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Susitna-Watana Hydroelectric Project Document
ARLIS Uniform Cover Page
Title:
SuWa 240
Geomorphology study (Study 6.5), updated mapping of aquatic
macrohabitat types in the middle Susitna River segment from 1980s and
current aerials, technical memorandum
Author(s) – Personal:
Author(s) – Corporate:
Tetra Tech, Inc.
AEA-identified category, if specified:
September 26, 2014 technical memorandum filings
AEA-identified series, if specified:
Series (ARLIS-assigned report number): Existing numbers on document:
Susitna-Watana Hydroelectric Project document number 240
Published by: Date published:
[Anchorage, Alaska : Alaska Energy Authority, 2014] September 2014
Published for: Date or date range of report: Alaska Energy Authority
Volume and/or Part numbers:
Final or Draft status, as indicated:
Attachment A
Document type: Pagination:
Technical memorandum 97 p. in various pagings
Related work(s): Pages added/changed by ARLIS:
Cover letter to this report: Susitna-Watana Hydroelectric
Project, FERC Project no. 14241-000; Second set of 2014
technical memoranda for Initial Study Plan meetings. (SuWa
239)
Attachments B-G (SuWa 241-246)
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/
September 26, 2014
Ms. Kimberly D. Bose
Secretary
Federal Energy Regulatory Commission
888 First Street, N.E.
Washington, D.C. 20426
Re: Susitna-Watana Hydroelectric Project, Project No. 14241-000
Second Set of 2014 Technical Memoranda for Initial Study Plan Meetings
Dear Secretary Bose:
As the Alaska Energy Authority (AEA) explained in its September 17, 2014 filing
with the Federal Energy Regulatory Commission (Commission or FERC) for the
proposed Susitna-Watana Hydroelectric Project, FERC Project No. 14241 (Project), the
June 3, 2014 Initial Study Report (ISR) provided for AEA to prepare certain technical
memoranda and other information based on 2014 work. In accordance with Commission
Staff direction, on September 17, 2014, AEA filed and distributed the first set of
technical memoranda and other information generated during the 2014 study season.
With this letter, AEA is filing and distributing the second set of technical
memoranda generated during the 2014 study season, as described below. As part of its
continued implementation of the study plan, AEA expects to file a third set of technical
memoranda prior to October 1, 2014.
This second set of technical memoranda includes:
• Attachment A: Geomorphology Study (Study 6.5) - Updated Mapping of
Aquatic Macrohabitat Types in the Middle Susitna River Segment from 1980s
and Current Aerials Technical Memorandum. This technical memorandum
updates the Middle Susitna River Segment portion of the aquatic macrohabitat
mapping results previously provided in the technical memorandum titled
Mapping of Aquatic Macrohabitat Types at Selected Sites in the Middle and
Lower Susitna River Segments from 1980s and 2012 Aerials (Tetra Tech
2013a).
• Attachment B: Geomorphology Study (Study 6.5) - Mapping of Geomorphic
Features and Turnover within the Middle and Lower Susitna River Segments
from 1950s, 1980s, and Current Aerials Technical Memorandum. This
technical memorandum updates the geomorphic mapping and assessment of
channel change that were initially provided in Mapping of Geomorphic
2
Features and Assessment of Channel Change in the Middle and Lower Susitna
River Segments from 1980s and 2012 Aerials (Tetra Tech 2013a). The initial
technical memorandum provided the results from tasks identified in Revised
Study Plan Study 6.5 Section 6.5.4.4. This update extends the previous 30
year analysis between the 1980s and 2012 by an additional 30 years with
aerial photography from the 1950s, and also provides a short term analysis of
geomorphic changes by comparing 2012 with 2013 aerial photography.
• Attachment C: Fluvial Geomorphology Modeling below Watana Dam Study
(Study 6.6) - Decision Point on Fluvial Geomorphology Modeling of the
Susitna River below PRM 29.9 Technical Memorandum. This technical
memorandum describes the decision of whether to extend the downstream
limit of the 1-D bed evolution model below Susitna Station at PRM 29.9.
• Attachment D: Fluvial Geomorphology Modeling Below Watana Dam (Study
6.6) - Winter Sampling of Main Channel Bed Material Technical
Memorandum. The overall purpose of this technical memorandum is to
quantify main channel bed material gradations at selected sites in the Upper,
Middle, and Lower Susitna River Segments. The data obtained from this
study serves as input for the 1-D and 2-D bed evolution modeling efforts
being conducted under the Fluvial Geomorphology Modeling Study (Study
6.6).
• Attachment E: Cook Inlet Beluga Whale Study (Study 9.17) - 2014 Cook Inlet
Beluga Whale Prey Study Implementation Technical Memorandum. This
technical memorandum summarizes activities implementing the Cook Inlet
Beluga Whale Study (Study 9.17) conducted in 2014 that tested methods to
document Cook Inlet Beluga Whale prey and prey habitat in the Susitna River
delta.
• Attachment F: River Productivity Study (Study 9.8) - 2013 Initial River
Productivity Results Technical Memorandum. This technical memorandum
provides a preliminary review and summary of 2013 river productivity sample
results based on laboratory data received after the ISR submittal in June 2014.
• Attachment G: River Productivity Study (Study 9.8) - 2014 Field Season River
Productivity Progress Report Technical Memorandum. This technical
memorandum presents an update on activities conducted during the Spring
field sampling event in June 2014, which was focused on data collection to
support the needs of the trophic modeling and stable isotope analysis
objectives of the River Productivity Study.
