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Susitna-Watana Hydroelectric Project Document
ARLIS Uniform Cover Page
Title:
Fluvial geomorphology modeling below Watana Dam study, Study plan
Section 6.6 : Final study plan SuWa 200
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Alaska Energy Authority
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Final study plan
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Series (ARLIS-assigned report number):
Susitna-Watana Hydroelectric Project document number 200
Existing numbers on document:
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[Anchorage : Alaska Energy Authority, 2013]
Date published:
July 2013
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Study plan Section 6.6
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Pagination:
64 p.
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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/
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Fluvial Geomorphology Modeling below Watana Dam
Study
Study Plan Section 6.6
Final Study Plan
Alaska Energy Authority
July 2013
FINAL STUDY PLAN FLUVIAL GEOMORPHOLOGY MODELING BELOW WATANA DAM STUDY 6.6
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6.6. Fluvial Geomorphology Modeling below Watana Dam Study
On December 14, 2012, Alaska Energy Authority (AEA) filed with the Federal Energy
Regulatory Commission (FERC or Commission) its Revised Study Plan (RSP), which included
58 individual study plans (AEA 2012). Included within the RSP was the Fluvial Geomorphology
Modeling below Watana Dam Study, Section 6.6. RSP Section 6.6 focuses on the modeling
planned for assessing the effects of the proposed Project and its operations on fluvial
geomorphology in the Susitna River basin.
On February 1, 2013, FERC staff issued its study determination (February 1 SPD) for 44 of the
58 studies, approving 31 studies as filed and 13 with modifications. On April 1, 2013 FERC
issued its study determination (April 1 SPD) for the remaining 14 studies; approving 1 study as
filed and 13 with modifications. RSP Section 6.6 was one of the 13 approved with
modifications. In its April 1 SPD, FERC recommended the following:
Modeling in Focus Areas
- We recommend that AEA file by June 30, 2013, the proposed technical memorandum
related to the selection and application of the one- and two-dimensional models (proposed
for development in the second quarter of 2013). We also recommend that the technical
memorandum include the following information:
1) specification of the one- and two-dimensional models to be used in the fluvial
geomorphology modeling pursuant to this study as well as the aquatic habitat models
pursuant to Study 8.5 (fish and aquatics instream flow);
2) location and extent of one- and two-dimensional geomorphology and aquatic habitat
modeling in project reaches, focus areas, and other study sites;
3) rationale and criteria for model selection including an overview of model
development;
4) for fluvial geomorphology modeling only, a detailed description of the processes and
methods by which ice and LWD would be incorporated into the modeling approach (as
described in our recommendations for Incorporating Large Woody Debris and Ice
Processes into Fluvial Geomorphic Modeling); and
5) documentation of consultation with the TWG, including how the TWG’s comments
were addressed.
We expect additional detail on model parameterization, model calibration, model validation,
and sensitivity analysis would be included in the initial and updated study reports.
Interaction of Geomorphic Processes in the Mainstem and Tributaries
- We recommend the study plan be modified to include a defined approach to evaluating
geomorphic changes at the confluence of the Chulitna, Talkeetna and Susitna Rivers. The
evaluation should extend from the mouth of both the Chulitna and Talkeetna Rivers to the
potentially affected upstream reaches of these tributaries. We recommend that AEA prepare
a technical memorandum detailing a proposed approach for evaluating geomorphic changes
in the three rivers confluence area, including explicitly stated objectives for evaluating
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geomorphic changes, an overview of the technical approach, additional data collection
required, models and model components to be used, and additional analyses that would be
conducted to address the stated objectives. We recommend that AEA file by June 30, 2013,
this technical memorandum to include documentation and consultation with the TWG,
including how the TWG’s comments were addressed.
Incorporating Large Woody Debris and Ice Processes into Fluvial Geomorphic Modeling
- As noted above in our analysis and recommendations for Modeling in Focus Areas, we are
recommending that AEA file a technical memorandum with additional information on AEA’s
proposed model selection process. We recommend that an additional provision be added to
the technical memorandum requiring that AEA describe in detail how ice and LWD would be
incorporated into both one- and two-dimensional modeling approaches. The technical
memorandum should explicitly state where and how each of the five scenarios for
incorporating ice processes into one-dimensional and/or two-dimensional fluvial
geomorphology modeling would be implemented, as well as details regarding where and how
LWD pieces and/or accumulations would be incorporated into two-dimensional modeling.
Operational Scenarios
- As discussed under the general comments section of this study plan determination, we
recommend the study plan be modified to include run-of-river operation.
In accordance with the April 1 SPD, on May 3 , 2013, AEA provided to the Technical Work
Group participants for comment a Draft Fluvial Geomorphology Modeling Approach Technical
Memorandum (Geomorphology Modeling TM) that was developed to provide responses to all
April 1 SPD recommendations. The Draft Geomorphology Modeling TM was made available on
the Project website (http://www.susitna-watanahydro.org). Consistent with the April 1 SPD,
AEA allowed a minimum of 15 days for comment. NMFS submitted comments on May 18,
2013. AEA also received comments on the Draft Geomorphology Modeling TM from one
individual and two non-government organizations.
Recommended modifications were addressed in detail in the Final Geomorphology Modeling
TM filed with FERC on July 1 , 2013. Information in the Final Geomorphology Modeling TM
supersedes relevant details within this Final Study Plan.
6.6.1. General Description of the Proposed Study
The overall goal of the Fluvial Geomorphology Modeling below Watana Dam Study is to model
the effects of the proposed Project on the fluvial geomorphology of the Susitna River to assist in
predicting the trend and magnitude of geomorphic response. More specifically, the purpose of
the modeling study, along with the Geomorphology Study (Section 6.5), is to assess the potential
impact of the Project on the behavior of the river downstream of the proposed dam, with
particular focus on potential changes in instream and riparian habitat. Whether the existing
channel morphology will remain the same or at least be in “dynamic equilibrium” under post-
Project conditions is a significant question in any instream flow study (i.e., Is the channel
morphology in a state of dynamic equilibrium such that the distribution of habitat conditions will
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be reflected by existing channel morphology, or will changes in morphology occur that will
influence the relative distribution or characteristics of aquatic habitat over the term of the
license? [Bovee 1982]). This key issue prompts four overall questions that must be addressed by
the two geomorphology studies:
• Is the system currently in a state of dynamic equilibrium?
• If the system is not currently in a state of dynamic equilibrium, what is the expected
evolution over the term of the license in the absence of the project?
• Will and in what ways will the Project alter the equilibrium status of the downstream
river (i.e., what is the expected morphologic evolution over the term of the license under
with-Project conditions)?
• What will be the expected effect of the Project-induced changes on the geomorphic
features that form the aquatic habitat and therefore are directly related to the quantity,
distribution and quality of the habitat?
The methods and results from the Geomorphology Study and the Fluvial Geomorphology
Modeling Study will address these questions.
Specific objectives of the Fluvial Geomorphology Modeling Study are as follows:
• Develop calibrated models to predict the magnitude and trend of geomorphic response to
the Project.
• Apply the developed models to estimate the potential for channel change for with-Project
operations compared to existing conditions.
• Coordinate with the Geomorphology Study to integrate model results with the
understating of geomorphic processes and controls to identify potential Project effects
that require interpretation of model results.
• Support the evaluation of Project effects by other studies in their resource areas providing
channel output data and assessment of potential changes in the geomorphic features that
help comprise the aquatic and riparian habitats of the Susitna River.
6.6.2. Existing Information and Need for Additional Information
Sediment transport issues downstream of Watana Dam are expected to stem from the influences
of the regulated outflows and the deficit of sediment supply due to trapping of sediments in the
reservoir. These issues are particularly important because fish resources have the greatest
potential to be affected by the Project, and most of the potential impacts would occur
downstream of the Project (AEA 2010). The effect of altered flows on anadromous and resident
fish habitats and their associated populations was the major focus of studies conducted in the
1980s (APA 1984). The major fish habitats are located in the Susitna River, side channels, side
sloughs, upland sloughs, and tributary mouths (APA 1984).
Modeling of the hydraulics of the Susitna River below the previously proposed project, a
necessary step in developing a sediment transport model, was performed in the 1980s. This work
included development and application of one-dimensional HEC-2 hydraulic models to support
the calculation of water-surface profiles and channel hydraulics (Acres 1983). The models
represented the reach between Devils Canyon (Susitna RM 186.8) and Talkeetna (RM 99),
excluding Devils Canyon (Susitna RM 162.1 to RM 150.2). The Aquatic Resources Data Gap
Analysis (HDR 2011) indicates that sediment transport modeling of a portion of the Susitna
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River was also undertaken. Realizing the complexity of the sediment transport problem at the
Chulitna River confluence, APA commissioned the Iowa Institute of Hydraulic Research to
develop a quasi-steady, one-dimensional numerical model of sediment transport for the 14-mile
reach of the Susitna River from the Chulitna confluence downstream to Sunshine Station (Holly
et al. 1985). The model was based on sediment transport data from 1981 and 1982, as the
following years of data collection had not yet been completed. The topography was derived from
28 cross-sections (approximately 1 every ½ mile) measured by R&M Consultants and aerial
photography (Ashton and R&M 1985). The model was still in development as of the writing of
the 1985 report; however, the companion report, referenced in Holly et al. (1985), was not found
in the Susitna documentation.
The Aquatic Resources Data Gap Analysis (HDR 2011) indicates that channel equilibrium, an
important macrohabitat variable, was not addressed in the APA Project instream flow study. The
question of whether the existing channel morphology will remain the same, or at least be in
“dynamic equilibrium” once the proposed action is implemented is a significant question in an
instream flow study. Instream flow versus habitat relationships developed for today’s river
assume that similar relationships will persist for the duration of the project, within a reasonably
defined range of variability. In the case of the proposed Project’s instream flow study, the
question is whether the river is currently in a state of equilibrium or disequilibrium. If it is in a
state of disequilibrium, will the state be exacerbated or reversed as a result of the Project? If it is
exacerbated or reversed, the impact of the Project cannot be assessed without estimating a post-
Project channel configuration (Bovee et al. 1998). The same holds true if the river is currently in
a state of equilibrium and shifts to disequilibrium for a significant period of time with the Project
in place.
The AEA Susitna Water Quality and Sediment Transport Data Gap Analysis Report (URS 2011)
concluded: “Numerical modeling of the sediment transport dynamics would provide a basis for
comparing the changes in channel morphology and aquatic habitat associated with the proposed
Project and the proposed operations.” The Fluvial Geomorphology Modeling below Watana
Dam Study addresses the need to develop a sediment transport model of the Susitna River. It
was also indicated in the Data Gap Analysis Report (URS 2011) that further quantification of the
sediment supply and transport capacity would help identify the sensitivity of the channel
morphology (and associated aquatic habitats) to the effects of the proposed Project. The report
indicated that information on sediment continuity could provide a basis for evaluating whether
the Susitna River below the Chulitna confluence would be at risk of aggradation, and if so,
whether the magnitude would alter aquatic habitats and hydraulic connectivity to these habitats.
URS (2011) also pointed out that side channels and sloughs are of particular importance to
fisheries, and changes to the relationships between flow and stage at which the habitats are
accessible could affect the fisheries. These relationships can be affected by not only flow
distribution, but also changes in the bed elevations due to sediment transport processes. Other
impacts to the sediment transport regime could affect the cleaning of spawning gravels,
hyporheic flows through redds, groundwater inflows, and hydraulic connectivity for out-
migration to the main channel.
6.6.3. Study Area
The study area for the Fluvial Geomorphology Modeling below Watana Dam is the portion of
the Susitna River from Watana Dam (RM 184) downstream to RM 75. This downstream limit
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has been set to extend the Study into the upper portion of the Lower Susitna River Segment. This
limit extends this study nine miles downstream of the lower limit of Geomorphic Reach LR-1.
Evaluation of information from the 1980s studies as well as current information indicates that it
is unlikely that Project effects on the geomorphology of the Susitna River will extend
downstream of Geomorphic Reach LR-1. This is initial assessment is based on the large
introduction of sediment and water at the Three Rivers Confluence where both the Chulitna and
Talkeetna rivers approximately double the flow in the Susitna River and increases the sediment
supply by approximately a factor of five. In response to the increase in sediment supply as well
as a reduction in gradient, the form of the Susitna River changes at the Three Rivers Confluence
from a single channel to a braided channel. The 15 miles of braided channel is expected to buffer
the downstream remaining portion of the Susitna River from the changes in flow regime and
sediment supply caused by the Project.
