,680 4,040 25,400 360 6,970 20,600 51,300
1996 1,860 648 4,260 6,800 6,790 3,120 17,700 245 4,750 13,800 38,300
1997 2,440 827 5,510 8,800 7,670 3,580 23,100 317 6,050 18,400 44,600
1998 2,670 907 5,890 9,380 8,230 3,850 24,600 336 6,380 19,500 47,100
1999 2,520 864 5,810 9,290 8,080 3,850 24,400 326 6,360 19,500 46,600
2000 2,750 963 6,400 10,200 8,900 4,450 26,600 429 6,910 21,100 50,300
2001 2,510 901 6,030 9,540 7,850 3,700 23,800 355 6,380 19,200 46,900
2002 2,420 865 5,360 8,480 8,090 3,800 21,700 315 5,800 17,100 45,100
2003 2,820 1,000 6,510 10,300 9,080 4,250 25,600 338 6,930 20,300 52,400
2004 2,570 912 5,960 9,400 7,900 3,610 23,300 268 6,400 18,900 47,700
2005 3,660 1,330 7,820 12,200 11,700 5,860 30,900 607 7,970 23,600 61,400
2006 2,710 983 6,550 10,300 8,290 4,010 24,900 434 6,800 20,000 49,500
2007 2,550 917 6,100 9,650 7,840 3,590 23,700 313 6,640 19,800 48,500
2008 2,360 844 5,630 8,900 7,460 3,420 22,000 314 6,120 18,000 45,300
2009 2,530 903 6,020 9,500 7,730 3,560 23,400 289 6,470 19,200 47,700
2010 2,720 983 6,440 10,100 8,180 3,760 24,800 293 6,870 20,500 50,300
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 27 February 2013
Water
Year
Average Annual Flow, Q (cfs), for Pre-Project Conditions
Susitna River
near Denali
Maclaren
River near
Paxson
Susitna
River near
Cantwell
Susitna
River at
Gold Creek
Chulitna
River near
Talkeetna
Talkeetna
River near
Talkeetna
Susitna River
at Sunshine
Willow
Creek near
Willow
Skwentna
River near
Skwentna
Yentna
River near
Susitna
Station
Susitna
River at
Susitna
Station
Average 2,790 980 6,190 9,730 8,600 4,060 24,050 370 6,660 19,460 48,560
Median 2,750 980 6,300 9,790 8,460 4,040 24,400 360 6,490 19,500 47,700
90%
Exceed-
ence
2,370 820 5,120 8,110 7,530 3,390 20,420 280 5,630 16,060 42,460
10%
Exceed-
ence
3,210 1,170 7,230 11,180 9,850 4,800 26,860 430 7,930 23,600 55,600
Annual
Volume
(af)
2,018,000 711,000 4,486,000 7,047,000 6,230,000 2,938,000 17,426,000 266,000 4,828,000 14,101,000 35,180,000
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 28 February 2013
Table 4.4-2. Average monthly flows (cfs) at USGS gages in the Susitna River watershed for pre-Project conditions based on the USGS extended record.
Period
Susitna
River near
Denali
Maclaren
River near
Paxson
Susitna
River near
Cantwell
Susitna
River at
Gold
Creek
Chulitna
River near
Talkeetna
Talkeetna
River near
Talkeetna
Susitna
River at
Sunshine
Willow
Creek
Near
Willow
Skwentna
River near
Skwentna
Yentna
River near
Susitna
Station
Susitna
River at
Susitna
Station
Drainage Area
(sq. mi.) 950 280 4,140 6,160 2,570 1,996 11,100 166 2,250 6,180 19,400
OCT 1,330 465 3,800 6,320 5,750 2,840 15,900 332 4,780 13,400 36,000
NOV 503 182 1,600 2,670 2,260 1,160 6,490 153 2,020 5,350 14,400
DEC 326 125 1,130 1,890 1,550 801 4,490 105 1,400 3,640 9,510
JAN 263 102 938 1,590 1,300 655 3,720 84 1,160 3,020 7,910
FEB 229 88 820 1,420 1,140 553 3,260 71 1,020 2,650 7,080
MAR 212 81 755 1,300 1,060 502 2,960 60 916 2,400 6,510
APR 293 106 1,030 1,740 1,370 670 4,030 79 1,330 3,480 8,990
MAY 3,120 1,140 8,630 13,800 10,400 5,120 33,200 487 9,280 26,900 66,100
JUN 7,400 2,800 16,900 26,300 21,500 10,700 63,700 1,040 17,400 50,600 120,000
JUL 8,580 2,920 15,800 24,000 23,200 10,300 60,500 745 16,700 49,900 122,000
AUG 7,300 2,420 13,900 21,400 20,600 9,210 54,200 666 14,200 43,100 109,000
SEP 3,640 1,290 8,620 13,700 12,600 5,940 34,900 573 9,320 27,900 72,800
Annual 2,780 982 6,190 9,720 8,600 4,060 24,100 368 6,660 19,500 48,600
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 29 February 2013
Table 4.4-3. Annual flow exceedence ordinates (cfs) for pre-Project conditions based on the USGS Extended Record.
Annual Flow Exceedence Ordinates
Percentile
Susitna
River
near
Denali
Maclaren
River near
Paxson
Susitna
River near
Cantwell
Susitna
River at
Gold
Creek
Chulitna
River near
Talkeetna
Talkeetna
River near
Talkeetna
Susitna
River at
Sunshine
Willow
Creek
near
Willow
Skwentna
River near
Skwentna
Yentna
River
near
Susitna
Station
Susitna
River at
Susitna
Station
99% 110 47 440 750 820 380 1,740 38 600 1,460 5,210
95% 181 60 560 960 965 450 2,310 51 750 1,910 5,840
90% 200 76 694 1,200 1,040 500 2,830 60 850 2,280 6,400
75% 263 100 940 1,600 1,230 621 3,750 80 1,140 2,970 7,710
50% 650 220 2,050 3,400 2,840 1,430 8,220 171 2,660 6,950 19,000
25% 5,070 1,820 11,400 17,800 16,100 7,240 45,000 526 12,000 36,500 94,000
10% 8,500 2,950 16,500 25,300 23,400 10,500 64,000 930 17,200 51,300 124,000
5% 9,570 3,400 19,400 29,800 26,200 12,800 72,800 1,240 19,900 58,700 138,000
1% 12,700 4,400 25,700 39,300 33,700 18,100 91,200 1,870 26,400 73,700 164,000
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 30 February 2013
Table 4.4-4. Mainstem Susitna River estimated return period peak flows (cfs) for pre-Project conditions based on the
USGS extended record.
Return Period (years) Flow (cfs)
Denali Cantwell Gold Creek Sunshine Susitna Station
1.25 11,300 23,100 35,100 90,200 152,000
2 13,500 27,300 43,500 106,000 170,000
5 17,200 33,400 56,200 129,000 197,000
20 23,100 41,900 74,600 160,000 233,000
50 27,500 47,600 87,500 181,000 258,000
100 31,200 52,100 98,000 197,000 276,000
Table 4.4-5. Susitna River Tributary estimated return period peak flows (cfs) for pre-Project conditions based on the
USGS extended record.
Return Period (years) Flow (cfs)
Maclaren Chulitna Talkeetna Willow Skwentna Yentna
1.25 4,220 30,200 17,700 1,970 25,000 74,100
2 4,900 35,200 23,200 2,700 29,100 83,600
5 5,950 43,000 32,700 3,990 35,300 97,400
20 7,510 54,800 49,100 6,240 44,400 116,000
50 8,620 63,200 62,300 8,080 50,800 129,000
100 9,510 70,100 73,900 9,700 55,900 139,000
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 31 February 2013
Table 4.4-6. Average monthly flows (cfs) at three USGS gages in the Susitna River watershed for Maximum Load
Following Scenario OS-1, based on the HEC-ResSim model.
Period Susitna River at Gold Creek Susitna River at Sunshine Susitna River at Susitna
Station
Drainage Area
(sq. mi.) 6,160 11,100 19,400
OCT 8,240 18,000 38,100
NOV 7,990 11,900 19,800
DEC 8,750 11,300 16,300
JAN 9,140 11,300 15,500
FEB 9,750 11,600 15,400
MAR 7,460 9,190 12,700
APR 6,950 9,160 14,100
MAY 8,490 27,400 60,200
JUN 10,200 47,500 104,000
JUL 10,800 47,200 108,000
AUG 15,400 48,400 103,000
SEP 12,700 34,100 72,000
Annual 9,660 24,000 48,500
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 32 February 2013
Table 4.4-7. Average annual flows (cfs) for Maximum Load Following OS-1 conditions based on the HEC-ResSim model.
Water Year
Average Annual Flow, Q (cfs), for Maximum Load Following OS-1 Conditions
Susitna River at Gold Creek Susitna River at Sunshine Susitna River at Susitna
Station
1950 8,470 20,100 42,900
1951 9,110 22,300 47,300
1952 9,000 22,400 46,300
1953 9,890 24,500 52,000
1954 9,640 23,700 49,700
1955 10,100 24,400 50,100
1956 11,400 27,500 55,100
1957 10,300 25,200 52,200
1958 9,440 23,000 48,700
1959 10,300 25,200 51,400
1960 9,630 23,500 47,600
1961 10,800 26,300 52,200
1962 11,500 27,500 47,900
1963 11,000 26,600 47,100
1964 9,740 22,600 42,600
1965 10,100 25,700 49,100
1966 9,410 23,700 46,300
1967 10,900 26,600 44,900
1968 9,770 24,600 46,800
1969 8,180 16,500 36,000
1970 6,880 19,000 45,900
1971 8,230 23,400 45,800
1972 10,800 26,400 46,700
1973 8,480 21,300 41,800
1974 8,860 20,700 41,200
1975 8,490 23,600 44,300
1976 8,550 20,900 43,400
1977 9,640 24,200 55,500
1978 8,420 20,700 42,300
1979 9,180 23,700 53,400
1980 10,600 25,900 61,800
1981 11,600 28,000 55,400
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 33 February 2013
Water Year
Average Annual Flow, Q (cfs), for Maximum Load Following OS-1 Conditions, cont.
Susitna River at Gold Creek Susitna River at Sunshine Susitna River at Susitna
Station
1982 9,610 24,000 47,000
1983 9,880 23,500 43,800
1984 9,550 23,500 45,400
1985 9,820 24,200 47,200
1986 8,550 20,600 46,400
1987 10,400 26,600 54,700
1988 10,200 24,800 53,500
1989 10,200 25,500 56,400
1990 12,900 31,600 61,100
1991 8,570 21,700 48,300
1992 8,620 21,500 43,800
1993 10,000 25,900 53,000
1994 9,960 25,100 51,800
1995 10,200 25,300 51,200
1996 8,450 19,400 40,000
1997 8,270 22,600 44,000
1998 8,680 23,800 46,400
1999 8,800 23,900 46,100
2000 10,100 26,400 50,100
2001 9,530 23,800 47,000
2002 8,530 21,700 45,100
2003 10,100 25,500 52,300
2004 9,440 23,400 47,800
2005 12,000 30,700 61,200
2006 10,100 24,800 49,300
2007 9,570 23,700 48,500
2008 8,860 22,000 45,200
2009 9,460 23,400 47,600
2010 10,100 24,800 50,300
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 34 February 2013
Table 4.4-8. Annual and monthly flow exceedence ordinates (cfs) for Maximum Load Following OS-1 conditions at Susitna River at Gold Creek based
on the HEC-ResSim model.
Susitna River at Gold Creek
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 1,400 6,440 7,140 6,880 7,070 795 800 952 2,240 7,980 7,880 7,900 6,200
95% 6,870 6,710 7,250 7,210 7,880 8,160 1,400 1,420 6,200 8,480 8,380 8,420 6,730
90% 7,210 6,920 7,330 7,660 8,220 8,500 6,900 6,250 6,620 8,700 8,600 8,730 7,170
75% 7,840 7,300 7,690 8,240 8,720 8,850 7,250 6,970 7,460 9,200 9,000 9,260 8,150
50% 8,750 7,730 8,010 8,740 9,190 9,800 7,850 7,390 8,300 9,890 9,480 12,600 11,000
25% 9,920 8,390 8,230 9,230 9,560 10,700 8,210 7,750 9,560 10,800 10,300 20,300 15,500
10% 12,300 10,100 8,450 9,760 10,300 11,400 8,620 7,990 10,800 11,900 12,000 25,600 21,100
5% 17,800 12,000 8,760 10,200 10,600 11,700 9,040 8,210 11,600 12,800 22,400 29,500 24,200
1% 26,900 15,900 9,610 11,300 11,700 13,200 9,650 8,730 13,300 16,500 29,700 39,600 32,200
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 35 February 2013
Table 4.4-9. Annual and monthly flow exceedence ordinates (cfs) for Maximum Load Following OS-1 conditions at Susitna River at Sunshine based on
the HEC-ResSim model.
Susitna River at Sunshine
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 3,240 11,000 9,300 8,880 8,840 2,110 2,080 2,360 5,400 26,400 32,000 21,900 13,800
95% 8,840 11,800 9,920 9,590 9,810 9,760 3,270 3,360 9,710 31,100 35,000 31,400 15,900
90% 9,470 12,400 10,300 10,000 10,200 10,100 8,290 7,850 10,700 33,400 37,400 34,900 18,300
75% 10,800 13,500 10,900 10,600 10,700 10,700 8,920 8,700 14,600 39,800 41,100 39,500 23,300
50% 13,200 15,800 11,600 11,300 11,400 11,700 9,510 9,320 25,900 48,000 45,800 46,000 31,300
25% 38,400 20,200 12,500 11,900 11,900 12,700 10,000 9,890 36,900 54,100 51,800 55,100 41,400
10% 51,000 26,800 13,800 12,500 12,600 13,500 10,600 10,700 48,500 60,400 58,200 64,800 54,300
5% 57,100 31,700 14,700 13,000 13,100 14,000 11,100 11,600 54,900 65,000 63,900 73,300 62,000
1% 71,300 42,900 16,500 14,000 13,900 15,100 11,700 17,000 60,400 77,200 77,000 97,800 80,300
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 36 February 2013
Table 4.4-10. Annual and monthly flow exceedence ordinates (cfs) for Maximum Load Following OS-1 conditions at Susitna River at Susitna Station
based on the HEC-ResSim model.
Susitna River at Susitna Station
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 6,810 16,500 13,200 12,500 11,900 6,020 5,450 5,760 10,100 58,200 73,700 45,200 22,900
95% 12,300 19,600 14,000 13,300 13,400 13,200 7,000 6,880 14,000 69,500 81,700 68,900 34,200
90% 13,000 21,900 14,800 13,800 13,900 13,600 11,500 11,300 17,400 77,400 88,100 76,600 39,400
75% 15,100 26,700 16,500 14,800 14,500 14,400 12,300 12,100 32,700 90,400 97,600 88,400 50,900
50% 23,100 33,600 18,500 16,000 15,400 15,500 12,900 12,900 57,700 106,000 107,000 102,000 68,000
25% 87,400 43,800 21,800 17,600 16,400 16,600 13,700 14,700 85,800 117,000 118,000 116,000 88,800
10% 112,000 60,200 25,800 18,800 17,500 17,600 14,600 18,100 106,000 128,000 129,000 129,000 112,000
5% 122,000 70,600 29,200 19,700 18,100 18,400 15,300 23,000 116,000 134,000 139,000 144,000 123,000
1% 145,000 97,000 40,900 25,400 19,000 19,700 16,300 39,000 128,000 149,000 162,000 188,000 152,000
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 37 February 2013
Table 4.4-11. Susitna River estimated return period peak flows (cfs) for Maximum Load Following OS-1
conditions based on the HEC-ResSim model.
Return Period
(years)
Flow (cfs)
Gold Creek Sunshine Susitna Station
1.25 16,900 60,500 125,000
2 23,900 72,000 142,000
5 34,300 88,200 169,000
20 48,800 110,000 209,000
50 58,600 125,000 238,000
100 66,400 137,000 261,000
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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Table 4.5-1. Average monthly flow (cfs) comparison for pre-Project and Maximum Load Following OS-1 conditions.
Period
Watana Dam Susitna River at Gold Creek Susitna River at Sunshine Susitna River at Susitna Station
Pre-Project Max LF
OS-1 Pre-Project Max LF
OS-1 Pre-Project Max LF
OS-1 Pre-Project Max LF
OS-1
OCT 5,100 7,020 1,920 6,320 8,240 1,920 15,900 18,000 2,100 36,000 38,100 2,100
NOV 2,150 7,520 5,370 2,670 7,990 5,320 6,490 11,900 5,410 14,400 19,800 5,400
DEC 1,520 8,540 7,020 1,890 8,750 6,860 4,490 11,300 6,810 9,510 16,300 6,790
JAN 1,280 8,840 7,560 1,590 9,140 7,550 3,720 11,300 7,580 7,910 15,500 7,590
FEB 1,130 9,450 8,320 1,420 9,750 8,330 3,260 11,600 8,340 7,080 15,400 8,320
MAR 1,040 7,170 6,130 1,300 7,460 6,160 2,960 9,190 6,230 6,510 12,700 6,190
APR 1,400 6,650 5,250 1,740 6,950 5,210 4,030 9,160 5,130 8,990 14,100 5,110
MAY 11,300 6,090 -5,210 13,800 8,490 -5,310 33,200 27,400 -5,800 66,100 60,200 -5,900
JUN 21,700 5,680 -16,020 26,300 10,200 -16,100 63,700 47,500 -16,200 120,000 104,000 -16,000
JUL 20,000 6,980 -13,020 24,000 10,800 -13,200 60,500 47,200 -13,300 122,000 108,000 -14,000
AUG 17,800 11,900 -5,900 21,400 15,400 -6,000 54,200 48,400 -5,800 109,000 103,000 -6,000
SEP 11,300 10,100 -1,200 13,700 12,700 -1,000 34,900 34,100 -800 72,800 72,000 -800
Annual 8,010 7,990 -20 9,720 9,660 -60 24,100 24,000 -100 48,600 48,500 -100
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 39 February 2013
Table 4.5-2. Average annual flow (cfs) comparison for pre-Project versus Maximum Load Following OS-1 conditions.
Water
Year
Average Annual Flow, Q (cfs), Comparison
Watana Dam Susitna River at Gold Creek Susitna River at Sunshine Susitna River at Susitna Station
Pre-Project Max LF OS-1 Pre-Project Max LF OS-1 Pre-Project Max LF OS-1 Pre-Project Max LF OS-1
1950 6600 7100 8,030 8,470 19,600 20,100 42,400 42,900
1951 7500 7500 9,110 9,110 22,300 22,300 47,300 47,300
1952 7800 7400 9,530 9,000 22,900 22,400 46,800 46,300
1953 8300 8100 10,100 9,890 24,700 24,500 52,200 52,000
1954 8000 8000 9,680 9,640 23,700 23,700 49,700 49,700
1955 8400 8300 10,300 10,100 24,600 24,400 50,300 50,100
1956 9400 9400 11,400 11,400 27,600 27,500 55,200 55,100
1957 8600 8500 10,400 10,300 25,300 25,200 52,300 52,200
1958 7800 7800 9,480 9,440 23,000 23,000 48,700 48,700
1959 8700 8500 10,600 10,300 25,500 25,200 51,700 51,400
1960 8000 8000 9,690 9,630 23,600 23,500 47,700 47,600
1961 8700 8700 10,800 10,800 26,300 26,300 52,200 52,200
1962 9800 9800 11,600 11,500 27,500 27,500 47,900 47,900
1963 9300 9300 11,100 11,000 26,700 26,600 47,100 47,100
1964 8200 8200 9,770 9,740 22,600 22,600 42,700 42,600
1965 8500 8400 10,200 10,100 25,800 25,700 49,300 49,100
1966 7400 7400 9,430 9,410 23,600 23,700 46,300 46,300
1967 9100 8900 11,200 10,900 26,900 26,600 45,200 44,900
1968 8000 8000 9,790 9,770 24,600 24,600 46,800 46,800
1969 4900 7500 5,600 8,180 14,000 16,500 33,400 36,000
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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Water
Year
Average Annual Flow, Q (cfs), Comparison
Watana Dam Susitna River at Gold Creek Susitna River at Sunshine Susitna River at Susitna Station
Pre-Project Max LF OS-1 Pre-Project Max LF OS-1 Pre-Project Max LF OS-1 Pre-Project Max LF OS-1
1970 6100 5400 7,590 6,880 19,700 19,000 46,600 45,900
1971 8600 6600 10,300 8,230 25,400 23,400 47,800 45,800
1972 8900 9000 10,900 10,800 26,500 26,400 46,700 46,700
1973 6600 7100 8,090 8,480 20,800 21,300 41,400 41,800
1974 6300 7500 7,630 8,860 19,500 20,700 40,000 41,200
1975 8500 6700 10,300 8,490 25,400 23,600 46,100 44,300
1976 6700 7100 8,170 8,550 20,500 20,900 43,000 43,400
1977 8300 7900 10,100 9,640 24,700 24,200 56,000 55,500
1978 6700 7000 8,190 8,420 20,400 20,700 42,000 42,300
1979 7800 7600 9,490 9,180 24,000 23,700 53,700 53,400
1980 8800 8700 10,700 10,600 26,100 25,900 61,900 61,800
1981 10000 9700 12,000 11,600 28,400 28,000 55,700 55,400
1982 7900 7900 9,670 9,610 24,100 24,000 47,100 47,000
1983 8300 8300 9,920 9,880 23,600 23,500 43,800 43,800
1984 8200 8200 9,580 9,550 23,500 23,500 45,400 45,400
1985 8000 8000 9,880 9,820 24,300 24,200 47,300 47,200
1986 7200 7200 8,530 8,550 20,600 20,600 46,300 46,400
1987 8700 8500 10,600 10,400 26,700 26,600 54,900 54,700
1988 8400 8400 10,200 10,200 24,800 24,800 53,600 53,500
1989 8400 8400 10,300 10,200 25,500 25,500 56,500 56,400
1990 10700 10600 13,000 12,900 31,800 31,600 61,200 61,100
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 41 February 2013
Water
Year
Average Annual Flow, Q (cfs), Comparison
Watana Dam Susitna River at Gold Creek Susitna River at Sunshine Susitna River at Susitna Station
Pre-Project Max LF OS-1 Pre-Project Max LF OS-1 Pre-Project Max LF OS-1 Pre-Project Max LF OS-1
1991 7000 7100 8,530 8,570 21,600 21,700 48,200 48,300
1992 7200 7100 8,720 8,620 21,600 21,500 43,900 43,800
1993 8300 8300 10,100 10,000 26,000 25,900 53,100 53,000
1994 8200 8200 9,960 9,960 25,100 25,100 51,800 51,800
1995 8500 8500 10,300 10,200 25,400 25,300 51,300 51,200
1996 5600 7300 6,800 8,450 17,700 19,400 38,300 40,000
1997 7200 6700 8,800 8,270 23,100 22,600 44,600 44,000
1998 7700 7000 9,380 8,680 24,600 23,800 47,100 46,400
1999 7600 7200 9,290 8,800 24,400 23,900 46,600 46,100
2000 8400 8300 10,200 10,100 26,600 26,400 50,300 50,100
2001 7800 7800 9,540 9,530 23,800 23,800 46,900 47,000
2002 7000 7100 8,480 8,530 21,700 21,700 45,100 45,100
2003 8500 8300 10,300 10,100 25,600 25,500 52,400 52,300
2004 7700 7800 9,400 9,440 23,300 23,400 47,700 47,800
2005 10100 10000 12,200 12,000 30,900 30,700 61,400 61,200
2006 8500 8300 10,300 10,100 24,900 24,800 49,500 49,300
2007 7900 7900 9,650 9,570 23,700 23,700 48,500 48,500
2008 7300 7300 8,900 8,860 22,000 22,000 45,300 45,200
2009 7800 7800 9,500 9,460 23,400 23,400 47,700 47,600
2010 8300 8300 10,100 10,100 24,800 24,800 50,300 50,300
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 42 February 2013
Table 4.5-3. Annual flow exceedence ordinate (cfs) comparison for Pre-Project and Maximum Load Following Scenario OS-1.
Annual Flow Duration Comparison (cfs)
Percentile Watana Dam Susitna River at Gold Creek Susitna River at Sunshine Susitna River at Susitna Station
Pre-Project Max LF OS-1 Pre-Project Max LF OS-1 Pre-Project Max LF OS-1 Pre-Project Max LF OS-1
99% 603 1,120 750 1,400 1,740 3,240 5,210 6,810
95% 777 4,960 960 6,870 2,310 8,840 5,840 12,300
90% 956 5,400 1,200 7,210 2,830 9,470 6,400 13,000
75% 1,280 6,140 1,600 7,840 3,750 10,800 7,710 15,100
50% 2,730 7,370 3,400 8,750 8,220 13,200 19,000 23,100
25% 14,700 8,670 17,800 9,920 45,000 38,400 94,000 87,400
10% 20,900 10,800 25,300 12,300 64,000 51,000 124,000 112,000
5% 24,600 14,700 29,800 17,800 72,800 57,100 138,000 122,000
1% 32,500 22,900 39,300 26,900 91,200 71,300 164,000 145,000
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 43 February 2013
Table 4.5-4. Susitna River estimated return period peak flow (cfs) comparison for pre-Project and Maximum Load Following Scenario OS-1.