3
AEA appreciates the opportunity to provide this additional information to the
Commission and licensing participants, which it believes will be helpful in determining
the appropriate development of the 2015 study plan as set forth in the ISR. 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 A
Geomorphology Study (Study 6.5) - Updated Mapping of Aquatic Macrohabitat Types in the
Middle Susitna River Segment from 1980s and Current Aerials Technical Memorandum
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Geomorphology Study (Study 6.5)
Updated Mapping of Aquatic Macrohabitat Types
in the Middle Susitna River Segment
from 1980s and Current Aerials
Technical Memorandum
Prepared for
Alaska Energy Authority
Prepared by
Tetra Tech, Inc.
September 2014
TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
TABLE OF CONTENTS
Summary ....................................................................................................................................... iv
1. Introduction ........................................................................................................................1
2. Study Objectives.................................................................................................................2
3. Study Area ..........................................................................................................................2
3.1. General .....................................................................................................................2
3.2. Middle Susitna River Segment ................................................................................2
4. Methods ...............................................................................................................................3
4.1. Variations from Study Plan ......................................................................................3
4.2. Middle River 2013 Aerial Photo Acquisition ..........................................................3
4.3. Processing of 2013 Aerial Photography ..................................................................4
4.4. Digitization Procedure .............................................................................................4
4.5. Riverine Habitat Classification Definitions .............................................................5
4.5.1. Quality Control ............................................................................... 6
5. Results .................................................................................................................................7
6. Summary .............................................................................................................................7
7. References ...........................................................................................................................9
8. Tables ................................................................................................................................10
9. Figures ...............................................................................................................................15
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page i September 2014
TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
LIST OF TABLES
Table 4.1-1. Summary of 2012 aerial photography. .................................................................... 10
Table 4.1-2. Summary of 1980s aerials, discharges, and project river mile extents. .................. 10
Table 4.2-1. Summary of 2013 aerial photography. .................................................................... 11
Table 4.2-2. Summary of aerial photography used to define the Middle River “Current
Conditions” ........................................................................................................................... 11
Table 5.1-1. Delineated habitat areas for the “1980s Condition” Middle Susitna River Segment,
Geomorphic Reaches MR-5 through MR-81. ....................................................................... 12
Table 5.1-2. Delineated habitat areas for the “Current Condition” Middle Susitna River Segment
............................................................................................................................................... 13
Table 5.1-3. Delineated habitat areas for the “2013 Conditions” Middle Susitna River Segment
from PRM 184.6 to PRM 153.9. ........................................................................................... 14
LIST OF FIGURES
Figure 4.2-1. 2013 Area of Interest (AOI) and image center coordinates for the four aerial
acquisition flights. ................................................................................................................. 16
Figure 4.2-2. Example of typical ice on channel margins and within the Susitna River channel
near PRM 167.5 .................................................................................................................... 17
Figure 4.2-3. Example of typical ice on channel margins and within the Susitna River channel
near PRM 162 ....................................................................................................................... 17
LIST OF APPENDICES
Appendix A: 1983 Middle Susitna River Segment Aquatic Macrohabitat Types
Appendix B: Current (2012/2013) Middle Susitna River Segment Aquatic Macrohabitat Types
Appendix C: 2013 Middle Susitna River Segment Aquatic Macrohabitat Types
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page ii September 2014
TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
LIST OF ACRONYMS AND SCIENTIFIC LABELS
Abbreviation Definition
AEA Alaska Energy Authority
AOI Area of Interest
AOW Additional open water
AT Aerotriangulation
cfs cubic feet per second
DEM Digital Elevation Modern
DMC Digital Mapping Camera
DTM Digital Terrain Model
FERC Federal Energy Regulatory Commission
FIPS Federal Information Processing Standard
GIS Geographic Information System
GPS Global Positioning System. A system of radio-emitting and -receiving satellites used
for determining positions on the earth.
Hz Hertz
ILP Integrated Licensing Process
IMU Inertial measurement unit
LiDAR Light Detection and Ranging
LR Lower River
MR Middle Susitna River Segment
NAD North American Datum
NAVD North American Vertical Datum
NEPA National Environmental Policy Act
PRM Project River Mile
QC Quality control
RM River Mile(s)
SC side channel
USGS U.S. Geological Survey
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iii September 2014
TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
SUMMARY
The overall purpose of this technical memorandum is to update the Middle Susitna River
Segment portion of the aquatic macrohabitat mapping results previously provided in the
technical memorandum titled Mapping of Aquatic Macrohabitat Types at Selected Sites in the
Middle and Lower Susitna River Segments from 1980s and 2012 Aerials (Tetra Tech 2013a). The
present conditions mapping results in the 2013 technical memorandum were based on 2012
aerials and were performed at selected sites that represent about 50 percent of the total length of
the Middle Susitna River Segment. The results in this technical memorandum add to the
mapping results in the earlier technical memorandum by: (1) expanding the 2012/2013 mapping
of aquatic macrohabitat types to 100 percent coverage of the Middle Susitna River Segment, (2)
replace mapping previously developed from 2012 aerials with information from 2013 aerials in
cases where the 2013 aerials are closer to the target flow and/or of higher quality than the 2012
aerials, and (3) digitize 100 percent of the available 1980s macrohabitat detailed in Response of
Aquatic Habitat Surface Areas to Mainstem Discharge in the Talkeetna-To-Devil Canyon
Segment of the Susitna River, Alaska (Trihey & Associates 1985). The aquatic habitat mapping
results presented in this technical memorandum supersede the mapping results presented in the
earlier technical memorandum (Tetra Tech 2013a).
