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Susitna-Watana Hydroelectric Project Document
ARLIS Uniform Cover Page
Title:
Technical Memorandum, Susitna River large woody debris reconnaissance
SuWa 10
Author(s) – Personal:
Author(s) – Corporate:
Alaska Energy Authority
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 10
Existing numbers on document:
Published by:
[Anchorage, Alaska : Alaska Energy Authority, 2013]
Date published:
March 1, 2013
Published for:
Prepared for Alaska Energy Authority
Date or date range of report:
Volume and/or Part numbers:
Attachment D
Final or Draft status, as indicated:
Document type:
Technical memorandum
Pagination:
vi, 48 p.
Related work(s):
Cover letter (SuWa 6), Attachments A-C, E-I (SuWa 7-9, 11-15)
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 D
Technical Memorandum, Susitna River Large Woody Debris Reconnaissance (March 2013)
Technical Memorandum
Susitna River Large Woody Debris Reconnaissance
Susitna- Watana Hydroelectric Project
FERC No. 14241
Alaska Energy Authority
March 1, 2013
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page i March 1, 2013
TABLE OF CONTENTS
1. INTRODUCTION..............................................................................................................1
1.1. Role and Function of Wood Debris ...................................................................2
1.2. Susitna River Floodplain Forests .......................................................................2
1.3. Study Objectives ................................................................................................3
1.4. Study Area .........................................................................................................3
2. METHODS .........................................................................................................................3
3. RESULTS AND DISCUSSION ........................................................................................3
3.1. Wood Recruitment Processes ............................................................................3
3.2. Wood Transport .................................................................................................4
3.3. Wood Debris: Channel Formation, Channel Splitting, and Island Development4
3.4. Stable Wood Jams ..............................................................................................4
3.5. Wood Debris and Bank Stabilization .................................................................5
3.6. Unstable Wood Debris .......................................................................................5
4. REFERENCES ...................................................................................................................6
5. TABLES ..............................................................................................................................7
6. FIGURES ............................................................................................................................8
7. PHOTOGRAPHS ............................................................................................................11
7.1. Wood Recruitment ...........................................................................................12
7.2. Wood Debris: Transport ..................................................................................15
7.3. Wood Debris: Stable Log Jams and Scour Pools.............................................22
7.4. Wood Debris: Channel Splitting and Island Formation ..................................24
7.5. Wood Debris: Bank Stabilization ....................................................................38
7.6. Unstable Wood Debris .....................................................................................42
LIST OF TABLES
Table 1. Wood debris terminology. ............................................................................................... 7
Table 2. Basic wood debris accumulation typology. ..................................................................... 7
Table 3. Middle and Lower Susitna River dominant floodplain tree characteristics (from Helm
and Collins 1997). ................................................................................................................... 7
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page ii March 1, 2013
LIST OF FIGURES
Figure 1. Susitna River Project Area. ............................................................................................ 9
Figure 2. 2012 Riparian Vegetation Survey Study Area. ............................................................ 10
LIST OF PHOTOGRAPHS
Photograph 1. June 26, 2012 Susitna Middle River between Three Rivers Confluence and Gold
Creek. Wind snapped and wind throw balsam poplar recruitment to channel. ................... 12
Photograph 2. June 26, 2012 Middle Susitna River between Three Rivers Confluence and Gold
Creek. Bank erosion and wind throw balsam poplar wood recruitment. ............................. 13
Photograph 3. June 26, 2012 Middle Susitna River between Three Rivers Confluence and Gold
Creek. Wind snap balsam poplar recruitment. ..................................................................... 14
Photograph 4. June 26, 2012 Three Rivers (Susitna, Chulitna, and Talkeetna rivers) Confluence.
Fresh recruited balsam poplar transport. ............................................................................... 15
Photograph 5. June 26, 2012 Three Rivers (Susitna, Chulitna, and Talkeetna rivers) Confluence.