Further review of information developed during the 1980s studies and study efforts initiated in
2012, such as sediment transport analyses, hydrologic analysis, assessment of channel change
and comparison of habitat mapping from the 1980s with current 2012 conditions in the
Geomorphology Study (Section 6.5), and additional 2012 habitat mapping (Section 9.9)
operations modeling and the Mainstem (Open-water) Flow Routing Model (Section 8.5.4.3) will
be used to determine the extent to which Project operations influence habitats in the Lower River
Segment. An initial assessment of the downstream extent of Project effects will be developed in
Q2 2013 in collaboration with the TWG. This assessment will guide the need to extend studies
into the Lower River and which geomorphic reaches will subject to Reach and Focus Area level
modeling of the fluvial geomorphology of the Susitna River in 2013. Results of the 2013 studies
will be used to determine the extent to which Lower Susitna River Segment studies will be
adjusted in 2014. Further discussion of the process and schedule for further assessing the
downstream limit for the Fluvial Geomorphology Modeling Study, additional information
becomes available, is provided in section 6.6.3.2.
The study area includes the entire Middle Susitna River Segment from the Watana Dam site (RM
184) downstream to the Three Rivers Confluence area (RM 98). (Note: Modeling of Devils
Canyon will not be performed because this reach is considered too dangerous to perform cross-
section and other surveys needed to develop the model. Devils Canyon will be assumed to be a
stable, pass-through reach in terms of sediment transport due to the high level of bedrock control
and steep gradient present in this reach.)
6.6.3.1. Focus Areas
The bed evolution modeling approach calls for the application of a 1-D bed evolution model to
predict the geomorphic response of the Susitna River to the Project for the entire study area
(excluding Devils Canyon). To provide a higher level of detail and to model physical processes
not adequately represented in a 1-D bed evolution model, a 2-D bed evolution model will be
applied in to some or all of the “Focus Areas” (in some instances, it may be appropriate to apply
a more detailed 1-D bed evolution model or series of 1-D models than a 2-D bed evolution
model). Focus Areas will involve portions of the Susitna River and its floodplain where detailed
study efforts will be jointly conducted by several study teams including the Fish and Aquatics
Instream Flow (Section 8.5), Riparian Instream Flow (Section 8.6), Geomorphology (Section
6.5), Ice Processes (Section 7.6), Groundwater (Section 7.5), and Characterization and Mapping
of Aquatic Habitats (Section 9.9) studies. The Focus Areas will allow for a highly integrated,
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multidisciplinary effort to be conducted, evaluating potential Project effects for key resource
areas across a range of representative sites.
The 2-D models will be used to evaluate the detailed hydraulic and sediment transport
characteristics on smaller, more local scales where it is necessary to consider the more complex
flow patterns to understand and quantify the issue(s). The 2-D models may be applied to specific
Focus Areas, within the selected 1-D modeling study area, that are representative of important
habitat conditions and the various geomorphic reach types. If site conditions at a particular Focus
Area do not warrant 2-D bed evolution and associated hydraulic modeling, 1-D modeling will be
applied at that focus site. The decision on what type of modeling to apply to each Focus Area
will be made as part of the site selection process conducted in collaboration with the licensing
participants. In addition, the Focus Areas will be chosen jointly by the Fish and Aquatics
Instream Flow (Section 8.5), Riparian Instream Flow (Section 8.6), Geomorphology (Section
8.5), Ice Processes (Section 7.6), and Characterization and Mapping of Aquatic Habitats Study
(Section 9.9) studies to facilitate maximum integration of available information among the
studies. Sites will be chosen such that there is at least one Focus Area for each geomorphic reach
(except reaches MR-3 and MR-4 where there are safety concerns associated with Devils Canyon
due to the extreme whitewater conditions) and the sites will cover the range of riverine aquatic
habitat types. At least one unstable site, likely representative of a braided channel reach, will be
included in the Focus Areas. If focus sites involve primary tributary deltas, 2-D modeling will
also be considered based on screening that considers the importance to the existing fishery and
the potential for adverse project effects. The 2-D hydraulic modeling could include the Three
Rivers Confluence area, though application of a 2-D bed evolution model would likely be
infeasible. (The distribution of the 2-D sites is based on the study requests submitted by NOAA-
NMFS and USFWS on May 31, 2012, and discussions during the June 14, 2012 Water
Resources TWG meeting.)
6.6.3.2. Determination of Downstream Study Limit
The downstream extent of the Lower Susitna River Segment modeling effort has been identified
as RM 75. The 1-D modeling will be continued downstream to this limit which is approximately
nine miles downstream of Sunshine Station (RM 84) (NOAA-NMFS and USFWS requested the
1-D modeling extend to Sunshine Station [study requests dated May 31, 2012]). The
downstream extent of the impacts of a dam on the geomorphic and physical habitat
characteristics of a river is fundamentally dependent on the rate of downstream tributary
mitigation of the reduced flows and sediment loads below the dam (Williams and Wolman 1984;
Grant et al. 2003). Under existing conditions, it is clear based on the change in morphology of
the Susitna River from a relatively confined single channel to extensively braided (Smith and
Smith 1984) that the Chulitna and Talkeetna Rivers, in combination, significantly increase both
the volumes of flow and sediment supply to the Susitna River, and thus potentially mitigate the
proposed Project impacts on the geomorphology of the river below the confluence. Because of
the geologically-controlled valley floor constriction at RM 84, there is extensive sediment
storage within the reach between the Susitna-Chulitna-Talkeetna Rivers confluence at RM 97
and RM 84 that is likely to mitigate any sediment impacts below the dam and thus make it
unlikely that Project geomorphic and related physical habitat impacts will extend below RM 84
(LR1). Sediment loads estimated by the USGS for Water Year 1985 (October 1984 through
September 1985) are presented in Table 6.5-2. This information suggests that the Chulitna River
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contributes the majority of the sediment load at the Three Rivers Confluence. The relative
contributions are 61 percent for the Chulitna River, 25 percent for the Susitna River, and 14
percent for the Talkeetna River. Of note is the relatively small amount of the gravel load
contributed by the Susitna River to the Three Rivers Confluence (about 4 percent, compared to
83 percent from the Chulitna River and 13 percent from the Talkeetna River, based on the 1985
data). The bedload component of the total sediment load typically has the most influence on the
form and behavior of the river channel. Based on the relatively small contribution of the Susitna
River to the bedload downstream from the Three Rivers Confluence and the indication from the
1985 data that the portion of the study reach between the Three Rivers Confluence and Sunshine
is a net sediment accumulation zone, it appears that changes in bedload associated with the
Project may not have a significant impact on channel form and process in the Lower River.
The hypothesis suggested by the above preliminary conclusion that changes in bedload due to the
Project will not affect channel form and process in the Lower River will be carefully tested with
an initial assessment of potential Project effects on channel morphology that will be completed in
early Q1 of 2013 as part of the Geomorphology Study (Section 6.5.4.6, Reconnaissance-Level
Assessment of Project Effects on the Lower and Middle Susitna River Segments). The technical
memorandum detailing the results of the Reconnaissance-Level Assessment of Project Effects on
the Lower Susitna River Segment will be presented to and reviewed by the agencies and
licensing participants as part of the first check-in on the downstream study limit of RM 75.
Discussions of the results and conclusions regarding the extent of Project effects on the
geomorphology of the Lower Susitna River Segment and the decision on adjusting the
downstream study limit for the 2013 efforts will occur at Technical Workgroup Meetings to be
held in February and/or March 2013. These discussions will include establishing the criteria for
identifying whether Project effects potentially extend downstream of RM 75. It is an objective
of the process to finalize the decision on the downstream study limit by the early Q2 of 2013 to
allow for planning of the 2013 field season.
The second check-in on the downstream study limit to be provided by the geomorphology
studies will be based on the results of the 1-D bed evolution model. If the results of the 1-D
modeling effort show differences between the modeled existing and the modeled with-Project
conditions that are beyond the range of natural variability below Geomorphic Reach LR-1 (RM
98 to RM 84), the 1-D modeling will be continued farther downstream in the Lower Susitna
River Segment in 2014. The criteria for determining what constitutes natural variability will be
made in collaboration with the licensing participants. As part of the process, a technical
memorandum documenting the 1-D modeling effort and its results will be prepared and
distributed for review by the licensing participants in January 2014. A Technical Workgroup
meeting(s) will be held in February and/or March 2014. If it is determined that the results of the
1-D modeling warrant extending the study limits farther downstream, the need for adding Focus
Areas in the Lower Susitna River Segment will also be determined through consultation with the
licensing participants and pertinent study leads at the February and March 2014 Technical
Workgroup meetings. Table 6.6-1 provides a summary of the steps and dates involved in the
process that will be used to assess and if necessary, adjust the downstream study limit for the
Fluvial Geomorphology Modeling Study.
The results of the Open-water Flow Routing Model (see Section 8.5.4.3), which is scheduled to
be completed in Q1 2013, as well as results of the operations model (Section 8.5.4.3.2), are an
important part of the determination of the downstream study extent for a variety of resource
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areas. The results of the Open-water Flow Routing Model completed in Q1 2013 will be used to
determine whether, and the extent to which, Project operations related to load-following as well
as seasonal flow changes occur within a section of the Lower Susitna River Segment that
includes all of Geomorphic Reach L-1 and a portion of L-2 (down to RM 75). Thus, an initial
assessment of the downstream extent of Project effects will be developed in Q1 2013 with
review and input of the TWG. This assessment will include a review of information developed
during the 1980s studies and study efforts initiated in 2012, such as sediment transport (Section
6.5), habitat mapping (Sections 6.5 and 9.9), operations modeling (Section 8.5.4.3.2), and the
Mainstem Open-water Flow Routing Model (Section 8.5.4.3). The assessment and the following
six criteria will be used to evaluate the need to extend studies into the Lower River Segment, and
if studies are needed, will identify which geomorphic reaches require instream flow analysis in
2013. The criteria include (1) Magnitude of daily stage change due to load-following operations
relative to the range of variability for a given location and time under existing conditions (i.e.,
unregulated flows); (2) Magnitude of monthly and seasonal stage change under Project
operations relative to the range of variability under unregulated flow conditions; (3) Changes in
surface area (as estimated from relationships derived from LiDAR and comparative evaluations
of habitat unit area depicted in aerial digital imagery under different flow conditions) due to
Project operations; (4) Anticipated changes in flow and stage to Lower River off-channel
habitats; (5) Anticipated Project effects resulting from changes in flow, stage and surface area
on habitat use and function, and fish distribution (based on historical and current information
concerning fish distribution and use) by geomorphic reaches in the Lower River Segment; and
(6) Initial assessment of potential changes in channel morphology of the Lower River (Section
6.5.4.6) based on Project-related changes to hydrology and sediment supply in the Lower River.
Results of the 2013 studies will then be used to determine the extent to which Lower River
Segment studies should be adjusted in 2014.
It is noted that a variety of resource areas require determination of their downstream study limits.
Although both Middle and Lower Susitna River segments are under consideration as part of the
IFS, the majority of detailed study elements for the IFS described in the RSP (Sections 8.5 and
8.6) are concentrated within the Middle River Segment. This is because Project operations
related to load-following and variable flow regulation will likely have the greatest potential
effects on this segment of the river. These effects tend to attenuate in a downstream direction as
channel morphologies change, and flows change due to tributary inflow and flow accretion. The
diversity of habitat types and the information from previous and current studies that indicate
substantial fish use of a number of slough and side channel complexes within this segment also
support the need to develop a strong understanding of habitat–flow response relationships in the
Middle Susitna River Segment. The determination for downstream study limits may also depend
on the outcome of 2013 efforts being conducted for the Water Quality Modeling Study (Section
5.6), Mainstem (Open-water) Flow Routing Model (Section 8.5.4.3), and the winter flow routing
model (Section 7.6). Whether there is need to integrate Fluvial Geomorphology Modeling Study
results with certain studies also depends on the final downstream limit for the modeling effort.
Specifically, the Eulachon Study (Section 9.16) is limited to the downstream-most portions of
the Lower Susitna River Segment and will not require detailed sediment transport modeling
input from the Fluvial Geomorphology Modeling Study if the modeling effort is not extended
downstream of RM 75.
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6.6.4. Study Methods
The Fluvial Geomorphology Modeling below Watana Dam is divided into three study
components:
• Bed Evolution Model Development, Coordination, and Calibration
• Model Existing and with-Project Conditions
• Coordination on Model Output
Each of these components is explained further in the following subsections.