The aquatic macrohabitat mapping was conducted using: (1) orthorectified digital aerial images
of black and white aerial photographs collected in 1983 at a discharge of 12,500 cfs in the
Middle River, and (2) aerial photographs collected in 2012 at flows of 12,900 and 17,000 cfs,
and in 2013 at flows of 6,200 and 11,300 cfs. The aerial photographs were used to delineate and
measure the wetted surface areas for the various aquatic macrohabitat types using Geographical
Information Software (GIS). This information can be used by aquatic resource studies to support
characterization of aquatic macrohabitat along the Middle Susitna River Segment.
As previously reported in Study 6.5 ISR Section 7.1.2.5, one variation from the study plan was
implemented; the use of a single target discharge rather than multiple flows for developing the
aquatic macrohabitat mapping. In the future, macrohabitat areas will be estimated using the
combination of 2-D hydraulic modeling, bathymetry, and topography collected in the Focus
Areas over the range of flows of interest, negating the need to develop aquatic macrohabitat
versus flow relationships from aerial photography as was done in the 1980s studies.
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iv September 2014
TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
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 320-mile-long river in the Southcentral region of Alaska. The
Project’s dam site will be located at Project River Mile (PRM) 187.11. The results of this study
will provide information to support the FERC’s National Environmental Policy Act (NEPA)
analysis for the Project license.
This technical memorandum updates the aquatic macrohabitat mapping results previously
provided in the technical memorandum titled Mapping of Aquatic Macrohabitat Types at
Selected Sites in the Middle and Lower Susitna River Segments from 1980s and 2012 Aerials
(Tetra Tech 2013a). The aquatic habitat mapping results presented in this technical
memorandum supersede the mapping results presented in the earlier technical
memorandum (Tetra Tech 2013a). The current conditions mapping results represented in the
2013 technical memorandum were based on 2012 aerials and were performed at selected sites
that represent about 50 percent of the total length of the Middle Susitna River Segment. This
mapping was extended to: (1) expand the current conditions mapping of aquatic macrohabitat
types to 100 percent of the Middle Susitna River Segment (“current conditions” refers to
mapping covering the entire Middle Susitna River Segment developed from 2012 and 2013
aerial photography), (2) replace mapping previously developed from 2012 aerials with
information from 2013 aerials in cases where the 2013 aerials are closer to the target flow and/or
of higher quality than the 2012 aerials, and (3) digitize 100 percent of the available 1980s
macrohabitat detailed in Response of Aquatic Habitat Surface Areas to Mainstem Discharge in
the Talkeetna-To-Devil Canyon Segment of the Susitna River, Alaska (Trihey & Associates
1985). The 1980s mapping is only available from PRM 102 to PRM 154, and therefore, does not
extend upstream of the downstream limit of Devils Canyon.
The mapping was coordinated with Study 9.9 (Characterization and Mapping of Aquatic
Habitats) and Study 8.5 (Fish and Aquatics Instream Flow Study).
This technical memorandum update results from tasks that are part of the following studies:
2012 Study Plan G-S2: Aquatic Habitat and Geomorphic Mapping of the Middle River using
Aerial Photography.
RSP Study 6.5 Section 6.5.4.5.2.2 study component “Riverine Habitat versus Flow
Relationship Middle Susitna River Segment” task “Digitize Riverine Habitat Types”.
The effort to update the current aquatic macrohabitat mapping is identified in ISR Study 6.5
Section 7.2.1.5. Study Component: Riverine Habitat versus Flow Relationship Middle Susitna
River Segment.
1 Note: Project River Miles (PRMs) are the river mile system used for the current Susitna-Watana Project. River Miles (RMs)
were the river mile system used in the 1980s project. The PRM delineation starts about 3 miles farther into Cook Inlet than the
RMs and has a slightly different thalweg than that of the 1980s. Thus, PRM values are generally 3 to 4 miles higher than the RM
values. Because this analysis is a temporal comparison, both systems are referenced.
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 1 September 2014
TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
2. STUDY OBJECTIVES
The objectives of the effort covered by this technical memorandum were:
Update the current conditions aquatic macrohabitat mapping using the 2013 aerials in cases
where the 2013 aerials were collected closer to the target flow of 12,500 cfs and/or of higher
quality than the 2012 aerials.
Expand the 1980s aquatic macrohabitat mapping to cover 100 percent of the area of available
mapping (PRM 102 to PRM 154) from the approximately 50 percent presented in the earlier
technical memorandum (Tetra Tech 2013a).
Expand the current (2012/2013) aquatic macrohabitat mapping to cover 100 percent of the
Middle Susitna River Segment (PRM 102 to PRM 187) from the approximately 50 percent
presented in the earlier technical memorandum (Tetra Tech 2013a).
Coordinate with the Characterization and Mapping of Aquatic Habitats (Study 9.9) and Fish
and Aquatics Instream Flow Study (Study 8.5) to ensure consistency between different
aquatic macrohabitat mapping efforts. The Characterization and Mapping of Aquatic
Habitats (Study 9.9) has also produced aquatic macrohabitat mapping (HDR 2013).