Return
Period
(Years)
Watana Dam Site Gold Creek Sunshine Susitna Station
Pre-
Project
Flow
(cfs)
Max LF
OS-1
(cfs)
Difference
(cfs)
Difference
(%)
Pre-
Project
Flow
(cfs)
Max LF
OS-1
(cfs)
Difference
(cfs)
Difference
(%)
Pre-
Project
Flow
(cfs)
Max LF
OS-1
(cfs)
Difference
(cfs)
Difference
(%)
Pre-
Project
Flow
(cfs)
Max LF
OS-1
(cfs)
Difference
(cfs)
Difference
(%)
1.01 21,100 12,800 -8,300 -39% 25,400 12,600 -12,800 -50% 64,000 47,600 -16,400 -26% 131,700 109,500 -22,200 -17%
1.25 27,800 14,100 -13,700 -49% 35,100 14,400 -20,700 -59% 80,200 60,500 -19,700 -25% 151,600 124,900 -26,700 -18%
1.5 30,700 15,800 -14,900 -49% 39,000 19,100 -19,900 -51% 87,000 65,800 -21,200 -24% 160,400 132,900 -27,500 -17%
2 34,200 20,700 -13,500 -39% 43,700 23,900 -19,800 -45% 94,700 72,000 -22,700 -24% 170,300 141,900 -28,400 -17%
5 43,700 28,700 -15,000 -34% 55,800 34,300 -21,500 -39% 115,400 88,200 -27,200 -24% 197,000 168,900 -28,100 -14%
20 57,600 40,200 -17,400 -30% 72,300 48,800 -23,500 -33% 143,600 110,400 -33,200 -23% 233,500 209,400 -24,100 -10%
50 67,300 48,200 -19,100 -28% 83,400 58,600 -24,800 -30% 162,500 125,100 -37,400 -23% 257,600 238,200 -19,400 -8%
100 75,100 54,600 -20,500 -27% 92,100 66,400 -25,700 -28% 177,300 136,700 -40,600 -23% 276,300 261,400 -14,900 -5%
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 44 February 2013
Table 4.5-5. Recurrence interval of annual peak flows for pre-Project and Maximum Load Following Scenario OS-1.
Watana Dam Site Gold Creek Sunshine Susitna Station
Discharge
(cfs)
Pre-Project
Return
Period (yrs)
Max Load
Following OS-
1 Return
Period (yrs)
Discharge
(cfs)
Pre-Project
Return
Period (yrs)
Max Load
Following
OS-1
Return
Period
(yrs)
Discharge
(cfs)
Pre-Project
Return
Period (yrs)
Max Load
Following
OS-1
Return
Period
(yrs)
Discharge
(cfs)
Pre-Project
Return
Period (yrs)
Max Load
Following
OS-1
Return
Period
(yrs)
21,100 1.01 2.1 25,400 1.01 2.2 64,000 1.01 1.4 131,700 1.01 1.5
27,800 1.25 4.5 35,100 1.25 5.4 80,200 1.25 3.1 151,600 1.25 2.7
30,700 1.5 6.4 39,000 1.5 7.8 87,000 1.5 4.6 160,426 1.5 3.6
34,200 2 9.8 43,700 2 12 94,700 2 7.4 170,300 2 5.2
43,700 5 30 55,800 5 39 115,400 5 27 197,000 5 13
57,600 20 136 72,300 20 166 143,600 20 149 233,500 20 43
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 45 February 2013
Table 5.2-1. USGS Measurements Used to Develop Representative Cross Section Geometry.
Gage
USGS
Measurement
No.
Date of
Measurement
Flow Rate
Measured
(cfs)
Stage
(ft)
Sunshine 55 a 9/22/2012 155,000 25.17
Susitna Station 127 7/18/2003 234,000 19.54
Notes:
a. Specifically, Transect 2 from Measurement 55 was used
Table 5.3-1. Annual Stage-exceedence Ordinate (feet) Comparison for pre-Project and Maximum Load Following OS-1
Hydrologic Conditions at Sunshine Gage and Susitna Station Gage.
Percentile
Sunshine Gage
(USGS 15292780)
Susitna Station Gage
(USGS 15292780)
Annual Stage-exceedence Value Annual Stage-exceedence Value
Pre-
Project
Max LF
OS-1 Delta a
Pre-
Project
Max LF
OS-1 Delta a
99% 10.93 11.08 0.15 2.59 3.03 0.44
95% 10.97 12.28 1.31 2.77 4.28 1.51
90% 10.99 12.40 1.41 2.93 4.43 1.50
75% 11.21 12.62 1.41 3.26 4.83 1.57
50% 12.17 13.02 0.85 5.53 6.21 0.68
25% 16.85 16.17 -0.68 13.00 12.57 -0.43
10% 18.60 17.42 -1.18 14.77 14.04 -0.73
5% 19.35 17.98 -1.37 15.51 14.66 -0.85
1% 20.81 19.22 -1.59 16.77 15.85 -0.92
Notes:
a. Delta calculated as Max LF OS-1 value minus pre-Project value, with negative
values indicated in red text.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 46 February 2013
Table 5.3-2. Monthly (October through March) Stage-exceedence Ordinate (feet) Comparison for pre-
Project and Maximum Load Following OS-1 Hydrologic Conditions at Sunshine Gage.
Sunshine Gage (USGS 15292780)
Percentile
October November December
Pre-Project Max LF OS-1 Delta Pre-
Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
99% 11.57 12.65 1.08 10.99 12.36 1.37 10.97 12.29 1.32
95% 11.91 12.78 0.87 11.17 12.47 1.30 10.98 12.42 1.44
90% 12.15 12.88 0.73 11.30 12.53 1.23 10.99 12.50 1.51
75% 12.57 13.07 0.50 11.54 12.65 1.11 11.21 12.59 1.38
50% 13.09 13.42 0.33 11.75 12.75 1.00 11.40 12.70 1.30
25% 13.94 14.02 0.08 12.02 12.91 0.89 11.55 12.82 1.27
10% 14.81 14.86 0.05 12.34 13.10 0.76 11.69 12.91 1.22
5% 15.40 15.44 0.04 12.57 13.26 0.69 11.81 12.98 1.18
1% 16.85 16.64 -0.21 13.00 13.52 0.52 12.22 13.13 0.91
Percentile January February March
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
99% 10.95 12.28 1.33 10.91 10.95 0.04 10.90 10.95 0.05
95% 10.95 12.46 1.50 10.94 12.45 1.51 10.92 11.09 0.16
90% 10.97 12.51 1.54 10.95 12.51 1.56 10.94 12.18 1.24
75% 11.08 12.62 1.54 10.99 12.62 1.63 10.97 12.29 1.32
50% 11.20 12.72 1.52 11.09 12.77 1.68 11.00 12.40 1.40
25% 11.36 12.80 1.44 11.21 12.93 1.72 11.14 12.50 1.36
10% 11.46 12.91 1.45 11.35 13.06 1.71 11.25 12.60 1.35
5% 11.49 12.99 1.50 11.39 13.13 1.74 11.37 12.67 1.30
1% 11.64 13.12 1.48 11.51 13.32 1.81 11.46 12.78 1.32
Notes:
a. Delta calculated as Max LF OS-1 value minus pre-Project value, with negative values indicated in red text.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 47 February 2013
Table 5.3-3. Monthly (April through September) Stage-exceedence Ordinate (feet) Comparison for pre-
Project and Maximum Load Following OS-1 Hydrologic Conditions at Sunshine Gage.
Sunshine Gage (USGS 15292780)
Percentile April May June
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
99% 10.91 10.97 0.05 11.03 11.60 0.57 15.22 14.81 -0.41
95% 10.94 11.10 0.17 11.58 12.44 0.86 16.03 15.36 -0.67
90% 10.95 12.09 1.14 11.93 12.62 0.69 16.42 15.62 -0.80
75% 10.98 12.26 1.28 13.01 13.24 0.23 17.39 16.32 -1.07
50% 11.15 12.37 1.22 15.37 14.76 -0.61 18.56 17.13 -1.43
25% 11.35 12.47 1.12 17.12 16.00 -1.12 19.44 17.71 -1.73
10% 11.70 12.62 0.92 18.76 17.18 -1.58 20.34 18.29 -2.05
5% 12.08 12.77 0.69 19.54 17.78 -1.76 20.98 18.69 -2.29
1% 13.41 13.58 0.17 20.34 18.28 -2.06 22.88 19.71 -3.17
Percentile July August September
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
99% 16.13 15.48 -0.65 14.14 14.26 0.12 12.83 13.10 0.27
95% 16.65 15.81 -0.84 15.69 15.41 -0.28 13.35 13.43 0.08
90% 16.98 16.07 -0.91 16.13 15.79 -0.34 13.73 13.78 0.05
75% 17.52 16.44 -1.08 16.80 16.29 -0.51 14.50 14.44 -0.06
50% 18.13 16.92 -1.21 17.61 16.94 -0.67 15.48 15.39 -0.09
25% 18.91 17.49 -1.42 18.36 17.80 -0.56 16.61 16.48 -0.13
10% 19.68 18.08 -1.60 19.23 18.67 -0.56 17.91 17.73 -0.18
5% 20.14 18.60 -1.54 19.94 19.39 -0.55 18.62 18.43 -0.20
1% 21.29 19.69 -1.60 22.30 21.30 -1.00 19.96 19.95 -0.01
Notes:
a. Delta calculated as Max LF OS-1 value minus pre-Project value, with negative values indicated in red text.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 48 February 2013
Table 5.3-4. Monthly (October through March) Stage-exceedence Ordinate (feet) Comparison for pre-
Project and Maximum Load Following OS-1 Hydrologic Conditions at Susitna Station Gage.
Susitna Station Gage (USGS 15294350)
Percentile
October November December
Pre-Project Max LF OS-1 Delta Pre-
Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
99% 4.02 5.09 1.07 3.00 4.47 1.47 2.82 4.32 1.5
95% 4.82 5.63 0.81 3.27 4.62 1.35 2.89 4.50 1.61
90% 5.36 6.02 0.66 3.51 4.78 1.27 3.04 4.59 1.55
75% 6.26 6.75 0.49 3.95 5.08 1.13 3.29 4.77 1.48
50% 7.45 7.74 0.29 4.43 5.44 1.01 3.57 5.01 1.44
25% 8.90 9.01 0.11 5.13 5.99 0.86 3.95 5.29 1.34
10% 10.57 10.58 0.01 5.91 6.62 0.71 4.23 5.49 1.26
5% 11.31 11.36 0.05 6.50 7.07 0.57 4.49 5.65 1.16
1% 13.21 13.18 -0.03 8.13 8.66 0.53 5.68 6.55 0.87
Percentile January February March
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
99% 2.73 4.21 1.48 2.51 2.82 0.31 2.44 2.66 0.22
95% 2.76 4.52 1.76 2.63 4.47 1.84 2.55 3.08 0.53
90% 2.87 4.60 1.73 2.76 4.55 1.79 2.61 4.12 1.51
75% 3.08 4.73 1.65 2.92 4.70 1.78 2.76 4.28 1.52
50% 3.30 4.90 1.60 3.08 4.90 1.82 2.94 4.42 1.48
25% 3.47 5.08 1.61 3.22 5.10 1.88 3.08 4.56 1.48
10% 3.74 5.27 1.53 3.45 5.29 1.84 3.22 4.75 1.53
5% 3.87 5.37 1.50 3.62 5.42 1.80 3.57 4.87 1.30
1% 4.02 5.53 1.51 3.80 5.64 1.84 3.69 5.05 1.36
Notes:
a. Delta calculated as Max LF OS-1 value minus pre-Project value, with negative values indicated in red text.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 49 February 2013
Table 5.3-5. Monthly (April through September) Stage-exceedence Ordinate (feet) Comparison for pre-
Project and Maximum Load Following OS-1 Hydrologic Conditions at Susitna Station Gage.
Susitna Station Gage (USGS 15294350)
Percentile
April May June
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-
Project Max LF OS-1 Delta
99% 2.53 2.75 0.22 3.12 3.82 0.70 10.96 10.43 -0.53
95% 2.65 3.05 0.40 3.89 4.63 0.74 11.85 11.27 -0.58
90% 2.69 4.07 1.38 4.76 5.26 0.50 12.49 11.88 -0.61
75% 2.85 4.26 1.41 7.62 7.60 -0.02 13.48 12.76 -0.72
50% 3.08 4.41 1.33 10.86 10.39 -0.47 14.56 13.69 -0.87
25% 3.62 4.75 1.13 13.07 12.46 -0.61 15.41 14.33 -1.08
10% 4.53 5.37 0.84 14.65 13.71 -0.94 16.21 14.99 -1.22
5% 5.53 6.19 0.66 15.36 14.29 -1.07 16.63 15.32 -1.31
1% 8.20 8.44 0.24 16.11 14.99 -1.12 17.59 16.07 -1.52
Percentile
July August September
Pre-Project Max LF OS-1 Delta Pre-
Project Max LF OS-1 Delta Pre-
Project Max LF OS-1 Delta
99% 12.08 11.60 -0.48 9.03 9.17 0.14 5.96 6.18 0.22
95% 12.79 12.18 -0.61 11.38 11.23 -0.15 7.66 7.81 0.15
90% 13.26 12.62 -0.64 12.04 11.82 -0.22 8.41 8.49 0.08
75% 13.83 13.21 -0.62 12.89 12.63 -0.26 9.77 9.78 0.01
50% 14.53 13.76 -0.77 13.77 13.45 -0.32 11.20 11.16 -0.04
25% 15.26 14.40 -0.86 14.71 14.30 -0.41 12.76 12.66 -0.10
10% 15.96 15.06 -0.90 15.51 15.06 -0.45 14.18 14.04 -0.14
5% 16.44 15.57 -0.87 16.23 15.79 -0.44 14.82 14.72 -0.10
1% 17.78 16.66 -1.12 18.18 17.85 -0.33 16.29 16.18 -0.11
Notes:
a. Delta calculated as Max LF OS-1 value minus pre-Project value, with negative values indicated in red text.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
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FERC Project No. 14241 Page 50 February 2013
Table 5.3-6. Monthly Stage Statistics for pre-Project and Max Load Following OS-1 Hydrologic Conditions
at Sunshine Gage.
Sunshine Gage (USGS 15292780)
Statistic Oct Nov Dec
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
Maximum 22.15 20.39 -1.76 14.25 14.23 -0.02 12.53 13.32 0.79
Median 13.09 13.42 0.33 11.75 12.75 1.00 11.40 12.70 1.30
Average 13.33 13.68 0.34 11.80 12.80 0.99 11.39 12.70 1.32
Minimum 11.09 12.33 1.24 10.98 12.29 1.31 10.96 12.13 1.17
Statistic Jan Feb Mar
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
Maximum 11.89 13.29 1.40 12.01 13.43 1.42 11.52 13.16 1.64
Median 11.20 12.72 1.52 11.09 12.77 1.68 11.00 12.40 1.40
Average 11.22 12.70 1.48 11.12 12.75 1.63 11.06 12.33 1.27
Minimum 10.94 10.96 0.01 10.89 10.95 0.06 10.90 10.95 0.05
Statistic Apr May June
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
Maximum 17.25 15.85 -1.40 22.01 19.13 -2.88 25.51 21.19 -4.32
Median 11.15 12.37 1.22 15.37 14.76 -0.61 18.56 17.13 -1.43
Average 11.28 12.32 1.04 15.28 14.77 -0.51 18.49 17.05 -1.45
Minimum 10.91 10.95 0.04 10.94 11.08 0.14 14.64 14.31 -0.33
Statistic July Aug Sept
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
Maximum 24.89 21.86 -3.03 25.57 23.26 -2.31 21.65 21.02 -0.63
Median 18.13 16.92 -1.21 17.61 16.94 -0.67 15.48 15.39 -0.09
Average 18.25 17.02 -1.23 17.65 17.11 -0.54 15.67 15.59 -0.08
Minimum 15.40 15.01 -0.39 12.98 13.42 0.44 12.36 12.83 0.47
Notes:
a. Delta calculated as Max LF OS-1 value minus pre-Project value, with negative values indicated in red text.
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Table 5.3-7. Monthly Stage Statistics for pre-Project and Max Load Following OS-1 Hydrologic Conditions
at Susitna Station Gage.
Susitna Station Gage (USGS 15294350)
Statistic Oct Nov Dec
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
Maximum 21.93 21.98 0.05 9.49 9.64 0.15 6.65 7.31 0.66
Median 7.45 7.74 0.29 4.43 5.44 1.01 3.57 5.01 1.44
Average 7.72 8.04 0.32 4.62 5.62 1.00 3.66 5.05 1.39
Minimum 3.14 4.45 1.31 2.93 4.31 1.38 2.82 4.14 1.32
Statistic Jan Feb Mar
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
Maximum 4.43 5.78 1.35 4.98 6.17 1.19 3.80 5.39 1.59
Median 3.30 4.90 1.60 3.08 4.90 1.82 2.94 4.42 1.48
Average 3.30 4.90 1.60 3.09 4.89 1.80 2.95 4.36 1.41
Minimum 2.72 2.89 0.17 2.35 2.70 0.35 2.42 2.66 0.24
Statistic Apr May June
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
Maximum 13.71 12.89 -0.82 17.28 16.46 -0.82 18.18 16.89 -1.29
Median 3.08 4.41 1.33 10.86 10.39 -0.47 14.56 13.69 -0.87
Average 3.45 4.58 1.13 10.27 9.95 -0.32 14.45 13.53 -0.92
Minimum 2.23 2.69 0.46 2.85 3.03 0.18 9.97 9.06 -0.91
Statistic July Aug Sept
Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta Pre-Project Max LF OS-1 Delta
Maximum 19.47 19.05 -0.42 19.55 19.14 -0.41 18.74 18.74 0.00
Median 14.53 13.76 -0.77 13.77 13.45 -0.32 11.20 11.16 -0.04
Average 14.57 13.81 -0.76 13.79 13.45 -0.34 11.26 11.22 -0.04
Minimum 10.65 10.40 -0.25 6.87 7.18 0.31 4.85 5.43 0.58
Notes:
a. Delta calculated as Max LF OS-1 value minus pre-Project value, with negative values indicated in red text.
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Table 5.4-1. Annual Flow-exceedence and Stage-exceedence Comparison for the pre-Project and Maximum Load Following OS-1 Hydrologic
Conditions at Sunshine Gage and Susitna Station Gage.
Percentile
Sunshine Gage
(USGS 15292780)
Susitna Station Gage
(USGS 15292780)
Sunshine Gage
(USGS 15292780)
Susitna Station Gage
(USGS 15292780)
Annual Flow
Exceedence Value
Annual Flow
Exceedence Value
Annual Stage
Exceedence Value
Annual Stage
Exceedence Value
Pre-
Project
(cfs)
Max LF
OS-1
(cfs)
Delta a
(cfs)
Pre-
Project
(cfs)
Max LF
OS-1
(cfs)
Delta a
(cfs)
Pre-
Project
(ft)
Max LF
OS-1
(cfs)
Delta a
(ft)
Pre-
Project
(ft)
Max LF
OS-1
(cfs)
Delta
a
(ft)
99% 1,740 3,240 1,500 5,210 6,810 1,600 10.93 11.08 0.15 2.59 3.03 0.44
95% 2,310 8,840 6,530 5,840 12,300 6,460 10.97 12.28 1.31 2.77 4.28 1.51
90% 2,830 9,470 6,640 6,400 13,000 6,600 10.99 12.40 1.41 2.93 4.43 1.50
75% 3,750 10,800 7,050 7,710 15,100 7,390 11.21 12.62 1.41 3.26 4.83 1.57
50% 8,220 13,200 4,980 19,000 23,100 4,100 12.17 13.02 0.85 5.53 6.21 0.68
25% 45,000 38,400 -6,600 94,000 87,400 -6,600 16.85 16.17 -0.68 13.00 12.57 -0.43
10% 64,000 51,000 -13,000 124,000 112,000 -12,000 18.60 17.42 -1.18 14.77 14.04 -0.73
5% 72,800 57,100 -15,700 138,000 122,000 -16,000 19.35 17.98 -1.37 15.51 14.66 -0.85
1% 91,200 71,300 -19,000 164,000 145,000 -19,000 20.81 19.22 -1.59 16.77 15.85 -0.92
Notes:
a. Delta calculated as Max LF OS-1 value minus pre-Project value, with negative values indicated in red text
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Table 6.2-1. USGS Ratings and Effective Dates at Sunshine Gage.
Rating
ID Effective Dates of Rating USGS Notes within Effective Period of Rating a
1 5/8/81 – 5/1/82
Gage established on 5/8/81
Gage datum established on 5/7/81
Gage located on right bank, 300 feet upstream of road
Stage values in this rating were adjusted by the USGS subsequent to the
5/28/82 lowering of the datum so that Rating 1 is relative to the same datum as
Rating 2
2 5/1/82 – 10/1/83 Datum was lowered by 5.0 feet on 5/28/82
Gage moved on 7/13/82 to left bank, 100 feet upstream of bridge
3 10/1/83 – 5/1/84
4 5/1/84 – 10/1/86 Gage discontinued on 6/30/86
5 10/1/86 – 10/6/11
6 10/6/11 - present
Gage re-established on 10/6/11, using the lowered datum
Gage located on left bank, 50 feet downstream of bridge
Datum was lowered by an additional 10.0 feet to prevent negative gage height
values
Note:
a. USGS notes were obtained from the USGS station description and from personal communication wit h USGS staff (Josh
Morse, personal communication, January 31, 2013)
Table 6.2-2. USGS Ratings and Effective Dates at Susitna Station Gage.
Rating
ID Effective Dates of Rating USGS Notes within Effective Period of Rating a
1 5/1/75 – 9/30/78
Gage installed on 5/23/75
Located on left bank approximately 1.5 miles downstream from Yentna
River
2 10/1/78 – 5/23/85
3 5/24/85 – 9/30/85
4 10/1/85 – 9/30/93 Gage discontinued on 9/30/93
Note:
a. USGS notes were obtained from the USGS station description
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Table 6.2-3. Flows Selected for Specific Gage Analysis, Susitna Station Gage.
Flow Magnitude a
(cfs) Flow Statistic a
30,000 Minimum flow common to all rating curves
43,000 40% annual exceedence flow
60,000 35% annual exceedence flow
80,000 30% annual exceedence flow
94,000 25% annual exceedence flow
132,000 1.01-year return period flow
152,000 1.25-year return period flow
170,000 2-year return period flow
197,000 5-year return period flow
Note:
a. Based on pre-Project flow duration and flood frequency analysis
Table 6.3-1. Stages at Selected Specific Discharges Calculated from USGS Published Ratings for the Susitna
Station Gage.
Rating
ID
Effective
Dates of
Rating
Stage (feet) at Specified Discharge a
30,000 43,000 60,000 80,000 94,000 132,000 152,000 170,000 197,000
1 5/1/75 –
9/30/78 7.4 9.2 10.4 11.8 12.7 15.1 16.3 17.3 18.8
2 10/1/78 –
5/23/85 7.3 8.7 10.3 11.9 12.9 15.3 16.5 17.5 18.8
3 5/24/85 –
9/30/85 7.3 8.7 10.3 11.9 12.9 15.1 16.1 17.1 18.3
4 10/1/85 –
12/31/02 7.2 8.9 10.6 12.1 13.0 15.2 16.2 17.0 18.3
Note:
a. All stages are relative to the gage datum established at the time the gage was installed
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Table 7.2.1. Ice Covered Discharge Measurement at USGS Susitna at Sunshine Gage.
Date of Measurement
Total
Discharge
(cfs)
Flow
Depth to
Ice
Thickness
Ratio
Total
Depth
(ft)
Average
Ice
Thickness
(ft)
Average
Flow
Depth
(ft)
Total
Ice
Area
(ft2)
Total
Flow
Area
(ft2)
Average
Velocity
(ft/s)
March 25, 1981 3,796 1.65 8.15 3.07 5.08 2,031 1,937 1.81
January 20, 1982 3,504 3.54 11.98 2.64 9.35 403 1,348 2.61
March 2, 1982 2,656 1.36 11.53 4.88 6.65 1,124 1,141 2.36
April 9, 1982 3,347 1.54 10.89 4.29 6.59 879 1,185 2.63
December 22, 1982 5,495 0.94 12.78 6.57 6.21 2,194 1,739 2.82
December 30, 1982 6,800 0.95 13.85 7.12 6.74 2,898 2,337 3.01
January 20, 1983 4,719 20.4 10.99 3.61 7.38 796 1,619 2.28
March 17, 1983 3,321 1.98 8.87 2.98 5.90 744 1,419 2.02
January 10, 1985 4,644 0.69 7.36 4.37 3.00 2,831 1,353 1.91
January 14, 1985 3,657 0.83 6.55 3.58 2.97 2,049 1,235 1.71
March 19, 1985 3,976 0.87 8.01 4.27 3.73 2,317 1,381 2.07
November 22, 1985 5,395 0.61 10.28 6.37 3.91 2,868 1,730 1.90
March 18, 1986 2,862 1.29 7.92 3.47 4.46 1,218 1,598 1.49
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Table 7.2.2. Ice Covered Discharge Measurement at USGS Susitna at Susitna Gage.