6.6.4.1. Study Component: Bed Evolution Model Development, Coordination, and
Calibration
The overall goal of the Bed Evolution Model Development, Coordination, and Calibration study
component is to develop a model that can simulate channel formation processes in the Susitna
River downstream of Watana Dam.
6.6.4.1.1. Existing Information and Need for Additional Information
Modeling of hydraulics of the Susitna River below the proposed Project, a necessary step in
developing a sediment transport model, was performed in the 1980s. One-dimensional HEC-2
hydraulic models were developed in the 1980s to support the calculation of water-surface
profiles and channel hydraulics (Acres 1983). However, the 1980s effort did not include
sediment transport modeling. Both 1-D and 2-D sediment transport models are required to
characterize the bed evolution for both the existing and with-Project conditions in the Susitna
River. This study component involves selection and development of the sediment transport
models.
6.6.4.1.2. Methods
The Bed Evolution Model Development, Coordination, and Calibration study component is
divided into three tasks:
• Development of Bed Evolution Modeling Approach and Model
• Coordination with other Studies on Processes Modeled
• Calibration/Validation of the Model
6.6.4.1.2.1. Development of Bed Evolution Model Approach and Model Selection
Development of the bed evolution model for a dynamic system such as the Susitna River is a
complex undertaking that requires considerable investigation and coordination. The work in the
Middle and Lower Susitna River Segments contained in the Geomorphology Study provides a
considerable part of the required investigation. Based on the study results and input from the
Mainstem (Open-water) Flow Routing Model (Section 8.5.4.3), Fish and Aquatics Instream Flow
(Section 8.5), Riparian Instream Flow (Section 8.6), Ice Processes (Section 7.6), and
Characterization and Mapping of Aquatic Habitats Study (Section 9.9) studies, models will be
developed that represent the physical processes that control the dynamic nature of the Susitna
River, and that will provide other studies with the required information on the potential changes
in the channel and floodplain for their analyses.
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Some of the important steps in the development of the modeling approach and model are as
follows:
• Review and understand available data.
• Develop an understanding of the dominant physical processes and governing physical
conditions in the study reach.
• Coordinate with other studies to understand their perspective on system dynamics, and
the physical features and processes that are important to their studies.
• Identify an overall modeling approach that is consistent with the study goals, the
constraints on information that is currently available or can practically be obtained, and
the needs of the other studies.
• Identify a modeling approach that is consistent with the spatial and temporal scale of the
area to be investigated.
• Determine the spatial limits of the modeling effort.
• Determine the time scales for the various models.
• Review potential models and select a model(s) that meets the previously-determined
needs and conditions.
• Identify data needs and data gaps for the specific model and study area being
investigated.
• Collect the required data to fill data gaps.
• Develop the model input.
• Identify information to be used to calibrate and validate the model.
• Perform initial runs and check basic information such as continuity for water and
sediment, hydraulic conditions, magnitude of sediment transport, and flow distributions.
• Collaborate with other studies on initial model results.
• Refine model inputs.
• Perform calibration and validation efforts, to include comparison of modeled water-
surface elevations, in-channel hydraulic conditions (e.g., velocity and depth), sediment
transport rates, and aggradation/degradation rates with available measured data.
• Perform model runs for existing conditions to provide a baseline for comparison of with-
Project scenarios.
• Work with other studies to develop scenarios to evaluate the potential Project effects, and
apply the model to those scenarios.
• Coordinate with other studies to evaluate and define the appropriate format for
presentation of the model results.
• Develop and run additional scenarios, as necessary, based on results from the initial
scenarios and identified Project needs.
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The following subsections outline the identified issues to be considered and summarize the
development of the modeling approach, the model selection, and the model development.
Issues to be Considered: To develop the modeling approach, specific issues that need to be
addressed have been identified. These specific issues have been further differentiated into reach-
scale and local-scale issues because the scale influences the proposed approach.
Reach-Scale Issues: Reach-scale issues refer to aspects of the system that involve the overall
behavior and general characteristics of the Susitna River over many miles. Each reach represents
a spatial extent of the Susitna River that has a consistent set of fluvial geomorphic
characteristics. Reach-scale issues include the following:
• Historical changes in the system and the existing status with respect to dynamic
equilibrium.
• Changes in both the bed material (sand and coarser sizes) and wash (fine sediment) load
sediment supply to the system due to trapping in Watana Reservoir.
• Long-term balance between sediment supply and transport capacity and the resulting
aggradation/degradation response of the system for pre- and post-Project conditions.
• Changes in bed material mobility in terms of size and frequency of substrate mobilized
due to alteration of the magnitude and duration of peak flows by the Project.
• Project-induced changes in supply and transport of finer sediments that influence
turbidity.
• Potential for changes in channel dimensions (i.e., width and depth) and channel pattern
(i.e., braiding versus single-thread or multiple-thread with static islands) due to the
Project and the magnitude of the potential change.
• Project-induced changes in river stage due to reach-scale changes in bed profile, channel
dimensions, and potentially hydraulic roughness.
Local-Scale Issues: Local-scale issues refer to aspects of the system that involve the specific
behavior and characteristics of the Susitna River at a scale associated with specific geomorphic
and habitat features. Local-scale issues are addressed using a more detailed assessment over a
finer Focus Area scale; however, these analyses must draw from and build upon the
understanding and characterization of the system behavior as determined at the reach scale.
Local-scale issues include the following:
• Processes responsible for formation and maintenance of the individual geomorphic
features and associated habitat types.
• Potential changes in geomorphic features and associated aquatic habitat types that may
result from effects of Project operation on riparian vegetation and ice processes.
• Effects of changes in flow regime and sediment supply on substrate characteristics in off-
channel habitat units.
• Changes in upstream connectivity (breaching) of off-channel habitats due to alteration of
flow regime and possibly channel aggradation/degradation. These changes may induce
further changes in the morphology of off-channel habitats, including the following:
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o Potential for accumulation of sediments at the mouth.
o Potential for accumulation of fines supplied during backwater connection with the
mainstem.
o Potential for changes in riparian vegetation that could alter the width of off-channel
habitat units.
• Project effects at representative sites on the magnitude, frequency, and spatial distribution
of hydraulic conditions that control bed mobilization, sediment transport, sediment
deposition, and bank erosion.
• Potential for change in patterns of bedload deposits at tributary mouths that may alter
tributary access or tributary confluence habitat, as discussed below.
Tributary confluences are areas of interest for determining the potential Project effects on
sediment transport and morphology. Modeling of tributary deltas is discussed as a topic separate
from the mainstem.
Synthesis of Reach-Scale and Local-Scale Analyses: The final step in the effort will be the
synthesis of the reach-scale and local-scale analyses to identify potential Project-induced
changes in the relative occurrence of aquatic habitat types and associated surface area versus
flow relationships. In addition to the results of the hydraulic and sediment transport modeling,
this synthesis will require application of fluvial geomorphic relationships to develop a
comprehensive and defensible assessment of potential Project effects. This type of integrated
analysis has been performed in the past by the study team on several projects including: instream
flow, habitat, and recreation flow assessments to support relicensing of Slab Creek Dam in
California; a broad range of integrated geomorphic assessments and modeling to assist the Platte
River Recovery Implementation Program in Central Nebraska; and ongoing work to support the
California Department of Water Resources and Bureau of Reclamation to design restoration
measures for the San Joaquin River in the Central Valley of California downstream of Friant
Dam.
Development of Modeling Approach: The proposed modeling approach considers the need to
address both reach-scale and local-scale assessments and the practicality of developing and
applying various models based on data collection needs, computational time, analysis effort, and
model limitations. Based on these considerations, an approach that uses 1-D models to address
reach-scale issues and 2-D models to address local-scale issues is proposed. Considering the
broad physical expanse of the Susitna River system, the general hydraulic and sediment transport
characteristics of the various sub-reaches that make up the overall study area will be evaluated
using 1-D computer models and/or established hydraulic relationships. The 2-D models will be
used to evaluate the detailed hydraulic and sediment transport characteristics on smaller, more
local scales where it is necessary to consider the more complex flow patterns to understand and
quantify the issues. The 2-D models will be applied to specific Focus Areas that are
representative of important habitat conditions—the various channel classification types and
selected primary tributaries. These sites will be chosen in coordination with the licensing
participants and the Fish and Aquatics Instream Flow (Section 8.5), Riparian Instream Flow
(Section 8.6), Ice Processes (Section 7.6), and Characterization and Mapping of Aquatic Habitats
(Section 9.9) studies to facilitate maximum integration of available information between the
studies.
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The proposed approach to integrating 1-D modeling at the reach-scale and 2-D modeling at the
local-scale will provide the following advantages:
• 1-D modeling will allow for efficient assessment of the hydraulic conditions and
sediment transport balance over the length of the study reach downstream of Watana
Dam.
• The 1-D model uses cross-sectional data that are being obtained as part of the Mainstem
(Open-water) Flow Routing Model (Section 8.5.4.3). (Note that some supplemental
cross-sections may be required for the 1-D sediment transport model.)
• The 1-D model will provide the boundary conditions for the 2-D model, including
starting water-surface elevations and upstream sediment supply.
• 2-D modeling applied at the Focus Areas that are also chosen for the Ice Processes
(Section 7.6) and Riparian Instream Flow (Section 8.6) studies will allow for the fullest
level of integration of these efforts, particularly as they relate to assessments of potential
changes in channel width and pattern for this study.
• 2-D modeling at the Focus Area will provide an understanding of the hydraulic
conditions and sediment transport processes that contribute to formation of individual
habitat types.
• 2-D modeling provides a much more detailed and accurate representation of the complex
hydraulic interaction between the main channel and the off-channel habitats than is
possible with a 1-D model.
Model Selection: Many computer programs are available for performing movable boundary
sediment-transport simulations. The choice of an appropriate model for this study depends on a
number of factors, including (1) the level of detail required to meet the overall project
objective(s); (2) the class, type, and regime of flows that are expected to be modeled; and (3) the
availability of necessary data for model development and calibration. While 2-D modeling would
provide the most comprehensive assessment of hydraulic and sediment transport conditions in
the study reach, the extent of required data, effort required for model development, and
computational time required for execution to model the entire system make this impractical.
Considering the very broad physical expanse of the overall Susitna River system, a one-
dimensional (1-D) computer model and/or engineering relationships that can be applied in a
spreadsheet application is the most practical approach to modeling overall system behavior at the
scale of the study reach. 2-D modeling will then be used for evaluating the detailed hydraulic
and sediment-transport characteristics that control the complex geomorphic features and habitat
at the local scale. A variety of candidate models will be evaluated for application on the Susitna
River. Potential candidate models for the 1-D and 2-D portions of the study are discussed below.
General Discussion of 1-D Models: Most 1-D movable boundary sediment-transport models are
designed to simulate changes in the cross-sectional geometry and river profile due to scour and
deposition over relatively long periods of time. In general, the flow record of interest is
discretized into a quasi-unsteady sequence of steady flows of variable discharge and duration.
For each model time-step and corresponding discharge, the water-surface profile is calculated
using the step-backwater method to compute the energy slope, velocity, depth, and other
hydraulic variables at each cross-section in the network. The sediment-transport capacity is then
calculated at each cross-section based on input bed material information and the computed
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hydraulics, and the aggradation or degradation volume is computed by comparing the transport
capacity with the upstream sediment supply (i.e., the supply from the next upstream cross-section
for locations not identified as an upstream boundary condition). The resulting
aggradation/degradation volume is then applied over the cross-section control volume (i.e., the
sub-channel concept), and the shape of the cross-section is adjusted accordingly. Because the
sediment-transport calculations are performed by size fraction, the models are capable of
simulating bed material sorting and armoring. The computations proceed from time-step to time-
step, using the updated cross-sectional and bed material gradations from the previous time-step.
1-D sediment-transport models should not be applied to situations where 2- and 3-dimensional
flow conditions control the sediment-transport characteristics because they do not consider
secondary currents, transverse movement and variation, turbulence, and lateral diffusion; thus,
the models cannot simulate such phenomena as point bar formation, pool-riffle formation, and
planform changes such as river meandering or local bank erosion. 1-D models typically
distribute the volume of aggradation or degradation across the entire wetted portion of the
channel cross-section after each time-step; thus, the effects of channel braiding are also not
directly considered. 1-D models are, however, useful in evaluating the general sediment-
transport characteristics and overall sediment balance of a given reach, and they are also useful
in providing boundary conditions for localized 2-D models.