The delineated macrohabitats are one of five levels of nested and tiered habitat classification
being applied to the Middle Susitna River Segment. The system is presented in Table 1.1-1 of
the Study 9.9 ISR Section 4.1. The classification levels include river segment, geomorphic reach,
macrohabitats, mesohabitat, and edge habitat. The Geomorphology Study (Study 6.5) defined
the Susitna River segments and geomorphic reaches in the updated technical memorandum
Geomorphic Reach Delineation and Characterization, Upper, Middle and Lower Susitna River
Segments (Tetra Tech 2014a).
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 Cook Inlet (U.S. Geological Survey [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 elevation in
the basin is Mt. McKinley at 20,320 feet while its lowest elevation is 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, which are also glacially fed in
their respective headwaters. The basin receives, on average, 35 inches of precipitation annually
with average annual air temperature of approximately 29o F.
3.2. Middle Susitna River Segment
The study effort for the work presented in this technical memorandum covers the Middle Susitna
River Segment from the Watana Dam site (PRM 187.1) to the Three Rivers Confluence (PRM
102.4). The Lower and Upper Susitna River Segments are not part of the 2014 study effort
documented in this technical memorandum.
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 2 September 2014
TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
4. METHODS
4.1. Variations from Study Plan
One variance was identified for this study component in 2013 that carries over as a modification
in 2014 and 2015 (ISR Study 6.5 Section 7.1.2.5) and affects some of the work described in this
technical memorandum. The modification involves the collection of aerial photography in the
Middle and Lower Susitna River Segments. In 2012 and 2013, aerial photography was acquired
at a single target flow rather than the three flows identified in Study 6.5 RSP Section 6.5.4.5.2.1.
The Study Plan detailed the acquisition of three sets of aerial photography in 2012 approximately
corresponding to the following discharges: 23,000, 12,500, and 5,100 cfs. Due to a combination
of weather and flow conditions, only one of the 3 datasets was collected. The 2012 aerial
photography was collected for approximately 50 percent of the Middle River at 12,900 cfs and
50 percent of the Middle River at 17,000 cfs (Table 4.1-1).
One goal of acquiring three sets of 2012 aerials was to compare the macrohabitat versus flow
relationships from current conditions to the 1980s information and determine if there is a
difference in the habitat areas for current conditions from those mapped in the 1980s at similar
flows. A summary of discharges corresponding to the 1980s aerial flight dates is shown in Table
4.1-2. This goal was met by collection of the single set of aerial photography in 2012 since,
based on analysis of the 2012 aerial photography data, AEA concluded that the macrohabitat
areas at specific locations were appreciably different from those mapped in 1983 (Tetra Tech
2013a). Subsequently, AEA also concluded that collection of aerial photography at 3 discharges
to develop macrohabitat versus flow relationships was not necessary for meeting the overall
objectives of the Study Plan. Instead, AEA supports the use of a combination of the 2-D
hydraulic modeling and bathymetry and topography collected in the Focus Areas to provide
direct determination of the area of the various macrohabitat types over the range of flows.
Therefore, development of macrohabitat area versus flow relationships from aerial photographs
collected at specified discharges as identified as a goal of this study component are not needed.
This variance and the alternative approach were presented at the September 25 and December 2,
2013 Technical Work Group meetings. The objectives of the study will be met without collecting
additional aerials at three flows as specified in RSP Study 6.5 Section 6.5.4.5.2.1.
4.2. Middle River 2013 Aerial Photo Acquisition
In 2013, a decision was made to acquire additional aerial photographs for the 12,500-cfs target
discharge in the Middle River. Due to a combination of weather and flows conditions, aerials
were obtained for about 60 percent of the Middle River at 11,300 cfs and 40 percent at 6,200 cfs.
The 2013 aerial photographs were collected on four flights on September 16, 20, 24, and
November 6, 2013 (Table 4.2-1). A total of 38 flight lines were flown. The 2013 area of interest
(AOI) and the image center coordinates for all four flights are shown in Figure 4.2-1.
The aerial photos collected on November 6, 2013, showed ice formations along the channel
margins and frazil ice within the Susitna River channel from PRM 185.0 to PRM 153.6. The
Susitna River was completely ice-covered in a short portion of Devils Canyon from PRM 164.1
to PRM 163.4. It was determined that the ice observed in the photos was minor and would not
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TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
have an appreciable effect on aquatic macrohabitat delineations. Two examples of the typical
amount of ice seen in the photos are shown in Figure 4.2-2 and Figure 4.2-3.
The 2013 aerial photographs were used to replace the 2012 mapping for the current conditions
from approximately PRM 143.6 to PRM 153.6. The 2013 aerials were collected at 11,300 cfs,
very close to the 12,500-cfs target flow. In this portion of the Middle River, the 2012 mapping
was based on aerial photography collected at 17,000 cfs. A summary of the flows used to
delineate the current conditions macrohabitat areas is presented in Table 4.2-2.
From PRM 153.6 to PRM 184.9, aquatic macrohabitat mapping was developed based on the
2013 6,200-cfs aerials; however, it was not used to replace the 2012 mapping in the current
conditions for this portion of the Middle River developed from the 17,000-cfs aerials. Instead,
the 2013 aerial photography collected at 6,200 cfs was used to develop a second set of
macrohabitat maps that is referred to as the “2013 conditions”. The 2013 conditions mapping
along with the mapping from 2012 aerial photography available in the current conditions at
17,000 cfs bracket the 12,500-cfs target flow for this portion of the Middle Susitna River
Segment.
4.3. Processing of 2013 Aerial Photography
The aerial photography was processed into orthoimagery (aka orthorectified aerial imagery).