Fresh recruited balsam poplar transport. ............................................................................... 16
Photograph 6. June 26, 2012 Three Rivers (Susitna, Chulitna, and Talkeetna rivers) Confluence
balsam poplar transport. ........................................................................................................ 17
Photograph 7. June 26, 2012 Middle Susitna River immediately upstream of Three Rivers
Confluence. Freshly recruited white spruce. ........................................................................ 18
Photograph 8. June 26, 2012 Middle Susitna River wood transport. Paper birch deposited on a
mid-channel island bar. ......................................................................................................... 19
Photograph 9. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Large wood
transport and deposition. Root wads are facing upriver. Flow is from right to left. ........... 20
Photograph 10. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Large wood
transport and deposition. Root wads are facing upriver. Flow is from left to right. ........... 21
Photograph 11. July 2, 2012 Lower Susitna River below Talkeetna. Large balsam poplar (79 cm
diameter, DBH) with root wad (210 cm diameter) and adjacent scour pool formation
(Sample Plot T19_04). .......................................................................................................... 22
Photograph 12. July 2, 2012 Middle Susitna River near Talkeetna. Wood jam with key and
racked members. ................................................................................................................... 23
Photograph 13. June 26, 2012 Middle Susitna River wood jam at head of mid channel island and
adjacent side-channel. ........................................................................................................... 24
Photograph 14. July 2, 2012 Lower Susitna River near Talkeetna. Partially buried key member
with racked members and unstable wood. Young balsam poplar establishment in
association with wood jam. ................................................................................................... 25
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iii March 1, 2013
Photograph 15. June 26-27, 2012 Middle Susitna River above Three Rivers Confluence. Wood
jam located at island apex and side channel entrance. Lower Photograph close up of wood
jam with small diameter racked and loose members. ........................................................... 26
Photograph 16. June 30, 2012 Lower Susitna River below Talkeetna. Rafts of racked and
unstable wood. Accumulations at island apex and main stem side-channels. ..................... 27
Photograph 17. July 2, 2012 Lower Susitna River side channel between Talkeetna and Willow.
Rafts of wood debris in side channel and along floodplain embankment. ........................... 28
Photograph 18. July 2, 2012 Lower Susitna River between Talkeetna and Willow. Close-up of
racked wood debris deposited on side channel gravel bar. ................................................... 29
Photograph 19. July 2, 2012 Lower Susitna River between Talkeetna and Willow. Racked wood
debris at island apex and side channel. ................................................................................. 30
Photograph 20. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Racked
wood on mid channel islands. ............................................................................................... 31
Photograph 21. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Unstable
accumulations of racked wood debris upon bars and stable island bar apex jams with racked
members. ............................................................................................................................... 32
Photograph 22. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Bar apex
wood jam with racked members at island apex and side channel entrance. ......................... 33
Photograph 23. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Wood jams
in side channel complex. ....................................................................................................... 34
Photograph 24. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Bar apex
wood jam at side channel exit. .............................................................................................. 35
Photograph 25. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Rafts of
wood in side channel complex. ............................................................................................. 36
Photograph 26. July 2, 2012 Lower Susitna River below Talkeetna. Bar apex wood jam with
buried key member and racked members. Young balsam poplar colonizing elevated wood
jam surface. ........................................................................................................................... 37
Photograph 27. June 26, 2012 Middle Susitna River above Three Rivers Confluence. In-situ key
member forming floodplain bench. ....................................................................................... 38
Photograph 28. June 26, 2012 Middle Susitna River above Three Rivers Confluence. Bench jam
with racked members. ........................................................................................................... 39
Photograph 29. July 1, 2012 Middle Susitna River immediately above Whiskers Slough. Bar
apex jam with large accumulation of racked members upstream of jam. ............................. 40
Photograph 30. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Long bench
jam with large accumulations of racked wood. Flow is from right to left. .......................... 41
Photograph 31. July 2, 2012 Middle Susitna River immediately above Three Rivers Confluence.
Typical unstable wood debris. Note orange tape measure for scale. ................................... 42
Photograph 32. July 2, 2012 Lower Susitna River below Talkeetna. Typical loose, unstable
wood debris. .......................................................................................................................... 43
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iv March 1, 2013
Photograph 33. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Mid
channel rafts of wood debris. Flow is from right to left. ..................................................... 44
Photograph 34. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Rafts of
racked wood debris. .............................................................................................................. 45
Photograph 35. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Racked
wood deposited at young balsam poplar/alder vegetation obstruction. ................................ 46
Photograph 36. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Racked
wood on mid channel gravel bar. .......................................................................................... 47
Photograph 37. June 30, 2012 Lower Susitna River at Talkeetna immediately below Three
Rivers Confluence. Balsam poplar (85 cm diameter, DBH; 18 m length; Plot T19). ......... 48
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page v March 1, 2013
LIST OF ACRONYMS AND SCIENTIFIC LABELS
Term Definition
Active floodplain The flat valley floor constructed by river during lateral channel migration and
deposition of sediment under current climate conditions.
Aggradation
1. Geologic process in which inorganic materials carried downstream are deposited
in streambeds, floodplains, and other water bodies resulting in a rise in elevation in
the bottom of the water body. 2. A state of channel disequilibrium, whereby the
supply of sediment exceeds the transport capacity of the stream, resulting in
deposition and storage of sediment in the active channel.