Potential 1-D Models: One-dimensional models that are being considered for this study include
the U.S. Army Corps of Engineers HEC-RAS (version 4.1; USACE 2010a), the U.S. Bureau of
Reclamation’s SRH-1D (version 2.8; Huang and Greimann 2011), DHI’s MIKE 11 (version
2011; DHI 2011a), and Mobile Boundary Hydraulics’ HEC-6T (version 5.13.22_08; MBH
2008). Each of these models, including potential benefits and limitations, is summarized in the
following sections.
• HEC-RAS: HEC-RAS, version 4.1.0 (USACE 2010a) is a publicly available software
package developed by the U.S. Army Corps of Engineers (USACE) to perform steady
flow water surface profile computations, unsteady flow simulations, movable boundary
sediment transport computations, and water quality analysis. HEC-RAS includes a
Windows-based graphical user interface that provides functionality for file management,
data entry and editing, river analyses, tabulation and graphical displays of input/output
data, and reporting facilities. The sediment-transport module is capable of performing
sediment-transport and movable boundary calculations resulting from scour and
deposition over moderate time periods, and uses the same general computational
procedures that were the basis of HEC-6 and HEC-6T (USACE 1993; MBH 2010). In
HEC-RAS, the sediment transport potential is estimated by grain size fraction, which
allows for simulation of hydraulic sorting and armoring. This model is designed to
simulate long-term trends of scour and deposition in streams and river channels that
could result from modifying the frequency and duration of the water discharge and stage,
sediment supply, or direct modifications to channel geometry. Benefits of the HEC-RAS
software include widespread industry acceptance, public availability, and ease of use.
Potential limitations of the program include excessive computer run-times, file size
output limitations, and the inherent problems associated with 1-D modeling of
aggradation and degradation by equal adjustment of the wetted portion of the bed that can
result in unrealistic channel geometries.
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• SRH-1D: SRH-1D (Huang and Greimann 2011) is a publicly-available, mobile boundary
hydraulic and sediment transport computer model for open channels that is capable of
simulating steady or unsteady flow conditions, internal boundary conditions, looped river
networks, cohesive and non-cohesive sediment transport (Ruark et al. 2011), and lateral
inflows. The hydraulic and sediment transport algorithms in SRH-1D are similar to those
in HEC-RAS 4.1 and HEC-6T except that it also includes the capability to perform fully-
unsteady sediment transport simulations. Advantages of SRH-1D include robust
algorithms for hydraulic conditions and sediment routing, including sediment sorting.
Potential disadvantages include limited testing under a broad range of conditions outside
the U.S. Bureau of Reclamation and the lack of graphical user interface that complicates
data input and manipulation and display of output.
• MIKE 11: Danish Hydraulic Institute’s (DHI) MIKE 11 is a proprietary software
package developed for 1-D dynamic modeling of rivers, watersheds, morphology, and
water quality. The model has the ability to solve the complete non-linear St. Venant
equations (in only the streamwise direction) for open channel flow, so the model can be
applied to any flow regime. MIKE 11 provides the choice of diffusive and kinematic
wave approximation and performs simplified channel routing using either the
Muskingum or Muskingum-Cunge methods. The program includes a module for
simulating erosion and deposition of non-cohesive sediments. Advantages of MIKE 11
include its robust hydrodynamic capabilities (though not necessarily better than HEC-
RAS), the user-friendly graphical interface, and the reporting and presentation
capabilities. Disadvantages primarily stem from the proprietary nature of this model and
high cost of the software license.
• HEC-6T: HEC-6T was written by William A. Thomas, former Chief of the Research
Branch at the USACE Hydrologic Engineering Center (HEC). Mr. Thomas planned,
designed, wrote, and applied the publically available version of HEC-6; HEC-6T is a
proprietary enhancement of the original version. HEC-6T is a DOS-based program that
includes a Windows-based graphical user interface for input data manipulation and post-
processing of simulation results. Limitations of this program include reduced capabilities
for modeling numerous ineffective flow areas as compared to HEC-RAS 4.1 and limited
capabilities of the graphical user interface. This software is relatively inexpensive; the
fact that it is proprietary is not a significant limitation.
One-Dimensional Model Selection Process and Initial Evaluation: Based on the information
provided above and experience with these models, the Geomorphology Study team tentatively
proposes to use HEC-6T for the reach-scale sediment transport analysis. This proposal is based
on confidence gained that HEC-6T is capable of effectively and efficiently modeling the
processes that are important for this scale of geomorphic analysis. The selection of the 1-D (as
well as the 2-D) model will be coordinated with the other pertinent studies and the licensing
participants. As part of the coordination process, a technical memorandum titled Fluvial
Geomorphology Modeling (Tetra Tech 2012) was posted on the AEA website in May 2012.
Specific model-selection criteria are identified in Table 6.6-2 along with an evaluation of each
candidate model relative to the criteria.
Potential 2-D Models: Potential 2-D models that are being considered for this study include the
U.S. Bureau of Reclamation’s SRH2-D version 3 (Lai 2008; Greimann and Lai 2008), USACE’s
Adaptive Hydraulics ADH version 3.3 (USACE 2010b), the U.S. Geological Survey’s (USGS)
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MD_SWMS suite (McDonald et al. 2005; Nelson et al. 2010), DHI’s MIKE 21 version 2011
(DHI 2011b), and the River2D modeling suite (University of Alberta 2002; University of British
Columbia 2009).
• SRH-2D: The U.S. Bureau of Reclamation’s SRH-2D (Lai 2008) is a finite-volume,
hydrodyn amic model that computes water-surface elevations and horizontal velocity
components by solving the depth-averaged St. Venant equations for free-surface flows in
2-D flow fields. SRH-2D is a well-tested 2-D model that can effectively simulate steady
or unsteady flows and is capable of modeling subcritical, transcritical, and supercritical
flow conditions. The model uses an unstructured arbitrarily-shaped mesh composed of a
combination of triangular and quadrilateral elements. SRH-2D incorporates very robust
and stable numerical schemes with a seamless wetting-drying algorithm that results in
minimal requirements by the user to adjust input parameters during the solution process.
A potential limitation of this software is that the mobile bed sediment transport module is
currently not publically available; however, Tetra Tech has gained permission to use the
sediment transport module on a number of other projects. Preliminary contact with the
model developers indicates that permission would be granted for use in this study. This
version of the model (Greimann and Lai 2008) includes a “Morphology” module that
calculates bedload transport capacities at each model node based on user-defined bed
material sediment gradations, but does not simulate routing of that sediment and related
adjustments to the channel bed. SRH-2D also includes a second module that uses the
capacities from the Morphology module to perform sediment-routing calculations and
associated bed adjustments. Based on guidance from the model developers and
confirmed by Tetra Tech’s use of the model for other studies, the maximum practical
model size is about 16,000 elements, which could be a potential limitation in applying the
model to larger-scale areas.
• ADH: The USACE ADH program was developed by the Coastal and Hydraulics
Laboratory (Engineer Research Development Center) to model saturated and unsaturated
groundwater, overland flow, 3D Navier-Stokes flow, and 2-D or 3-D shallow-water,
open-channel flow conditions. ADH is a depth-averaged, finite-element hydrodynamic
model that has the ability to compute water-surface elevations, horizontal velocity
components, and sediment transport characteristics (including simulations to predict
aggradation and degradation) for subcritical and supercritical free-surface flows in 2-D
flow fields. The ADH mesh is composed of triangular elements with corner nodes that
represent the geometry of the modeled reach with the channel topography represented by
bed elevations assigned to each node in the mesh. A particular advantage of the ADH
mesh is the ability to increase the resolution of the mesh—and thereby the model
accuracy—by decreasing the size of the elements during a simulation in order to better
predict the hydraulic conditions in areas of high hydraulic variability. However, use of
the adaptive mesh option often results in excessively long simulation run times (several
days per run) that could be impractical for this study. Additionally, the wetting and
drying algorithm in this model has significant numerical stability limitations when
applied to shallow, near-shore flows that occur in rivers like the Susitna River. The
model is publically available.
• MD_SWMS Modeling Suite (FaSTMECH/SToRM): The USGS Multi-Dimensional
Surface-Water Modeling System (MD_SWMS; McDonald et al. 2005) is a pre- and post-
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processing application for computational models of surface-water hydraulics. This
system has recently been incorporated into iRIC, a public-domain software interface for
river modeling distributed by the International River Interface Cooperative (iRIC)
(Nelson et al. 2010). iRIC is an informal organization made up of academic faculty and
government scientists whose goal is to develop, distribute, and provide education for the
software. iRIC consists of a graphical user interface (GUI) that allows the modeler to
build and edit data sets, and provides a framework that links the GUI with a range of
modeling applications. The GUI is an interactive 1-D, 2-D, and 3-D tool that can be used
to build and visualize all aspects of computational surface-water applications, including
grid building, development of boundary conditions, simulation execution, and post-
processing of the simulation results. The models that are currently included in iRIC
include FaSTMECH (Flow and Sediment Transport with Morphologic Evolution of
Channels) and SToRM (System for Transport and River Modeling) that were part of the
MD-SWMS package, as well as NAYS, MORPHO2D, and a Habitat Calculator for
assessing fish habitat under 2-D conditions. Of these models, SToRM appears to be the
most relevant for modeling the Susitna River for purposes of this Project, primarily
because it uses an unstructured triangular mesh (in contrast to the structured, curvilinear
mesh required for FaSTMECH) and provides both steady-flow and unsteady-flow
capability. NAYS is a fully unsteady, 2-D model designed for a general, non-orthogonal
coordinate system with sophisticated turbulence methods that can evaluate the unsteady
aspects of the turbulence, and MORPHO2D is 2-D model capable of analyzing the
interactions between sediment transport and vegetation and between surface water and
groundwater. Both NAYS and MORPHO2D were developed in Japan, and have not
been widely used or tested in the U.S. The SToRM model blends some of the features of
finite volumes and finite elements, and uses multi-dimensional streamline upwinding
methods and a dynamic wetting and drying algorithm that allows for the computation of
flooding. Subcritical, supercritical, and transcritical flow regimes (including hydraulic
jumps) can be simulated. The program includes advanced turbulence models and an
automatic mesh refinement tool to better predict the hydraulic conditions in areas of high
hydraulic variability. The most recent version of the SToRM model does not include the
capability to model sediment-transport, but the program authors are currently working on
implementing sediment-transport algorithms that may be available for use in this study
(pers. Comm., Jonathon Nelson, USGS, June 18, 2012). MD_SWMS has been
successfully applied to a number of rivers in Alaska, including the Tanana River near
Tok (Conaway and Moran 2004) and the Copper River near Cordova (Brabets 1997);
some of the modules are currently being validated using high-resolution scour data from
the Knik River near Palmer.
• MIKE 21: Developed by DHI, MIKE 21 is a proprietary modeling system for 2-D free-
surface flows that can be applied in rivers, lakes, coastal, and ocean environments. It has
the ability to simulate sediment transport and associated erosion and deposition patterns.
The software includes a Windows-based GUI as well as pre- and post-processing
modules for use in data preparation and analysis of simulation results, and reporting
modules that have graphical presentation capabilities. MIKE 21 has the ability to model
a range of 2-D mesh types that include Single Grid, Multiple Grid, Flexible Mesh, and
Curvilinear Grid. The primary limitation to MIKE-21 is that it is proprietary software
and is relatively expensive compared to other available software.
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• River2D Modeling Suite: River2D is a two-dimensional, depth-averaged finite-element
hydrodynamic model developed at the University of Alberta and is publically available
from the university. The River2D suite consists of four programs: R2D_Mesh, R2D_Bed,
River2D, and R2D_Ice, each of which contains a GUI. The R2D_Mesh program is a pre-
processor that is used to develop the unstructured triangular mesh. R2D_Bed is used for
editing the bed topography data and R2D_Ice is used to develop the ice thickness
topography at each node for simulating ice-covered rivers. Following mesh development,
the hydrodynamic simulations are run using the River2D program, which also includes a
post-processor for visualizing the model output. River2D is a very robust model capable
of simulating complex, transcritical flow conditions using algorithms originally
developed in the aerospace industry to analyze the transitions between subsonic and
supersonic conditions (transonic flow). Many 2-D models become numerically unstable
due to wetting and drying of elements; however, River2D uniquely handles these
conditions by changing the surface flow equations to groundwater flow equations in these
areas. The model computes a continuous free surface with positive (above ground) and
negative (below ground) water depths, which allows the simulation to continue without
changing or updating the boundary conditions, increasing model stability. River2D also
has the capability to assess fish habitat using the PHABSIM weighted-usable area
approach (Bovee 1982). Habitat suitability indices are input to the model and integrated
with the hydraulic output to compute a weighted useable area at each node in the model
domain. River2D Morphology (R2DM) is a depth-averaged, two-dimensional
hydrodynamic-morphological and gravel transport model developed at the University of
British Columbia. The model was developed based on the River2D program, and is
capable of simulating flow hydraulics and computing sediment transport for uni-size and
mixed-size sediment using the Wilcock-Crowe (2003) equation over the duration of a
hydrograph. R2DM can be used to evaluate the changes in grain size distributions,
including fractions of sand in sediment deposits and on the bed surface. The sediment-
transport module has been verified using experimental data, and was successfully applied
to the Seymour River in North Vancouver, British Columbia (Smiarowski 2010).