Date of Measurement
Total
Discharge
(cfs)
Flow
Depth to
Ice
Thickness
Ratio
Total
Depth
(ft)
Average
Ice
Thickness
(ft)
Average
Flow
Depth
(ft)
Total
Ice
Area
(ft2)
Total
Flow
Area
(ft2)
Average
Velocity
(ft/s)
March 22, 1993 6,952 2.13 9.97 3.19 6.78 1,627 3,172 2.10
January 8, 1993 10,305 1.79 9.42 3.38 6.04 3,416 4,209 2.22
April 2, 1992 9,726 1.11 10.49 4.98 5.51 3,735 4,130 1.96
February 7, 1992 9,410 1.57 9.88 3.84 6.04 3,674 4,926 1.75
April 5, 1991 6,135 1.02 11.48 5.68 5.80 5,145 3,953 1.58
February 27, 1991 7,280 1.24 12.75 5.70 7.06 4,304 5,371 1.74
April 5, 1990 9,993 1.29 11.34 4.95 6.39 5,292 4,247 2.10
March 22, 1989 6,884 1.06 8.82 4.29 4.53 6,965 3,909 1.72
February 6, 1989 6,052 0.96 10.07 5.14 4.94 9,857 3,547 1.54
March 8, 1988 9,370 1.06 10.68 5.19 5.49 4,888 4,941 1.60
January 7, 1988 11,285 1.40 10.80 4.49 6.31 6,596 6,973 1.46
March 31, 1987 7,211 1.59 10.47 4.04 6.43 2,635 3,969 1.59
February 4, 1987 7,442 1.28 10.35 4.55 5.81 3,397 3,985 1.69
April 1, 1986 5,399 1.80 7.88 2.82 5.06 2,468 3,606 1.51
December 4, 1985 12,319 2.32 9.80 2.95 6.85 3,312 6,079 1.97
March 27, 1985 6,015 2.36 12.69 3.78 8.91 1,655 3,406 1.66
February 23, 1985 6,606 1.10 12.31 5.88 6.44 4,614 4,619 1.50
February 11, 1985 6,333 2.53 11.83 3.35 8.48 1,702 3,816 1.89
April 6, 1984 9,276 1.17 12.77 5.90 6.87 7,378 4,932 1.63
April 4, 1983 6,520 1.39 10.93 4.57 6.36 3,921 4,356 1.43
January 20, 1983 7,947 1.35 11.48 4.88 6.60 4,334 5,464 1.36
April 4, 1982 4,004 0.82 11.82 6.49 5.33 5,630 4,861 0.83
January 12, 1982 8,960 1.33 10.03 4.30 5.73 3,597 5,074 1.58
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10. FIGURES
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Figure 3.2-1. Susitna River study area and large-scale river segments.
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Figure 4.4-1. Average monthly flows (cfs) in the Susitna River and major tributaries downstream from the
Watana Dam site under pre-Project conditions based on the USGS (2012) 61-year extended record. Solid bars are
mainstem gages; cross-hatched bars are tributaries.
0
20
40
60
80
100
120
140
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEPAverage Monthly Flow (cfs)ThousandsGold Creek
Chulitna River
Talkeetna River
Sunshine
Yentna River
Susitna Station
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Figure 4.4-2. Annual flow-duration curves mainstem gages for pre-Project conditions based on the USGS extended record.
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Figure 4.4-3. Annual flow-duration curves tributary gages for pre-Project conditions based on the USGS extended record.
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Figure 4.4-4. Monthly Flow-duration curves for January for mainstem gages for pre-Project conditions based on the USGS extended record.
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Figure 4.4-5. Relationship between recorded annual instantaneous peak discharge and the corresponding mean daily
discharge at Gold Creek. Similar plots for other gages are provided in Appendix D.
y = 1.0738x -699.22
R² = 0.9809
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000Annual Peak Discharge (cfs)Mean Daily Discharge (cfs)
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Figure 4.4-6. Average monthly flows (cfs) in the Susitna River under Maximum Load Following Scenario OS-1, based on the HEC-ResSim model
results. Also shown are major tributary inflows.
0
20
40
60
80
100
120
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEPAverage Monthly Flow (cfs)ThousandsGold Creek
Chulitna River
Talkeetna River
Sunshine
Yentna River
Susitna Station
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Figure 4.4-7. Annual flow-duration curves for three mainstem gages for Maximum Load Following OS-1 Conditions based on HEC-ResSim model.
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Figure 4.4-8. Flood-frequency curve for Susitna River at Gold Creek for Maximum Load Following OS-1 conditions based on the HEC-ResSim model.
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Figure 4.4-9. Flood-frequency curve for Susitna River at Sunshine for Maximum Load Following OS-1 conditions based on the HEC-ResSim model.
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Figure 4.4-10. Flood-frequency curve for Susitna River at Susitna Station for Maximum Load Following OS-1 conditions based on estimated HEC-
ResSim model output.
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Figure 4.5-1. Average monthly flows (cfs) in the Susitna River watershed for pre-Project and Maximum Load Following OS-1 conditions.
0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEPMonthly Average Flow (cfs) Susitna Station (Pre-Project)
Susitna Station (Post-Project)
Sunshine (Pre-Project)
Sunshine (Post-Project)
Gold Creek (Pre-Project)
Gold Creek (Post-Project)
Watana Dam (Pre-Project)
Watana Dam Post-Project
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Figure 4.5-2. Annual flow-duration curve comparison for Pre-Project and Maximum Load Following OS-1 conditions.
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Figure 4.5-3. Flood-frequency curve for Susitna River at the Watana Dam for Maximum Load Following OS-1 conditions based on estimated HEC-
ResSim model output.
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Figure 4.5-4. Flood-frequency curve for Susitna River at Gold Creek (USGS Gage No. 1529200) for Maximum Load Following OS-1 conditions based
on estimated HEC-ResSim model output.
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Figure 4.5-5. Flood-frequency curve for Susitna River at Sunshine (USGSG Gage No. 15292780) for Maximum Load Following OS-1 conditions based
on estimated HEC-ResSim model output.
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Figure 4.5-6. Flood-frequency curve for Susitna River at Susitna Station (USGS Gage No. 1524350) for Maximum Load Following OS-1 conditions
based on estimated HEC-ResSim model output.
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Figure 5.2-1. USGS Published and Extrapolated Stage-Discharge Rating for Susitna River USGS Gage at
Sunshine.
y = 10.005x0.0119
R² = 1
1
10
100
1,000 10,000 100,000 1,000,000Stage (ft)Discharge (cfs)
USGS Published Rating ID 6.0
Extrapolated Rating
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Figure 5.2-2. USGS Published and Extrapolated Stage-Discharge Ratings for Susitna River USGS Gage at Susitna
Station.
y = 0.0662x0.461
R² = 1
y = 0.0173x0.5854
R² = 0.9981
1
10
100
1,000 10,000 100,000 1,000,000Stage (ft)Discharge (cfs)
USGS Published Rating ID 4.0, Stage > 10 feet
USGS Published Rating ID 4.0, Stage < 10 feet
Extrapolated Rating, Stage > 10 feet
Extrapolated Rating, Stage < 10 feet
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Figure 5.3-1. Annual Stage-exceedence Relationships for pre-Project and Max LF OS-1 Conditions, Sunshine Gage.
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Figure 5.3-2. Annual Stage-exceedence Relationships for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage.
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Figure 5.3-3. Monthly Stage-exceedence Relationships for May for pre-Project and Max LF OS-1 Conditions, Sunshine Gage.
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Figure 5.3-4. Monthly Stage-exceedence Relationships for May for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage.
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Figure 5.3-5. Select Annual Water-surface Elevation exceedence Values for pre-Project and Max LF OS-1 Conditions, Sunshine Gage.
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Figure 5.3-6. Select Annual Water-surface Elevation exceedence Values for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage.
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Figure 5.4-1. Comparison of Stage-Discharge Ratings for Susitna Station and Sunshine Gages.
0
5
10
15
20
25
30
35
0 50,000 100,000 150,000 200,000 250,000 300,000 350,000Stage (ft)Discharge (cfs)
Sunshine Gage
Susitna Station Gage
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Figure 5.4-2. Monthly 90 percent pre-Project and Max LF OS-1 Stage-exceedence Values, Sunshine Gage.
Figure 5.4-3. Monthly 90 percent pre-Project and Max LF OS-1 Stage-exceedence Values, Susitna Station Gage.
0
5
10
15
20
25
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepStage
Month
Pre-Project 90% Exceedance
Max LF OS-1 90% Exceedance
0
5
10
15
20
25
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepStage
Month
Pre-Project 90% Exceedance
Max LF OS-1 90% Exceedance
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Figure 5.4-4. Monthly 50 percent pre-Project and Max LF OS-1 Stage-Exceedence Values, Sunshine Gage.
Figure 5.4-5. Monthly 50 percent pre-Project and Max LF OS-1 Stage-exceedence Values, Susitna Station Gage.
0
5
10
15
20
25
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepStage
Month
Pre-Project 50% Exceedance
Max LF OS-1 50% Exceedance
0
5
10
15
20
25
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepStage
Month
Pre-Project 50% Exceedance
Max LF OS-1 50% Exceedance
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Figure 5.4-6. Monthly 10 percent pre-Project and Max LF OS-1 Stage-exceedence Values, Sunshine Gage.
Figure 5.4-7. Monthly 10 percent pre-Project and Max LF OS-1 exceedence Values, Susitna Station Gage.
0
5
10
15
20
25
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepStage
Month
Pre-Project 10% Exceedance
Max LF OS-1 10% Exceedance
0
5
10
15
20
25
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepStage
Month
Pre-Project 10% Exceedance
Max LF OS-1 10% Exceedance
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 87 February 2013
Figure 6.2-1. Vicinity Map for Susitna River at Sunshine Gage.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 88 February 2013
Figure 6.2-2. Vicinity Map for Susitna River at Susitna Station Gage.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 89 February 2013
-40,000
0
40,000
80,000
120,000
160,000
200,000
240,000
280,000
1972 1976 1980 1984 1988 1992 1996 2000 2004 2008 2012 2016Measured Discharge (cfs)Date
POOR
GOOD/FAIR
Figure 6.2-3. USGS Stage and Discharge Measurements at Susitna River at Sunshine Gage (USGS 15292780).
Figure 6.2-4. USGS Stage and Discharge Measurements at Susitna River at Susitna Station Gage (USGS
15294350).
-20,000
0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
180,000
1980 1984 1988 1992 1996 2000 2004 2008 2012 2016Measured Discharge (cfs)Date
POOR
GOOD/FAIR/EXCL
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 90 February 2013
Figure 6.2-5. Historical Stage-Discharge Ratings for Susitna River at Susitna Station Gage.
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 91 February 2013
Figure 6.3-1. Specific Gage Curves for Susitna River at Susitna Station Gage.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1975 1979 1983 1987 1991 1995Stage (feet)Calendar Year
197,000 cfs (5-yr)
170,000 cfs (2-yr)
152,000 cfs (1.25-yr)
132,000 cfs (1.01-yr)
94,000 cfs (25% Exc.)
80,000 cfs (30% Exc.)
43,000 cfs (40%Exc.)
60,000 cfs (35% Exc.)
30,000 cfs
Notes:
(1)The indicated flow rates are from the Pre-Project hydrologic analysis
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 92 February 2013
Figure 7.3.1. Velocity versus discharge for ice-covered and open-water conditions based on USGS measurements at the Susitna River at Sunshine gage.
1
10
1,000 10,000 100,000 1,000,000Velocity (ft/s)Discharge(cfs)
Ice Covered Flow
Open Channel Flow
Ice
Open Water
All Data
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 93 February 2013
Figure 7.3.2. Hydraulic (i.e., average) depth versus discharge for ice-covered and open-water conditions based on USGS measurements at the Susitna
River at Sunshine gage.
1
10
1,000 10,000 100,000 1,000,000Hydraulic Depth (feet)Discharge(cfs)
Ice Covered Flow
Open Water Flow
Ice
Open Water
All Data
2012 STUDY REPORT STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 94 February 2013
Figure 7.3.3. Cross-sectional area versus discharge for ice-covered and open-water conditions based on USGS measurements at the Susitna River at
Sunshine gage.
1000
10000
1,000 10,000 100,000 1,000,000Cross Sectional Area (ft^2)Discharge(cfs)
Ice Covered Flow
Open Channel Flow
Ice
Open Water
All Data
APPENDIX A. AVERAGE MONTHLY FLOW (CFS) BY WATER YEAR
FOR PRE-PROJECT CONDITIONS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 1 February 2013
Table A-1 – Average Monthly Flow for Susitna River near Denali for Pre-Project Conditions based on the USGS
Extended Record
WY Susitna River near Denali
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 1,320 432 238 202 183 179 191 2,850 5,640 7,220 6,080 1,620
1951 681 219 207 197 187 181 290 3,750 6,110 7,400 5,870 6,190
1952 1,040 463 305 252 200 192 194 1,360 9,050 8,070 6,060 3,630
1953 1,620 608 269 207 187 187 289 5,620 8,260 6,190 6,320 4,020
1954 1,040 342 234 219 200 184 222 5,150 8,180 6,200 8,440 3,110
1955 985 465 332 286 224 207 213 2,270 8,320 8,360 7,190 3,690
1956 902 306 219 199 198 196 197 4,860 9,090 9,050 7,480 5,330
1957 1,070 520 350 269 234 213 213 3,470 12,200 11,200 9,770 4,020
1958 1,280 610 288 219 150 120 210 1,160 8,370 9,150 6,540 1,880
1959 939 390 170 119 81 42 43 1,780 8,890 8,330 7,880 2,500
1960 1,580 760 575 444 321 275 265 3,350 5,240 9,040 7,910 4,820
1961 1,780 660 483 331 271 281 415 2,960 6,410 8,080 7,250 2,690
1962 1,290 680 440 280 240 220 280 2,200 9,090 10,200 9,450 3,650
1963 1,080 510 310 250 230 200 210 3,250 6,760 10,500 10,200 3,950
1964 925 290 185 140 140 110 130 910 11,600 7,580 6,550 2,630
1965 1,470 702 279 220 200 208 320 2,460 4,650 6,760 5,760 6,960
1966 920 300 240 210 200 200 280 1,630 6,850 8,290 6,430 3,200
1967 957 321 278 252 227 205 195 3,550 7,870 8,140 8,770 4,640
1968 911 471 382 344 320 312 368 4,930 9,010 11,800 9,830 2,190
1969 700 304 172 145 140 145 229 1,770 8,150 9,450 3,920 2,210
1970 1,000 501 339 265 221 193 319 2,210 5,010 8,450 6,220 1,950
1971 528 395 276 170 125 120 135 629 8,100 10,400 10,400 3,290
1972 1,040 478 380 339 307 286 270 3,470 6,560 10,400 8,660 2,780
1973 667 323 211 178 164 153 153 1,040 5,740 8,350 7,270 2,450
1974 876 462 366 310 271 235 262 2,540 5,640 9,550 9,290 5,450
1975 2,140 673 381 300 200 200 200 1,640 7,040 12,100 7,290 3,570
1976 1,540 375 169 112 97 90 123 1,810 5,940 8,560 10,100 1,820
1977 894 467 331 266 240 231 246 1,500 8,250 10,000 10,200 3,710
1978 1,150 652 439 348 300 246 263 2,030 5,250 8,990 8,640 3,620
1979 865 463 312 263 229 203 250 2,790 7,650 9,500 9,180 4,510
1980 2,160 878 533 395 330 290 280 1,890 6,410 11,800 7,170 2,640
1981 1,300 745 473 344 274 235 210 3,010 7,160 11,900 12,000 2,740
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 2 February 2013
WY Susitna River near Denali cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 831 481 326 227 157 127 120 2,460 5,870 9,750 6,450 4,450
1983 1,150 439 363 330 300 277 281 1,970 7,450 10,500 8,050 2,600
1984 1,220 433 277 220 205 200 196 2,050 8,380 10,800 8,820 2,150
1985 1,300 611 438 357 306 291 376 2,480 8,060 10,500 7,220 3,860
1986 1,270 589 404 304 238 201 229 2,670 7,060 13,200 5,710 3,440
1987 3,920 615 325 267 253 249 344 3,170 7,170 9,400 7,140 3,580
1988 1,180 564 360 321 297 292 331 5,090 9,260 9,090 6,230 3,400
1989 1,540 503 281 251 234 265 331 3,230 8,160 8,500 8,950 6,060
1990 2,240 599 306 290 281 310 770 7,710 9,620 7,910 7,210 6,900
1991 1,280 406 308 283 275 234 276 2,240 8,910 7,600 6,180 3,100
1992 1,310 458 403 350 315 324 581 2,100 7,500 8,250 5,580 1,820
1993 721 476 369 320 275 253 412 6,260 7,790 6,540 5,870 7,070
1994 2,770 662 422 337 287 231 516 4,490 8,740 6,690 6,070 1,840
1995 819 447 337 284 252 249 377 4,910 7,340 7,900 5,430 5,650
1996 1,230 464 229 204 199 202 274 2,220 4,240 5,170 5,610 2,100
1997 638 350 299 262 230 200 260 2,280 5,650 7,610 7,720 3,500
1998 726 308 241 202 187 172 283 2,420 7,650 8,120 7,070 4,430
1999 1,610 551 379 285 204 155 207 2,300 7,110 6,980 7,560 2,680
2000 1,370 562 361 277 238 210 281 2,850 9,230 8,830 4,480 4,200
2001 1,730 556 377 307 254 222 261 2,320 8,750 6,350 6,420 2,360
2002 905 426 294 235 217 200 204 3,940 4,590 5,300 7,080 5,480
2003 3,140 1,070 441 229 294 214 431 2,250 7,650 8,520 6,210 3,180
2004 1,630 517 321 256 223 204 424 6,370 7,540 6,640 5,210 1,390
2005 975 409 294 260 230 244 831 8,480 9,450 8,200 6,910 7,370
2006 1,940 366 283 255 220 212 242 3,870 6,120 7,130 8,320 3,250
2007 3,270 598 333 269 232 202 345 3,330 4,780 6,760 6,160 4,050
2008 1,140 509 369 248 197 198 244 2,560 6,490 6,500 6,110 3,620
2009 1,110 315 258 253 225 219 678 6,170 6,970 5,980 5,100 2,820
2010 1,630 615 328 257 232 218 314 4,560 5,520 7,920 6,630 4,230
Average 1,330 503 326 263 229 212 293 3,120 7,400 8,580 7,300 3,640
Maximum 3,920 1,070 575 444 330 324 831 8,480 12,200 13,200 12,000 7,370
Minimum 528 219 169 112 81 42 43 629 4,240 5,170 3,920 1,390
Median 1,150 476 325 262 230 207 265 2,560 7,500 8,350 7,140 3,500
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 3 February 2013
Table A-2 – Average Monthly Flow for Maclaren River near Paxson for Pre-Project Conditions based on the USGS
Extended Record
WY Maclaren River near Paxson
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 477 162 91 66 51 47 56 1,060 2,150 2,710 2,270 558
1951 240 83 70 61 52 47 102 1,390 2,310 2,720 2,240 2,360
1952 358 172 120 101 64 56 59 496 3,480 3,000 2,270 1,350
1953 575 219 108 70 52 52 102 2,130 3,090 2,380 2,390 1,530
1954 348 132 95 83 64 50 79 1,950 2,980 2,370 3,040 1,160
1955 333 173 129 113 89 70 76 853 3,200 3,130 2,780 1,380
1956 308 120 83 63 62 60 61 1,840 3,520 3,410 2,780 1,950
1957 360 191 135 108 95 76 76 1,380 3,270 2,790 2,440 2,270
1958 545 247 204 124 83 73 97 1,270 3,530 3,520 2,700 784
1959 378 115 123 129 95 62 78 587 2,880 2,680 2,080 856
1960 549 250 190 150 110 94 92 1,740 2,120 3,360 3,050 2,440
1961 687 195 149 110 94 96 145 1,240 2,680 3,370 3,300 1,170
1962 381 210 170 120 100 92 120 632 2,920 3,260 2,930 1,130
1963 383 210 130 100 91 80 83 2,130 3,110 4,650 3,140 1,210
1964 416 140 98 85 88 71 72 386 4,300 2,760 2,220 871
1965 379 147 49 44 42 41 62 984 2,270 3,220 2,410 2,100
1966 522 180 55 45 45 43 50 265 2,990 2,510 2,090 954
1967 369 95 70 65 60 55 53 1,020 3,630 3,250 3,610 1,420
1968 417 130 100 97 95 95 95 208 3,250 3,430 2,130 680
1969 265 121 69 58 55 58 95 849 2,610 2,690 974 470
1970 249 117 73 59 50 53 69 746 1,750 2,440 2,370 773
1971 301 192 131 83 60 55 66 365 3,410 3,530 3,660 1,170
1972 375 156 123 115 107 97 99 1,220 3,070 3,260 2,680 1,370
1973 550 243 136 87 65 53 51 576 2,910 2,860 2,270 821
1974 307 123 83 69 62 57 57 649 2,070 2,630 2,440 1,540
1975 385 232 140 115 110 100 103 768 3,180 3,650 1,980 1,570
1976 553 235 139 106 94 90 105 781 2,870 2,810 2,600 600
1977 302 168 119 97 92 90 93 366 3,940 3,830 3,390 1,300
1978 512 265 186 162 140 121 134 709 2,320 3,200 2,360 924
1979 307 192 142 122 110 100 111 634 2,430 3,060 2,220 1,140
1980 734 370 246 160 106 82 81 901 2,520 3,530 2,470 917
1981 368 257 202 159 130 111 95 1,160 2,500 3,670 4,120 1,110
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 4 February 2013
WY Maclaren River near Paxson cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 443 230 170 138 93 77 69 496 1,940 2,730 1,680 1,560
1983 516 287 199 148 123 116 123 853 2,750 3,000 2,540 1,200
1984 481 200 121 95 90 83 88 967 3,140 2,940 2,400 598
1985 278 164 128 113 102 107 110 1,560 4,230 3,340 1,530 1,140
1986 380 145 101 100 100 115 105 992 2,610 4,760 1,910 1,340
1987 1,480 255 142 114 105 100 132 1,170 2,550 3,090 2,410 1,220
1988 316 161 121 111 102 96 99 1,640 2,980 2,780 2,120 1,220
1989 490 179 135 119 105 103 118 1,030 2,920 2,510 2,820 1,810
1990 681 205 134 129 126 135 283 2,700 3,380 2,470 2,480 2,650
1991 430 142 124 110 94 84 106 901 3,060 2,460 1,760 940
1992 337 133 116 106 99 104 122 551 2,730 2,940 2,270 804
1993 252 174 136 116 102 95 151 2,270 2,820 2,310 2,080 2,560
1994 931 225 153 126 110 93 185 1,540 3,260 2,380 2,160 649
1995 278 162 127 110 101 100 144 1,750 2,650 2,820 1,910 2,040
1996 422 164 90 79 75 74 99 742 1,510 1,790 1,940 745
1997 210 125 111 99 90 80 98 758 1,850 2,610 2,650 1,170
1998 248 113 93 81 76 71 105 822 2,580 2,820 2,350 1,460
1999 548 180 133 106 81 65 81 759 2,440 2,320 2,680 897
2000 468 183 128 104 92 83 105 941 3,390 3,190 1,450 1,410
2001 585 181 133 112 97 87 99 811 3,230 2,300 2,300 816
2002 307 155 114 94 87 79 80 1,410 1,640 1,890 2,560 1,910
2003 1,050 359 158 93 116 85 149 767 2,700 3,130 2,220 1,120
2004 580 177 120 98 85 74 152 2,280 2,650 2,350 1,850 470
2005 326 140 110 99 85 84 279 3,120 3,590 2,970 2,440 2,650
2006 666 135 106 97 87 84 96 1,430 2,230 2,530 3,110 1,120
2007 1,120 211 128 108 96 86 129 1,280 1,780 2,400 2,180 1,390
2008 378 181 142 100 79 80 98 931 2,320 2,330 2,160 1,300
2009 372 114 95 95 86 85 254 2,250 2,480 2,110 1,820 1,010
2010 547 207 122 99 90 84 118 1,680 2,020 2,860 2,350 1,520
Average 465 182 125 102 88 81 106 1,140 2,800 2,920 2,420 1,290
Maximum 1,480 370 246 162 140 135 283 3,120 4,300 4,760 4,120 2,650
Minimum 210 83 49 44 42 41 50 208 1,510 1,790 974 470
Median 383 177 124 101 92 83 99 967 2,820 2,820 2,360 1,170