Alluvial Relating to, composed of, or found in alluvium.
Bank
The sloping land bordering a stream channel that forms the usual boundaries of a
channel. The bank has a steeper slope than the bottom of the channel and is
usually steeper than the land surrounding the channel.
Braid Pattern of two or more interconnected channels typical of alluvial streams.
Channel A natural or artificial watercourse that continuously or intermittently contains water,
with definite bed and banks that confine all but overbank streamflows.
Confinement Ratio of valley width (VW) to channel width (CW). Confined channel VW:CW <2;
Moderately confined channel VW:CW 2-4; Unconfined channel VW:CW >4.
Confluence The junction of two or more streams.
Cubic feet per second (cfs)
A standard measure of the total amount of water passing by a particular location of
a river, canal, pipe or tunnel during a one second interval. One cfs is equal to
7.4805 gallons per second, 28.31369 liters per second, 0.028 cubic meters per
second, or 0.6463145 million gallons per day (mgd). Also called second-feet.
Deposition The settlement or accumulation of material out of the water column and onto the
streambed.
Disturbance regime
Floodplain vegetation disturbance types found within the Susitna River Study Area
corridor include: channel migration (erosion and depositional processes), ice
processes (shearing impacts, flooding and freezing), herbivory (beaver, moose, and
hare), wind, and, to an infrequent extent, fire. Floodplain soil disturbance is
primarily ice shearing and sediment deposition.
Drainage area The total land area draining to any point in a stream. Also called catchment area,
watershed, and basin.
Embeddedness
The degree that larger particles (boulders, large wood, rubble, or gravel) are
surrounded or covered by fine sediment. Usually measured in classes according to
percent of coverage.
Floodplain
1. The area along waterways that is subject to periodic inundation by out-of-bank
flows. 2. The area adjoining a water body that becomes inundated during periods of
over-bank flooding and that is given rigorous legal definition in regulatory programs.
3. Land beyond a stream channel that forms the perimeter for the maximum
probability flood. 4. A relatively flat strip of land bordering a stream that is formed by
sediment deposition. 5. A deposit of alluvium that covers a valley flat from lateral
erosion of meandering streams and rivers.
Geomorphic mapping
A map design technique that defines, delimits and locates landforms. It combines a
description of surface relief and its origin, relative age, and the environmental
conditions in which it formed. This type of mapping is used to locate and
differentiate among relief forms related to geologic structure, internal dynamics of
the lithosphere, and landforms shaped by external processes governed by the bio-
climate environment.
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page vi March 1, 2013
Term Definition
Geomorphology The scientific study of landforms and the processes that shape them.
Gradient The rate of change of any characteristic, expressed per unit of length (see Slope).
May also apply to longitudinal succession of biological communities.
Gravel Substrate particles between 0.1 and 3.0 inches in size, larger than sand and smaller
than cobble.
Groundwater In general, all subsurface water that is distinct from surface water; specifically, that
part which is in the saturated zone of a defined aquifer.
Habitat
The environment in which the fish live, including everything that surrounds and
affects its life, e.g. water quality, bottom, vegetation, associated species (including
food supplies). The locality, site and particular type of local environment occupied
by an organism.
Ice dam A stationary accumulation of fragmented ice or frazil that restricts or blocks a stream
channel.
Large woody debris (LWD) Pieces of wood larger than 10 feet long and 6 inches in diameter, in a stream
channel. Minimum sizes vary according to stream size and region.
Instream flow The rate of flow in a river or stream channel at any time of year.
Pool Part of a stream with reduced velocity, often with water deeper than the surrounding
areas, which is usable by fish for resting and cover.
Riparian Pertaining to anything connected with or adjacent to the bank of a stream or other
body of water.
Riparian vegetation Vegetation that is dependent upon an excess of moisture during a portion of the
growing season on a site that is perceptively more moist than the surrounding area.
River A large stream that serves as the natural drainage channel for a relatively large
catchment or drainage basin.
River mile The distance of a point on a river measured in miles from the river's mouth along
the low-water channel.
Scour The localized removal of material from the streambed by flowing water. This is the
opposite of fill.
Sediment Solid material, both mineral and organic, that is in suspension in the current or
deposited on the streambed.
Three Rivers Confluence
The confluence of the Susitna, Chulitna, and Talkeetna rivers at Susitna River Mile
(RM) 98.5 represents the downstream end of the Middle River and the upstream
end of the Upper River.
Wood recruitment Process by which large woody debris is transferred from upland or riparian
communities to the river system.