River2D is available in the most recent version of iRIC (Version 2.0).
Two-Dimensional Model Selection Process and Initial Evaluation: The selection of the 2-D
model will be coordinated with the other pertinent studies and the licensing participants. Specific
model selection criteria are identified in Table 6.6-3, along with an evaluation of each candidate
model relative to the criteria.
Model Development: The manner in which the models are developed will depend on the model
software programs that are ultimately selected for use. Regardless of the selected modeling
software, the models will be developed in accordance with the software developers’ guidance
and recommendations.
6.6.4.1.2.2. Coordination with other Studies
As previously discussed, it is envisioned that a combination of 1-D and 2-D sediment transport
models will be used to assess potential changes in the aggradation/degradation behavior and
related processes in the Susitna River downstream from Watana Dam due to the potential size
and complexity of the system to be modeled. As a result, the current vision for the modeling
approach is to use a reach-scale 1-D model to evaluate the potential effects of the Project on the
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overall aggradation/degradation behavior of the study reach, and then use a series of
representative, local-scale 2-D models at key locations where the dynamic behavior of the
channel and habitat cannot be adequately assessed using the 1-D modeling approach. The 1-D
model will provide boundary conditions for the individual 2-D models. Because of this
modeling approach, it will be very important to coordinate with other studies because results
from the detailed 2-D model will only be available at specified locations that will be selected
from the key locations (e.g. Focus Areas) identified by the Fish and Aquatics Instream Flow
(Section 8.5), Riparian Instream Flow (Section 8.6), Ice Processes (Section 7.6), and
Characterization and Mapping of Aquatic Habitats (Section 9.9) study teams and in consultation
with the licensing participants. Ten proposed Focus Areas have been identified, with each
representing a length of river on the order of one to several miles that includes a representation
of each geomorphic reach (excluding Devils Canyon) and one unstable reach (likely a braided
reach). The 2-D modeling will be applied at the vast majority if not all of the Focus Areas
(selection of modeling approach at each Focus Area will be determined during the Q1 2013
TWG meetings concerning the confirmation or adjustment of the proposed Focus Areas). The
Focus Areas also include selected primary tributary confluences. Coordination among the
studies will also be necessary to ensure efficient collection of field data, because it is likely that a
considerable amount of the data necessary for development and calibration of the 1-D and 2-D
models will either be required for the other studies, or will be easily obtained along with data that
will be required for those studies. For example, the Fish and Aquatics Instream Flow Study
(Section 8.5) will obtain velocity magnitude and direction, flow depth, and discharge
measurements, the data from which would be very useful for calibration of the 2-D models. It
may also be possible to obtain subaqueous bed material data for the modeling by lowering a
laser/video through the ice thickness transect holes that will be bored as part of the Ice Study
when turbidity levels are expected to be low.
The temporal resolution for model execution will be selected to ensure model stability and
proper representation of important variability in flow conditions (e.g., daily fluctuations
associated with load-following). The overall time-scale for model execution will also be an
important factor. Because a key purpose of the 1-D model will be to assess the long-term
sediment balance in the study reach, this model will likely be executed for a continuous period of
50 years to represent the length of a FERC license. On the other hand, due to the computational
requirements of the 2-D model, much shorter time-periods will be evaluated.
Close coordination between the study leads and key study team members will be required
throughout the model development process. It is important that all the study teams have an
understanding of the capabilities and limitations of the models, the information that will be
provided by the model, and the selection of the Focus Areas. This will be accomplished through
frequent informal communication and more formal Technical Workgroup meetings. The study
leads and other key participants will spend time together in the field to develop a practical
understanding of each study’s needs.
An important aspect of coordination between other studies is to establish which models will be
the source for what type of information. There are a number of hydraulic models being applied
to various aspects of this study. In order to avoid inconsistencies in reported information such as
flows and stage, the model that will take precedence for reporting of information has been
established. Table 6.6-4 provides the model precedence as it has currently been established. This
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table will be distributed to all study leads. In the event that the precedence established in the
table changes, a revised table will be provided to all study leads.
Due to application of several hydraulic models, there will be opportunities to perform cross-
checking between models. For instance, water surface elevations and stage can be checked
between the mainstem open-water flow routing model, 1-D bed evolution model, and the water
quality model. If there are significant discrepancies, then parameters within the models will be
checked and adjusted if necessary. In some case, the discrepancies may be explained by the
formulation of the models or the resolution of the data used by each model.
6.6.4.1.2.3. Model Resolution and Mesh Size Considerations
Selection of the appropriate mesh size for the 2-D bed evolution model is dictated by several
factors including the following:
1. The size and complexity of the site features of primary interest.
2. The overall area of the site.
3. The desired resolution of output information such as velocity, depth, and bed material
gradation.
Factors that can also influence mesh resolution, subject to meeting the needs indicated by the
above critical factors include:
4. Limitations on the maximum number of elements that the model can simulate.
5. Model execution time.
In general, the mesh resolution in any particular portion of the model should be consistent with
the dimension of the scale of the processes that are being analyzed (Pasternack, 2011; Horritt, et
al, 2006). For example, bed evolution modeling to predict aggradation/degradation in the
mainstem can typically be performed using a relatively coarse mesh because the topographic and
hydraulic variability is less pronounced that in smaller habitat features where a relatively high
resolution mesh is necessary to describe the hydraulic variability that is important to habitat
quality and processes. The need to provide a high level of spatial resolution to satisfy items 1, 2,
and 3 to develop and accurate model can push the limitations imposed by items 4 and 5. One
approach to avoid trade-offs between model complexity and physical limitations of the model is
to use a variable mesh (also referred to as flexible mesh) that allows a finer mesh to be applied in
areas where either the information desired or the condition being modeled requires higher spatial
resolution (i.e., a finer mesh). The 2-D models being considered for this study allow the use of a
variable mesh. Figure 6.6-1 and Figure 6.6-2 provide examples of a relatively coarse and
relatively fine mesh applied to the potential Focus Area at Whiskers Slough in the Middle
Susitna River Segment Geomorphic Reach MR-8.
Areas that will require finer mesh sizes include the following:
• Side sloughs
• Upland sloughs
• Smaller side channels
• Spawning areas
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• Tributary mouths
• Locations where circulation is of interest such as eddies between the main channel and
backwater areas
• Other specific habitat features of interest
Areas where lower spatial resolution may be appropriate include the following:
• Main channel
• Floodplains
• Large side channels
In the areas of higher resolution such as side sloughs, spawning areas, and critical eddies, the
mesh size will be on the order of several feet to 25 feet. In areas where lower spatial resolution is
acceptable, the mesh size may be in the range of 25 to 100 feet.
At some Focus Areas, two model meshes may need to be developed. In these cases, a higher-
resolution mesh will be used to evaluate detailed hydraulic conditions for use in assessing factors
such as mobilization of spawning gravels in the side sloughs and side channels where channel
widths and depths are small relative to the main channel and connections between side channels
and side sloughs and at the tributary mouths where circulation plays a key role. Where necessary
due to model size limitations, the coarser mesh will be used for the bed evolution model because
issues related to bed evolution associated with sediment transport processes can be adequately
addressed at a coarser scale.
6.6.4.1.2.4. Focus Area Selection
The use of “Focus Areas” to conduct concentrated interdisciplinary studies at selected areas
within the study area was introduced in Section 6.6.3.1. Such areas represent specific sections of
the river that will be investigated across resource disciplines and will provide for an overall
understanding of interrelationships of river flow dynamics on the physical, chemical, and
biological factors that influence fish habitat. Focus Areas will involve portions of the Susitna
River and its floodplain where detailed study efforts will be jointly conducted by the Fish and
Aquatics Instream Flow (Section 8.5), Riparian Instream Flow (Section 8.6), Geomorphology
(Section 6.5), Ice Processes (Section 7.6), Groundwater (Section 7.5), and Characterization and
Mapping of Aquatic Habitats (Section 9.9) studies. The Focus Areas will allow for a highly
integrated, multidisciplinary effort to be conducted evaluating potential Project effects on key
resource areas across a range of representative sites.
The entire process for identifying candidate Focus Areas and selecting the specific portions of
the study area to conduct the Focus Area studies is detailed in Section 8.5.4.2 of the Fish and
Aquatics Instream Flow Study. This section describes the involvement of the geomorphology
studies in the selection of the proposed Focus Areas.
The Geomorphology Study has provided input on the selection of proposed Focus Areas. The
geomorphic reach classification system and resulting reach delineation were utilized in the
selection process. A total of 10 proposed Focus Areas were selected. A primary criterion was to
select at least one Focus Area for each geomorphic reach (except reaches MR-3 and MR-4 where
there are safety concerns associated with Devils Canyon due to the extreme whitewater
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conditions). Since several of the geomorphic reach types are represented by multiple reaches in
the study area, there is duplication of reach types within the candidate sites. Table 6.6-5 lists the
proposed Focus Areas, the upstream and downstream limits, the associated geomorphic reach,
and the geomorphic reach type. The proposed Focus Areas represent five areas within the SC2
reach type, four within the SC3 reach type, and one within the transitional MC1/SC2 reach type.
The locations of the Middle Susitna River Segment proposed Focus Areas are shown on Figure
6.6-3. More detailed maps that show individual proposed Focus Areas on recent (2011) color
aerial photographs are provided in the FA-IFS (Section 8.5.4.2). The areas selected were those
deemed representative of the major features in the geomorphic reach and included mainstem
habitat types of known biological significance (i.e., where fish have been observed based on
previous and/or contemporary studies), as well as some locations (e.g., Slough 17) where
previous sampling revealed few/no fish. The proposed Focus Areas include representative side
channels, side sloughs, upland sloughs, and tributary mouths.
The Geomorphology Study also helped establish the upstream and downstream limits of the
focus study areas. The upstream and downstream boundaries as well as the lateral extents of the
Focus Areas have been chosen so that appropriate boundary conditions, upstream inflow and
downstream water surface elevation on the main channel, as well as the off-channel features, can
be established for the hydraulic and bed evolution modeling. Considerations included
encompassing potential inflow and outflow points to preserve the mass balance and minimize
difficulties and assumptions associated with inflow points. Potential upstream connections for
side channels, side sloughs, and upland sloughs were also identified and included in the
modeling domain. The upstream and downstream limits on the main channel were identified to
either provide relatively uniform flow conditions or sufficient distance upstream and downstream
from areas of interest so that flow conditions in the area of interest are not significantly affected
by the flow directions at the boundary.
The Geomorphology Study is also collaborating on the selection of the modeling approach for
each Focus Area. In some instances, it may be appropriate to utilize a 1-D model rather than a 2-
D model. The 1-D model could be appropriate when there are not numerous flow splits and
junctions, flow paths are primarily linear, and specific habitat features do not have the
streamwise and lateral resolution of the 2-D model. The determination of modeling approach will
be made in Q1 2013 as part of the TWG meetings involving confirmation or adjustment of the
Focus Areas selected.
6.6.4.1.2.5. Model Calibration and Validation
Calibration and validation of the models will be a stepwise process. First, the hydraulic
components of the models will be calibrated by adjusting roughness and loss coefficients to
achieve reasonable agreement between measured and modeled water-surface elevations, and to
measured and modeled velocities. Discharges along the study reach will be obtained from the
three USGS gages. These gages will also provide a continuous record of stages and water-
surface elevations at the gage locations. These data will be supplemented with stage data from at
least 10 pressure-transducer type water-level loggers that have been or will be installed as part of
various studies being conducted in the Middle and Lower Susitna River Segments. Water-levels
measured during the cross-section and bathymetric surveys will also be used to calibrate the
models. In addition to water-surface elevations, the depths and velocities predicted by the 2-D
model should be compared with measured data from ADCP measurements at the Focus Areas.