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 5 February 2013
Table A-3 – Average Monthly Flow for Susitna River near Cantwell for Pre-Project Conditions based on the USGS
Extended Record
WY Susitna River near Cantwell
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 3,920 1,540 842 594 452 415 501 7,260 12,600 14,500 12,700 5,160
1951 2,330 758 638 554 471 424 954 8,930 13,300 14,500 12,600 13,600
1952 3,420 1,640 1,120 940 578 507 530 3,390 20,900 17,000 13,400 9,180
1953 5,100 2,110 1,000 638 471 471 955 12,300 17,600 12,900 13,200 9,690
1954 3,440 1,240 879 758 578 447 721 11,000 16,300 13,000 16,700 8,150
1955 3,290 1,650 1,210 1,060 819 638 698 5,850 19,300 17,800 16,400 9,050
1956 3,030 1,120 758 566 560 542 548 11,300 21,400 20,200 15,800 11,700
1957 3,570 1,830 1,270 1,000 879 698 698 8,750 19,500 15,000 13,100 12,700
1958 5,100 2,400 1,970 1,160 763 667 900 8,170 16,600 14,700 14,400 4,680
1959 2,930 1,280 887 848 763 566 729 10,200 15,000 16,100 19,800 10,800
1960 4,050 1,710 1,310 1,090 850 696 759 10,000 9,840 14,800 15,200 13,100
1961 4,840 1,800 1,610 1,460 1,030 1,070 1,590 9,690 15,700 14,800 16,700 6,720
1962 3,280 1,800 1,400 1,300 1,000 940 1,200 10,000 28,300 20,900 16,000 9,410
1963 4,330 2,200 1,400 1,000 850 760 720 11,300 15,000 22,800 18,200 9,190
1964 3,850 1,300 877 644 586 429 465 2,810 34,600 17,000 11,500 5,350
1965 3,130 1,910 921 760 680 709 1,100 8,820 16,400 18,300 13,400 12,900
1966 3,120 1,000 750 700 650 650 875 4,390 18,500 12,200 12,700 6,520
1967 2,320 780 720 680 640 560 513 9,450 19,600 16,900 19,200 10,300
1968 3,080 1,490 1,330 1,230 1,200 1,200 1,220 9,270 19,500 17,500 10,900 5,410
1969 2,410 1,060 618 508 485 548 998 7,470 12,300 13,500 6,600 3,380
1970 1,640 815 543 437 426 463 887 7,580 9,910 13,900 12,300 5,210
1971 2,150 1,530 1,050 731 503 470 529 1,910 22,000 18,100 22,700 9,800
1972 4,060 2,050 1,370 1,070 922 881 876 9,690 20,000 16,700 15,600 9,420
1973 2,940 1,340 858 698 698 578 594 5,160 17,900 11,600 13,000 5,660
1974 2,260 893 598 504 446 415 574 10,400 11,400 12,000 10,300 7,720
1975 2,270 1,000 942 889 862 819 936 9,800 20,900 17,900 11,500 10,400
1976 4,800 1,180 626 563 548 519 806 7,960 15,700 12,100 12,700 4,250
1977 2,350 1,580 1,430 1,080 951 879 988 8,070 24,400 14,700 12,300 7,960
1978 4,690 2,130 1,540 1,200 981 943 1,000 7,530 12,200 13,500 10,400 5,360
1979 3,000 1,510 988 817 749 698 849 8,840 15,900 18,700 13,100 6,750
1980 4,530 2,550 1,440 1,030 858 819 984 7,490 17,400 20,500 14,900 8,570
1981 5,470 2,490 1,660 1,690 1,190 919 1,220 12,100 14,000 20,900 22,800 9,420
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 6 February 2013
WY Susitna River near Cantwell cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 3,830 1,630 1,300 1,060 698 573 573 8,220 16,500 16,500 11,000 9,940
1983 3,310 1,600 1,400 1,300 1,200 1,150 1,210 8,200 16,500 16,200 17,000 8,660
1984 5,380 2,130 1,600 1,500 1,500 1,480 1,400 8,570 18,800 17,700 14,300 5,140
1985 2,760 1,630 1,170 990 880 844 1,030 5,540 15,800 19,900 12,700 7,520
1986 3,090 1,370 891 729 674 660 735 7,250 15,500 18,900 11,000 8,110
1987 8,020 2,080 1,150 949 890 879 1,220 8,210 14,800 19,300 13,900 8,440
1988 3,640 1,480 940 916 879 879 931 11,100 19,200 16,600 12,500 8,720
1989 4,760 1,810 1,180 1,180 1,060 1,060 1,270 8,690 17,300 15,200 14,400 9,790
1990 4,990 1,800 1,090 1,040 1,000 1,090 2,590 16,500 21,800 15,100 15,300 16,900
1991 4,270 1,460 1,310 1,120 1,060 952 948 3,750 16,500 13,600 11,700 7,780
1992 3,580 1,450 1,310 1,160 1,060 1,100 1,250 3,800 14,900 16,500 13,500 6,380
1993 2,660 1,640 1,210 1,100 1,030 963 1,520 13,400 15,100 12,400 12,000 13,700
1994 6,210 2,000 1,510 1,220 1,050 895 1,950 9,260 20,000 13,400 11,900 5,850
1995 2,760 1,660 1,240 1,090 1,010 1,000 1,710 11,300 15,900 16,400 11,700 12,200
1996 4,000 1,590 844 727 690 638 789 4,120 9,970 10,200 10,900 6,520
1997 2,080 1,140 1,010 907 817 730 900 6,000 12,200 15,600 15,800 8,520
1998 2,360 1,030 848 735 689 644 969 5,990 15,700 16,500 14,600 10,200
1999 4,740 1,790 1,230 968 740 592 743 5,840 14,700 14,600 16,200 7,060
2000 4,200 1,830 1,180 947 839 759 964 7,190 19,900 18,700 10,400 9,770
2001 4,980 1,810 1,230 1,030 884 792 902 5,640 20,100 14,200 14,000 6,490
2002 2,950 1,570 1,120 908 832 760 776 7,320 10,500 11,600 15,300 10,300
2003 6,870 3,300 1,550 973 1,330 886 1,300 5,000 15,700 18,800 13,600 8,560
2004 5,050 1,490 1,070 862 744 626 1,640 15,200 16,300 12,900 11,300 3,980
2005 1,990 1,020 946 842 722 605 1,580 17,400 22,200 17,300 14,100 14,700
2006 5,130 1,270 877 819 812 795 900 10,100 15,000 14,900 19,700 7,750
2007 6,530 1,890 1,380 1,200 1,120 1,030 1,350 11,000 12,600 13,800 12,300 8,540
2008 3,070 1,940 1,680 1,090 784 795 982 7,480 13,500 14,100 12,600 9,190
2009 3,400 909 758 810 758 783 2,800 14,700 14,900 12,400 11,800 7,870
2010 4,410 1,680 1,090 860 789 761 1,090 12,600 12,800 17,800 12,900 10,100
Average 3,800 1,600 1,130 938 820 755 1,030 8,630 16,900 15,800 13,900 8,620
Maximum 8,020 3,300 1,970 1,690 1,500 1,480 2,800 17,400 34,600 22,800 22,800 16,900
Minimum 1,640 758 543 437 426 415 465 1,910 9,840 10,200 6,600 3,380
Median 3,570 1,600 1,120 947 817 759 948 8,570 16,300 15,600 13,200 8,560
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 7 February 2013
Table A-4 – Average Monthly Flow for Susitna River at Gold Creek for Pre-Project Conditions based on the USGS
Extended Record
WY Susitna River at Gold Creek
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 6,330 2,580 1,440 1,030 788 726 870 11,500 19,600 22,600 19,900 8,300
1951 3,850 1,300 1,100 960 820 740 1,620 14,100 20,800 22,600 19,700 21,200
1952 5,570 2,740 1,900 1,600 1,000 880 920 5,420 32,400 26,400 20,900 14,500
1953 8,200 3,500 1,700 1,100 820 820 1,620 19,300 27,300 20,200 20,600 15,300
1954 5,600 2,100 1,500 1,300 1,000 780 1,240 17,300 25,300 20,400 26,100 12,900
1955 5,370 2,760 2,050 1,790 1,400 1,100 1,200 9,320 29,900 27,600 25,800 14,300
1956 4,950 1,900 1,300 980 970 940 950 17,700 33,300 31,100 24,500 18,300
1957 5,810 3,050 2,140 1,700 1,500 1,200 1,200 13,800 30,200 23,300 20,500 19,800
1958 8,210 3,950 3,260 1,960 1,310 1,150 1,530 12,900 25,700 22,900 22,500 7,550
1959 4,810 2,150 1,510 1,450 1,310 980 1,250 16,000 23,300 25,000 31,200 16,900
1960 6,560 2,850 2,200 1,850 1,450 1,200 1,300 15,800 15,500 23,000 23,600 20,500
1961 7,790 3,000 2,690 2,450 1,750 1,810 2,650 17,400 29,500 24,600 22,100 13,400
1962 5,920 2,700 2,100 1,900 1,500 1,400 1,700 12,600 43,300 25,900 23,600 15,900
1963 6,720 2,800 2,000 1,600 1,500 1,000 830 19,000 26,000 34,400 23,700 12,300
1964 6,450 2,250 1,490 1,050 966 713 745 4,310 50,600 22,900 16,400 9,570
1965 6,290 2,800 1,210 960 860 900 1,360 13,000 25,700 27,800 21,100 19,400
1966 7,210 2,100 1,630 1,400 1,300 1,300 1,780 9,650 33,000 19,900 21,800 11,800
1967 4,160 1,600 1,500 1,500 1,400 1,200 1,170 15,500 29,500 26,800 32,600 16,900
1968 4,900 2,350 2,050 1,980 1,900 1,900 1,910 16,200 31,600 26,400 17,200 8,820
1969 3,820 1,630 882 724 723 816 1,510 11,000 15,500 16,100 8,880 5,090
1970 3,120 1,220 866 824 768 776 1,080 11,400 18,600 22,700 20,000 9,120
1971 5,290 3,410 2,290 1,440 1,040 950 1,080 3,750 32,900 23,900 31,900 14,400
1972 5,850 3,090 2,510 2,240 2,030 1,820 1,710 21,900 34,400 22,800 19,300 12,400
1973 4,830 2,250 1,460 1,200 1,200 1,000 1,030 8,240 27,800 18,300 20,300 9,070
1974 3,730 1,520 1,030 874 777 724 992 16,200 17,900 18,800 16,200 12,200
1975 3,740 1,700 1,600 1,520 1,470 1,400 1,590 15,400 32,300 27,700 18,100 16,300
1976 7,740 1,990 1,080 974 950 900 1,370 12,600 24,400 18,900 19,800 6,880
1977 3,870 2,650 2,400 1,830 1,620 1,500 1,680 12,700 38,000 22,900 19,200 12,600
1978 7,570 3,530 2,590 2,030 1,670 1,600 1,700 11,900 19,100 21,000 16,400 8,610
1979 4,910 2,530 1,680 1,400 1,290 1,200 1,450 13,900 24,700 28,900 20,500 10,800
1980 7,310 4,190 2,420 1,750 1,470 1,400 1,670 12,100 29,100 32,700 21,000 13,300
1981 7,720 3,570 1,910 2,010 1,980 1,590 2,040 16,600 19,300 33,900 37,900 13,800
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 8 February 2013
WY Susitna River at Gold Creek cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 7,460 3,260 1,880 1,680 1,490 1,350 1,780 13,400 26,100 24,100 15,300 17,800
1983 6,890 2,630 2,360 2,260 2,000 1,690 1,900 14,900 24,500 21,100 24,500 13,600
1984 8,300 3,150 2,260 2,050 1,970 1,900 1,810 13,000 26,800 23,500 20,400 9,430
1985 5,670 3,090 2,390 1,940 1,640 1,730 1,980 11,200 26,300 26,500 19,900 15,600
1986 6,940 2,670 1,930 1,660 1,560 1,390 1,570 12,100 20,000 21,900 17,300 12,900
1987 12,700 3,450 1,950 1,610 1,520 1,500 2,050 13,000 23,000 29,900 21,800 13,300
1988 5,920 2,480 1,600 1,560 1,500 1,500 1,590 17,400 29,700 25,700 19,500 13,800
1989 7,670 3,010 2,000 2,000 1,800 1,800 2,140 13,700 26,800 23,700 22,400 15,400
1990 8,030 3,000 1,850 1,760 1,700 1,850 4,250 25,600 33,800 23,500 23,700 26,500
1991 6,900 2,450 2,200 1,900 1,800 1,620 1,610 6,050 25,600 21,200 18,300 12,300
1992 5,820 2,440 2,200 1,960 1,800 1,870 2,100 6,100 23,100 25,500 21,100 10,200
1993 4,380 2,730 2,040 1,860 1,750 1,640 2,540 20,900 23,500 19,300 18,700 21,300
1994 9,910 3,330 2,530 2,060 1,790 1,530 3,220 14,600 31,100 21,000 18,600 9,360
1995 4,530 2,780 2,100 1,850 1,720 1,700 2,850 17,700 24,700 25,500 18,400 19,100
1996 6,480 2,660 1,440 1,250 1,190 1,100 1,350 6,610 15,700 16,000 17,100 10,400
1997 3,510 1,960 1,750 1,630 1,510 1,400 1,640 9,660 19,100 24,400 24,700 13,600
1998 3,940 1,780 1,550 1,410 1,350 1,290 1,750 9,620 24,600 25,800 22,800 16,200
1999 7,740 3,040 2,110 1,700 1,420 1,220 1,410 9,380 23,100 22,900 25,400 11,400
2000 6,890 3,100 2,020 1,670 1,540 1,440 1,720 11,500 31,300 29,500 16,400 15,500
2001 8,110 3,070 2,100 1,770 1,590 1,480 1,620 9,020 31,000 22,000 21,800 10,400
2002 4,840 2,630 1,900 1,550 1,420 1,300 1,330 11,500 16,500 18,100 23,800 16,300
2003 11,000 5,390 2,590 1,650 2,240 1,510 2,170 8,020 24,300 29,200 21,100 13,500
2004 8,110 2,500 1,810 1,470 1,280 1,080 2,730 23,600 25,300 20,200 17,700 6,450
2005 3,300 1,730 1,610 1,440 1,240 1,050 2,610 26,900 34,300 26,800 22,000 22,900
2006 8,240 2,140 1,500 1,400 1,390 1,360 1,540 15,700 23,300 23,100 30,800 12,300
2007 10,400 3,140 2,320 2,020 1,910 1,740 2,270 17,200 19,700 21,600 19,300 13,500
2008 5,020 3,220 2,810 1,840 1,340 1,360 1,670 11,900 21,100 22,000 19,700 14,500
2009 5,530 1,550 1,300 1,390 1,300 1,340 4,550 22,900 23,100 19,400 18,500 12,500
2010 7,120 2,810 1,840 1,470 1,350 1,300 1,850 19,600 20,000 27,500 20,100 15,800
Average 6,320 2,670 1,890 1,590 1,420 1,300 1,740 13,800 26,300 24,000 21,400 13,700
Maximum 12,700 5,390 3,260 2,450 2,240 1,900 4,550 26,900 50,600 34,400 37,900 26,500
Minimum 3,120 1,220 866 724 723 713 745 3,750 15,500 16,000 8,880 5,090
Median 6,290 2,700 1,910 1,630 1,450 1,340 1,620 13,000 25,600 23,300 20,500 13,500
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 9 February 2013
Table A-5 – Average Monthly Flow for Chulitna River near Talkeetna for Pre-Project Conditions based on the USGS
Extended Record
WY Chulitna River near Talkeetna
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 5,320 1,870 1,130 1,020 924 903 959 10,500 18,200 21,500 18,900 7,080
1951 2,970 1,100 1,040 993 942 910 1,340 13,000 19,000 21,700 18,700 19,400
1952 4,530 1,990 1,300 1,180 1,010 965 979 4,620 26,200 23,400 18,900 13,100
1953 7,010 2,630 1,200 1,040 942 942 1,350 17,900 23,900 19,400 19,600 14,200
1954 4,540 1,460 1,150 1,100 1,010 926 1,070 16,500 23,400 19,400 23,800 11,700
1955 4,290 2,000 1,420 1,280 1,130 1,040 1,070 8,320 24,500 24,100 21,800 13,200
1956 3,930 1,330 1,100 1,000 997 986 990 15,500 26,300 25,900 22,000 17,000
1957 4,700 2,240 1,490 1,200 1,150 1,070 1,070 12,100 24,900 22,000 19,800 18,800
1958 6,990 3,020 2,430 1,390 1,040 948 1,220 10,500 23,200 25,000 20,800 8,000
1959 4,200 1,880 1,260 1,100 1,050 738 890 7,410 23,700 25,700 22,100 9,960
1960 4,720 2,280 1,700 1,450 1,100 933 1,000 13,900 17,400 23,700 19,300 12,400
1961 5,140 1,950 1,750 1,450 1,100 1,080 1,600 10,100 20,500 27,400 24,600 16,000
1962 5,780 2,400 1,500 1,300 1,000 930 1,170 7,740 20,600 27,200 22,000 13,500
1963 3,510 1,500 1,550 1,600 1,300 846 700 11,100 17,700 28,900 18,400 11,300
1964 8,060 2,300 1,000 1,010 820 770 1,130 2,350 40,300 24,400 20,300 9,230
1965 5,640 2,900 2,100 1,600 1,400 1,300 1,400 7,450 20,100 23,200 22,500 22,300
1966 6,070 1,620 1,350 1,200 1,100 1,100 1,300 3,970 21,700 23,700 27,700 12,200
1967 4,680 1,680 1,500 1,460 1,260 1,050 972 12,400 25,500 35,600 33,700 12,500
1968 3,480 1,660 1,400 1,240 1,200 1,150 1,350 10,900 29,000 30,100 20,700 7,380
1969 2,900 1,480 1,140 974 900 824 1,330 6,000 18,600 20,800 11,300 6,700
1970 4,580 1,890 1,320 1,200 1,150 1,100 1,440 9,640 19,700 26,100 24,700 11,300
1971 3,830 2,210 1,400 1,110 950 934 982 4,470 22,200 27,300 23,800 11,100
1972 5,440 2,160 1,430 1,170 1,040 939 893 9,760 17,900 25,800 21,000 12,100
1973 5,520 2,130 1,440 1,260 1,170 1,110 1,110 6,610 21,100 19,700 20,500 8,990
1974 3,720 1,910 1,490 1,300 1,190 1,100 1,200 10,800 17,600 20,700 20,000 13,300
1975 6,120 2,380 1,550 1,310 1,150 1,100 1,110 7,480 23,400 26,500 19,600 15,400
1976 6,320 1,560 1,110 1,020 977 960 1,110 7,480 20,400 21,400 21,200 7,170
1977 3,810 2,090 1,780 1,290 1,160 1,120 1,160 7,620 27,200 22,800 21,400 13,100
1978 6,030 2,470 1,760 1,450 1,240 1,120 1,170 7,280 16,600 23,500 18,900 9,800
1979 3,520 2,120 1,590 1,340 1,220 1,150 1,340 13,000 22,900 26,100 20,700 11,600
1980 8,020 3,620 1,950 1,610 1,410 1,300 1,680 9,140 22,500 34,900 20,800 8,240
1981 5,710 3,210 2,020 1,620 1,410 1,170 1,440 9,970 22,400 29,900 33,200 12,000
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 10 February 2013
WY Chulitna River near Talkeetna cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 4,830 2,250 1,220 1,030 873 789 1,070 6,290 18,400 25,600 20,400 18,200
1983 5,500 2,510 1,850 1,570 1,040 1,050 1,250 8,880 18,900 22,300 22,200 11,000
1984 8,620 2,920 2,390 2,050 1,510 1,260 1,380 7,310 18,600 22,300 22,800 9,920
1985 4,730 2,670 2,160 1,900 1,400 1,160 1,130 5,710 18,900 27,100 20,800 13,200
1986 6,360 1,900 1,480 1,320 1,130 959 956 4,750 14,700 22,800 17,900 14,800
1987 17,600 4,070 2,210 1,600 1,410 1,300 1,770 11,000 20,800 23,500 20,700 11,600
1988 3,490 2,240 1,880 1,580 1,370 1,240 1,230 11,600 21,800 21,300 17,700 11,100
1989 5,210 2,230 1,880 1,370 1,200 1,170 1,230 7,650 22,800 18,600 25,000 18,700
1990 8,810 3,120 2,060 1,940 1,930 2,070 3,910 22,300 25,900 18,700 18,900 21,100
1991 4,570 1,580 1,320 1,240 975 877 1,520 13,100 25,700 21,100 14,000 8,730
1992 3,890 1,330 1,150 1,090 1,080 1,130 1,360 5,870 22,200 23,700 18,500 8,570
1993 3,160 2,400 1,870 1,390 1,170 1,100 1,820 19,900 23,900 20,600 18,300 24,000
1994 11,200 3,360 1,880 1,520 1,330 1,140 2,110 15,400 26,300 19,300 19,400 6,350
1995 3,680 1,900 1,490 1,270 1,170 1,160 1,290 14,800 21,600 22,000 16,600 16,700
1996 5,200 2,140 1,150 1,050 1,020 1,060 1,520 10,200 13,600 17,900 18,600 7,660
1997 2,850 1,560 1,350 1,250 1,160 1,070 1,280 8,150 16,700 22,000 22,400 11,600
1998 3,220 1,390 1,190 1,080 1,030 984 1,370 8,280 22,000 23,500 20,300 13,900
1999 6,440 2,460 1,690 1,320 1,080 928 1,080 7,900 20,800 20,300 22,800 9,560
2000 5,720 2,510 1,610 1,290 1,180 1,100 1,340 9,720 28,200 26,600 14,000 13,400
2001 6,770 2,480 1,680 1,380 1,230 1,130 1,250 7,790 25,100 17,500 18,500 8,910
2002 4,150 1,830 1,310 1,150 1,090 1,010 1,020 14,100 14,400 16,000 21,400 19,100
2003 12,600 4,970 2,020 1,050 1,120 989 2,150 9,600 21,400 24,600 18,200 9,630
2004 6,130 2,760 1,570 1,300 1,160 1,080 1,720 16,700 19,500 20,000 16,100 6,290
2005 5,810 2,440 1,510 1,330 1,200 1,310 4,130 27,000 29,500 23,400 19,500 22,600
2006 7,910 1,700 1,480 1,330 1,120 1,080 1,200 9,870 16,700 19,800 24,700 11,900
2007 13,100 2,940 1,310 1,100 940 828 1,550 6,930 12,000 19,000 19,000 14,700
2008 5,620 2,080 1,250 1,070 985 988 1,150 8,120 18,700 18,500 18,900 11,900
2009 5,090 1,690 1,340 1,300 1,160 1,130 1,700 17,000 19,500 17,800 14,800 9,780
2010 7,490 3,390 1,610 1,310 1,200 1,120 1,550 9,790 15,200 21,600 20,500 12,700
Average 5,750 2,260 1,550 1,300 1,140 1,060 1,370 10,400 21,500 23,200 20,600 12,600
Maximum 17,600 4,970 2,430 2,050 1,930 2,070 4,130 27,000 40,300 35,600 33,700 24,000
Minimum 2,850 1,100 1,000 974 820 738 700 2,350 12,000 16,000 11,300 6,290
Median 5,210 2,160 1,490 1,290 1,130 1,070 1,250 9,720 21,400 22,800 20,400 11,900
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 11 February 2013
Table A-6 – Average Monthly Flow for Talkeetna River near Talkeetna for Pre-Project Conditions based on the USGS
Extended Record
WY Talkeetna River near Talkeetna
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 2,580 1,020 591 507 459 449 477 4,780 8,240 9,550 8,370 3,400
1951 1,540 550 519 495 469 452 700 5,880 8,770 9,540 8,280 8,960
1952 2,260 1,080 741 621 502 480 488 2,240 13,800 11,200 8,830 6,040
1953 3,360 1,390 661 519 469 469 697 8,100 11,600 8,500 8,680 6,370
1954 2,270 822 581 550 502 460 550 7,250 10,700 8,570 11,100 5,360
1955 2,170 1,090 800 698 564 519 535 3,850 12,700 11,700 11,000 5,950
1956 1,990 742 550 499 497 491 493 7,450 14,300 13,300 10,400 7,700
1957 2,350 1,210 839 661 581 535 535 5,760 12,900 9,850 8,650 8,330
1958 3,360 1,580 1,300 767 536 498 617 5,170 10,400 10,200 9,300 3,570
1959 2,020 896 632 559 537 428 489 5,040 10,000 10,700 11,300 5,860
1960 2,490 1,130 855 722 562 497 524 6,410 7,270 9,970 9,220 7,140
1961 2,840 1,070 959 833 611 615 910 5,990 10,600 11,000 9,940 6,550
1962 2,660 1,140 782 692 537 510 620 4,430 13,400 11,200 9,740 6,430
1963 2,190 911 778 719 619 459 405 6,370 9,370 13,200 9,070 5,340
1964 3,370 1,030 547 507 450 413 516 1,470 17,100 9,820 8,400 3,820
1965 3,120 1,570 1,100 720 620 540 580 3,470 11,100 12,200 11,200 10,600
1966 4,440 1,460 876 711 526 395 422 2,410 13,000 10,100 10,700 5,370
1967 2,390 897 750 637 546 471 427 4,110 9,290 12,600 14,200 6,970
1968 2,030 1,250 987 851 777 743 983 8,840 14,100 11,200 7,550 4,120
1969 1,640 827 556 459 401 380 519 3,870 5,210 7,080 3,790 2,070
1970 1,450 765 587 504 458 440 545 3,950 7,980 10,300 8,750 5,990
1971 2,820 1,650 1,100 679 459 402 503 2,140 19,000 11,800 16,800 5,990
1972 2,630 1,310 845 727 628 481 519 3,520 12,700 12,000 9,580 8,710
1973 3,630 1,370 889 748 654 574 577 3,860 12,200 7,680 9,930 3,860
1974 1,810 960 745 645 559 482 535 5,680 8,030 7,750 7,700 4,760
1975 1,970 1,000 774 694 586 508 522 4,080 13,200 12,100 8,490 7,960
1976 2,880 773 558 524 480 470 613 3,440 10,600 9,030 8,090 3,210
1977 1,860 1,100 1,070 700 549 506 548 4,240 18,300 9,340 8,000 5,960
1978 3,270 1,120 860 746 576 485 534 2,950 7,430 10,800 7,000 3,570
1979 1,660 1,140 932 762 652 577 710 7,790 12,000 14,400 8,270 4,040
1980 3,380 1,720 868 808 741 700 1,040 4,820 11,400 13,900 7,220 5,400
1981 2,600 1,140 717 652 535 545 671 4,530 6,590 15,400 14,700 4,380
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 12 February 2013
WY Talkeetna River near Talkeetna cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 2,350 1,240 708 650 467 285 480 3,310 12,900 11,100 7,270 9,560
1983 3,350 1,240 1,080 836 580 565 669 4,550 9,010 8,700 8,800 3,940
1984 3,280 1,100 781 690 626 600 555 4,010 9,330 8,900 9,760 3,820
1985 2,200 1,160 897 717 548 498 522 4,170 10,400 11,100 10,200 8,430
1986 3,320 1,000 783 681 590 400 396 2,540 6,210 9,150 8,030 6,890
1987 10,000 1,990 1,120 832 737 659 894 5,060 9,710 11,100 9,870 5,360
1988 1,720 1,140 965 818 707 606 595 5,270 10,100 9,670 7,970 5,120
1989 2,500 1,130 965 697 577 550 600 3,630 10,700 8,360 12,400 8,550
1990 4,100 1,550 1,050 996 990 1,060 1,910 11,500 13,100 8,450 8,710 11,000
1991 2,210 820 673 610 407 340 716 6,160 12,800 9,970 6,360 4,080
1992 1,900 672 540 494 480 521 690 2,800 10,400 11,200 8,530 3,990
1993 1,570 1,210 961 716 552 502 907 10,200 11,600 9,210 8,390 12,100
1994 5,150 1,660 968 790 675 531 1,050 6,920 13,600 8,640 8,830 3,010
1995 1,810 973 773 637 548 540 629 6,740 10,300 10,200 7,480 7,630
1996 2,500 1,090 538 457 440 467 749 4,720 6,180 8,070 8,370 3,600
1997 1,420 808 698 616 545 478 609 3,790 7,610 10,200 10,500 5,380
1998 1,590 718 569 481 446 413 660 3,990 10,400 11,100 9,240 6,330
1999 3,060 1,240 873 666 486 374 492 3,670 9,690 9,480 11,400 4,440
2000 2,740 1,270 834 648 562 500 658 4,490 15,200 13,800 6,340 6,230
2001 3,200 1,250 869 715 598 525 613 3,620 12,300 8,010 8,360 4,150
2002 2,020 943 665 539 493 430 439 7,200 6,540 7,210 10,100 8,700
2003 5,740 2,400 1,020 464 513 417 1,020 4,440 9,840 12,000 8,270 4,460
2004 2,920 1,380 816 656 541 482 843 7,530 8,710 8,950 7,230 2,990
2005 2,780 1,230 777 682 579 666 1,970 14,200 16,500 10,900 8,700 11,000
2006 3,700 880 771 671 514 479 573 4,680 7,700 9,050 13,300 5,440
2007 6,150 1,460 665 500 382 309 717 3,270 5,480 8,520 8,590 6,700
2008 2,690 1,060 615 479 414 416 531 3,790 8,520 8,460 8,540 5,440
2009 2,450 873 694 654 547 517 823 7,790 8,870 7,960 6,710 4,540
2010 3,530 1,680 834 665 575 515 763 4,500 6,860 9,930 9,220 5,800
Average 2,840 1,160 801 655 553 502 670 5,120 10,700 10,300 9,210 5,940
Maximum 10,000 2,400 1,300 996 990 1,060 1,970 14,200 19,000 15,400 16,800 12,100