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 1 March 1, 2013
1. INTRODUCTION
The Alaska Energy Authority (AEA) is preparing a license application that will be submitted to
the FERC for the Susitna-Watana Hydroelectric Project (Project) using the Integrated Licensing
Process. The Project is located at RM 184 on the Susitna River, an approximately 300-mile long
river in the South central region of Alaska (Figure 1). As currently envisioned, the Project would
include a large dam with an approximately 35,000-acre, 41-mile long reservoir. Project
construction and operation would have an effect on the flows downstream of the dam site, the
degree of which will ultimately depend on final Project design and operations. Key flow
changes will likely occur in the form of load following during the critical winter months of
November through April each year. Seasonal variation will result in flows higher during the
winter months and lower during summer reservoir refill. The alteration in flows would influence
downstream resources and processes, including fish and aquatic biota, and their habitats and
riparian and wildlife communities. Alterations to channel form and function would include
sediment transport, large woody debris recruitment and transport, water quality,
groundwater/surface water interactions, and ice dynamics.
Potential impacts of Project operations on large woody debris recruitment, transport and
function, and subsequent effects upon geomorphologic processes include: (1) operations
alterations of the extent and area of winter river ice and spring river ice break-up associated large
woody debris transport, (2) changes in the deposition pattern of large woody debris down river
from the Project dam site, (3) changes in the pattern of in-channel habitat associated with large
woody debris resulting from recruitment and transport changes, (4) changes in pattern of wood
generated patchwork floodplain development below the Three Rivers confluence, (5) changes in
floodplain forest large woody debris source area and volume of wood down river of the Project
dam site, and (7) changes in large woody debris generated side channel formation.
The potential operational flow-induced effects of the Project will be evaluated as part of the
licensing process, through studies spanning 2012 through 2014. The evaluation is important
from both the impact minimization and operational optimization perspectives. In both cases,
AEA desires to move from study results to decisions affecting flow releases in terms of (i) timing
(seasonal, daily, diurnal), (ii) steady flow rates, and (iii) unsteady flow rates. These three aspects
of flow regime influence physical habitat quantity and quality and geomorphic processes, which
in turn influence carrying capacity and overall suitability for target fish species and riparian
vegetation.
As part of the broader geomorphology study, Study Component G-1.9: Large Woody Debris will
be conducted in 2013-2014 (see Section 6.5.4.9 of the Revised Study Plan (RSP) submitted to
FERC December 14, 2012). The goal of the Large Woody Debris study is to assess the potential
for project construction and operations to affect the recruitment, transport, storage and function
of large woody debris in the Susitna River. The Susitna River Large Woody Debris
Reconnaissance was identified as an original task of Riparian IFS 2012 work plan. This study
was conducted to support development of the final 2013-2014 Large Woody Debris Study plan,
Study Component G-1.9: Large Woody Debris. The Large Woody Debris Reconnaissance effort
was implemented in coordination with, and conducted during, the 2012 Riparian Vegetation
Study.
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 2 March 1, 2013
This technical memorandum reports preliminary observations of the role and function of Susitna
River large woody debris made by the Riparian Vegetation Survey team over a 10-day period
between June 23, 2012 and July 3, 2012. The 2012 large woody debris reconnaissance data will
inform operations planning for the 2013-2014 Geomorphology Large Woody Debris Study by
providing an on-the-ground and aerial overview of the types of large wood and wood debris
accumulations throughout the Project Area (see RSP Section 6.5.4.9). In this technical
memorandum we first define large wood terminology and then discuss the role of large wood in
rivers. Second, we present study objectives. Third, we present photographic, and narrative,
observations of Susitna River woody debris types, processes and functions.
1.1. Role and Function of Wood Debris
Large woody debris, hereafter referred to as “wood debris,” is a fundamental geomorphic
element in forested river networks (Collins et al. 2012; Montgomery et al. 2003). Wood debris
has been identified to play a significant role in coastal Pacific rivers in the formation of fish
habitat including pools and sediment sorting; channel planform type; generation of
anastomozing/anabranching channel pattern; development of patchwork floodplains; and
development of floodplain forests (Collins et al., 2012; Abbe and Montgomery 1996 and 2003;
Montgomery et al. 2003). For consistency, wood debris nomenclature proposed by Abbe and
Montgomery (2003) will be utilized throughout this technical memorandum and is provided in
Tables 1 and 2.