Orthoimagery is aerial imagery that has been rectified to a map projection by removing
displacement caused by terrain undulation and camera geometry. The orthoimagery has a ground
resolution of 1 foot. The datum and projection is Alaska State Plane, Zone 4, North American
Datum of 1983 coordinate system. The four band imagery consisted of the natural color bands
red, green, blue, and with near infrared. The processing of both the 2012 and 2013 the aerial
photography followed the methods presented in ISR Study 6.5 Section 4.5.2.1.1.2.
4.4. Digitization Procedure
Within the area of geomorphic delineation (see Tetra Tech 2014b), polygons were delineated for
wetted habitat types (see Section 4.5 for definitions of the habitat types). Wetted areas were
mapped as one of the aquatic habitat types only if the area had a connection to the Susitna River.
This connection did not have to be direct, but could be through one or more additional wetted
habitat types. For example, an upland slough could connect to a side slough, which connects to a
side channel and ultimately the main channel. If the water body was isolated and there was not a
connection to the Susitna River, then the wetted area was mapped as background.
The habitat areas were delineated using ArcGIS 10.0 (a Geographic Information Systems [GIS]
software package) at a scale of 1:3000. The 2011 Mat Su LiDAR (Matanuska-Susitna Borough
2011) was used to determine elevation differences to better define the boundary between channel
areas and floodplain or island areas. The LiDAR was used to determine bank and water-surface
elevations in areas of shadows and under vegetation cover in the upper ends of sloughs. The
LiDAR dataset is referenced to the following coordinate system: North American Datum (NAD)
1983 State Plane Alaska 4 Federal Information Processing Standard (FIPS) 5,004 Feet.
The delineated habitat areas are reported to the sixth decimal point and tabulated to an accuracy
of 1,000 square feet. Each habitat type within the habitat sites as well as the total area of the
habitat site (control area) was measured and cross checked with the area of geomorphic
delineation to ensure all the habitat areas were measured.
Susitna-Watana Hydroelectric Project Alaska Energy Authority
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TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
4.5. Riverine Habitat Classification Definitions
Two sets of aquatic macrohabitat classification definitions were used: one for the sites in the
Lower Susitna River Segment and one for the sites in the Middle Susitna River Segment. This
technical memorandum only addresses the Middle Susitna River Segment. The riverine aquatic
macrohabitat classifications apply to the wetted area of a feature. The aquatic macrohabitat along
with the exposed substrate contained within the banks of perennial vegetation comprise
geomorphic features that are bounded at their mouths and inlets. Geomorphic feature mapping
was performed for all areas within the geomorphic boundary of the Middle and Lower Susitna
River Segments. This is in contrast to aquatic macrohabitat mapping which was also performed
for the Middle Susitna River Segment, but only five habitat sites in the Lower Susitna River
Segment. Further, while many habitat types are classified similarly, or the same as geomorphic
types (i.e., main channel, side channel), there were distinctions made pertaining to the wetted
connectivity of the area. For example, while a wetted area in a side slough with regions of
exposed substrate isolating it from the main wetted slough region would be classified as part of
the side slough in the geomorphic classification system, the isolated wetted region would be
classified as background in the habitat classification system. This distinction is due to the lack of
a wetted connection through which aquatic organisms can pass. This reflects a change in the
definition of background in this technical memorandum compared to the earlier definition (Tetra
Tech 2013a). Previously, the isolated wetted regions which were classified as: additional open
water (AOW), vegetated islands (VI), and exposed substrate was classified as background to
eliminate variance with the geomorphic feature mapping. The results of the geomorphic feature
mapping are presented in a separate technical memorandum (Tetra Tech 2013b [initial technical
memorandum] and Tetra Tech 2014b [updated technical memorandum]).
The aquatic macrohabitat in the Middle Susitna River Segment was classified using categories as
defined in Trihey & Associates (1985). The Middle River macrohabitat types were classified into
the following categories: main channel, side channel, side sloughs, upland sloughs, and tributary
mouths. As previously mentioned, isolated wetted areas (mapped as AOWs in Tetra Tech
(2013a) were mapped as background and were not considered part of the riverine habitat. With
the inclusion of tributaries, the classifications were defined in 2014 as follows:
Main Channel habitat types are those channels of the river that normally convey streamflow
throughout the entire year. They are visually recognizable by their turbid glacial water and
high velocities. In general, they convey more than 10 percent (approximate) of the total flow
passing a given location.
Side Channel habitat types are also characterized by turbid glacial water. Velocities often
appear lower than in mainstem sites. In general, they convey less than 10 percent
(approximate) of the total flow passing a given location. Side-channel habitat may exist in
well-defined channels or in areas possessing numerous islands and submerged gravel bars.
When the upstream berms of side channels are dewatered and the channels contain clear
water, they are classified as side sloughs.
Side Slough habitat types contain clear water. Small tributaries, upwelling groundwater, and
local surface runoff are the primary sources of clear water for these areas. Side sloughs have
non-vegetated upper thalwegs that are overtopped during periods of moderate to high
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TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
mainstem discharge. When these areas are overtopped they convey turbid water and are then
classified as side channels.
Upland Slough habitat types also contain clear water and depend on small streams,
upwelling, and local surface runoff for their water supply. Upland sloughs possess vegetated
upper thalwegs that are rarely overtopped by mainstem discharge.
Tributary habitat is the portion of a tributary channel flowing across the floodplain.
Tributaries are typically clear water channels.