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Depending on the range of conditions and spatial coverage of the depth and velocity data from
the Fish and Aquatics Instream Flow Study, additional data may be needed for calibration
specifically for this study. Specific calibration criteria will be established for both the 1-D and 2-
D models during the model selection phase. The 2-D water surface elevations will also be
compared against water surface elevations generated by the 1-D model and the Mainstem (Open-
water) Flow Routing Model to ensure that the models are producing consistent results.
Calibration of the velocities and depth are critical to the FA-IFS. Calibration of the flow depths
is achieved directly through calibration of the water surface elevations. Calibration of the local
flow velocities will be achieved by comparing predicted velocities from the 2-D models with
measured velocities at the key locations from the field data collection, including ADCP and
current meter data. PHABSIM studies have typically required measurements at at least three
flows levels (low, medium, and high discharges). Calibration activities for this study will
include all available flow data. Pasternack (2011) provides guidelines for evaluating 2-D model
performance with respect to the velocity magnitude. These guidelines suggest that the
calibration is reasonable when the following criteria are met:
• Variance (r2) between the predicted and corresponding measured values is in the
range of 0.4 to 0.8.
• Median and mean error of individual points is in the range of 15 to 30 percent.
Pasternak (2011) also notes that the relative error for low velocity conditions is
typically much greater than for normal to high velocity conditions.
The sediment transport portions of both the 1-D and 2-D model will be first calibrated based on
the available measured sediment transport data and the associated sediment rating curves for
both bedload and suspended load. For coarse-grained rivers such as the Susitna River, the bed
material load transport is dominant with respect to channel forming processes; however, the fine-
grained suspended load (i.e., wash load) may be important in evaluating the changes to other
features including turbidity, instream habitat, side channels, sloughs and floodplains. The
sediment transport model will also be validated, to the extent that available information allows,
by comparing modeled and measured (or if necessary, qualitatively observed) changes in bed
elevations and bed material gradations from the Geomorphology Study, by making model runs
for specific time-periods. This effort will include comparison of 1980s and current 2012 transect
data if sufficient data are available.
6.6.4.1.2.6. Tributary Delta Modeling
Tributary confluences are areas of interest for determining the potential Project effects on
sediment transport and morphology. Alteration of the mainstem flow regime has the potential to
change the elevation at which tributary sediments are initially deposited because the mainstem
may be at a different stage when the tributaries are at peak flow. Additionally, the ability to
mobilize and transport bedload delivered by tributaries may also be altered. Changes in the
configuration of sediments deposited at the tributary confluences can affect the ability of fish to
access the tributaries and the extent of clear water habitat associated with some tributary
confluences. Modeling sediment transport and deposition processes at select tributary mouths
will therefore be necessary.
The tributaries to be modeled will be determined in conjunction with the instream flow and fish
and aquatic resources studies and the licensing participants based on fish use and the potential
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for Project effects. The Geomorphology Study will model a subset of tributary confluences with
the Susitna River that represent the range of conditions among all the tributaries. The selection of
primary tributary deltas for 2-D modeling will be based on screening that considers the
importance of the existing fishery and potential adverse Project effects. Based on the discussion
at the June 14, 2012 Water Resources TWG meeting, it is possible that the effort will include the
Three Rivers Confluence area (Susitna, Talkeetna, and Chulitna confluence), though bed
evolution modeling in this area may not be feasible. The selection of the tributary delta sites for
2-D modeling will be coordinated with the other pertinent studies and in consultation with the
licensing participants.
It is currently proposed that a model will be created for the tributary deltas that uses estimated
bedload transport from the tributary, the topography and the bathymetry of the confluence,
measurements of the characteristics of the tributary deposits, and the ability of the mainstem in
the area of the confluence to mobilize and transport those deposits. The approach will include
field observations to characterize the sediment transport regime that will be used to identify
appropriate methods of estimating bedload transport. Surveys of tributary channel geometry and
sampling of bed material gradations will be coupled with an appropriate bed material transport
function to calculate sediment yield rating curves. Hydrology synthesized for ungaged
tributaries will be needed from other studies for each of the selected tributaries for this purpose
as well as for the purpose of the flow routing models (summer ice-free model and winter ice-
covered model). The yield and topography in the area of the expected delta, along with the
ability of the mainstem to mobilize and transport the bed material, will provide a basis for
characterizing how Project operations would affect the formation of tributary deposits. At this
time, it is envisioned that a relatively detailed 1-D hydraulic model of the mainstem in the
vicinity of each tributary will provide sufficient hydraulic information to evaluate the potential
for, and likely extent of, additional growth of the tributary deposits into the mainstem. For
complex tributary confluences that are of particular interest to the Fish and Aquatics Instream
Flow Study, local-scale 2-D models can be developed and applied to support the analysis.
6.6.4.1.2.7. Large Woody Debris Modeling
The assessment of the Project effects on the large woody debris processes within the Middle
Susitna River will be assisted by the Fluvial Geomorphology Modeling Study, recognizing that
bank erosion is a key process in large woody debris recruitment. Both the 1-D hydraulic and 2-D
model results will be used to estimate changes in bank erosion rates by using the model output,
along with the long-term pre- and post-Project flow records and measurements of the channel
planform, to estimate pre- and post-Project Bank Energy Indices (BEI) (Mussetter et al. 1995;
Mussetter and Harvey 1996). The BEI values for relevant periods will be correlated with historic
bank erosion rates determined from the available aerial photography. Anticipated changes in the
erosion rates, and thus, this aspect of large woody debris recruitment, under Project conditions
will then be estimated based on the correlation results and the Project-conditions BEI values. A
similar approach will be used to evaluate large woody debris recruitment at the local scale at the
Focus Areas using output from the 2-D model where various levels of large woody debris are
present based on the localized hydraulic and scour conditions. This information will be provided
to the Fish and Aquatics Instream Flow Study for quantification of the change in habitat resulting
from Project-induced changes in large woody debris. Review of the overall role of large woody
debris in formation and maintenance of the geomorphic features and the potential impacts of
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changes in the large woody debris supply on these features will be identified using model results
and the analysis described in Section 6.5.4.9.
In developing the change in large woody debris supply under the post-Project condition, the
primary questions are the sources of the large woody debris, the current rate of large woody
debris loading to the river, and the impact of the Project on the large woody debris loading rate.
The existing supply of large woody debris from recruitment within the Middle Susitna River
Segment and from upstream of the Watana Dam site (RM 184) will be estimated in the
Geomorphology Study (Section 6.5.4.9). The Project will change the upstream supply of large
woody debris by retention in the reservoir. Project operations may also change large woody
debris recruitment from bank erosion. Changes in bank erosion can be addressed by an
assessment of the pre- and post-Project rates of erosion of vegetated geomorphic surfaces
(vegetated islands and floodplain segments) that deliver large woody debris to the river. The
rates of bank erosion and thus large woody debris loading can be ascertained by comparison of
time sequential aerial photography, the turnover analysis in the Geomorphology Study (Section
6.5.4.4) in conjunction with an estimate of the density of the vegetation (volume and sizes of the
trees) growing on the geomorphic surfaces from the Riparian Instream Flow Study (Section 8.6)
and the Riparian Botanical Resources Study (Section11.6).
The impacts of the Project on the rates of bank erosion and large woody debris recruitment can
be semi-quantitatively addressed with a comparison of pre- and post-Project Bank Erosion Index
(BEI) (Mussetter et al. 1995; Mussetter and Harvey 1996) values at specific sites along the river
where the output from both 1-D and 2-D models can be used to compute the pre- and post-
Project BEI values. The BEI is an index of the total energy applied to the banks at specific
locations, and is computed based on the hydraulic characteristics of the channel, the channel
planform, and the magnitude and duration of flows (Mussetter and Harvey 1996). The BEI
values will be calibrated with site-specific bank erosion rates determined from the aerial
photography-based turnover analysis. The pre-Project rate of large woody debris recruitment
from bank erosion along the mainstem Susitna River will be scaled using the ratio of the pre- and
Post-Project BEI based erosion rate estimates to develop the post-Project rate of large woody
debris recruitment. These data will be incorporated into the analysis of pre- and post-Project
large woody debris loading from all mechanisms as described in Section 6.5.4.9.
A detailed survey of large woody debris within the Focus Areas will be also performed as part of
the fieldwork in 2013 as described in Section 6.5.4.9. This information will be used to
incorporate large woody debris within the 2-D bed evolution model mesh. This will permit
determination of the influence on flow patterns, local hydraulics, and scour that accumulations of
large woody debris have. At selected Focus Areas, adjustment of the amount of large woody
debris at the site will be performed and the 2-D bed evolution model executed again for a range
of hydrologic conditions. The resulting comparison of flow patterns, local hydraulics, and scour
between the various large woody debris densities will assist in determining the potential
influences the change in density of large woody debris at the site may have on the geomorphic
features associated with the aquatic habitats. These results will be provided to the Fish and
Aquatics Instream Flow Study (Section 8.5) to develop estimated changes in the aquatic habitat
indicators.
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6.6.4.1.2.8. Wintertime Modeling and Load-Following Operations
It is currently not proposed to execute the sediment transport models—either 1-D or 2-D—
during the winter period when flows are low and the bed material is not mobilized. However, if
the Characterization of Bed Material Mobility component of the Geomorphology Study indicates
that the bed material is mobilized during winter-time flows, including higher than existing flows
due to load-following, the sediment transport modeling will be extended to include the winter
flow period. One winter operational issue of potential importance is the resuspension of fine
sediments during load-following that could result in increased turbidity during the early portion
of the otherwise clear water conditions during the winter months. To address this, an effort to
model the resuspension of fines can be undertaken for the 1-D model and the 2-D model for the
early portion of the winter period. This effort would include investigation of a controlled release
to flush the fines from the system prior to commencement of winter load-following operations.
Decisions on continuing the 1-D and 2-D modeling into the winter period will be made in
consultation with the licensing participants and in coordination with the Fish and Aquatics
Instream Flow (Section 8.5), Instream Riparian Flow (Section 8.6), Ice Processes (Section 7.6),
and Characterization and Mapping of Aquatic Habitats (Section 9.9) studies. (This section on
Wintertime Modeling and Load-Following Operations was added based on a study comment
supplied by NOAA-NMFS in its May 31, 2012, study request; the Natural Resources Defense
Council May 30, 2012, study request; and discussions on load-following and turbidity during the
June 14, 2012 Water Resources TWG meeting.
6.6.4.1.2.9. Field Data Collection Efforts
The field data collection effort to support both the Geomorphology Study and the Fluvial
Geomorphology Modeling Study are presented in this section. The majority of this effort will be
conducted in the 2013 field season. If the subsequent need for additional data is identified during
the model development process, more Focus Areas are added, or the downstream limit of the 1-D
model is extended, additional data will be collected during the 2014 field season.
Much of the data collection performed in this task will be shared with and used by other studies
including Fish and Aquatics Instream Flow (Section 8.5), Riparian Instream Flow (Section 8.6),
Groundwater (Section 7.5), and Ice Processes (Section 7.6) studies. The exchange of data
between these studies will be highest at the Focus Areas.
At the start of the summer 2013 field season, a reconnaissance of the entire Fluvial
Geomorphology Modeling study area (RM 184 to RM 75) as well as the remainder of the Lower
Susitna River Segment (RM 75 to RM 0) will be conducted. This site reconnaissance will be
carried out to observe and characterize the following:
• Hydraulic and geomorphic controls (natural and man-made) that will influence sediment-
transport conditions.
• Verification of mapping of geologic and geomorphic features performed in the
Geomorphology Study.
• Hydraulic roughness conditions along the main channel and in the overbanks.
• Variations in bed material size.
• The sediment-transport regime, and areas that appear to be in equilibrium, or are
aggradational or degradational.
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• In areas that are not in equilibrium, qualitative assessment of the degree of erosion or
deposition.
To support the site reconnaissance as well as all other field data collection activities, maps of the
study area will be developed to assist crews during field activities. The mapping will include
topography (from available LiDAR), aerial photo base layer, geologic units and controls,
geomorphic features, aquatic habitat types, geomorphic reach boundaries, existing cross-section
locations, proposed supplemental cross-section locations, survey control points, focus site
locations, location of installed instrumentation, and safety related information.
Beyond the general site reconnaissance, detailed information will be collected to support the
development of the 1-D model for the entire study area and the Focus Areas where 2-D and
possibly 1-D modeling will be applied. Additional data will also be collected for the tributary
confluences that are identified for modeling. The field data to be collected for each of these study
components are provided below.