Minimum 1,420 550 519 457 382 285 396 1,470 5,210 7,080 3,790 2,070
Median 2,580 1,130 782 666 547 491 595 4,500 10,400 9,970 8,710 5,440
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 13 February 2013
Table A-7 – Average Monthly Flow for Susitna River at Sunshine for Pre-Project Conditions based on the USGS
Extended Record
WY Susitna River at Sunshine
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 15,000 5,820 3,150 2,210 1,670 1,530 1,860 28,100 48,400 56,400 49,500 19,800
1951 8,860 2,830 2,370 2,060 1,740 1,560 3,580 34,600 51,300 56,600 48,900 52,300
1952 13,100 6,200 4,210 3,520 2,150 1,880 1,970 13,000 77,200 64,900 51,400 35,400
1953 19,600 8,000 3,750 2,370 1,740 1,740 3,580 47,700 66,800 50,300 51,300 37,600
1954 13,100 4,680 3,280 2,830 2,150 1,650 2,690 42,900 63,000 50,700 64,500 31,500
1955 12,600 6,230 4,550 3,970 3,060 2,370 2,600 22,600 71,500 67,500 61,800 35,100
1956 11,500 4,220 2,830 2,100 2,080 2,010 2,030 43,000 78,900 75,200 60,700 45,600
1957 13,600 6,920 4,780 3,750 3,280 2,600 2,600 33,500 72,500 58,100 51,200 49,300
1958 19,600 9,100 7,440 4,360 2,850 2,480 3,370 31,700 63,800 57,000 54,500 18,000
1959 11,200 4,800 3,320 3,170 2,850 2,100 2,720 38,900 58,200 62,200 73,400 40,900
1960 15,500 6,450 4,910 4,080 3,170 2,590 2,830 38,400 38,200 56,400 58,800 50,300
1961 18,600 6,810 6,070 5,500 3,870 4,000 5,970 43,000 70,300 61,700 55,200 32,700
1962 14,000 6,090 4,680 4,210 3,280 3,060 3,750 30,600 97,200 64,400 59,000 39,000
1963 15,900 6,320 4,440 3,520 3,280 2,150 1,760 45,100 65,300 81,300 58,800 30,000
1964 15,200 5,030 3,280 2,260 2,070 1,510 1,580 10,000 103,000 58,700 44,700 23,800
1965 16,600 7,460 3,900 2,790 2,460 2,410 3,230 28,800 64,100 68,900 55,600 51,900
1966 20,700 6,060 4,190 3,500 3,050 2,850 3,690 21,500 76,200 52,500 57,200 30,800
1967 11,400 4,170 3,740 3,540 3,240 2,800 2,670 35,200 68,500 66,600 76,200 42,200
1968 12,000 6,110 5,110 4,730 4,460 4,400 4,850 41,900 76,000 66,200 44,900 23,000
1969 9,370 4,100 2,400 2,000 1,910 2,030 3,400 26,500 37,500 42,100 22,600 12,400
1970 7,810 3,290 2,420 2,230 2,070 2,050 2,710 27,600 47,400 58,600 51,600 26,700
1971 14,200 8,670 5,720 3,530 2,510 2,280 2,650 10,300 79,300 61,600 76,000 36,700
1972 14,800 7,490 5,620 4,950 4,420 3,850 3,720 44,900 78,000 60,600 51,400 36,900
1973 14,900 6,160 3,930 3,240 3,070 2,620 2,670 21,700 67,600 47,200 53,000 23,000
1974 9,550 4,160 2,950 2,520 2,240 2,040 2,560 38,000 46,900 48,500 43,000 30,600
1975 9,870 4,530 3,950 3,660 3,420 3,180 3,530 34,700 76,400 69,000 47,900 43,400
1976 18,700 4,630 2,730 2,510 2,400 2,300 3,330 28,800 61,400 50,300 50,200 17,800
1977 9,870 6,340 5,850 4,200 3,610 3,350 3,720 30,100 88,000 57,900 49,500 33,600
1978 19,100 7,890 5,790 4,620 3,730 3,490 3,730 26,600 48,200 56,200 42,400 21,600
1979 11,300 6,210 4,380 3,590 3,210 2,960 3,610 37,100 63,400 72,200 51,600 26,500
1980 18,900 10,200 5,500 4,260 3,660 3,480 4,560 30,300 69,700 77,400 51,200 33,000
1981 18,200 8,010 4,380 4,430 4,200 3,550 4,530 36,200 50,900 85,600 84,900 32,500
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 14 February 2013
WY Susitna River at Sunshine cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 16,500 7,030 4,040 3,500 3,230 2,880 3,800 26,600 62,800 63,000 45,600 48,800
1983 16,200 6,300 5,610 5,220 4,660 3,480 4,200 31,400 58,100 55,400 60,600 30,000
1984 21,300 8,270 5,550 4,900 4,600 4,500 4,550 25,900 59,300 59,100 58,700 23,900
1985 12,400 6,250 4,880 4,560 3,820 3,750 4,090 25,800 60,900 68,000 55,000 40,800
1986 16,700 6,080 4,310 3,700 3,380 2,880 3,100 22,000 46,900 56,000 45,900 35,200
1987 36,600 9,390 5,180 4,080 3,740 3,580 4,940 32,600 58,200 71,200 55,500 33,600
1988 13,300 6,120 4,300 3,960 3,660 3,500 3,640 41,100 69,900 63,500 50,100 34,200
1989 17,900 7,030 4,970 4,490 3,960 3,920 4,570 30,900 65,900 58,500 60,100 42,800
1990 21,600 7,780 4,870 4,630 4,510 4,890 10,700 62,800 78,400 57,900 58,300 63,200
1991 16,000 5,470 4,780 4,170 3,700 3,290 3,920 21,200 66,000 55,400 44,900 29,400
1992 13,400 5,200 4,580 4,110 3,810 3,990 4,650 15,600 59,800 64,500 53,300 25,300
1993 10,200 6,690 5,030 4,290 3,840 3,580 5,820 53,200 61,100 51,500 48,800 56,800
1994 27,000 8,550 5,880 4,750 4,090 3,430 7,290 38,900 74,400 53,800 49,200 22,000
1995 10,900 6,320 4,790 4,140 3,780 3,740 5,850 44,000 61,100 63,600 47,100 48,200
1996 15,800 6,340 3,300 2,860 2,730 2,630 3,510 20,300 39,700 43,400 46,100 25,000
1997 9,510 5,330 4,600 4,120 3,740 3,370 4,150 25,800 50,600 64,000 64,700 36,100
1998 10,700 4,730 3,860 3,380 3,190 3,000 4,480 25,500 64,300 67,200 60,000 42,800
1999 20,800 8,270 5,770 4,420 3,410 2,770 3,440 25,000 60,500 60,100 65,800 30,300
2000 18,500 8,430 5,500 4,300 3,830 3,490 4,420 30,700 79,600 75,500 43,500 41,000
2001 21,700 8,340 5,740 4,710 4,020 3,630 4,120 23,600 73,900 54,200 54,300 25,900
2002 11,900 6,010 4,260 3,480 3,200 2,900 2,960 31,800 42,000 46,200 59,300 44,600
2003 30,000 13,600 6,090 3,550 4,630 3,230 5,470 22,200 61,300 70,600 52,900 32,400
2004 19,500 6,600 4,380 3,520 3,030 2,620 6,070 56,000 61,800 52,800 45,500 16,600
2005 10,600 5,010 3,970 3,510 3,030 2,840 7,970 68,800 81,900 66,300 55,900 59,200
2006 21,200 5,060 3,770 3,440 3,180 3,080 3,510 36,100 54,800 58,200 72,600 31,900
2007 29,300 7,850 4,980 4,220 3,840 3,450 5,060 36,900 45,900 54,800 50,300 36,400
2008 13,500 7,250 5,750 3,880 2,950 2,980 3,680 28,100 53,600 54,800 50,900 36,100
2009 13,900 4,040 3,300 3,380 3,080 3,100 9,340 54,900 57,600 49,800 45,900 30,600
2010 18,800 7,680 4,460 3,530 3,200 3,040 4,370 44,000 48,900 66,200 52,700 39,200
Average 15,900 6,490 4,490 3,720 3,260 2,960 4,030 33,200 63,700 60,500 54,200 34,900
Maximum 36,600 13,600 7,440 5,500 4,660 4,890 10,700 68,800 103,000 85,600 84,900 63,200
Minimum 7,810 2,830 2,370 2,000 1,670 1,510 1,580 10,000 37,500 42,100 22,600 12,400
Median 15,000 6,300 4,460 3,700 3,240 2,980 3,690 31,400 63,000 58,700 52,700 33,600
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 15 February 2013
Table A-8 – Average Monthly Flow for Willow Creek near Willow for Pre-Project Conditions based on the USGS
Extended Record
WY Willow Creek near Willow
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 290 132 87 73 52 56 55 141 886 658 559 326
1951 166 97 88 78 63 52 65 422 1,140 848 774 923
1952 298 130 99 69 45 43 48 300 1,480 1,120 753 686
1953 292 192 104 88 62 51 65 503 1,060 534 763 476
1954 196 123 88 63 51 43 55 400 563 679 852 560
1955 278 142 54 60 50 38 34 200 1,080 1,280 914 529
1956 200 103 78 61 51 34 51 279 971 1,010 704 556
1957 201 143 92 71 59 36 54 626 1,130 584 436 896
1958 355 193 115 72 63 47 60 315 703 472 569 277
1959 249 117 89 54 50 47 52 405 1,270 807 1,130 563
1960 249 139 87 84 60 43 58 651 719 672 661 643
1961 282 152 117 135 73 54 62 373 1,010 872 790 637
1962 328 161 91 100 79 73 74 300 1,500 959 872 617
1963 227 125 102 92 72 67 71 554 1,350 1,590 1,290 406
1964 349 149 104 79 68 60 72 163 1,450 801 559 369
1965 272 156 112 87 77 75 94 256 838 859 780 1,000
1966 369 172 124 86 74 63 68 197 925 660 721 444
1967 247 170 113 78 69 64 68 472 1,260 1,040 889 577
1968 207 122 93 85 83 79 77 643 1,430 1,000 459 257
1969 132 72 60 71 67 56 65 348 550 474 351 195
1970 183 121 92 76 62 60 60 383 728 748 753 405
1971 263 173 115 86 72 56 57 133 1,080 1,030 1,330 367
1972 215 159 97 88 75 60 56 254 1,370 1,190 563 706
1973 422 191 117 89 79 73 71 323 1,100 678 698 344
1974 210 132 100 91 79 60 63 654 1,060 725 483 368
1975 222 143 99 85 75 65 63 283 1,190 1,170 639 882
1976 329 162 119 81 70 58 61 267 1,150 758 433 235
1977 183 133 118 88 75 66 73 356 1,800 1,030 483 801
1978 374 154 126 83 73 60 76 291 647 607 307 259
1979 232 91 110 83 74 75 100 1,050 1,430 1,150 398 368
1980 402 364 152 112 85 73 102 473 1,410 1,290 955 700
1981 288 127 57 57 53 58 86 481 484 1,020 1,290 367
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 16 February 2013
WY Willow Creek near Willow cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 398 177 99 96 74 34 75 579 1,190 816 500 1,080
1983 409 150 119 94 78 64 103 600 889 338 766 565
1984 631 170 118 95 84 72 75 394 828 579 537 380
1985 177 82 69 66 70 67 66 340 1,340 1,230 1,130 952
1986 419 131 91 69 53 42 51 371 608 669 612 705
1987 1,200 191 137 101 77 61 87 497 823 573 581 632
1988 264 96 80 67 74 62 88 632 997 672 563 587
1989 408 185 128 90 74 69 141 577 1,140 541 784 808
1990 475 215 138 109 99 98 205 1,580 1,500 481 378 1,140
1991 321 181 144 104 83 71 89 782 1,230 704 402 463
1992 269 165 126 93 73 59 67 456 1,260 582 440 437
1993 188 102 76 62 60 64 75 968 1,020 356 439 1,180
1994 508 248 141 110 105 65 100 501 1,540 727 538 365
1995 263 154 121 97 80 72 100 574 1,040 691 524 592
1996 254 136 106 82 68 56 72 397 528 392 525 313
1997 169 147 101 82 74 68 82 455 923 488 666 538
1998 237 141 119 100 88 80 91 308 965 608 773 509
1999 321 166 124 100 83 70 64 280 941 626 700 425
2000 344 198 149 112 93 76 86 375 1,340 1,060 607 700
2001 351 181 126 89 75 66 78 376 1,470 660 457 325
2002 190 95 71 60 56 50 46 664 662 310 666 905
2003 794 246 130 94 134 59 98 328 790 496 469 401
2004 449 169 83 70 58 50 85 829 634 228 210 340
2005 622 164 123 111 92 75 258 1,620 1,580 701 651 1,260
2006 403 100 71 60 54 51 50 555 928 558 1,680 654
2007 790 212 115 79 66 50 84 359 580 362 412 632
2008 300 119 72 60 52 51 66 414 822 745 553 505
2009 262 127 103 88 57 50 117 943 708 337 370 290
2010 354 134 106 94 69 48 74 457 541 563 528 529
Average 332 153 105 84 71 60 79 487 1,040 745 666 573
Maximum 1,200 364 152 135 134 98 258 1,620 1,800 1,590 1,680 1,260
Minimum 132 72 54 54 45 34 34 133 484 228 210 195
Median 288 149 104 85 73 60 72 405 1,040 679 607 538
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 17 February 2013
Table A-9 – Average Monthly Flow for Skwentna River near Skwentna for Pre-Project Conditions based on the USGS
Extended Record
WY Skwentna River near Skwentna
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 4,510 1,950 1,120 813 631 585 694 7,950 13,100 15,100 13,400 5,870
1951 2,830 1,020 867 762 657 596 1,240 9,650 13,800 15,100 13,300 14,100
1952 4,010 2,060 1,460 1,240 792 702 732 3,790 19,700 17,000 13,800 9,880
1953 5,790 2,590 1,310 867 657 657 1,240 12,900 17,500 13,600 13,900 10,400
1954 4,040 1,600 1,160 1,020 792 626 968 11,700 16,700 13,700 16,900 8,920
1955 3,890 2,070 1,560 1,380 1,090 867 942 6,490 18,400 17,700 16,100 9,800
1956 3,590 1,460 1,020 777 770 747 755 11,600 20,000 19,500 16,100 12,400
1957 4,180 2,280 1,630 1,310 1,160 942 942 9,230 18,700 15,500 13,800 13,400
1958 5,810 2,910 2,420 1,500 1,020 903 1,190 8,860 17,000 15,200 14,400 5,370
1959 3,500 1,640 1,170 1,120 1,020 777 976 10,500 15,600 16,500 18,600 11,100
1960 3,530 1,850 1,400 1,100 961 843 835 10,500 13,400 16,700 16,000 9,170
1961 3,890 1,600 1,600 1,400 1,150 1,150 1,700 11,200 20,600 16,500 13,900 12,000
1962 4,600 2,200 1,400 1,200 860 760 1,000 6,610 15,600 14,900 12,100 6,720
1963 2,800 1,250 1,100 1,000 810 700 650 7,760 14,000 20,400 12,000 7,180
1964 5,360 1,550 840 970 750 600 840 1,640 27,300 16,500 12,700 6,220
1965 4,430 1,790 1,300 920 800 740 770 4,810 17,200 19,400 14,000 13,100
1966 4,120 1,580 1,150 1,100 1,100 1,100 1,300 4,500 19,600 14,200 17,300 9,810
1967 5,580 1,400 900 720 650 650 780 1,790 14,400 14,700 15,800 9,520
1968 3,830 1,560 1,180 1,020 1,000 950 1,290 13,500 20,800 17,500 10,600 3,860
1969 1,930 678 624 600 600 626 1,490 11,100 19,600 13,700 7,470 3,780
1970 5,650 1,610 832 766 700 650 728 11,700 22,900 21,100 13,000 6,660
1971 2,920 2,020 1,180 865 721 613 607 5,960 25,400 20,600 15,900 6,020
1972 3,020 1,330 1,100 989 898 811 742 8,050 15,300 16,800 13,400 9,260
1973 4,550 2,340 1,320 910 702 606 727 6,350 15,200 13,800 9,870 6,160
1974 3,540 1,700 1,260 1,020 902 811 1,010 6,770 10,700 11,700 10,500 11,800
1975 4,560 2,330 919 800 750 750 767 7,850 19,100 19,500 11,700 8,470
1976 4,700 1,970 1,260 971 897 800 1,270 8,810 15,100 14,600 11,100 8,160
1977 6,200 2,880 2,870 2,830 1,820 1,200 1,200 8,910 36,700 25,300 20,200 10,300
1978 5,800 2,370 1,550 1,210 944 841 1,020 9,010 13,800 18,100 13,700 7,480
1979 4,940 1,580 1,550 1,160 1,040 981 1,600 11,700 15,000 15,800 16,200 7,450
1980 7,250 4,190 2,230 1,780 1,620 1,350 1,960 11,800 24,800 28,600 13,900 8,780
1981 5,630 2,690 1,480 1,240 1,270 925 2,140 22,400 24,700 21,400 16,500 7,640
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 18 February 2013
WY Skwentna River near Skwentna cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 5,180 2,270 1,480 1,170 986 777 770 5,160 16,000 14,000 10,500 15,200
1983 4,400 2,010 1,470 1,190 1,150 1,100 1,570 9,040 16,900 15,500 16,300 5,530
1984 3,790 1,930 1,280 944 828 817 2,040 10,800 17,300 18,200 18,500 6,640
1985 4,820 1,560 1,080 1,060 1,020 938 895 6,730 16,800 20,300 16,000 10,400
1986 5,700 1,720 1,340 1,170 1,050 895 1,020 8,030 15,500 17,500 13,500 9,950
1987 13,200 2,740 1,440 1,180 1,140 1,110 1,530 8,540 14,500 20,000 17,000 9,990
1988 5,010 3,000 1,960 1,660 1,500 1,460 1,730 11,000 19,500 20,400 13,600 9,240
1989 5,840 2,160 1,060 935 933 1,060 1,370 9,170 15,700 17,800 23,200 15,900
1990 7,920 2,890 1,360 1,280 1,250 1,390 3,200 17,200 20,800 16,400 14,300 14,900
1991 4,880 1,780 1,140 1,140 1,140 988 1,330 7,810 19,200 17,300 14,400 9,430
1992 5,280 2,230 1,920 1,650 1,460 1,490 3,180 7,580 14,600 16,400 11,400 5,530
1993 2,960 2,160 1,760 1,460 1,170 1,070 1,910 13,800 15,600 13,100 12,700 14,000
1994 6,930 2,470 1,910 1,570 1,370 1,180 2,380 10,000 19,000 14,100 12,600 6,560
1995 3,310 2,090 1,600 1,420 1,320 1,310 2,130 11,900 16,000 16,900 12,400 12,900
1996 4,630 1,990 1,120 980 932 867 1,050 4,670 10,700 10,900 11,600 7,270
1997 2,590 1,470 1,270 1,120 992 869 1,110 6,880 13,200 16,500 16,600 9,530
1998 2,890 1,300 1,030 875 812 751 1,200 6,710 16,500 17,200 15,500 11,300
1999 5,560 2,260 1,590 1,210 883 680 894 6,670 15,600 15,600 16,800 8,070
2000 4,980 2,300 1,520 1,180 1,020 909 1,200 8,150 20,100 19,100 11,500 10,800
2001 5,820 2,280 1,580 1,300 1,090 956 1,110 6,310 19,300 14,700 14,500 7,230
2002 3,520 1,980 1,450 1,200 1,110 1,020 1,040 7,820 11,300 12,300 15,400 11,100
2003 7,620 3,900 1,950 1,280 1,700 1,170 1,630 5,650 16,200 18,300 14,100 9,270
2004 5,710 1,890 1,390 1,140 1,000 852 2,030 15,400 16,800 13,600 12,000 4,620
2005 2,450 1,330 1,250 1,120 973 826 1,930 17,300 20,700 17,400 14,700 15,200
2006 5,800 1,630 1,160 1,090 1,080 1,060 1,190 10,300 15,100 15,400 18,700 8,510
2007 7,190 2,340 1,760 1,550 1,460 1,340 1,720 11,600 13,300 14,500 13,000 9,300
2008 3,640 2,400 2,110 1,410 1,050 1,060 1,290 8,200 14,200 14,600 13,200 9,960
2009 3,980 1,200 1,020 1,080 1,020 1,050 3,250 14,900 15,500 13,100 12,500 8,630
2010 5,070 2,100 1,410 1,140 1,060 1,020 1,410 13,200 13,500 17,700 13,500 10,800
Average 4,780 2,020 1,400 1,160 1,020 916 1,330 9,280 17,400 16,700 14,200 9,320
Maximum 13,200 4,190 2,870 2,830 1,820 1,490 3,250 22,400 36,700 28,600 23,200 15,900
Minimum 1,930 678 624 600 600 585 607 1,640 10,700 10,900 7,470 3,780
Median 4,600 1,990 1,340 1,140 1,000 869 1,200 8,860 16,500 16,500 13,900 9,270
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 19 February 2013
Table A-10 – Average Monthly Flow for Yentna River near Susitna Station for Pre-Project Conditions based on the
USGS Extended Record
WY Yentna River near Susitna Station
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 12,600 4,770 2,550 1,780 1,340 1,230 1,490 23,700 40,200 47,000 41,400 16,600
1951 7,320 2,280 1,910 1,650 1,400 1,250 2,920 29,100 42,100 47,100 41,100 42,900
1952 10,900 5,080 3,430 2,850 1,730 1,510 1,580 10,500 59,000 51,600 41,900 29,500
1953 16,400 6,590 3,040 1,910 1,400 1,400 2,920 39,700 53,000 42,600 43,000 31,800
1954 10,900 3,820 2,660 2,280 1,730 1,320 2,170 36,300 51,000 42,600 51,900 26,600
1955 10,400 5,110 3,710 3,220 2,470 1,910 2,100 19,000 55,200 53,400 49,000 29,600
1956 9,560 3,430 2,280 1,690 1,670 1,620 1,640 34,800 59,700 57,900 48,700 37,700
1957 11,300 5,680 3,900 3,040 2,660 2,100 2,100 27,300 56,000 48,000 43,300 41,400
1958 16,400 7,510 6,120 3,560 2,300 2,000 2,730 26,500 51,400 47,800 43,700 15,000
1959 9,270 3,920 2,690 2,560 2,300 1,690 2,200 31,200 47,800 50,400 56,100 33,200
1960 10,000 5,260 3,990 3,130 2,750 2,410 2,390 29,400 37,600 46,600 44,600 25,700
1961 11,000 4,560 4,550 4,000 3,290 3,300 4,840 31,400 57,300 46,100 38,900 33,600
1962 13,000 6,240 3,990 3,420 2,460 2,180 2,860 18,600 43,700 41,800 33,800 18,900
1963 7,930 3,570 3,140 2,860 2,320 2,000 1,860 21,800 39,300 57,000 33,600 20,200
1964 15,100 4,410 2,400 2,770 2,150 1,720 2,400 4,650 75,800 46,000 35,500 17,500
1965 12,500 5,090 3,710 2,630 2,290 2,120 2,210 13,500 47,900 54,000 39,100 36,600
1966 11,600 4,490 3,280 3,140 3,140 3,140 3,700 12,700 54,500 39,700 48,300 27,500
1967 15,700 3,990 2,570 2,060 1,860 1,860 2,230 5,090 40,300 41,200 44,000 26,700
1968 10,800 4,440 3,370 2,920 2,860 2,720 3,690 37,600 57,900 48,800 29,600 10,900
1969 5,480 1,940 1,790 1,720 1,720 1,790 4,230 31,000 54,600 38,200 21,000 10,700
1970 15,900 4,570 2,380 2,200 2,000 1,860 2,080 32,700 63,700 58,900 36,500 18,700
1971 8,270 5,750 3,380 2,470 2,070 1,760 1,740 16,700 70,700 57,400 44,500 16,900
1972 8,540 3,780 3,150 2,830 2,570 2,320 2,120 22,600 42,800 47,000 37,400 26,000
1973 12,800 6,640 3,750 2,600 2,010 1,740 2,080 17,900 42,500 38,700 27,700 17,300
1974 10,000 4,830 3,600 2,920 2,580 2,320 2,870 19,000 29,900 32,700 29,400 33,000
1975 10,300 5,470 3,210 2,890 2,670 2,540 2,530 20,900 54,800 57,100 35,600 27,900
1976 12,700 4,860 3,100 2,770 2,490 2,300 3,330 26,800 44,100 45,200 36,600 21,300
1977 14,500 7,630 6,740 6,160 4,460 3,150 3,050 24,300 89,000 67,300 55,700 31,900
1978 15,700 5,920 3,810 3,210 2,770 2,590 2,940 22,500 38,600 50,800 41,000 21,700
1979 14,000 5,140 4,130 3,470 3,120 2,880 4,080 33,500 46,800 53,300 50,600 25,700
1980 22,000 12,000 6,060 4,610 4,170 3,760 5,200 30,500 66,400 81,100 46,700 28,400
1981 18,500 8,370 4,370 3,710 3,740 2,750 5,480 45,600 55,100 64,400 58,900 25,900
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 20 February 2013
WY Yentna River near Susitna Station cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 12,300 6,250 4,540 3,660 2,850 2,230 2,180 13,900 40,900 46,700 39,800 47,600
1983 12,500 5,660 4,120 3,340 3,240 3,090 4,420 25,900 48,800 44,600 47,100 15,800
1984 10,700 5,440 3,580 2,640 2,310 2,280 5,750 30,900 50,100 52,500 53,400 19,000
1985 13,700 4,370 3,010 2,960 2,850 2,620 2,500 19,300 48,500 58,800 46,200 29,800
1986 16,300 4,850 3,740 3,280 2,930 2,500 2,850 23,000 44,600 55,000 43,600 32,000
1987 38,400 6,760 3,830 3,240 3,140 3,080 4,000 27,000 46,900 61,500 52,600 30,700
1988 13,100 7,320 4,980 4,330 3,980 3,890 4,480 35,300 60,100 62,400 44,300 29,100
1989 16,100 5,430 2,940 2,650 2,650 2,940 3,640 29,000 50,200 55,800 69,500 50,400
1990 24,100 7,170 3,640 3,470 3,400 3,720 8,340 53,100 63,400 52,100 46,100 46,600
1991 13,000 4,570 3,140 3,140 3,130 2,770 3,540 23,300 59,300 54,400 45,900 29,600
1992 14,800 5,540 4,890 4,290 3,890 3,960 8,410 22,400 47,100 52,000 36,800 15,400
1993 7,210 5,410 4,530 3,870 3,210 2,950 4,700 41,300 48,000 40,800 39,100 42,600
1994 20,100 6,240 4,650 3,730 3,210 2,710 6,100 30,400 57,100 44,100 39,000 18,900
1995 8,690 5,150 3,810 3,340 3,080 3,040 5,300 36,100 48,200 51,200 38,000 40,200
1996 12,800 4,920 2,550 2,190 2,070 1,910 2,380 13,300 32,800 33,400 35,700 21,100
1997 7,520 4,090 3,490 3,050 2,760 2,550 3,150 21,400 40,900 50,400 50,900 29,800
1998 8,490 3,600 2,870 2,550 2,440 2,330 3,420 20,500 50,600 52,400 47,800 35,600
1999 17,000 6,470 4,430 3,330 2,570 2,180 2,660 20,900 47,800 48,200 51,800 25,300
2000 15,100 6,610 4,220 3,230 2,830 2,620 3,320 25,600 61,000 58,200 36,400 33,600
2001 17,900 6,530 4,410 3,580 2,970 2,700 3,080 19,300 57,700 45,400 44,200 21,000
2002 9,330 4,850 3,420 2,750 2,510 2,290 2,340 23,400 34,600 38,200 46,600 33,900
2003 22,300 10,500 4,780 2,960 4,110 2,690 4,030 16,100 49,300 55,300 42,900 27,600
2004 16,300 4,600 3,250 2,600 2,240 1,880 5,120 46,400 51,100 42,400 37,300 12,700
2005 6,200 3,110 2,870 2,540 2,170 1,810 4,960 52,100 61,300 52,700 45,700 46,400
2006 16,600 3,910 2,650 2,470 2,450 2,400 2,730 30,900 45,400 47,600 56,300 25,300
2007 21,000 5,870 4,240 3,670 3,440 3,130 4,170 35,500 41,200 45,300 40,400 27,900
2008 9,700 6,020 5,220 3,320 2,360 2,400 2,990 24,400 44,000 44,900 40,400 30,100
2009 10,800 2,760 2,280 2,440 2,280 2,360 8,920 45,600 46,900 40,600 38,500 25,600
2010 14,100 5,200 3,320 2,600 2,380 2,290 3,340 40,700 42,100 53,300 41,800 33,100
Average 13,400 5,350 3,640 3,020 2,650 2,400 3,480 26,900 50,600 49,900 43,100 27,900
Maximum 38,400 12,000 6,740 6,160 4,460 3,960 8,920 53,100 89,000 81,100 69,500 50,400
Minimum 5,480 1,940 1,790 1,650 1,340 1,230 1,490 4,650 29,900 32,700 21,000 10,700
Median 12,700 5,140 3,580 2,960 2,570 2,330 2,990 25,900 48,800 48,800 43,000 27,900
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 21 February 2013
Table A-11 – Average Monthly Flow for Susitna River at Susitna Station for Pre-Project Conditions based on the USGS
Extended Record
WY Susitna River at Susitna Station