Tributary Mouth habitat types are clear water areas that exist where clear water tributaries
flow into main channel or side channel habitats. This habitat type is located in the area of the
clear-water plume that extends from the tributary into the turbid receiving water. Tributary
mouth habitat also extends upstream into the tributary to the upper extent of any backwater
influence that might exist. The surface area of tributary mouth habitat is affected both by
tributary and mainstem discharges.
Background was defined as any area within the defined boundary that did not provide
connected aquatic macrohabitat. This included floodplain, vegetated islands, exposed
substrate, and additional open water.
4.5.1. Quality Control
The Geomorphology Program Lead and the Geomorphology Task Lead provided training to the
senior hydraulic engineers/geomorphologist and GIS analysts to ensure appropriate and
consistent identification and delineation of the habitat categories. Senior hydraulic engineers/
geomorphologists reviewed the macrohabitat delineations for completeness, adherence to the
classifications and scale criteria. The senior hydraulic engineers/geomorphologists frequently
consulted with the Geomorphology Program Lead and the Geomorphology Task Lead on
application of the definitions and for advice when differentiation between macrohabitat types
was challenging.
Markups were provided to the staff performing the delineation in comments on the GIS files,
marked up Adobe Acrobat PDFs and written instructions. Comments were provided for specific
items such as changing the classification of a feature or general concerns such as the quality of
the digitization and proper interpretation of the definitions. After the revisions were made, the
mapping was re-checked by the reviewers, and if necessary, the process was repeated.
Throughout the process, the senior hydraulics engineers/geomorphologists consulted with the
Geomorphology Program Lead or the Geomorphology Task Lead to refine the application of
definitions and help make decisions for unique situations encountered. The files were then
reviewed for topology errors such as gaps between delineations (slivers) and overlaps. A final
check was run on the tabulated areas for the reaches. The measured areas of the features and
habitats were compared to their outer boundary to ensure complete and non-overlapping
coverage. Comparisons between summed individual areas and the total reach area were
considered acceptable if the difference was less than 0.5 percent.
Coordination with Fish and Aquatics Instream Flow Study (Study 8.5) and the Characterization
and Mapping of Fish Habitat Study (Study 9.9) leads was conducted to ensure that delineated
macrohabitat types were consistently identified in each of the three studies. Differences in the
aquatic macrohabitat classification of features between the studies that were not related to the
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discharge associated with the datasets being used to perform the delineation were updated, along
with the mapping and analysis results. The emphasis of the comparison was on the classification
rather than the variations in the upstream/downstream or lateral extents of the delineated habitat
areas that may be due to differences in approaches (line mapping versus area mapping) or
discharge. The emphasis for the coordination between studies was looking for macrohabitat call
overlap where there was a difference in habitat classification that was not related to flow used in
the specific studies. Also, side channel versus main channel differences were not addressed. The
call between side channel and main channel is subjective without accurately knowing the actual
volume of flow in the channels as the definition is based on conveyance of 10 percent or less of
the flow (if greater than 10 percent then the feature is considered a main channel). However,
there was consistency with the Study 6.5 area mapping and Study 9.9 2012 line mapping. Side-
channel classification was not consistent between the studies due to the flow differences, but
future application of aquatic macrohabitat mapping will use the Study 9.9 2012 line mapping as
the official reference moving forward.
5. RESULTS
The Middle Susitna River Segment habitat site analysis provides the area of the various aquatic
macrohabitat types for the entire Middle Susitna River Segments for 1983 and current conditions
(2012/2013). Tabulated areas for each aquatic macrohabitat type are provided in Table 5.1-1 for
1980s conditions, Table 5.1-2 for the current conditions, and Table 5.1-3 for 2013 conditions at
6,200-cfs discharge from PRM 184.9 to PRM 153.6. Aerial photographs with the aquatic habitat
types mapped for the Middle River are provided in Appendix A for 1980s conditions and
Appendix B for the current conditions. The habitat mapping for the 2013 conditions 6,200-cfs
discharge from PRM 184.9 to PRM 153.6 is provided in Appendix C.
6. SUMMARY
This technical memorandum describes the aquatic macrohabitat mapping conducted for portions
of the Middle Susitna River Segment in which 1983 mapping was available (PRM 102.4 to PRM
154) from the 1980s studies (Trihey & Associates 1985) along with mapping for the entire
Middle Susitna River Segment for current conditions.
Current conditions macrohabitat areas were developed based on 2012 and 2013 aerial
photography collected at flows closest to the target flow of 12,500 cfs. A third mapping set,
referred to as the 2013 conditions, was developed from aerial photographs collected from PRM
153.6 to PRM 184.9 on November 6, 2013 when the flow was approximately 6,200 cfs. This
additional mapping was conducted to bracket the target flow of 12,500 cfs with the 6,200-cfs
2013 condition and the 17,000-cfs current condition. This will allow for interpolation of habitat
area at 12,500 cfs, if necessary in the future. The current mapping was reviewed in coordination
with the Characterization and Mapping of Aquatic Habitats (Study 9.9) and Fish and Aquatics
Instream Flow Study (Study 8.5) to ensure consistency between studies. The Characterization
and Mapping of Aquatic Habitats (Study 9.9) has also produced aquatic macrohabitat
quantification in the form of line mapping rather than the area-based mapping in this document
(HDR 2013).
The aquatic habitat mapping results presented in this technical memorandum supersede
the mapping results presented in the earlier technical memorandum (Tetra Tech 2013a).
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This effort represents the completion of the study component identified in RSP Study 6.5 Section
6.5.4.5 and ISR Study 6.5 Section 7.2.1.5 “Riverine Habitat versus Flow Relationship Middle
Susitna River Segment.”