1.2. Susitna River Floodplain Forests
The size of logs has been shown to be a principal factor controlling log stability in river channels
(Abbe and Montgomery 2003). Log length, diameter, and root wad occurrence all contribute to
log stability and geomorphic and habitat functions (Abbe and Montgomery 1996; Abbe and
Montgomery 2003; Collins et al. 2012). Floodplain forests are the primary source of in-channel
wood debris. Regionally specific floodplain forest tree composition and size contributes to
regional variations in the types and degree of wood debris functions (Collins et al. 2012). For
example, floodplain forests of the Olympic Mountains in coastal Washington State have very
large diameter Sitka spruce (Picea sitchensis) that form frequent, large stable wood jams (Abbe
and Montgomery 1996, 2003). Key member pieces in Olympic River channels have been
measured at approximately 1.5 meters in diameter. By comparison, dominant trees of Susitna
River floodplain forests−Balsam poplar (Populus balsamifera), White spruce (Picea glauca),
paper birch (Betula papyrifera)−are much smaller in stature due, in part, to the shorter growing
season in south central Alaska (Table 3; Helm and Collins 1997). Given that the size of logs
controls log stability (Abbe and Montgomery 1996), it would be expected that Susitna floodplain
balsam poplar (average DBH, 53 cm; DBH is tree diameter at breast height 1.4 above ground
surface), white spruce (average DBH 26 cm), and paper birch (average DBH 28 cm) wood debris
would produce smaller and less geomorphically functional wood jams than those found in
coastal Pacific northwest rivers with larger stature trees. Furthermore, in contrast to coastal
Pacific Northwest Rivers, the Susitna River is strongly influenced by the effects of river ice that
effectively entrains unstable pieces of wood during annual spring river ice break-up mobilizing
and transporting wood through the network.
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 3 March 1, 2013
1.3. Study Objectives
The objectives of the Susitna River Large Woody Debris study are as follows:
(1) provide the Geomorphology team with on-the-ground preliminary observations of the
role and function of wood debris in the Susitna River;
(2) document and photograph occurrence and distribution of wood debris and wood debris
accumulations both in-channel and on the floodplain; and
(3) provide observations concerning wood debris recruitment, transport, types of
accumulations, and function.
1.4. Study Area
The 2012 riparian vegetation survey included the middle and lower Susitna River from the
Project dam site (River mile 184) to the town of Willow (Figures 1 and 2). The vegetation
survey study area, on-the-ground surveys, extended laterally from active channel edge
approximately 200 meters across the floodplain to adjacent hillslopes (Figure 2). Large woody
debris was observed and documented from both aerial surveys of the study area as well as on-
the-ground observations during the riparian vegetation survey.
2. METHODS
Wood debris reconnaissance was conducted during the riparian vegetation survey over a 10-day
period between June 23 2012 and July 3 2012. The entire study area was flown by helicopter
and aerial photographic surveys of wood debris were conducted (Figure 2). On-the ground
photographs and observations were made of wood debris encountered during the riparian
vegetation survey. Photo-documentation focused on characterizing the following woody debris
processes and elements: (1) wood recruitment, (2) wood transport, (3) wood debris and channel
formation, including channel splitting and island development, (4) wood debris and channel bank
stabilization, (5) stable wood jams and associated scour pools, and (6) unstable wood debris.
Additionally, field measurements were made of select stable large wood piece diameters and
length at a number of locations.
3. RESULTS AND DISCUSSION
3.1. Wood Recruitment Processes
Trees are recruited to river channels through a number of physical disturbance processes
including: wind throw, wind snap, fire, bank erosion, beavers, and debris flows. Based upon
summer 2012 observations, and review of previous studies of Middle Susitna River channel and
floodplain stability (Labelle et al. 1985), it appears that most wood within the Middle Susitna
River is recruited through wind throw, wind snap, and bank erosion (channel migration and ice
process driven). Analysis of geomorphic change within the Middle Susitna River indicates that
channel planform is relatively stable, at least since 1949 (Labelle et al. 1985). Therefore, current
wood debris input in the Middle Susitna River does not appear to result from major channel
SUSITNA RIVER LARGE WOODY DEBRIS RECONNAISSANCE
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 4 March 1, 2013
migration and bank erosion, although significant episodic floodplain erosion and large wood
recruitment may occur on the Susitna River.
Incremental wind throw and wind snap of large trees, primarily Balsam poplar, along floodplain
margins, and incremental bank erosion were the primary recruitment processes observed in
summer 2012 (Photographs 1-3). Many mid-channel trees observed being transported below the
Three Rivers confluence have attached root wads, evidence of a recent bank erosion recruitment
(Photographs 4-8). Although details were not documented for this report, the 78,000 cfs flood
event of September 22, 2012 (Gold Creek gage) was observed in early October, 2012 to have
caused large scale recruitment of trees to the river as a result of bank erosion.