6.6.4.1.2.9.1. 1-D Bed Evolution Model
The primary field data to be collected in support of the 1-D bed evolution model include the
following:
1. Supplemental cross-sections
2. Bed material samples
a. Surface pebble count (Wolman count) or photo grid
b. Subsurface bulk or photo grid samples
3. Bank material samples
4. Spot elevations to verify LiDAR in the area of the supplemental cross-sections (LiDAR
will be used to provide the floodplain portion of the cross-sections)
5. Estimation of n-values at supplemental cross-sections
6. Observations on depositional or erosional features at the supplemental cross-sections
Supplemental cross-sections will be required to provide the level of detail in the hydraulic model
necessary to properly model sediment transport conditions. The cross-sections collected in 2012
for the Mainstem (Open-water) Flow Routing Model will be used in development of the 1-D
model; however, their spacing is such that additional cross-sections will need to be collected in
2013 to complete the 1-D sediment transport model. There were 88 cross-sections collected
between RM 75 and 184 (excluding the 12-mile length of river in the Devils Canyon area) with
an average spacing of just over 1 mile. The minimum and maximum spacing between the cross-
sections was 0.1 and 3 miles, respectively. It is estimated that on the order of 80 to 100
supplemental cross-sections will need to be surveyed to complete the cross-sectional database for
the 1-D sediment transport model. The transects and bathymetric data to be collected at the
focus sites will meet a portion of this requirement, likely reducing the number of supplemental
sections to be surveyed by 20 to 25 percent. Supplemental cross-sections collected for the Fish
and Aquatics Instream Flow Study may also fulfill part of the 1-D model supplemental cross-
section needs.
Bed material samples will be collected using pebble count, photographic grid, or bulk sampling
procedures. Approximately 50 bed material samples will be collected to support the 1-D model
development. A similar number of subsurface and bank material samples will be obtained.
These samples will be supplemented by similar samples collected at the Focus Areas. The
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sampling will be performed at low flow to allow as much of the bed to be sampled as possible. In
addition, the Geomorphology Study (Section 6.5) will work with the Ice Processes Study
(Section 7.6) in the winter of 2013 to determine whether video bed material samples can be
collected using a camera equipped with two lasers to provide scale. The winter period is when
the Susitna River is sufficiently clear to support this type of effort.
6.6.4.1.2.9.2. Focus Areas
The primary field data to be collected at the Focus Areas by the Geomorphology Study include
the following:
1. A combination of bathymetry (single and multi-beam), cross-section data, and spot
elevations necessary to develop a digital terrain model for the portion of the site for
which LiDAR is not available. (These will be the main channel, side channels, side
sloughs, upland sloughs, tributaries, and open water areas that were inundated at the time
the LiDAR was acquired.)
2. All obstructions in the off-channel habitats such as beaver dams and debris jams will be
surveyed.
3. Large woody debris survey and characterization of its influence on the geomorphology of
the channels, side channels and sloughs.
4. Bed material samples in the main channel, sloughs, and side channels
a. Surface pebble count (Wolman count) or photo grid
b. Subsurface bulk or photo grid samples
c. Possible winter sampling in conjunction with the Ice Processes Study (Section7.6)
(see 1-D Bed Evolution Model field data section and description of geomorphic
mapping below)
5. Bank material samples.
6. Spot elevations to verify LiDAR in the Focus Area (LiDAR will be used to provide the
floodplain portion of the cross-sections).
7. Estimation of n-values in the channels, side channels, sloughs, and tributaries.
8. Observations on depositional or erosional features at the supplemental cross-sections.
9. Field verification, and correction and/or mapping if necessary, of the geomorphic
features, geologic controls, and terraces previously identified from available information
for the Focus Area.
10. ADCP measurements to calibrate and determine the accuracy of the 2-D hydraulic model
velocities.
11. Installation of level loggers and associated readings to support calibration of water
surface elevations produced by the 2-D model.
12. Current meter measurements of velocity for areas where the ADCP cannot be used.
13. Mapping of depositional and erosional features.
14. Identification and mapping of evidence of ice processes at the site along with
observations of their potential influence on the geomorphology of the Focus Area.
15. Any evidence of past extreme events.
16. Overall narrative description and assessment of the geomorphology of the Focus Area
including identification of key physical processes and controls.
If it is determined that 1-D modeling is appropriate for a Focus Area, rather than collecting
bathymetric, cross-sectional and topographic information required to build a digital terrain model
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(DTM) to support 2-D mesh development, cross-sectional data will be collected on the hydraulic
features to be modeled.
Geomorphic mapping of the Focus Area sites will be prepared during the field data collection at
an appropriate level of resolution to delineate the key geomorphic features that control the
dynamics and the availability of habitat at the site. This mapping will identify features at the
scale of the individual habitat units that include riffles, pools, runs, meso-scale bars (i.e.,
dimensions on the order of the channel width in side channels and sloughs), banklines, large
LWD clusters, and similar features. Characteristics of the substrate making up these features
will be measured using techniques appropriate to the size range of the material in each unit. In
coarse-grained areas (i.e., gravel and cobbles), surface samples will be taken using the pebble
count method (Wolman 1954). In areas where the material is sufficiently fine (i.e., sand and
fine- to medium-gravel), bulk samples will be collected for laboratory grain size
analysis. Considering the generally coarse-grained nature of the substrate in the Focus Areas,
subsurface sampling that will be conducted on the bars will most likely be done using a
combination of the two techniques. After completion the surface sampling in each area, the
surface layer over an appropriately-sized area will be removed and a sufficient quantity of
material will be exhumed and placed on a tarp. The sample will then be weighed in increments
with a field scale to determine the total bulk weight and the relative weights of the fine and
coarse fractions. The coarse fraction will then be segregated into size classes and individual
classes weighed to determine the gradation. A suitably-sized bulk sample of fine fraction will
then be collected for laboratory sieve analysis. The overall gradation will then be determined by
recombining the field-measured coarse fraction and laboratory-analyzed fine fraction into a
single gradation based on the relative weights of each in the original field sample. The minimum
size of the bulk samples will be determined based on the maximum particle size in the sample
using guidelines in ASTM D75-71.
Surveys to develop the topography and bathymetry will be conducted at each Focus Area to
provide the level of feature definition required for accurate 2-D modeling and to provide data at
sufficient resolution to meet the needs to the FA-IFS. Surveys will be tied to the control network
established along the Susitna River during the 2012 cross-section surveys performed to collect
data for the Mainstem Open-water Flow Routing model. A single beam fathometer linked to
survey grade RTK-GPS will be used to collect cross-sections at sufficient intervals to properly
define the grids and define geomorphic features. In addition to the cross-sections, longitudinal
stream-wise profiles will be run with the fathometer to define the channel thalweg and the
transition from the channel bed to banks. These profiles will serve as break-lines when
developing the digital terrain model (DTM). In areas where the river is shallow or dry, then the
cross-sections will be completed with RTK-GPS or by total station.
In side channels and other off-channel features where the width and depth is sufficient for the use
of the fathometer, these areas will be surveyed similar to the mainstem In areas where the
channels are too small to utilize the boat-mounted survey equipment, the survey will be
performed using RTK GPS or total station (in areas where vegetation may preclude the use of
GPS). Since these areas will require fine mesh for both the 2-D modeling and for development
of hydraulic conditions for the FA-IFS, care will be taken to survey the longitudinal break lines,
in addition to the cross-sections, that will be needed to develop the detailed DTM. This survey
will be combined with the geomorphic mapping.
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It is anticipated that the upper portions of channels and the overbank or floodplain areas will be
represented in the DTM by the Mat-Su LiDAR. However, points will be taken in these areas
with the RTK-GPS to verify the accuracy of the LiDAR. In some cases, this information may be
used to adjust the LiDAR data.
6.6.4.1.2.9.3. Tributary Deltas
A site reconnaissance and data collection effort will also be necessary for each of the key
tributaries that have the potential to deliver significant quantities of sediment to the reach and/or
are important to other study teams. The reconnaissance to these sites will be relatively detailed,
because specific data will need to be collected, in addition to the general observations, to
facilitate the modeling at the tributary mouths. Cross-sectional surveys of approximately six
transects over a representative reach above the confluence will be necessary, with a spacing of
about three- to five-times the active channel width. Surface and sub-surface bed material
samples will be collected to characterize the gradation of the sediments along the reach, and will
include at least two representative samples of the surface material on the fan. Observations and
photographs of erosional and depositional features will be taken.
6.6.4.1.2.9.4. Field Data from Other Studies
In addition to the above field data collected as part of the Geomorphology Study (Section 6.5),
the following data collected by the Fish and Aquatics Instream Flow (Section 8.5), Riparian
Instream Flow (Section 8.6), Ice Processes (Section 7.6), and Groundwater (Section 7.5) studies
will need to be obtained to support the Geomorphology Study:
• Mainstem (Open-water) Flow Routing Model cross-sections collected in 2012.
• Fish and Aquatics Instream Flow Study supplemental transects collected in 2013.
• Hydraulic calibration information used in the development of the Mainstem (Open-water)
Flow Routing Model (water surface elevations and associated discharges).
• Information describing the influence of ice processes on channel and floodplain
morphology.
• Information describing the influence of riparian vegetation on channel and floodplain
morphology.
• Soil classification and gradation from Riparian Instream Flow Study test pits in the
floodplain and on island.
• Thickness and aging of floodplain and island deposits from the Riparian Instream Flow
Study.
• Mapping of vegetation and associated age classes from the Riparian Instream Flow
Study.
• Information developed in the Geomorphology Study on channel changes that have
occurred since the 1980s.
• Information developed in the Geomorphology Study on the physical processes most
important to accurately modeling the study reach.
• The velocity and depth measurements collected by the Fish and Aquatics Instream Flow
Study to characterize habitat for calibrating the hydraulic model(s).
• Data collected on the distribution of flow between the main channel and off-channel
habitat to help calibrate the hydraulic portion of the 2-D model.
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6.6.4.1.2.10. Information Required
In addition to the field data collection effort described in the previous section, the following
existing information will be needed to conduct this study:
• Historical and current aerial photographs.
• Historical channel cross-sections.
• LiDAR to develop sub-aerial topography and extend surveyed transects across the
floodplain.
• Extended flow records from USGS mainstem and tributary gages.
• Estimated flows from key ungaged tributaries that will be accounted for in the water and
sediment inflows, and where potential development of tributary fans is to be evaluated.
• Historical bed material sample data.
• List of key indicators from the other studies (FA-IFS, R-IFS, Ice Process, Groundwater)
to ensure that the models are structured to either directly quantify the indicators or
provide quantitative data from which the indicators can be quantified using other
relationships outside the context of the model.
6.6.4.1.3. Study Products
The products of this component of the modeling study will include the following:
• 1-D hydraulic models that will be used to estimate sediment loading from each of the
tributaries that supply significant volumes of bedload along the modeled reach.
• A single, calibrated, 1-D bed evolution sediment-transport model, or a series of models,
that extend from the proposed dam to a yet-to-be determined downstream limit.
• A number of calibrated 2-D sediment-transport models for proposed Focus Areas.
• Model calibration data and documentation.
• A report describing model calibration and application to existing conditions.
6.6.4.2. Study Component: Model Existing and with-Project Conditions
The goal of the Model Existing and with-Project Conditions study component is to provide a
baseline and series of with-Project scenarios of future channel conditions for assessing channel
change. The extent of the study area is the Susitna River downstream of Watana Dam, the
specific downstream boundary of which will be determined in study component Bed Evolution
Model Development, Coordination, and Calibration.
6.6.4.2.1. Existing Information and Need for Additional Information
Once the 1-D and 2-D bed evolution models are developed in the previous study component, the
model will be run for the existing condition (the Susitna River without Watana Dam in place) in
order to establish a baseline for comparison with Project model runs. The model will also be run
for various Project scenarios to determine the potential effects of the Project on the fluvial
geomorphology of the Susitna River.
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6.6.4.2.2. Methods
6.6.4.2.2.1. Existing Conditions – Base Case Modeling
The RSP includes four operation scenarios. The first is the existing conditions or without-
Project scenarios. This scenario provides the baseline against which all other with-Project
scenarios are compared against to identify Project effects.
The time period and representative hydrologic conditions to be assessed with the bed evolution
model will be determined through coordination with the Technical Workgroup, based on the
availability of data, study objectives, and model limitations. The hydrologic inputs for the
various with-Project scenarios will be obtained from the Reservoir Operations (Engineering) and
Mainstem (Open-water) Flow Routing Model (Section 8.5.4.3) and the model run for flows
representative of each scenario. It is currently envisioned that a 50-year, continuous period of
record that represents the length of the FERC licensing period will be used for the 1-D modeling,
and shorter modeling periods will be used for the 2-D model due to computational limitations.