As previously identified and presented in ISR Study 6.5 Section 7.1.2.5 and in Section 4.1 of this
document, one modification was made to the effort that involved the use of a single-target
discharge rather than multiple flows for developing the aquatic macrohabitat mapping.
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7. REFERENCES
HDR Alaska, Inc. 2013. Middle Susitna River Segment Remote Line Habitat Mapping.
Technical Memorandum prepared for Alaska Energy Authority. Anchorage. January.
27p.
Matanuska-Susitna Borough. 2011. Matanuska Susitna Borough LiDAR/Imagery Project.
http://matsu.gina.alaska.edu.
Tetra Tech, Inc. 2013a. Mapping of Aquatic Macrohabitat Types at Selected Sites in the Middle
and Lower Susitna River Segments from 1980s and 2012 Aerials. Susitna-Watana
Hydroelectric Project. 2012 Study Technical Memorandum. Prepared for the Alaska
Energy Authority. Anchorage, Alaska.
Tetra Tech, Inc. 2013b. Mapping of Geomorphic Features and Assessment of Channel Change in
the Middle and Lower Susitna River Segments from 1980s and 2012 Aerials. Susitna-
Watana Hydroelectric Project. 2012 Study Technical Memorandum. Prepared for the
Alaska Energy Authority. Anchorage, Alaska.
Tetra Tech, Inc. 2014a. Geomorphic Reach Delineation and Characterization, Upper, Middle and
Lower Susitna River Segments. Susitna-Watana Hydroelectric Project. Updated
Technical Memorandum. Prepared for the Alaska Energy Authority. Anchorage, Alaska.
Tetra Tech, Inc. 2014b. Mapping of Geomorphic Features and Assessment of Channel Change in
the Middle and Lower Susitna River Segments from 1950s, 1980s and Current Aerial
Photography. Susitna-Watana Hydroelectric Project. 2014 Technical Memorandum.
Prepared for the Alaska Energy Authority. Anchorage, Alaska.
Trihey & Associates. 1985. Response of Aquatic Habitat Surface Areas to Mainstem Discharge
in the Talkeetna-To-Devil Canyon Segment of the Susitna River, Alaska. Prepared under
contract to Harza-Ebasco, for Alaska Power Authority, document No. 2945.
U.S. Geological Survey (USGS). 2012. Streamflow Record Extension for Selected Streams in
the Susitna River Basin, Alaska. Scientific Investigations Report 2012–5210. 46 p.
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TECHNICAL MEMORANDUM UPDATED MAPPING OF AQUATIC MACROHABITAT TYPES
8. TABLES
Table 4.1-1. Summary of 2012 aerial photography.
Aerial Coverage (PRM) Date Discharge (cfs)
From To Gold Creek Sunshine Station
Upper Susitna River Segment
266.5 231.5 10/20/2012 7,410 ---
231.5 187 9/30/2012 17,000 ---
Middle Susitna River Segment
187 143.6 9/30/2012 17,000 ---
143.6 102 9/10/2012 12,900 ---
119 102 07/27/2012 22,200 ---
Lower Susitna River Segment
102 63 07/27/2012 --- 53,000
102 78 09/10/2012 38,200
78 69 09/30/2012 --- 48,000
69 33.5 10/10/2012 --- 55,000
33.5 22.5 09/30/2012 48,000
22.5 0 10/10/2012 --- 55,000
Table 4.1-2. Summary of 1980s aerials, discharges, and project river mile extents.
Aerial Coverage (PRM) Date Discharge (cfs)
From To Gold Creek Sunshine Station
Upper Susitna River Segment
251 187 07/19-20/1980 35,800 & 31,600 ---
Middle Susitna River Segment
187 152 07/19-07/20/1980 35,800 & 31,600 ---
158 102 09/11/1983 12,500 (12,200
published) ---
Lower Susitna River Segment
102 0 09/6/1983 --- 36,600
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Table 4.2-1. Summary of 2013 aerial photography.
Aerial Coverage (PRM)
Date
Discharge (cfs)
From To Gold Creek Sunshine
Upper Susitna River Segment
265.2 247.2 09/16/2013 19,200 ---
247.2 214.8 09/20/2013 15,300 ---
214.8 187.1 09/16/2013 19,200 ---
Middle Susitna River Segment
187.1 184.9 09/16/2013 19,200 ---
184.9 153.6 11/6/2013 6,2001 ---
153.6 106.8 09/24/2013 11,300 ---
106.8 102.4 09/20/2013 15,300
Lower Susitna River Segment
102.4 0 09/20/2013 --- 35,500
Notes:
1 USGS Gold Creek gage was not in operation on November 6, 2013, due to ice cover, the average daily flow on
November 6, 2013, was extrapolated from the preceding week's daily discharges.
Table 4.2-2. Summary of aerial photography used to define the Middle River “Current Conditions” ¹.
Aerial Coverage (PRM) Date Discharge (cfs)
From To Gold Creek
187.1 153.6 09/30/2012 17,000
153.6 143.6 09/24/2013 11,300
143.6 102 09/10/2012 12,900
Notes:
1 From PRM 153.6 to PRM 184.9 aquatic macrohabitat mapping was also produced from the 2013 aerials
obtained at 6,200 cfs. It is referred to as “2013 Conditions” and was developed to provide a set of flows, 17,000
and 6,200 cfs, which bracket the target flow of 12,500 cfs.