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 35,500 13,100 7,050 5,890 5,070 4,880 5,370 62,100 101,000 116,000 103,000 46,600
1951 21,800 6,690 6,120 5,680 5,210 4,930 8,680 75,300 105,000 116,000 102,000 107,000
1952 31,500 14,200 8,480 7,500 5,810 5,420 5,550 27,600 146,000 127,000 105,000 76,800
1953 46,000 19,400 7,750 6,120 5,210 5,210 8,790 99,500 131,000 105,000 107,000 81,700
1954 31,900 9,730 7,240 6,700 5,810 5,070 6,440 91,200 126,000 106,000 128,000 69,900
1955 31,200 14,100 9,410 8,270 6,970 6,120 6,410 51,100 137,000 132,000 122,000 76,600
1956 28,400 8,740 6,700 5,740 5,710 5,620 5,650 88,000 148,000 143,000 121,000 95,300
1957 33,500 16,200 10,000 7,750 7,240 6,410 6,410 70,500 138,000 118,000 107,000 103,000
1958 46,100 22,600 17,900 9,190 6,710 6,260 7,670 68,900 126,000 117,000 109,000 42,800
1959 27,600 10,400 7,340 7,100 6,710 5,740 6,530 78,900 118,000 124,000 139,000 85,400
1960 28,800 12,100 9,220 7,820 6,980 6,430 6,550 78,000 96,100 117,000 115,000 85,200
1961 33,500 12,100 11,100 10,000 7,670 7,970 11,100 87,900 132,000 122,000 109,000 79,800
1962 31,600 12,700 8,920 8,030 6,860 6,540 7,340 56,300 143,000 121,000 105,000 64,400
1963 26,800 10,900 8,160 7,240 6,770 5,860 5,490 71,300 117,000 141,000 103,000 58,700
1964 36,400 9,790 6,810 6,450 5,920 5,180 5,730 15,500 151,000 120,000 102,000 45,900
1965 33,600 14,300 10,700 7,930 7,130 6,560 6,840 37,400 122,000 130,000 110,000 103,000
1966 39,600 13,100 9,230 8,230 7,210 6,490 6,970 30,500 129,000 110,000 120,000 72,900
1967 35,600 9,770 8,060 7,050 6,380 5,960 6,020 28,600 109,000 121,000 124,000 77,500
1968 25,000 12,000 9,880 8,850 8,400 8,120 10,200 92,200 136,000 126,000 86,700 36,600
1969 15,900 7,990 6,370 5,780 5,460 5,400 8,180 66,500 104,000 96,600 52,100 25,000
1970 31,100 10,100 7,020 6,420 6,010 5,790 6,540 70,000 122,000 129,000 103,000 58,700
1971 25,300 15,400 10,500 7,590 6,060 5,490 6,030 35,600 147,000 130,000 126,000 56,400
1972 25,000 11,900 8,970 8,110 7,380 6,390 6,440 51,400 120,000 124,000 108,000 82,000
1973 37,500 15,100 9,570 8,060 7,090 6,430 6,720 47,800 115,000 105,000 90,200 45,800
1974 22,600 10,700 8,700 7,720 7,000 6,400 7,080 56,000 90,900 95,200 87,300 78,000
1975 19,500 10,400 9,420 8,600 7,800 7,050 6,870 47,500 129,000 136,000 91,400 77,700
1976 31,500 9,930 6,000 6,530 5,610 5,370 7,250 70,500 107,000 115,000 99,600 48,900
1977 30,100 18,300 13,100 10,100 8,910 6,770 6,230 56,200 166,000 144,000 125,000 83,800
1978 38,200 12,600 7,530 6,970 6,770 6,590 7,030 48,700 90,900 118,000 102,000 55,500
1979 36,800 15,000 9,310 8,820 7,950 7,030 8,680 81,300 120,000 142,000 128,000 74,300
1980 58,600 31,600 14,700 10,100 9,020 8,910 12,000 66,600 143,000 181,000 126,000 78,000
1981 35,000 16,200 8,520 7,770 7,590 6,180 10,400 83,600 109,000 153,000 160,000 67,200
APPENDIX A STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix A---Page 22 February 2013
WY Susitna River at Susitna Station cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 33,900 17,600 11,700 9,030 7,210 5,440 5,820 44,900 108,000 115,000 94,600 110,000
1983 34,000 15,200 9,890 8,370 8,420 7,120 7,680 62,100 104,000 103,000 108,000 54,900
1984 39,400 19,000 11,500 7,440 6,700 6,470 13,000 60,400 107,000 109,000 111,000 51,000
1985 30,800 11,000 8,230 7,970 6,950 6,500 6,820 45,700 113,000 135,000 109,000 84,100
1986 50,700 18,400 11,100 8,870 7,750 5,970 7,190 47,600 91,000 125,000 102,000 77,000
1987 88,500 17,500 9,350 7,790 7,500 7,350 9,860 65,400 109,000 139,000 120,000 73,500
1988 34,400 19,100 12,500 10,700 9,740 9,500 11,100 83,600 136,000 141,000 103,000 70,400
1989 41,400 13,800 7,000 6,240 6,230 7,000 8,900 70,300 115,000 127,000 155,000 116,000
1990 59,100 18,700 8,840 8,370 8,210 9,060 21,400 121,000 142,000 119,000 107,000 107,000
1991 33,700 11,400 7,500 7,500 7,480 6,560 8,620 56,500 134,000 124,000 106,000 71,700
1992 37,500 14,000 12,200 10,600 9,500 9,690 21,500 55,100 109,000 119,000 87,200 39,200
1993 18,800 13,700 11,300 9,470 7,700 7,030 12,500 105,000 123,000 108,000 101,000 116,000
1994 60,500 19,800 12,700 9,940 8,510 7,220 15,600 83,800 140,000 110,000 103,000 46,600
1995 25,300 13,700 9,980 8,370 7,590 7,520 12,100 89,400 120,000 124,000 96,700 98,500
1996 35,200 14,000 7,140 6,360 6,170 6,180 8,220 47,300 82,700 93,400 97,800 53,000
1997 18,900 10,800 9,340 8,250 7,300 6,410 8,150 50,100 97,400 122,000 123,000 69,500
1998 21,100 9,600 7,620 6,450 5,990 5,540 8,820 49,000 123,000 128,000 115,000 82,400
1999 40,500 16,500 11,700 8,910 6,510 5,020 6,600 48,400 116,000 115,000 123,000 58,600
2000 36,200 16,900 11,100 8,670 7,530 6,700 8,810 59,300 145,000 139,000 83,400 78,900
2001 42,300 16,700 11,600 9,540 8,000 7,040 8,210 47,000 139,000 107,000 108,000 56,000
2002 27,400 12,900 8,730 7,300 6,840 6,290 6,380 67,100 87,100 95,400 117,000 95,900
2003 66,800 31,500 13,300 7,070 9,340 6,680 12,800 50,700 121,000 134,000 106,000 66,200
2004 42,200 15,000 9,380 7,870 6,900 6,230 13,200 108,000 120,000 109,000 94,400 38,100
2005 26,300 11,600 8,780 7,980 7,060 7,250 19,000 134,000 151,000 129,000 113,000 119,000
2006 47,200 10,900 8,580 7,850 6,920 6,670 7,480 68,500 105,000 115,000 136,000 69,000
2007 65,300 18,000 10,100 8,120 7,050 6,230 10,400 69,400 89,300 111,000 104,000 79,100
2008 31,900 16,000 11,800 7,610 6,260 6,300 7,500 57,900 108,000 109,000 104,000 75,200
2009 31,800 9,320 7,830 7,730 6,970 6,860 18,300 107,000 113,000 102,000 93,000 64,300
2010 43,200 17,900 9,620 7,920 7,220 6,790 9,560 83,000 98,000 127,000 109,000 80,600
Average 36,000 14,400 9,510 7,910 7,080 6,510 8,990 66,100 120,000 122,000 109,000 72,800
Maximum 88,500 31,600 17,900 10,700 9,740 9,690 21,500 134,000 166,000 181,000 160,000 119,000
Minimum 15,900 6,690 6,000 5,680 5,070 4,880 5,370 15,500 82,700 93,400 52,100 25,000
Median 33,700 13,800 9,310 7,870 7,000 6,430 7,670 65,400 120,000 121,000 107,000 74,300
APPENDIX B. FLOW DURATION CURVES FOR PRE-PROJECT
CONDITIONS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 1 February 2013
Figure B-1 – Monthly Flow-duration Curves for October for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 2 February 2013
Figure B-2 – Monthly Flow-duration Curves for November for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 3 February 2013
Figure B-3 – Monthly Flow-duration Curves for December for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 4 February 2013
Figure B-4 – Monthly Flow-duration Curves for January for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 5 February 2013
Figure B-5 – Monthly Flow-duration Curves for February for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 6 February 2013
Figure B-6 – Monthly Flow-duration Curves for March for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 7 February 2013
Figure B-7 – Monthly Flow-duration Curves for April for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 8 February 2013
Figure B-8 – Monthly Flow-duration Curves for May for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 9 February 2013
Figure B-9 – Monthly Flow-duration Curves for June for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 10 February 2013
Figure B-10 – Monthly Flow-duration Curves for July for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 11 February 2013
Figure B-11 – Monthly Flow-duration Curves for August for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 12 February 2013
Figure B-12 – Monthly Flow-duration Curves for September for Mainstem Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 13 February 2013
Figure B-13 – Monthly Flow-duration Curves for October for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 14 February 2013
Figure B-14 – Monthly Flow-duration Curves for November for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 15 February 2013
Figure B-15 – Monthly Flow-duration Curves for December for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 16 February 2013
Figure B-16 – Monthly Flow-duration Curves for January for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 17 February 2013
Figure B-17 – Monthly Flow-duration Curves for February for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 18 February 2013
Figure B-18 – Monthly Flow-duration Curves for March for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 19 February 2013
Figure B-19 – Monthly Flow-duration Curves for April for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 20 February 2013
Figure B-20 – Monthly Flow-duration Curves for May for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 21 February 2013
Figure B-21 – Monthly Flow-duration Curves for June for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 22 February 2013
Figure B-22 – Monthly Flow-duration Curves for July for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 23 February 2013
Figure B-23 – Monthly Flow-duration Curves for August for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX B STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix B---Page 24 February 2013
Figure B-24 – Monthly Flow-duration Curves for September for Tributary Gages for Pre-Project Conditions based on the USGS Extended Record
APPENDIX C. FLOW EXCEEDENCE SUMMARY DATA (CFS) FOR PRE-
PROJECT CONDITIONS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX C STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix C---Page 1 February 2013
Table C-1 – Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Susitna River near
Denali based on the USGS Extended Record
Susitna River near Denali
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 110 391 219 160 100 87 50 36 218 2,400 4,310 2,260 900
95% 181 524 269 190 140 140 120 122 322 3,520 5,180 3,580 1,200
90% 200 600 300 215 190 150 140 150 520 4,090 5,750 4,200 1,440
75% 263 794 378 269 219 200 190 197 960 5,560 7,000 5,260 2,020
50% 650 1,100 471 310 260 227 207 243 2,380 7,630 8,400 7,040 3,070
25% 5,070 1,500 600 380 300 264 242 300 4,610 8,990 9,600 8,690 4,690
10% 8,500 2,350 740 440 340 300 290 438 7,210 10,100 11,500 10,500 6,990
5% 9,570 2,960 809 500 361 320 311 588 8,720 11,300 12,800 12,100 8,070
1% 12,700 5,200 1,000 580 440 340 323 1,240 9,550 14,000 17,100 15,800 9,850
Table C-2 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Maclaren River near
Paxson based on the USGS Extended Record
Maclaren River near Paxson
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 47 137 83 48 44 42 40 50 75 1,010 1,540 613 331
95% 60 194 98 70 60 50 47 50 110 1,370 1,810 1,240 428
90% 76 220 110 75 64 55 52 59 147 1,600 2,050 1,450 515
75% 100 280 139 100 85 76 64 72 280 2,160 2,410 1,820 715
50% 220 380 170 122 101 90 83 93 890 2,850 2,830 2,340 1,070
25% 1,820 531 210 140 117 100 96 110 1,700 3,380 3,290 2,900 1,640
10% 2,950 798 262 180 135 110 110 148 2,780 3,870 3,830 3,400 2,400
5% 3,400 1,010 300 198 150 126 120 190 3,260 4,200 4,350 3,890 2,870
1% 4,400 1,800 400 260 170 140 133 418 3,800 5,070 5,610 5,390 3,640
APPENDIX C STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix C---Page 2 February 2013
Table C-3 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Susitna River near
Cantwell based on the USGS Extended Record
Susitna River near Cantwell
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 440 1,100 700 548 440 414 400 431 750 7,130 9,440 5,760 2,980
95% 560 1,550 800 638 548 471 430 491 1,210 9,160 10,700 8,400 3,680
90% 694 1,900 950 720 578 500 465 530 1,650 10,400 11,500 9,370 4,320
75% 940 2,490 1,200 879 758 670 578 698 3,180 13,200 13,100 10,900 5,890
50% 2,050 3,300 1,550 1,120 940 819 758 879 8,190 15,900 15,200 13,300 7,770
25% 11,400 4,670 1,900 1,310 1,120 970 879 1,130 12,400 19,900 18,000 16,000 10,800
10% 16,500 6,310 2,200 1,500 1,300 1,060 1,060 1,490 17,000 24,000 20,800 18,800 14,000
5% 19,400 7,410 2,600 1,610 1,430 1,200 1,200 2,000 19,700 27,000 22,900 21,700 16,100
1% 25,700 10,100 3,230 2,090 1,700 1,500 1,500 4,320 23,700 34,400 27,500 30,000 20,800
Table C-4 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Susitna River at Gold
Creek based on the USGS Extended Record
Susitna River at Gold Creek
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 750 1,900 1,100 850 750 700 660 710 1,400 12,100 14,600 8,240 4,910
95% 960 2,710 1,400 1,100 950 800 750 830 2,100 14,900 16,400 12,900 6,000
90% 1,200 3,300 1,700 1,200 980 860 800 930 2,800 16,400 17,800 14,500 7,340
75% 1,600 4,200 2,100 1,600 1,400 1,200 1,000 1,200 5,000 20,000 20,000 17,000 9,560
50% 3,400 5,500 2,600 1,900 1,600 1,400 1,300 1,520 13,000 25,100 23,000 20,400 12,500
25% 17,800 7,790 3,100 2,200 1,900 1,690 1,500 1,820 20,000 30,500 26,900 24,000 16,800
10% 25,300 10,300 3,690 2,500 2,000 1,850 1,800 2,500 27,100 36,700 31,300 28,500 21,800
5% 29,800 12,000 4,200 2,700 2,200 2,000 1,900 3,300 31,000 41,100 34,500 32,700 25,000
1% 39,300 16,100 5,100 3,460 2,500 2,400 2,100 7,000 37,800 58,800 42,600 51,100 32,000
APPENDIX C STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix C---Page 3 February 2013
Table C-5 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Chulitna River near
Talkeetna based on the USGS Extended Record
Chulitna River near Talkeetna
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 820 1,700 1,100 1,000 950 820 730 750 1,200 9,600 13,800 9,410 4,310
95% 965 2,370 1,300 1,080 995 900 800 884 1,540 11,900 16,100 12,700 5,540
90% 1,040 2,790 1,440 1,100 1,010 942 877 933 2,100 13,500 17,300 14,000 6,460
75% 1,230 3,440 1,620 1,300 1,100 1,010 950 1,000 4,000 17,100 19,600 16,600 8,400
50% 2,840 4,780 2,110 1,500 1,280 1,130 1,070 1,170 8,940 21,800 22,700 20,000 11,500
25% 16,100 6,990 2,640 1,740 1,420 1,210 1,130 1,350 14,800 25,100 25,600 23,400 15,100
10% 23,400 9,820 3,230 2,100 1,600 1,400 1,230 1,810 21,400 28,600 30,000 26,900 20,900
5% 26,200 12,000 3,890 2,200 1,800 1,440 1,300 2,580 25,000 31,200 33,400 30,700 24,200
1% 33,700 19,100 5,400 2,920 2,000 1,930 2,060 5,190 30,600 39,000 39,100 40,000 31,400
Table C-6 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Talkeetna River near
Talkeetna based on the USGS Extended Record
Talkeetna River near Talkeetna
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 380 900 550 500 440 350 260 340 600 4,170 5,890 3,670 1,900
95% 450 1,200 661 520 460 400 350 390 800 5,310 6,830 5,600 2,600
90% 500 1,400 746 550 495 440 390 420 1,000 6,120 7,400 6,240 3,000
75% 621 1,770 900 661 550 480 440 488 2,000 7,940 8,280 7,250 3,800
50% 1,430 2,360 1,100 791 660 550 500 550 4,160 9,990 9,680 8,460 5,220
25% 7,240 3,400 1,310 900 720 600 540 682 7,200 12,800 11,400 10,200 7,110
10% 10,500 4,690 1,700 1,040 800 680 600 965 10,200 16,000 13,700 12,600 9,890
5% 12,800 5,640 2,000 1,100 855 750 700 1,350 13,200 18,600 15,900 15,000 12,000
1% 18,100 8,530 2,630 1,520 1,000 990 1,050 2,510 17,600 23,800 20,600 23,400 17,100
APPENDIX C STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix C---Page 4 February 2013
Table C-7 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Susitna River at
Sunshine based on the USGS Extended Record
Susitna River at Sunshine
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 1,740 5,280 2,820 2,340 2,030 1,570 1,390 1,560 3,060 29,700 38,000 21,000 12,000
95% 2,310 6,880 3,590 2,500 2,110 1,900 1,650 1,850 5,340 37,000 43,000 33,900 15,300
90% 2,830 8,120 4,100 2,830 2,370 2,120 1,920 2,030 6,990 40,800 46,400 38,000 18,000
75% 3,750 10,400 5,140 3,750 3,260 2,830 2,370 2,660 13,100 50,600 52,000 44,500 23,800
50% 8,220 13,600 6,100 4,520 3,700 3,280 2,930 3,520 31,100 63,500 58,600 52,900 32,000
25% 45,000 19,500 7,470 5,190 4,350 3,760 3,490 4,330 47,800 73,900 67,600 61,200 42,600
10% 64,000 26,300 9,150 5,840 4,780 4,330 3,920 5,900 65,800 85,100 76,800 71,400 56,200
5% 72,800 31,300 10,400 6,370 4,940 4,510 4,390 7,760 75,100 93,400 82,500 80,000 64,200
1% 91,200 45,000 13,000 8,490 5,620 4,990 4,790 15,700 85,100 119,000 97,600 111,000 80,300
Table C-8 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Willow Creek near
Willow based on the USGS Extended Record
Willow Creek near Willow
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 38 108 58 47 51 42 32 29 68 391 209 159 177
95% 51 141 80 65 60 49 34 38 92 461 288 266 223
90% 60 163 97 70 61 51 43 44 117 521 367 325 253
75% 80 203 119 88 71 60 50 55 195 711 491 421 328
50% 171 268 149 101 85 71 61 65 374 968 666 548 455
25% 526 373 171 121 94 80 68 78 624 1,320 912 737 693
10% 930 559 211 140 106 90 76 115 1,010 1,630 1,230 1,090 1,040
5% 1,240 708 249 150 112 96 80 161 1,310 1,850 1,400 1,480 1,290
1% 1,870 1,140 349 170 130 130 93 353 2,160 2,330 2,030 2,610 2,050
APPENDIX C STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix C---Page 5 February 2013
Table C-9 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Skwentna River near
Skwentna based on the USGS Extended Record
Skwentna River near Skwentna
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 600 1,460 700 650 600 585 596 600 970 8,080 9,610 5,730 3,030
95% 750 2,000 1,090 867 762 651 600 650 1,290 10,200 11,400 8,360 4,320
90% 850 2,400 1,240 900 800 700 636 700 1,960 11,500 12,400 9,520 4,860
75% 1,140 3,080 1,500 1,100 976 810 747 800 4,500 13,700 14,000 11,100 6,460
50% 2,660 4,200 1,950 1,350 1,100 1,000 873 1,090 8,880 16,600 16,000 13,500 8,520
25% 12,000 5,800 2,330 1,570 1,270 1,140 1,050 1,460 12,900 20,100 18,800 16,300 11,400
10% 17,200 7,800 2,900 1,880 1,530 1,380 1,300 2,200 17,800 23,600 22,000 19,900 14,700
5% 19,900 9,050 3,300 2,130 1,710 1,500 1,400 2,970 19,600 27,400 24,200 22,700 17,000
1% 26,400 13,400 4,460 2,900 2,800 1,950 1,470 5,630 24,600 37,000 29,600 29,400 22,200
Table C-10 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Yentna River near
Susitna Station based on the USGS Extended Record
Yentna River near Susitna Station
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 1,460 3,600 2,000 1,860 1,650 1,260 1,250 1,360 2,770 22,800 27,300 16,200 7,840
95% 1,910 5,380 2,850 2,280 1,720 1,670 1,400 1,600 3,420 29,800 33,900 24,900 11,900
90% 2,280 6,530 3,140 2,400 2,100 1,730 1,690 1,850 5,120 34,100 37,500 28,500 13,700
75% 2,970 8,300 3,990 2,970 2,570 2,280 1,910 2,150 12,100 40,800 42,800 34,200 18,600
50% 6,950 11,300 5,120 3,440 2,860 2,570 2,290 2,720 25,400 50,000 48,500 41,900 25,400
25% 36,500 16,300 6,230 4,200 3,420 3,050 2,800 3,800 39,000 58,700 55,400 49,700 35,200
10% 51,300 22,600 7,750 4,810 4,000 3,430 3,140 5,680 51,200 66,500 64,100 59,000 45,800
5% 58,700 27,300 8,770 5,590 4,380 3,960 3,810 7,590 56,700 73,600 70,100 67,100 51,100
1% 73,700 41,900 12,900 6,990 6,010 4,710 3,890 15,200 64,700 95,300 81,700 84,600 67,000
APPENDIX C STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix C---Page 6 February 2013
Table C-11 - Annual and Monthly Flow Exceedence Ordinates (cfs) for Pre-Project Conditions for Susitna River at
Susitna Station based on the USGS Extended Record
Susitna River at Susitna Station
Percentile Annual Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
99% 5,210 11,000 6,700 6,000 5,670 4,930 4,700 5,000 7,160 65,500 80,200 44,100 21,600
95% 5,840 15,000 7,750 6,280 5,810 5,340 5,070 5,400 10,400 77,000 90,800 70,900 33,100
90% 6,400 18,000 8,720 6,850 6,190 5,810 5,280 5,550 14,700 86,200 98,300 79,700 38,800
75% 7,710 23,500 10,700 7,840 7,000 6,380 5,800 6,120 32,800 102,000 108,000 92,400 50,800
50% 19,000 31,700 13,000 9,000 7,880 6,990 6,440 7,000 64,000 121,000 120,000 107,000 68,600
25% 94,000 42,900 16,700 10,700 8,570 7,530 7,000 9,210 95,200 136,000 133,000 123,000 90,300
10% 124,000 60,000 21,300 12,000 9,720 8,500 7,520 13,500 122,000 152,000 147,000 138,000 114,000
5% 138,000 70,000 25,000 13,300 10,300 9,200 9,000 19,000 135,000 161,000 157,000 153,000 125,000
1% 164,000 97,500 36,500 19,900 11,000 10,000 9,500 37,100 150,000 182,000 186,000 195,000 154,000
APPENDIX D. FLOOD FREQUENCY REGRESSION PLOTS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 1 February 2013
Figure D-1 – Susitna River near Denali regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 2 February 2013
Figure D-2 – Maclaren River near Paxson regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 3 February 2013
Figure D-3 – Susitna River near Cantwell regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 4 February 2013
Figure D-4 – Susitna River at Gold Creek regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 5 February 2013
Figure D-5 – Chulitna River near Talkeetna regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 6 February 2013
Figure D-6 – Talkeetna River near Talkeetna regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 7 February 2013
Figure D-7 – Susitna River at Sunshine regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 8 February 2013
Figure D-8 – Willow Creek near Willow regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 9 February 2013
Figure D-9 – Skwentna River near Skwentna regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 10 February 2013
Figure D-10 – Yentna River near Susitna Station regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX D STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix D---Page 11 February 2013
Figure D-11 – Susitna River at Susitna Station regression to extend the Pre-Project USGS available record annual peak data.