3.2. Wood Transport
Wood transport, in June and July 2012, was observed to be predominantly occurring at and
below the Three Rivers Confluence (Photographs 4, 5, 6, 9, 10). The Chulitna River appears to
be a major source of the wood transported into the Lower Susitna River (Photographs 4-6) as
large amounts of wood were observed in the main stem Chulitna River at Three Rivers
Confluence. The braided reach below Three Rivers Confluence is a transport limited segment of
the Susitna River as evidenced by both channel braiding and the large amount of deposited
racked and unstable wood debris (Photographs 9 and 10). Wood transport was observed in the
Middle Susitna; however, it was limited to single trees with root wads attached, evidence of
incremental bank erosion recruitment (Photographs 7 and 8).
Ice processes, ice break-up and ice damming, likely have dramatic effects on initiating transport
of wood debris through the channel network. The shear forces of moving ice would easily
entrain wood during ice break-up causing large scale transport of unstable wood debris.
Therefore, annual ice break-up likely initiates mass transport of wood debris. Furthermore, ice
damming and associated backwater increases in flood stage is also likely to mobilize and
transport any unstable wood.
3.3. Wood Debris: Channel Formation, Channel Splitting, and Island
Development
Wood debris has been documented to influence channel form and development, floodplain
formation, and island development influencing the formation of valley wide channel and
floodplain planform and associated aquatic and riparian habitat (Collins et al. 2012). Wood
debris was observed in 2012 to be associated with islands (Photographs 13, 14, 15, 16, 19, 20,
21, 23, 25, 26), channel splits (Photographs 15, 16, 18, 19) and side channel confluences
(Photographs 22 and 24). The role that wood debris plays in Susitna River channel, floodplain
and island formation needs to be further documented in terms of occurrence of key member size
and function. This will occur in the geomorphology study, Study Component G-1.9: Large
Woody Debris to be conducted in 2013-2014 (see Section 6.5.4.9 of the Revised Study Plan
(RSP) submitted to FERC December 14, 2012).
3.4. Stable Wood Jams
Stable wood jams are accumulations of wood debris anchored by key members (Tables 1 and 2;
Abbe and Montgomery 2003). Wood debris accumulations, or “jams,” may be classified as to
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whether wood debris has been fluvially transported some distance downstream, or not, and
further typed based upon systematic ways in which jams form and affect alluvial terrain and
habitat forming processes (Tables 1 and 2; Abbe and Montgomery 2003). It is beyond the scope
of this memorandum to differentiate all of the 2012 reconnaissance observations by wood jam
type. However, significantly, the vast majority of wood debris and wood debris accumulations
observed during the 2012 reconnaissance survey appear to be unstable racked members and not
stable wood jams anchored by large key member sized wood. Most of the wood debris observed
appears to be transported long distances, multiple active channel widths, through the channel
network. On-the-ground surveys are necessary to confirm this observation.
Also, observed stable wood jams were associated with scour pools, islands, channel
embankments, and side channel complexes (Photographs 12-17, 19-30).
3.5. Wood Debris and Bank Stabilization
In large alluvial rivers, such as the Susitna, recruitment of floodplain streamside trees through
bank erosion can result in wood debris structures composed of logs hydraulically aligned parallel
to the channel bank that become embedded into the floodplain further stabilizing channel banks
(Abbe and Montgomery 2003; Photographs 12, 17, 27, 28, 29, 30). Additionally, loose mobile
wood debris was observed accumulating along river embankments forming unstable wood debris
accumulations (Photographs 12, 17, 28, 29, 30).
3.6. Unstable Wood Debris
Bar top accumulations of unstable wood debris appear to be a defining characteristic of the
Susitna River. Large quantities of unstable wood debris were observed throughout the Project
study area with largest accumulations occurring in the Lower Susitna (Photographs 9, 10, 21)
with apparently large contributions from the Chulitna River. However, unstable wood debris
was observed throughout both Middle and Lower River segments during the 2012 aerial
reconnaissance (Photographs 16, 21, 31, 32, 33, 34, 35, 36, 37). Loose, mobile wood was
observed along river banks (Photographs 2, 3), mid channel islands (Photographs 18, 20), and
throughout side channel complexes (Photographs 16, 17, 18, 21, 34).
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4. REFERENCES
Abbe, T.B. and Montgomery, D.R. 1996. Large woody debris jams, channel hydraulics and
habitat formation in large rivers, Regulated Rivers Research & Management 12, 201-221.