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Table 5.1-1. Delineated habitat areas for the “1980s Condition” Middle Susitna River Segment, Geomorphic Reaches MR-5 through MR-81.
Reach Aerial Date PRM Discharge
Main
Channel
(MC)
Side
Channel (SC)
Side
Slough (SS)
Upland
Slough (US)
Tributary
(TR)
Tributary
Mouth (TM)
Background
(BG) Total Area
cfs ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103
MR-5 09/11/1983 148.4 - 153.9 12,500 12,470 0 0 0 442 100 22,304 35,316
MR-6 09/11/1983 122.7 - 148.4 12,500 66,698 24,547 4,490 648 562 650 249,001 346,596
MR-7 09/11/1983 107.8 - 122.7 12,500 46,992 8,350 302 567 78 53 117,847 174,188
MR-8 09/11/1983 102.4 - 107.8 12,500 19,820 3,366 600 744 250 0 205,078 229,858
Total
Area 09/11/1983 102.4 – 153.9 12,500 145,980 36,264 5,392 1,959 1,332 802 594,229 785,958
Notes:
1 Data to produce the 1980s aquatic macrohabitat mapping are not available upstream of Geomorphic Reach MR-5.
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Table 5.1-2. Delineated habitat areas for the “Current Condition” Middle Susitna River Segment
Reach Aerial
Date PRM Discharge
Main
Channel
(MC)
Side
Channel
(SC)
Side
Slough
(SS)
Upland
Slough
(US)
Tributary
(TR)
Tributary
Mouth
(TM)
Background
(BG) Total Area
cfs ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103
MR-1 09/30/2012 184.6 - 187.1 17,000 5,964 222 0 0 0 0 6,530 12,715
MR-2 09/30/2012 169.6 - 184.6 17,000 41,764 247 667 77 1,014 40 122,716 166,525
MR-3 09/30/2012 166.1 - 169.6 17,000 8,801 6 30 0 10 0 11,508 20,356
MR-4 09/30/2012 153.9 - 166.1 17,000 18,175 0 0 0 90 0 24,651 42,916
MR-5 09/30/2012 153.6 - 153.9 17,000 579 0 0 0 2 0 640 1,221
MR-5 09/24/2013 148.4 - 153.6 11,300 12,084 0 5 0 429 119 21,457 34,094
MR-6 09/24/2013 143.6 - 148.4 11,300 16,060 622 517 82 51 78 30,616 48,025
MR-6 09/10/2012 122.7 - 143.6 12,900 66,812 10,932 1,850 559 479 358 217,585 298,575
MR-7 09/10/2012 107.8 - 122.7 12,900 52,807 2,057 393 353 115 52 118,411 174,189
MR-8 09/10/2012 102.4 - 107.8 12,900 23,175 1,485 203 1,016 285 57 202,409 228,631
Total
Area Varies 102.4 -187.1 Varies 246,221 15,571 3,697 2,056 2,474 706 756,523 1,027,248
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Table 5.1-3. Delineated habitat areas for the “2013 Conditions” Middle Susitna River Segment from PRM 184.6 to PRM 153.9.
Reach Aerial Date PRM Discharge
Main
Channel
(MC)
Side
Channel (SC)
Side
Slough (SS)
Upland
Slough (US)
Tributary
(TR)
Tributary
Mouth (TM)
Background
(BG)
Total
Area
cfs ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103 ft2 x 103
MR-1 11/06/2013 184.6 - 184.91 6,200 NA NA NA NA NA NA NA NA
MR-22 11/06/2013 169.6 - 184.6 6,200 33,160 1,264 312 11 658 2,016 129,104 166,525
MR-3 110/6/2013 166.1 - 169.6 6,200 7,757 18 21 0 10 0 12,550 20,356
MR-4 11/06/2013 153.9 - 166.1 6,200 16,222 0 13 0 61 0 26,548 42,844
MR-5 11/06/2013 153.6 - 153.93 6,200 NA NA NA NA NA NA NA NA
Total
Area 11/06/2013 153.9 - 184.64 6,200 57,787 1,282 346 11 729 2,016 169,393 231,564
Notes:
1 The 11/06/2013 aerial photography covers the lower 0.3 miles of MR-1, PRM 184.6 to PRM 184.9. Since this is only 12 percent of the total geomorphic
reach length, the results are not reported in the above table, but the aquatic macrohabitat mapping based on the 11/06/2013 aerial photography of the 0.3
miles of MR-1 is provided in Appendix C.
2 September 30, 2012, aerials were used to supplement the November 6, 2013, aerials to provide full coverage of background and tributaries within the area of
geomorphic delineation.
3 The 11/06/2013 aerial photography covers the upper 0.3 miles of MR-5, PRM 153.6 to PRM 153.9. Since this is only 5 percent of the total geomorphic reach
length, the results are not reported in the above table, but the aquatic macrohabitat mapping based on the 11/06/2013 aerial photography of the 0.3 miles of
MR-5 is provided in Appendix C.
4 The total aquatic macrohabitat areas are reported for geomorphic reaches MR-2 through MR-4. The short, partial portions of MR-1 and MR-5 covered by
the 11/06/2013 aerial photography are excluded from the totals.
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9. FIGURES
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Figure 4.2-1. 2013 Area of Interest (AOI) and image center coordinates for the four aerial acquisition flights.
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Figure 4.2-2. Example of typical ice on channel margins and within the Susitna River channel near PRM 167.5.
Figure 4.2-3. Example of typical ice on channel margins and within the Susitna River channel near PRM 162.
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