APPENDIX E. FLOOD FREQUENCY CURVES FOR PRE-PROJECT
CONDITIONS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 1 February 2013
Figure E-1 – Flood Frequency Curve for Susitna River near Denali for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 2 February 2013
Figure E-2 – Flood Frequency Curve for Maclaren River near Paxson for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 3 February 2013
Figure E-3 – Flood Frequency Curve for Susitna River near Cantwell for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 4 February 2013
Figure E-4 – Flood Frequency Curve for Susitna River at Gold Creek for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 5 February 2013
Figure E-5 – Flood Frequency Curve for Chulitna River near Talkeetna for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 6 February 2013
Figure E-6 – Flood Frequency Curve for Talkeetna River near Talkeetna for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 7 February 2013
Figure E-7 – Flood Frequency Curve for Susitna River at Sunshine for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 8 February 2013
Figure E-8 – Flood Frequency Curve for Willow Creek near Willow for Pre-Project Conditions based on the USGS Extended Record
High Outlier
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 9 February 2013
Figure E-9 – Flood Frequency Curve for Skwentna River near Skwentna for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 10 February 2013
Figure E-10 – Flood Frequency Curve for Yentna River near Susitna Station for Pre-Project Conditions based on the USGS Extended Record
APPENDIX E STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix E---Page 11 February 2013
Figure E-11 – Flood Frequency Curve for Susitna River at Susitna Station for Pre-Project Conditions based on the USGS Extended Record.
APPENDIX F. AVERAGE MONTHLY FLOW (CFS) BY WATER YEAR
FOR POST-PROJECT CONDITIONS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX F STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix F---Page 1 February 2013
Table F-1 – Average Monthly Flow for Susitna River at Gold Creek for Max LF OS-1 Conditions based on the HEC-
ResSim model
WY Susitna River at Gold Creek
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 7,580 7,900 8,570 9,030 9,760 7,810 7,390 8,320 9,370 9,610 9,200 7,210
1951 7,310 7,950 8,930 9,570 10,500 8,590 8,420 9,530 9,950 9,890 9,450 9,340
1952 7,610 8,170 8,970 9,510 10,200 8,350 7,940 7,990 11,700 10,200 9,430 8,020
1953 7,850 8,020 8,540 8,940 9,590 7,710 7,380 9,320 9,980 9,030 16,700 15,600
1954 7,630 7,780 8,570 9,060 9,710 7,800 7,410 9,140 9,740 9,160 16,200 13,500
1955 7,360 7,900 8,630 9,100 9,730 7,760 7,280 7,860 10,600 9,990 20,200 14,800
1956 7,440 7,760 8,550 9,060 9,810 7,900 7,450 9,340 11,100 14,800 24,900 18,500
1957 7,690 7,940 8,630 9,050 9,740 7,740 7,230 8,460 10,500 9,360 17,800 19,900
1958 9,010 8,050 8,750 8,950 9,490 7,560 7,110 8,130 9,750 9,320 19,300 7,770
1959 7,270 7,810 8,590 9,120 9,810 7,850 7,430 9,000 9,590 9,670 19,800 17,500
1960 8,500 7,910 8,640 9,100 9,690 7,770 7,270 8,810 8,830 9,610 9,890 19,700
1961 9,330 7,910 8,700 9,150 9,650 7,760 7,340 9,510 11,800 12,200 22,400 13,400
1962 8,350 7,810 8,580 9,050 9,700 7,750 7,240 7,350 12,300 20,100 23,600 16,300
1963 8,020 7,630 8,470 8,980 9,670 7,590 7,020 9,670 10,500 18,000 23,900 12,500
1964 8,100 7,800 8,540 8,980 9,670 7,770 7,300 7,190 13,000 12,100 16,600 9,820
1965 7,990 7,780 8,370 8,850 9,560 7,680 7,220 8,160 10,000 9,860 16,600 19,000
1966 9,860 7,930 8,720 9,170 9,850 7,960 7,590 8,800 12,500 9,330 9,890 11,500
1967 7,280 7,810 8,710 9,290 9,990 8,030 7,570 9,190 10,200 10,100 25,600 17,200
1968 7,340 7,790 8,590 9,140 9,790 7,870 7,340 9,390 11,000 12,200 17,400 9,310
1969 7,070 7,710 8,480 9,040 9,830 7,970 7,620 8,210 8,460 8,340 8,230 7,250
1970 8,290 9,340 10,900 5,270 771 772 1,030 6,960 10,600 10,400 9,780 7,910
1971 8,660 9,360 10,300 10,900 10,800 953 1,060 3,390 11,600 9,120 10,100 12,900
1972 7,450 7,850 8,750 9,260 9,870 7,900 7,310 11,600 12,200 15,500 19,500 12,700
1973 7,270 7,830 8,570 9,080 9,830 7,860 7,400 7,840 10,500 9,070 9,330 7,240
1974 7,240 7,930 8,820 9,450 10,300 8,430 8,140 9,780 9,500 9,480 9,140 8,130
1975 7,780 8,700 9,900 10,800 12,200 1,660 1,550 8,280 11,400 10,200 8,960 10,800
1976 9,050 7,730 8,450 8,980 9,710 7,820 7,410 8,450 9,830 9,100 9,130 6,960
1977 7,250 8,110 8,980 9,460 10,200 8,240 7,810 8,770 12,100 9,420 13,000 12,500
1978 8,580 7,990 8,660 9,030 9,600 7,710 7,180 8,040 9,080 9,250 8,790 7,170
1979 7,370 7,980 8,750 9,250 9,960 8,060 7,650 8,810 9,960 10,300 11,200 11,000
1980 8,340 8,100 8,610 8,980 9,560 7,690 7,190 8,090 10,800 14,700 21,600 13,400
1981 8,510 7,820 8,270 8,760 9,640 7,670 7,190 7,910 8,580 15,800 34,500 14,300
APPENDIX F STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix F---Page 2 February 2013
WY Susitna River at Gold Creek
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 8,160 8,110 8,450 8,970 9,750 7,820 7,500 8,470 9,960 9,200 11,300 17,900
1983 8,740 7,840 8,660 9,190 9,770 7,710 7,240 9,120 9,490 8,500 18,300 14,000
1984 9,180 7,810 8,490 8,900 9,490 7,560 7,000 8,030 9,410 8,950 19,900 9,680
1985 7,740 8,070 8,830 9,200 9,790 7,920 7,440 8,780 10,500 8,980 14,900 15,700
1986 8,810 7,990 8,740 9,210 9,900 7,890 7,450 8,460 8,590 8,200 8,880 8,520
1987 11,400 7,970 8,530 8,970 9,610 7,720 7,260 8,190 9,460 10,100 21,500 13,600
1988 7,450 7,840 8,550 9,080 9,740 7,850 7,350 9,010 10,300 11,100 19,500 14,300
1989 8,910 7,920 8,590 9,100 9,720 7,800 7,310 8,300 9,940 9,390 19,700 15,600
1990 9,320 7,910 8,570 9,050 9,720 7,830 7,670 10,100 11,200 23,700 23,700 25,600
1991 8,920 7,820 8,660 9,130 9,780 7,810 7,300 7,290 9,980 9,330 8,990 7,890
1992 7,510 7,860 8,690 9,170 9,790 7,910 7,430 7,320 9,740 9,840 9,220 8,980
1993 7,190 7,930 8,680 9,180 9,840 7,880 7,520 9,580 9,480 8,980 12,700 21,500
1994 10,800 7,960 8,650 9,030 9,630 7,690 7,410 8,410 10,500 10,700 18,700 9,870
1995 7,220 7,940 8,680 9,150 9,850 7,890 7,570 9,040 9,700 9,610 16,700 19,300
1996 8,350 7,870 8,530 9,020 9,730 7,820 7,370 7,500 9,090 9,110 9,220 7,800
1997 7,720 8,730 9,880 10,800 12,100 2,600 1,570 7,240 9,970 10,400 10,200 8,200
1998 7,580 8,350 9,450 10,200 11,300 9,480 2,450 6,360 10,600 10,400 9,680 8,480
1999 7,970 8,130 8,850 9,340 10,100 8,140 7,700 8,230 9,920 9,720 10,000 7,530
2000 7,680 7,960 8,620 9,060 9,770 7,850 7,390 8,160 10,800 11,500 16,500 15,400
2001 9,550 7,950 8,610 9,050 9,750 7,790 7,280 7,700 10,600 9,280 16,100 10,700
2002 7,270 7,890 8,630 9,090 9,780 7,840 7,360 8,250 9,020 9,150 9,820 8,310
2003 9,830 8,280 8,570 8,860 9,580 7,550 7,120 7,310 9,610 10,200 20,700 13,800
2004 9,760 7,820 8,590 9,040 9,710 7,790 7,550 9,960 9,570 9,000 16,800 7,510
2005 7,040 7,820 8,710 9,230 9,930 8,010 7,780 10,700 10,900 19,500 22,100 22,700
2006 9,860 7,760 8,530 9,040 9,750 7,810 7,350 8,850 9,700 9,460 20,800 12,600
2007 11,100 7,940 8,620 9,080 9,730 7,760 7,300 8,850 9,080 9,210 12,500 13,700
2008 7,430 7,990 8,780 9,090 9,630 7,790 7,320 8,190 9,380 9,450 9,140 12,200
2009 7,690 7,680 8,540 9,120 9,840 7,910 7,900 9,880 9,370 8,970 13,700 12,900
2010 8,130 7,860 8,560 9,010 9,690 7,750 7,330 9,310 9,080 9,960 18,100 16,500
Average 8,240 7,990 8,750 9,140 9,750 7,460 6,950 8,490 10,200 10,800 15,400 12,700
Maximum 11,400 9,360 10,900 10,900 12,200 9,480 8,420 11,600 13,000 23,700 34,500 25,600
Minimum 7,040 7,630 8,270 5,270 771 772 1,030 3,390 8,460 8,200 8,230 6,960
Median 7,970 7,910 8,630 9,080 9,750 7,810 7,350 8,450 9,960 9,610 16,200 12,600
APPENDIX F STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix F---Page 3 February 2013
Table F-2 – Average Monthly Flow for Susitna River at Sunshine for Max LF OS-1 Conditions based on the HEC-ResSim
model
WY Susitna River at Sunshine
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 16,700 11,200 10,200 10,200 10,700 8,680 8,360 24,400 38,200 43,200 39,200 18,800
1951 12,400 9,520 10,100 10,700 11,400 9,470 10,300 29,800 40,400 43,700 38,600 40,900
1952 15,300 11,700 11,200 11,400 11,400 9,410 8,980 14,900 56,500 48,500 40,400 29,100
1953 19,400 12,600 10,500 10,200 10,500 8,690 9,260 37,300 49,500 39,100 47,300 38,500
1954 15,300 10,400 10,300 10,600 10,900 8,730 8,820 34,200 47,400 39,700 54,100 32,900
1955 14,600 11,400 11,100 11,300 11,400 9,100 8,660 20,700 51,800 50,200 55,900 36,300
1956 14,200 10,100 10,000 10,200 10,900 9,030 8,510 34,200 56,500 58,400 61,700 45,900
1957 15,800 11,900 11,200 11,100 11,500 9,210 8,620 27,500 53,100 44,100 48,000 49,800
1958 20,900 13,300 12,900 11,400 11,000 8,960 8,890 26,300 47,900 43,200 51,600 18,400
1959 13,700 10,500 10,300 10,900 11,400 9,040 8,860 31,400 44,400 46,800 61,300 42,600
1960 17,700 11,600 11,300 11,400 11,400 9,230 8,780 30,900 31,600 42,600 45,300 49,600
1961 20,600 11,800 12,000 12,200 11,800 10,000 10,600 34,700 52,500 49,100 56,000 32,800
1962 16,600 11,300 11,100 11,400 11,500 9,480 9,280 24,500 66,200 58,600 59,100 39,900
1963 17,400 11,200 10,900 10,900 11,500 8,820 7,950 34,800 50,100 64,600 59,300 30,500
1964 17,100 10,600 10,300 10,200 10,800 8,630 8,120 12,100 65,800 47,600 45,200 24,300
1965 18,300 12,500 11,000 10,700 11,200 9,250 9,070 23,100 48,600 51,100 51,300 51,100
1966 24,100 12,000 11,200 11,300 11,600 9,570 9,470 20,200 55,700 41,800 45,500 30,800
1967 14,700 10,400 10,900 11,300 11,900 9,700 9,060 28,300 49,500 49,800 69,000 43,100
1968 14,600 11,600 11,600 11,900 12,400 10,400 10,200 34,500 55,600 51,800 45,500 23,900
1969 12,700 10,200 9,920 10,300 11,000 9,240 9,450 23,500 30,400 34,200 22,300 14,600
1970 13,000 11,500 12,400 7,050 2,080 2,040 2,610 22,700 38,900 46,600 41,700 25,700
1971 17,600 14,700 13,600 13,000 12,700 2,290 2,600 9,450 57,400 47,100 54,300 35,400
1972 16,600 12,300 11,800 12,000 12,300 10,000 9,290 33,700 56,100 53,100 52,000 37,400
1973 17,500 11,800 11,000 11,100 11,700 9,550 9,030 20,900 50,100 38,000 42,000 21,600
1974 13,100 10,600 10,700 11,100 11,800 9,810 9,660 30,900 38,900 39,100 35,900 26,700
1975 14,000 11,600 12,100 13,000 14,100 3,750 3,440 26,700 55,500 51,500 39,100 37,600
1976 20,500 10,500 10,000 10,500 11,200 9,290 9,290 24,300 46,700 40,500 39,800 17,900
1977 13,300 11,800 12,400 11,900 12,200 10,200 9,820 25,500 62,200 44,600 43,400 33,300
1978 20,500 12,400 11,800 11,600 11,700 9,660 9,180 22,500 38,000 44,400 35,100 20,300
1979 13,800 11,700 11,400 11,500 11,900 9,880 9,750 31,300 49,000 53,500 42,500 26,900
1980 20,000 14,200 11,700 11,500 11,800 9,840 9,990 25,500 51,200 59,000 52,600 33,200
1981 19,200 12,300 10,700 11,200 11,900 9,700 9,640 27,200 39,800 67,100 81,800 33,700
APPENDIX F STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix F---Page 4 February 2013
WY Susitna River at Sunshine cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 17,200 12,000 10,500 10,800 11,500 9,410 9,480 21,300 46,500 47,800 41,800 49,100
1983 18,400 11,600 11,800 12,200 12,500 9,570 9,470 25,100 43,000 42,900 54,000 30,900
1984 22,500 13,000 11,700 11,800 12,100 10,200 9,720 20,700 41,600 44,400 58,500 24,600
1985 14,500 11,300 11,200 11,800 12,000 10,000 9,530 22,600 45,100 50,700 50,100 40,900
1986 18,900 11,500 11,000 11,300 11,700 9,440 8,940 18,000 35,400 42,300 37,600 30,900
1987 35,500 14,000 11,700 11,400 11,900 9,860 10,100 27,400 44,500 51,000 55,700 34,200
1988 14,900 11,500 11,200 11,500 11,900 9,910 9,380 32,200 50,500 48,800 50,000 35,200
1989 19,200 12,000 11,500 11,600 11,900 9,980 9,680 24,800 49,300 44,100 57,300 43,300
1990 23,200 12,800 11,500 11,900 12,500 10,900 13,900 46,700 55,700 58,300 58,200 62,700
1991 18,400 10,900 11,200 11,400 11,700 9,550 9,550 22,000 50,200 43,600 35,900 25,000
1992 15,300 10,600 11,000 11,300 11,800 10,100 9,950 16,300 46,400 48,800 41,600 24,400
1993 13,100 11,900 11,600 11,600 12,000 9,890 10,700 41,300 47,400 41,100 42,600 57,300
1994 28,200 13,300 11,900 11,700 12,000 9,650 11,300 32,500 53,700 43,300 49,500 23,000
1995 13,600 11,500 11,300 11,400 11,900 10,000 10,500 35,100 45,800 47,800 45,300 48,600
1996 17,900 11,600 10,300 10,600 11,300 9,410 9,480 20,700 33,000 36,400 38,300 22,600
1997 13,800 12,100 12,600 13,300 14,300 4,890 3,980 22,800 41,400 49,700 50,300 31,100
1998 14,400 11,300 11,700 12,200 13,100 11,200 5,300 21,300 50,600 51,700 47,100 35,100
1999 21,300 13,400 12,400 12,100 12,100 9,760 9,660 23,700 47,000 46,700 50,900 26,700
2000 19,400 13,400 12,000 11,700 12,100 9,970 10,000 26,900 58,800 57,600 43,900 40,900
2001 23,700 13,300 12,200 12,000 12,200 10,000 9,750 21,700 53,500 41,200 48,800 26,700
2002 14,400 11,300 10,900 11,000 11,600 9,510 8,970 28,100 34,600 37,200 45,300 36,600
2003 29,100 16,600 12,100 10,800 12,000 9,360 10,300 21,200 46,600 51,300 52,600 33,100
2004 21,400 12,000 11,100 11,100 11,500 9,390 10,700 42,000 46,000 41,700 44,600 18,000
2005 14,400 11,100 11,000 11,300 11,700 9,860 12,600 52,300 58,500 58,800 56,200 59,000
2006 23,500 10,700 10,700 11,100 11,600 9,580 9,310 28,700 41,200 44,500 62,300 32,800
2007 30,300 12,800 11,200 11,300 11,700 9,530 9,970 28,300 35,300 42,200 43,700 36,800
2008 16,000 12,100 11,700 11,200 11,200 9,470 9,290 24,100 41,700 41,800 40,700 33,800
2009 16,300 10,200 10,500 11,100 11,600 9,740 12,200 41,900 44,000 39,300 40,800 31,600
2010 19,900 12,800 11,100 11,100 11,600 9,550 9,750 33,200 37,900 48,700 50,200 40,700
Average 18,000 11,900 11,300 11,300 11,600 9,190 9,160 27,400 47,600 47,200 48,400 34,100
Maximum 35,500 16,600 13,600 13,300 14,300 11,200 13,900 52,300 66,200 67,100 81,800 62,700
Minimum 12,400 9,520 9,920 7,050 2,080 2,040 2,600 9,450 30,400 34,200 22,300 14,600
Median 17,200 11,700 11,200 11,300 11,700 9,550 9,470 26,300 47,400 46,700 47,300 33,200
APPENDIX F STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix F---Page 5 February 2013
Table F-3 – Average Monthly Flow for Susitna River at Susitna Station for Max LF OS-1 Conditions based on the HEC-
ResSim model
WY Susitna River at Susitna Station
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1950 37,200 18,500 14,100 13,900 14,100 12,000 11,900 58,400 90,800 102,000 92,900 45,600
1951 25,300 13,400 13,900 14,300 14,900 12,800 15,400 70,400 94,400 103,000 92,100 95,700
1952 33,800 19,600 15,500 15,400 15,100 13,000 12,600 29,500 125,000 111,000 94,100 70,500
1953 45,800 24,000 14,500 14,000 14,000 12,200 14,500 89,200 113,000 94,200 103,000 82,500
1954 34,100 15,500 14,200 14,500 14,500 12,200 12,600 82,500 110,000 94,700 118,000 71,300
1955 33,200 19,300 15,900 15,600 15,300 12,800 12,500 49,300 117,000 115,000 116,000 77,900
1956 31,100 14,600 13,900 13,800 14,600 12,600 12,100 79,200 125,000 126,000 122,000 95,600
1957 35,700 21,200 16,500 15,100 15,500 13,000 12,400 64,500 119,000 104,000 104,000 104,000
1958 47,400 26,700 23,400 16,200 14,900 12,700 13,200 63,600 110,000 103,000 106,000 43,200
1959 30,100 16,100 14,300 14,800 15,200 12,700 12,700 71,300 104,000 109,000 127,000 87,100
1960 31,000 17,200 15,600 15,100 15,200 13,100 12,500 70,500 89,500 104,000 102,000 84,400
1961 35,500 17,100 17,000 16,700 15,600 14,000 15,700 79,600 114,000 109,000 110,000 80,000
1962 34,300 17,900 15,300 15,200 15,100 13,000 12,900 50,300 112,000 115,000 106,000 65,300
1963 28,200 15,800 14,600 14,600 15,000 12,500 11,700 61,000 102,000 124,000 103,000 59,200
1964 38,200 15,400 13,800 14,400 14,600 12,300 12,300 17,500 114,000 109,000 102,000 46,400
1965 35,400 19,400 17,800 15,800 15,900 13,400 12,700 31,700 106,000 112,000 105,000 102,000
1966 42,900 19,000 16,200 16,000 15,800 13,200 12,800 29,100 108,000 99,100 108,000 72,900
1967 38,900 16,000 15,200 14,800 15,000 12,900 12,400 21,700 90,100 104,000 117,000 78,400
1968 27,600 17,500 16,400 16,000 16,300 14,200 15,600 84,700 116,000 111,000 87,400 37,500
1969 19,200 14,100 13,900 14,100 14,600 12,600 14,200 63,400 96,700 88,600 51,800 27,100
1970 36,200 18,200 17,000 11,200 6,020 5,780 6,430 65,000 113,000 117,000 93,300 57,700
1971 28,700 21,400 18,400 17,100 16,200 5,500 5,980 34,800 125,000 115,000 104,000 55,000
1972 26,700 16,700 15,100 15,100 15,200 12,500 12,000 40,100 97,900 117,000 108,000 82,500
1973 40,100 20,800 16,600 16,000 15,700 13,400 13,100 47,000 97,300 95,400 79,200 44,300
1974 26,100 17,100 16,400 16,300 16,600 14,200 14,200 48,900 83,000 85,800 80,200 74,200
1975 23,700 17,400 17,600 17,900 18,500 7,620 6,780 39,600 108,000 118,000 82,600 72,000
1976 33,300 15,800 13,300 14,500 14,400 12,300 13,200 66,000 92,300 105,000 89,300 49,000
1977 33,600 23,700 19,600 17,700 17,500 13,600 12,300 51,600 140,000 131,000 119,000 83,500
1978 39,600 17,200 13,500 14,000 14,700 12,800 12,500 44,500 80,700 106,000 94,800 54,200
1979 39,300 20,500 16,300 16,700 16,600 14,000 14,800 75,500 105,000 124,000 119,000 74,800
1980 59,700 35,600 20,800 17,400 17,100 15,300 17,500 61,800 124,000 163,000 128,000 78,200
1981 36,000 20,500 14,800 14,500 15,300 12,300 15,500 74,600 97,600 134,000 156,000 68,400
APPENDIX F STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix F---Page 6 February 2013
WY Susitna River at Susitna Station cont.