Abbe, T.B. and Montgomery, D.R. 2003. Patterns and processes of wood debris accumulation
in the Queets river basin, Washington. Geomorphology 51: 81-107.
Collins, B., D. Montgomery, K.L. Fetherston, and T. Abbe. 2012. The floodplain large-wood
cycle hypothesis: a mechanism for the physical and biotic structuring of temperate
forested alluvial valleys in the North Pacific coastal ecoregion. Geomorphology 139-
140: 460-470.
Helm, D.J. and W.B. Collins. 1997. Vegetation succession and disturbance on a boreal forest
floodplain, Susitna River, Alaska. Canadian Field-Naturalist 111: 553-566.
Labelle, J.C., M.S. Arend, L.D. Leslie, and W.J. Wilson. 1985. Geomorphic change in the
Middle Susitna River since 1949. Susitna Hydroelectric Project. Alaska Power
Authority.
Montgomery, D.R., Collins, B.D., Buffington, J.M., Abbe, T.B. 2003. Geomorphic effects of
wood in rivers. In: Gregory, S.V., Boyer, K.L., Gurnell, A.M. (Eds.). The Ecology and
Management of Wood in World Rivers. American Fisheries Society, Bethesda, MD. pp
21-47.
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5. TABLES
Table 1. Wood debris terminology.
Wood Debris Terminology1
Key member Large wood anchoring other woody debris
Racked member Wood debris lodged against a channel obstruction (e.g., boulder, key member, or other debris)
Loose member Wood debris filling wood jam interstitial space; add little physical integrity to the jam.
Wood jam Stable accumulation of wood debris associated with key member.
Notes:
1. After Abbe and Montgomery (2003).
Table 2. Basic wood debris accumulation typology.
Basic Wood Debris Accumulation Typology1
Types Distinguishing characteristics
In-situ (autochthonous) Key member has not moved down channel
Bank input Some or all of key member in channel
Log steps Key member forming log step in channel bed
Combination In-situ key members with additional racked wood debris
Valley Jam width exceeds channel width and influences valley bottom
Flow deflection Key members may be rotated, jam deflects channel course
Transport (allochthonous) Key members moved some distance downstream.
Debris flow/flood Chaotic wood debris accumulation, key members uncommon or absent, catastrophically
emplaced.
Bench Key members along channel edge forming bench-like surface.
Bar apex One or more distinct key members downstream of jam, often associated with development
of bar and island.
Meander Several key members buttressing large accumulation of racked wood debris upstream.
Typically found along outside of meanders.
Raft Large accumulation of wood debris capable of plugging even large channels and causing
significant backwater.
Unstable Unstable accumulations composed of racked wood debris upon bar tops or pre-existing
banks.
Notes:
1. After Abbe and Montgomery (2003).
Table 3. Middle and Lower Susitna River dominant floodplain tree characteristics (from Helm and Collins
1997).
Tree species Common name DBH (cm) Height (m)
Populus balsamifera Balsam poplar 53.2 ±2.4 24.7 ±0.5
Picea glauca White spruce 26.3 ±1.8 13.8±1.0
Betula papyrifera Paper birch 28.1±1.5 12.8±0.6
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6. FIGURES
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Figure 1. Susitna River Project Area.
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Figure 2. 2012 Riparian Vegetation Survey Study Area.
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7. PHOTOGRAPHS
Photographic Documentation of Role and Function of Susitna River Wood Debris
7.1 Wood Recruitment
Photographs 1-3
7.2 Wood Debris: Transport
Photographs 4-10
7.3 Wood Debris: Stable Log Jams and Scour Pools
Photographs 11-12
7.4 Wood Debris: Channel Splitting & Island Formation
Photographs 13-26
7.5 Wood Debris: Bench Development and Bank Stabilization
Photographs 27-30
7.6 Unstable Wood Debris
Photographs 31-37
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7.1. Wood Recruitment
Photograph 1. June 26, 2012 Susitna Middle River between Three Rivers Confluence and Gold Creek. Wind
snapped and wind throw balsam poplar recruitment to channel.
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Photograph 2. June 26, 2012 Middle Susitna River between Three Rivers Confluence and Gold Creek. Bank
erosion and wind throw balsam poplar wood recruitment.
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Photograph 3. June 26, 2012 Middle Susitna River between Three Rivers Confluence and Gold Creek. Wind
snap balsam poplar recruitment.
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7.2. Wood Debris: Transport
Photograph 4. June 26, 2012 Three Rivers (Susitna, Chulitna, and Talkeetna rivers) Confluence. Fresh
recruited balsam poplar transport.