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1982 34,700 22,500 18,300 16,300 15,500 12,000 11,500 39,700 91,800 99,600 90,900 110,000
1983 36,200 20,500 16,100 15,300 16,200 13,200 13,000 55,800 88,700 90,800 101,000 55,800
1984 40,600 23,800 17,600 14,300 14,200 12,200 18,200 55,300 89,400 94,400 111,000 51,700
1985 32,900 16,000 14,600 15,200 15,200 12,800 12,300 42,600 96,900 117,000 104,000 84,200
1986 52,900 23,800 17,900 16,400 16,100 12,500 13,000 43,600 79,500 112,000 93,400 72,700
1987 87,400 22,100 15,900 15,200 15,600 13,600 15,000 60,200 94,900 119,000 120,000 74,100
1988 36,000 24,500 19,400 18,200 18,000 15,900 16,900 74,600 116,000 126,000 103,000 71,500
1989 42,800 18,800 13,500 13,400 14,200 13,100 14,000 64,300 98,800 113,000 152,000 116,000
1990 60,800 23,700 15,500 15,700 16,200 15,100 24,600 105,000 120,000 120,000 107,000 107,000
1991 36,100 16,800 13,900 14,700 15,500 12,800 14,200 57,300 118,000 112,000 97,500 67,200
1992 39,300 19,500 18,600 17,800 17,500 15,800 26,800 55,700 95,800 103,000 75,500 38,300
1993 21,600 18,900 17,800 16,800 15,800 13,300 17,300 93,400 110,000 98,000 95,000 117,000
1994 61,700 24,600 18,800 16,900 16,400 13,400 19,600 77,400 119,000 99,500 103,000 47,500
1995 28,000 18,900 16,500 15,700 15,700 13,800 16,700 80,500 104,000 109,000 94,900 98,800
1996 37,400 19,300 14,200 14,100 14,700 13,000 14,200 47,800 76,100 86,400 90,100 50,700
1997 23,200 17,600 17,400 17,400 17,900 7,930 7,980 47,100 88,200 108,000 109,000 64,500
1998 24,900 16,200 15,400 15,200 15,900 13,800 9,640 44,900 109,000 112,000 102,000 74,700
1999 41,000 21,700 18,300 16,600 15,200 12,000 12,800 47,000 102,000 101,000 108,000 54,900
2000 37,100 21,800 17,700 16,100 15,800 13,200 14,400 55,400 124,000 121,000 83,800 78,700
2001 44,300 21,600 18,100 16,800 16,200 13,400 13,800 45,100 118,000 94,100 103,000 56,800
2002 29,900 18,300 15,400 14,900 15,200 12,900 12,400 63,400 79,800 86,300 103,000 87,900
2003 65,900 34,500 19,300 14,300 16,700 12,800 17,600 49,600 106,000 115,000 106,000 66,900
2004 44,000 20,400 16,100 15,500 15,400 13,000 17,800 93,600 104,000 98,400 93,500 39,400
2005 30,100 17,700 15,800 15,800 15,800 14,300 23,700 118,000 127,000 121,000 113,000 119,000
2006 49,400 16,600 15,500 15,500 15,300 13,200 13,300 61,100 91,400 102,000 125,000 69,800
2007 66,300 22,900 16,400 15,200 14,900 12,300 15,300 60,800 78,700 98,300 97,700 79,400
2008 34,400 20,800 17,700 14,900 14,600 12,800 13,100 54,000 96,300 95,900 94,200 72,900
2009 34,100 15,500 15,000 15,500 15,500 13,500 21,200 93,600 99,800 92,000 88,000 65,300
2010 44,300 23,100 16,300 15,500 15,600 13,300 14,900 72,300 86,900 109,000 107,000 82,100
Average 38,100 19,800 16,300 15,500 15,400 12,700 14,100 60,300 104,000 108,000 103,000 72,100
Maximum 87,400 35,600 23,400 18,200 18,500 15,900 26,800 118,000 140,000 163,000 156,000 119,000
Minimum 19,200 13,400 13,300 11,200 6,020 5,500 5,980 17,500 76,100 85,800 51,800 27,100
Median 36,000 19,000 16,100 15,400 15,500 13,000 13,200 60,200 104,000 109,000 103,000 72,700
APPENDIX G. MONTHLY FLOW DURATION CURVES FOR POST-
PROJECT CONDITIONS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 1 February 2013
Figure G-1 – Monthly Flow-duration Curves for October for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 2 February 2013
Figure G-2 – Monthly Flow-duration Curves for November for three Mainsem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 3 February 2013
Figure G-3 – Monthly Flow-duration Curves for December for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 4 February 2013
Figure G-4 – Monthly Flow-duration Curves for January for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 5 February 2013
igure G-5 – Monthly Flow-duration Curves for February for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 6 February 2013
Figure G-6 – Monthly Flow-duration Curves for March for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 7 February 2013
Figure G-7 – Monthly Flow-duration Curves for April for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 8 February 2013
Figure G-8 – Monthly Flow-duration Curves for May for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 9 February 2013
Figure G-9 – Monthly Flow-duration Curves for June for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 10 February 2013
Figure G-10 – Monthly Flow-duration Curves for July for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 11 February 2013
Figure G-11 – Monthly Flow-duration Curves for August for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX G STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix G---Page 12 February 2013
Figure G-12 – Monthly Flow-duration Curves for September for three Mainstem Gages for Max LF OS-1 Conditions based on the HEC-ResSim Model
APPENDIX H. MONTHLY FLOW DURATION COMPARISON FOR PRE-
PROJECT AND POST-PROJECT CONDITIONS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 1 February 2013
Figure H-1 – Monthly Flow-duration Curves for October to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 2 February 2013
Figure H-2 – Monthly Flow-duration Curves for November to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 3 February 2013
Figure H-3 – Monthly Flow-duration Curves for December to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 4 February 2013
Figure H-4 – Monthly Flow-duration Curves for January to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 5 February 2013
Figure H-5 – Monthly Flow-duration Curves for February to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 6 February 2013
Figure H-6 – Monthly Flow-duration Curves for March to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 7 February 2013
Figure H-7 – Monthly Flow-duration Curves for April to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 8 February 2013
Figure H-8 – Monthly Flow-duration Curves for May to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 9 February 2013
Figure H-9 – Monthly Flow-duration Curves for June to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 10 February 2013
Figure H-10 – Monthly Flow-duration Curves for July to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 11 February 2013
Figure H-11 – Monthly Flow-duration Curves for August to compare Pre-Project and Max LF OS-1 Conditions
APPENDIX H STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix H---Page 12 February 2013
Figure H-.12 – Monthly Flow-duration Curves for September to compare Pre-Project and Max LF OS-1 Conditions.
APPENDIX I. MONTHLY FLOW EXCEEDENCE COMPARISON (CFS)
FOR PRE-PROJECT AND POST-PROJECT CONDITIONS
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX I STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix I---Page 1 February 2013
Table I-1 – Monthly Flow Exceedence Ordinate (cfs) Comparison for Pre-Project and Max LF OS-1 Conditions at the
Proposed Watana Dam Site
Watana Dam
Perce
ntile
Oct Nov Dec Jan Feb Mar
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
99% 1,540 5,440 924 6,750 696 6,510 618 656 588 597 532 643
95% 2,170 5,640 1,120 6,830 875 6,990 756 7,670 635 7,960 595 1,120
90% 2,610 5,890 1,340 6,900 981 7,640 795 7,910 750 8,250 643 6,650
75% 3,410 6,320 1,680 7,090 1,210 8,070 1,060 8,420 957 8,580 807 6,990
50% 4,460 6,680 2,100 7,540 1,520 8,460 1,280 8,910 1,120 9,360 1,040 7,590
25% 6,300 7,450 2,510 7,770 1,770 8,990 1,520 9,260 1,320 10,400 1,200 7,930
10% 8,390 8,230 2,950 8,010 1,980 9,740 1,640 9,790 1,450 11,100 1,440 8,270
5% 9,740 9,450 3,400 8,360 2,170 9,960 1,790 10,300 1,600 11,400 1,520 8,540
1% 13,000 12,600 4,220 9,170 2,820 11,300 2,030 11,500 1,930 12,800 1,700 9,260
Perce
ntile
Apr May Jun Jul Aug Sep
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
99% 581 776 1,150 2,010 10,100 4,040 12,300 4,370 6,790 4,650 3,970 4,830
95% 694 1,150 1,690 4,760 12,100 4,400 13,700 4,670 10,700 4,950 4,960 5,170
90% 755 5,910 2,260 5,120 13,600 4,670 14,800 4,930 12,100 5,220 5,910 5,520
75% 956 6,700 4,090 5,610 16,700 5,230 16,700 5,310 14,000 5,750 7,860 6,090
50% 1,220 7,050 10,700 6,220 20,700 5,680 19,200 5,700 17,000 10,400 10,100 8,710
25% 1,520 7,470 16,400 6,690 25,200 6,100 22,600 6,150 19,900 17,200 13,800 12,500
10% 2,010 7,750 22,200 7,040 30,400 6,620 26,100 7,440 23,600 21,400 17,900 17,200
5% 2,650 7,940 25,000 7,290 34,100 6,890 28,700 19,300 27,000 24,600 20,600 19,900
1% 5,680 8,450 30,800 7,820 49,200 7,430 35,200 26,000 42,200 31,000 26,200 26,000
APPENDIX I STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix I---Page 2 February 2013
Table I-2 – Monthly Flow Exceedence Ordinate (cfs) Comparison for Pre-Project and Max LF OS-1 Conditions for the
Susitna River at Gold Creek
Susitna River at Gold Creek
Perce
ntile
Oct Nov Dec Jan Feb Mar
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
99% 1,900 6,440 1,100 7,140 850 6,880 750 7,070 700 795 660 800
95% 2,710 6,710 1,400 7,250 1,100 7,210 950 7,880 800 8,160 750 1,400
90% 3,300 6,920 1,700 7,330 1,200 7,660 980 8,220 860 8,500 800 6,900
75% 4,200 7,300 2,100 7,690 1,600 8,240 1,400 8,720 1,200 8,850 1,000 7,250
50% 5,500 7,730 2,600 8,010 1,900 8,740 1,600 9,190 1,400 9,800 1,300 7,850
25% 7,790 8,390 3,100 8,230 2,200 9,230 1,900 9,560 1,690 10,700 1,500 8,210
10% 10,300 10,100 3,690 8,450 2,500 9,760 2,000 10,300 1,850 11,400 1,800 8,620
5% 12,000 12,000 4,200 8,760 2,700 10,200 2,200 10,600 2,000 11,700 1,900 9,040
1% 16,100 15,900 5,100 9,610 3,460 11,300 2,500 11,700 2,400 13,200 2,100 9,650
Perce
ntile
Apr May Jun Jul Aug Sep
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
99% 710 952 1,400 2,240 12,100 7,980 14,600 7,880 8,240 7,900 4,910 6,200
95% 830 1,420 2,100 6,200 14,900 8,480 16,400 8,380 12,900 8,420 6,000 6,730
90% 930 6,250 2,800 6,620 16,400 8,700 17,800 8,600 14,500 8,730 7,340 7,170
75% 1,200 6,970 5,000 7,460 20,000 9,200 20,000 9,000 17,000 9,260 9,560 8,150
50% 1,520 7,390 13,000 8,300 25,100 9,890 23,000 9,480 20,400 12,600 12,500 11,000
25% 1,820 7,750 20,000 9,560 30,500 10,800 26,900 10,300 24,000 20,300 16,800 15,500
10% 2,500 7,990 27,100 10,800 36,700 11,900 31,300 12,000 28,500 25,600 21,800 21,100
5% 3,300 8,210 31,000 11,600 41,100 12,800 34,500 22,400 32,700 29,500 25,000 24,200
1% 7,000 8,730 37,800 13,300 58,800 16,500 42,600 29,700 51,100 39,600 32,000 32,200
APPENDIX I STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix I---Page 3 February 2013
Table I-3 – Monthly Flow Exceedence Ordinate (cfs) Comparison for Pre-Project and Max LF OS-1 Conditions for the
Susitna River at Sunshine
Susitna River at Sunshine
Perce
ntile
Oct Nov Dec Jan Feb Mar
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
99% 5,280 11,000 2,820 9,300 2,340 8,880 2,030 8,840 1,570 2,110 1,390 2,080
95% 6,880 11,800 3,590 9,920 2,500 9,590 2,110 9,810 1,900 9,760 1,650 3,270
90% 8,120 12,400 4,100 10,300 2,830 10,000 2,370 10,200 2,120 10,100 1,920 8,290
75% 10,400 13,500 5,140 10,900 3,750 10,600 3,260 10,700 2,830 10,700 2,370 8,920
50% 13,600 15,800 6,100 11,600 4,520 11,300 3,700 11,400 3,280 11,700 2,930 9,510
25% 19,500 20,200 7,470 12,500 5,190 11,900 4,350 11,900 3,760 12,700 3,490 10,000
10% 26,300 26,800 9,150 13,800 5,840 12,500 4,780 12,600 4,330 13,500 3,920 10,600
5% 31,300 31,700 10,400 14,700 6,370 13,000 4,940 13,100 4,510 14,000 4,390 11,100
1% 45,000 42,900 13,000 16,500 8,490 14,000 5,620 13,900 4,990 15,100 4,790 11,700
Perce
ntile
Apr May Jun Jul Aug Sep
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
99% 1,560 2,360 3,060 5,400 29,700 26,400 38,000 32,000 21,000 21,900 12,000 13,800
95% 1,850 3,360 5,340 9,710 37,000 31,100 43,000 35,000 33,900 31,400 15,300 15,900
90% 2,030 7,850 6,990 10,700 40,800 33,400 46,400 37,400 38,000 34,900 18,000 18,300
75% 2,660 8,700 13,100 14,600 50,600 39,800 52,000 41,100 44,500 39,500 23,800 23,300
50% 3,520 9,320 31,100 25,900 63,500 48,000 58,600 45,800 52,900 46,000 32,000 31,300
25% 4,330 9,890 47,800 36,900 73,900 54,100 67,600 51,800 61,200 55,100 42,600 41,400
10% 5,900 10,700 65,800 48,500 85,100 60,400 76,800 58,200 71,400 64,800 56,200 54,300
5% 7,760 11,600 75,100 54,900 93,400 65,000 82,500 63,900 80,000 73,300 64,200 62,000
1% 15,700 17,000 85,100 60,400 119,000 77,200 97,600 77,000 111,000 97,800 80,300 80,300
APPENDIX I STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix I---Page 4 February 2013
Table I-4 – Monthly Flow Exceedence Ordinate (cfs) Comparison for Pre-Project and Max LF OS-1 Conditions for the
Susitna River at Susitna Station
Susitna River at Susitna Station
Perce
ntile
Oct Nov Dec Jan Feb Mar
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
99% 11,000 16,500 6,700 13,200 6,000 12,500 5,670 11,900 4,930 6,020 4,700 5,450
95% 15,000 19,600 7,750 14,000 6,280 13,300 5,810 13,400 5,340 13,200 5,070 7,000
90% 18,000 21,900 8,720 14,800 6,850 13,800 6,190 13,900 5,810 13,600 5,280 11,500
75% 23,500 26,700 10,700 16,500 7,840 14,800 7,000 14,500 6,380 14,400 5,800 12,300
50% 31,700 33,600 13,000 18,500 9,000 16,000 7,880 15,400 6,990 15,500 6,440 12,900
25% 42,900 43,800 16,700 21,800 10,700 17,600 8,570 16,400 7,530 16,600 7,000 13,700
10% 60,000 60,200 21,300 25,800 12,000 18,800 9,720 17,500 8,500 17,600 7,520 14,600
5% 70,000 70,600 25,000 29,200 13,300 19,700 10,300 18,100 9,200 18,400 9,000 15,300
1% 97,500 97,000 36,500 40,900 19,900 25,400 11,000 19,000 10,000 19,700 9,500 16,300
Perce
ntile
Apr May Jun Jul Aug Sep
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
Pre-
Project
Max LF
OS-1
99% 5,000 5,760 7,160 10,100 65,500 58,200 80,200 73,700 44,100 45,200 21,600 22,900
95% 5,400 6,880 10,400 14,000 77,000 69,500 90,800 81,700 70,900 68,900 33,100 34,200
90% 5,550 11,300 14,700 17,400 86,200 77,400 98,300 88,100 79,700 76,600 38,800 39,400
75% 6,120 12,100 32,800 32,700 102,000 90,400 108,000 97,600 92,400 88,400 50,800 50,900
50% 7,000 12,900 64,000 57,700 121,000 106,000 120,000 107,000 107,000 102,000 68,600 68,000
25% 9,210 14,700 95,200 85,800 136,000 117,000 133,000 118,000 123,000 116,000 90,300 88,800
10% 13,500 18,100 122,000 106,000 152,000 128,000 147,000 129,000 138,000 129,000 114,000 112,000
5% 19,000 23,000 135,000 116,000 161,000 134,000 157,000 139,000 153,000 144,000 125,000 123,000
1% 37,100 39,000 150,000 128,000 182,000 149,000 186,000 162,000 195,000 188,000 154,000 152,000
APPENDIX J. ANNUAL AND MONTHLY STAGE EXCEEDANCE
CURVES (PRE-PROJECT AND MAXIMUM LOAD FOLLOWING OS-1
CONDITIONS) FOR SUNSHINE GAGE LOCATION AND SUSITNA
STATION GAGE LOCATION
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 1 February 2013
Figure J-1 - Annual Stage Exceedence Curves for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 2 February 2013
Figure J-2 - Monthly Stage Exceedence Curves for October for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 3 February 2013
Figure J-3 - Monthly Stage Exceedence Curves for November for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 4 February 2013
Figure J-4 - Monthly Stage Exceedence Curves for December for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 5 February 2013
Figure J-5 - Monthly Stage Exceedence Curves for January for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 6 February 2013
Figure J-6 - Monthly Stage Exceedence Curves for February for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 7 February 2013
Figure J-7 - Monthly Stage Exceedence Curves for March for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 8 February 2013
Figure J-8 - Monthly Stage Exceedence Curves for April for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 9 February 2013
Figure J-9 - Monthly Stage Exceedence Curves for May for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 10 February 2013
Figure J-10 - Monthly Stage Exceedence Curves for June for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 11 February 2013
Figure J-11 - Monthly Stage Exceedence Curves for July for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 12 February 2013
Figure J-12 - Monthly Stage Exceedence Curves for August for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 13 February 2013
Figure J-13 - Monthly Stage Exceedence Curves for September for pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 14 February 2013
Figure J-14 - Annual Stage Exceedence Curves for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 15 February 2013
Figure J-15 - Monthly Stage Exceedence Curves for October for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 16 February 2013
Figure J-16 - Monthly Stage Exceedence Curves for November for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 17 February 2013
Figure J-17 - Monthly Stage Exceedence Curves for December for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 18 February 2013
Figure J-18 - Monthly Stage Exceedence Curves for January for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 19 February 2013
Figure J-19 - Monthly Stage Exceedence Curves for February for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 20 February 2013
Figure J-20 - Monthly Stage Exceedence Curves for March for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 21 February 2013
Figure J-21 - Monthly Stage Exceedence Curves for April for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 22 February 2013
Figure J-22 - Monthly Stage Exceedence Curves for May for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 23 February 2013
Figure J-23 - Monthly Stage Exceedence Curves for June for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 24 February 2013
Figure J-24 - Monthly Stage Exceedence Curves for July for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 25 February 2013
Figure J-25 - Monthly Stage Exceedence Curves for August for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX J STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix J---Page 26 February 2013
Figure J-26 - Monthly Stage Exceedence Curves for September for pre-Project and Max LF OS-1 Conditions, Susitna Station Gage.
APPENDIX K. PLOTS OF SELECT WATER-SURFACE ELEVATION
EXCEEDENCE VALUES (PRE-PROJECT AND MAXIMUM LOAD
FOLLOWING OS-1 CONDITIONS) FOR SUNSHINE GAGE AND
SUSITNA STATION GAGE CROSS SECTION
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Stream Flow Assessment
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech
February 2013
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 1 February 2013
Figure K-1 - Select Annual Water-surface Elevation Exceedence Values, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 2 February 2013
Figure K-2 – Select Water-surface Elevation Exceedence Values for October, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 3 February 2013
Figure K-3 – Select Water-surface Elevation Exceedence Values for November, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 4 February 2013
Figure K-4 – Select Water-surface Elevation Exceedance Values for December, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 5 February 2013
Figure K-5 – Select Water-surface Elevation Exceedence Values for January, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 6 February 2013
Figure K-6 – Select Water-surface Elevation exceedence Values for February, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 7 February 2013
Figure K-7 – Select Water-surface Elevation Exceedence Values for March, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 8 February 2013
Figure K-8 – Select Water-surface Elevation Exceedence Values for April, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 9 February 2013
Figure K-9 – Select Water-surface Elevation Exceedence Values for May, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 10 February 2013
Figure K-10 – Select Water-surface Elevation Exceedence Values for June, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 11 February 2013
Figure K-11 – Select Water-surface Elevation Exceedence Values for July, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 12 February 2013
Figure K-12 – Select Water-surface Elevation Exceedence Values for August, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 13 February 2013
Figure K-13 – Select Water-surface Elevation Exceedence Values for September, pre-Project and Max LF OS-1 Conditions, Sunshine Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 14 February 2013
Figure K-14 - Select Annual Water-surface Elevation Exceedence Values, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 15 February 2013
Figure K-15 – Select Water-surface Elevation Exceedence Values for October, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 16 February 2013
Figure K-16 – Select Water-surface Elevation Exceedence Values for November, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 17 February 2013
Figure K-17 – Select Water-surface Elevation Exceedence Values for December, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 18 February 2013
Figure K-18 – Select Water-surface Elevation Exceedence Values for January, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 19 February 2013
Figure K-19 – Select Water-surface Elevation Exceedence Values for February, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 20 February 2013
Figure K-20 – Select Water-surface Elevation Exceedence Values for March, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 21 February 2013
Figure K-21 – Select Water-surface Elevation Exceedence Values for April, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 22 February 2013
Figure K-22 – Select Water-surface Elevation Exceedence Values for May, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 23 February 2013
Figure K-23 – Select Water-surface Elevation Exceedence Values for June, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 24 February 2013
Figure K-24 – Select Water-surface Elevation Exceedence Values for July, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 25 February 2013
Figure K-25 – Select Water-surface Elevation Exceedence Values for August, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage
APPENDIX K STREAM FLOW ASSESSMENT
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Appendix K---Page 26 February 2013
Figure K-26 – Select Water-surface Elevation Exceedence Values for September, pre-Project and Max LF OS-1 Conditions, Susitna Station Gage