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Photograph 5. June 26, 2012 Three Rivers (Susitna, Chulitna, and Talkeetna rivers) Confluence. Fresh
recruited balsam poplar transport.
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Photograph 6. June 26, 2012 Three Rivers (Susitna, Chulitna, and Talkeetna rivers) Confluence balsam
poplar transport.
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Photograph 7. June 26, 2012 Middle Susitna River immediately upstream of Three Rivers Confluence.
Freshly recruited white spruce.
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Photograph 8. June 26, 2012 Middle Susitna River wood transport. Paper birch deposited on a mid-channel
island bar.
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Photograph 9. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Large wood transport
and deposition. Root wads are facing upriver. Flow is from right to left.
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Photograph 10. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Large wood transport
and deposition. Root wads are facing upriver. Flow is from left to right.
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7.3. Wood Debris: Stable Log Jams and Scour Pools
Photograph 11. July 2, 2012 Lower Susitna River below Talkeetna. Large balsam poplar (79 cm diameter,
DBH) with root wad (210 cm diameter) and adjacent scour pool formation (Sample Plot T19_04).
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Photograph 12. July 2, 2012 Middle Susitna River near Talkeetna. Wood jam with key and racked
members.
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7.4. Wood Debris: Channel Splitting and Island Formation
Photograph 13. June 26, 2012 Middle Susitna River wood jam at head of mid channel island and adjacent
side-channel.
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Photograph 14. July 2, 2012 Lower Susitna River near Talkeetna. Partially buried key member with racked
members and unstable wood. Young balsam poplar establishment in association with wood jam.
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Photograph 15. June 26-27, 2012 Middle Susitna River above Three Rivers Confluence. Wood jam located
at island apex and side channel entrance. Lower Photograph close up of wood jam with small diameter
racked and loose members.
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Photograph 16. June 30, 2012 Lower Susitna River below Talkeetna. Rafts of racked and unstable wood.
Accumulations at island apex and main stem side-channels.
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Photograph 17. July 2, 2012 Lower Susitna River side channel between Talkeetna and Willow. Rafts of
wood debris in side channel and along floodplain embankment.
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Photograph 18. July 2, 2012 Lower Susitna River between Talkeetna and Willow. Close-up of racked wood
debris deposited on side channel gravel bar.
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Photograph 19. July 2, 2012 Lower Susitna River between Talkeetna and Willow. Racked wood debris at
island apex and side channel.
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Photograph 20. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Racked wood on mid
channel islands.
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Photograph 21. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Unstable accumulations
of racked wood debris upon bars and stable island bar apex jams with racked members.
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Photograph 22. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Bar apex wood jam with
racked members at island apex and side channel entrance.
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Photograph 23. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Wood jams in side
channel complex.
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Photograph 24. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Bar apex wood jam at
side channel exit.
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Photograph 25. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Rafts of wood in side
channel complex.
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Photograph 26. July 2, 2012 Lower Susitna River below Talkeetna. Bar apex wood jam with buried key
member and racked members. Young balsam poplar colonizing elevated wood jam surface.
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7.5. Wood Debris: Bank Stabilization
Photograph 27. June 26, 2012 Middle Susitna River above Three Rivers Confluence. In-situ key member
forming floodplain bench.
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Photograph 28. June 26, 2012 Middle Susitna River above Three Rivers Confluence. Bench jam with racked
members.
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Photograph 29. July 1, 2012 Middle Susitna River immediately above Whiskers Slough. Bar apex jam with
large accumulation of racked members upstream of jam.
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Photograph 30. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Long bench jam with
large accumulations of racked wood. Flow is from right to left.
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7.6. Unstable Wood Debris
Photograph 31. July 2, 2012 Middle Susitna River immediately above Three Rivers Confluence. Typical
unstable wood debris. Note orange tape measure for scale.
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Photograph 32. July 2, 2012 Lower Susitna River below Talkeetna. Typical loose, unstable wood debris.
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Photograph 33. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Mid channel rafts of
wood debris. Flow is from right to left.
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Photograph 34. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Rafts of racked wood
debris.
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Photograph 35. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Racked wood deposited
at young balsam poplar/alder vegetation obstruction.
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Photograph 36. June 30, 2012 Lower Susitna River between Talkeetna and Willow. Racked wood on mid
channel gravel bar.
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Photograph 37. June 30, 2012 Lower Susitna River at Talkeetna immediately below Three Rivers
Confluence. Balsam poplar (85 cm diameter, DBH; 18 m length; Plot T19).