The 50-year period will be divided into three points in time to provide comparison: year-0, year-
25, and year-50. As previously indicated, the 1-D model will be applied to address the analysis
of reach-scale issues and the 2-D model to address local-scale issues.
The shorter periods for the 2-D model will include specific years or portions of annual
hydrographs for selected years of wet, average, and dry hydrologic conditions and warm and
cold Pacific Decadal Oscillation (PDO) phases. Therefore, up to six annual hydrologic
conditions will be considered. (The inclusion of the warm and cold PDO phases was requested
by NOAA-NMFS and USFWS in the May 31, 2012, study requests; the rationale for the request
was discussed at the June 14, 2012 Water Resources TWG meeting and it was agreed that the
PDO phases would be included in the suite of representative annual hydrologic conditions.)
Other scenarios might include rapid release of flows from an ice jam or larger flood events that
are not contained in the period of the hydrologic record chosen for simulation.
Each run will be subjected to a quality control process to ensure that the appropriate data were
used and model outputs are reasonable. Naming conventions for the model input and output
files for the various scenario files will be applied so that files can be easily archived and
retrieved in the future.
6.6.4.2.2.2. Future Conditions – with-Project Scenarios
The three with-Project scenarios will represent a maximum load-following, an intermediate load-
following, and a base-load scenario. The three with-Project scenarios will provide bookends and
an intermediate assessment of potential Project effects. These will provide an understanding of
the range of potential Project effects. Similar to the existing conditions, the with-Project
scenarios will be modeled with both the 1-D model to determine the reach-scale Project effect
and the 2-D model to determine the local-scale Project effects. The with-Project scenarios will be
evaluated over the same time periods as the existing conditions base case.
6.6.4.2.2.3. Uncertainty
To assist in identifying and understanding uncertainties, sensitivity analysis will be performed
for the 1-D and 2-D bed evolution modeling efforts by varying key input parameters within the
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range of physically reasonable values. Additionally, the 50-year simulation period to be used for
the 1-D bed evolution model includes a broad range of hydrologic conditions, and will be used to
assess the sensitivity of the study reach to hydrologic variability. Variation in response to the
six representative years (wet, average, and dry for wet and cold PDO) based on both the 1-D and
2-D bed evolution model results will also provide an understanding of the uncertainty associated
with hydrologic conditions. Specific parameters that will be varied in the uncertainty analysis
include hydraulic roughness coefficients, magnitude and gradations of inflowing sediment loads,
substrate size gradations, and dimensionless critical shear (i.e., Shields) values.
6.6.4.2.2.4. Synthesis of Reach-Scale and Local-Scale Analyses
In general, based on the spatial resolution of the input and output data, the 1-D model results are
used to facilitate analysis of processes at the reach-scale, while the 2-D model is used for local-
scale analysis. It is important to recognize that the downstream stage and upstream discharge
boundary conditions for the local-scale 2-D models will be taken from the 1-D Mainstem (Open-
water) Flow Routing Model, and the inflowing sediment loads will be taken from the 1-D bed-
evolution model, ensuring consistency at the model boundaries. (Although this is not anticipated,
it may be necessary to take downstream stage boundary conditions from the 1-D bed evolution
model for purposes of analyzing future conditions if this model shows sufficient change over the
duration of the model runs.) In addition, results from the models are compared within the 2-D
model domain to further ensure consistency. This comparison often leads to important
adjustments to one or both of the models to improve consistency and predictive quality.
As described in the Section 6.6.4.1.2.4, the Focus Areas have been selected to represent the
range of geomorphic and habitat conditions that occur within the study area. The detailed
analysis at these sites that relies on the 2-D model results will be extrapolated to the overall study
reach using the 1-D model results and other relevant information from the Geomorphology, FA-
IFS, R-IFS, Ice Process studies, where appropriate, to quantify anticipated Project impacts at the
Study Reach Scale.
6.6.4.2.2.5. Information Required
The following available existing information will be needed to conduct this study:
• The calibrated existing conditions model(s) developed in the previous tasks, including the
data used to develop them.
• Extended flow records for mainstem gages and major tributaries for existing conditions.
• With-Project mainstem flows corresponding to the periods and locations in the extended
flow record.
• The with-Project sediment outflow rating curve from Watana Dam.
• List of key indicators from the other studies (FA-IFS, R-IFS, Ice Process, Groundwater)
to ensure that the models are structured to either directly quantify the indicators or
provide quantitative data from which the indicators can be quantified using other
relationships outside the context of the Fluvial Geomorphology Modeling Study.
6.6.4.2.3. Study Products
The products of this component of the modeling study will include the following:
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• Results from the 1-D mobile boundary sediment-transport model(s) that extend from the
location of the proposed dam to a yet-to-be determined downstream limit.
• Results from the 2-D sediment-transport models for proposed Focus Areas.
• A report describing the model runs, and interpreting the model results.
6.6.4.3. Study Component: Coordination and Interpretation of Model Results
The goal of this study component is to ensure that the information from Geomorphology Study is
properly considered and incorporated into the modeling studies, that the results the modeling
studies are used to update and refine the understanding of key processes identified in the
Geomorphology Study, and to provide the necessary results to the other resources studies that
will require knowledge, and where possible and appropriate, quantification of potential natural
and Project-induced geomorphic changes. The extent of the study area is the Susitna River
downstream of Watana Dam, the specific downstream boundary of which will be determined in
the Bed Evolution Model Development, Coordination, and Calibration study component (Section
6.6.4.1).
6.6.4.3.1. Existing Information and Need for Additional Information
Several studies require the results of the Fluvial Geomorphology Modeling Study to conduct
their efforts. These include the Fish and Aquatics Instream Flow (FA-IFS) (Section 8.5),
Groundwater (Section 7.5), Riparian Instream Flow (R-IFS) (Section 8.6), and Ice Processes
(Section 7.6) studies. The primary concern is whether the Project will affect aspects of the
channel morphology including, but not limited to, substrate characteristics, cross-sectional
geometry, connectivity with off-channel habitats and in the most general sense, the distribution
of geomorphic features that comprise the aquatic and riparian habitats.
6.6.4.3.2. Methods
As discussed in Section 6.5.4.11, initial work for the Geomorphology Study identifies the
specific geomorphic processes that affect aquatic and riparian habitat, channel stability and
related issues that require further quantification, identifies a significant portion of the data needs,
and provides the basic information and context for the Fluvial Geomorphology Modeling Study.
During the Fluvial Geomorphology Modeling Study, results from the Geomorphology Study are
used in conjunction with knowledge of the specific needs of the other resource teams to insure
that the models are developed in an appropriate manner to address the key issues and to provide
a reality check on the model results. After completion of the modeling, the study team uses the
results from both studies in an integrated manner to provide interpretations with respect to the
issues that must be addressed, including predictions of potential changes to key geomorphic
features that comprise the aquatic and riparian habitat. This information is then provided to the
other resource teams for use in their evaluation of potential project effects.
6.6.4.3.2.1. Integration of Geomorphology and Fluvial Geomorphology Modeling Study
Results
The purpose of this task is to integrate the Geomorphology and Fluvial Geomorphology
Modeling Studies to insure that results from both studies are used in a coordinated manner to
identify and, to the extent possible, quantify the potential influence of the Project on key
geomorphic and habitat features. Section 6.5.4.11 provides a detailed discussion of the specific
aspects of the Geomorphology Study that will be used to guide development of the models and
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interpretation of the model results for the Fluvial Geomorphology Modeling Study, particularly
as they relate to the habitat indicators. Additional examples of key coordination activities
between the two studies include the following (It is important to understand that other activities
may be identified as the study teams gain additional understanding of the key processes that
drive potential Project effects):
• The LWD component of the Geomorphology Study will provide information on the
status of LWD recruitment to the project reach under existing conditions and qualitative
information about the potential effect of the Project on future LWD recruitment. Results
from the bed evolution modeling will provide quantitative estimates of certain key
processes that affect LWD recruitment under both existing and Project conditions,
including potential changes in bank erosion rates.
• The Geomorphology Study will identify key locations that control connectivity between
the main channel and the side channels, side sloughs and upland sloughs, and will assess
how these locations have evolved over the period of coverage of the historical aerial
photography. The Fluvial Geomorphology Modeling study will quantify the hydraulic
and sediment transport behavior of the existing locations, and will provide quantitative
projections of how these areas will change in the future under both existing (no Project)
and Project conditions based on the bed evolution modeling results.
• The Geomorphology Study, coupled with the field data collection activities for the
Fluvial Geomorphology Modeling Study, will identify the geomorphic characteristics
(i.e., channel geometry, gradient, substrate, bank material and vegetation) that are
important drivers of habitat conditions within the side channels, side sloughs, and upland
sloughs under existing and Project conditions. The modeling, particularly 2-D bed
evolution modeling at the Focus Areas, will provide a means of directly quantifying these
processes by providing detailed hydraulic information and projections of changes in
substrate and bed elevations. This will include quantification of the frequency and
duration of substrate mobilization and the potential for fines infiltrations and flushing in
spawning areas. Other aspects, such as potential changes in channel width, will be
estimated based on a combination of the model output and relevant geomorphic
relationships.
6.6.4.3.2.2. Coordination of Results with Other Resources Studies
The Fluvial Geomorphology Modeling and Geomorphology Study (Section 6.5) teams will
interact extensively with the Mainstem (Open-water) Flow Routing Model (Section 8.5.4.3), Fish
and Aquatics Instream Flow (Section 8.5), Riparian Instream Flow (Section 8.6), Ice Processes
(Section 7.6), and Characterization and Mapping of Aquatic Habitats (Section 9.9) study teams.
The types of interaction will vary depending on the specific study, but a considerable amount of
physical data describing the system, including transects, topography/bathymetry, substrate
characterization, aerial photography, and pre- and post-Project flows generally will be shared.
Selection of joint Focus Areas for detailed studies will be an important aspect of the
collaboration. By selecting common sites, the potential for exchange of information between the
study teams will be maximized to ensure the most effective and extensive use of Focus Area
data.
Because of the detailed spatial nature of the information produced by the models, GIS will likely
be an important tool for visually illustrating and conveying model results for use in the other
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studies. Development of the plan for transferring results in a manner that will facilitate efficient
and effective use by other studies will require considerable effort. The details of the plan will be
worked out as the overall modeling approach is developed in the Technical Workgroup meetings
and through informal coordination with the respective study teams.
The 1-D and 2-D bed evolution models provide quantitative predictions of a range of key
variables that are directly related to the geomorphic and habitat conditions along the study reach
at a range of spatial and temporal resolutions (Table 6.6-5 and Table 6.6-7). As noted in Table
6.6-6, the values of many of these variables can be used directly to assess geomorphic and
habitat conditions, while additional analysis of other variables outside the context of the model is
required to obtain useful predictions (Table 6.6-7). The output variables can be broadly grouped
into hydraulic conditions (water-surface elevations, depth, velocity, bed shear stress) and
sediment transport/bed morphology conditions (substrate size gradations, sediment transport
rates, changes in bed elevation).
Mainstem (Open-water) Flow Routing Study (Section 8.5.4.3): It is anticipated that the
Mainstem (Open-water) Flow Routing Study will provide the pre- and post-Project hydrology
information for all studies, including the Fluvial Geomorphology Modeling Study. This
hydrology information will include mainstem pre- and post-Project flows at various points along
the study area and inflows for gaged and ungaged tributaries. This information is expected to be
provided for the 50-year, extended flow record.
For the Fluvial Geomorphology Modeling effort, the upstream boundary condition at RM 184
will be the existing condition or pre-Project daily flows from the extended flow record. For the
post-Project condition, the upstream boundary condition will be the average daily releases from
Watana Dam unless load-following scenarios are evaluated. In the latter case, the Project
outflows will need to be on an hourly or possibly finer time increment. Estimated daily inflows
from tributaries provided by the Mainstem (Open-water) Flow Routing Model will be input
along the length of the 1-D sediment transport model and may be inputs to the localized 2-D
models depending on the location and specific issues to be addressed.
Fish and Aquatics Instream Flow Study (FA-IFS) (Section 8.5): The primary initial interaction
with the FA-IFS will be in the selection of the Focus Areas for detailed study. Part of the
selection process will consider the use of the specific sites as well as the types of habitat present
at the site by target fish species. The local-scale 2-D models can be used to evaluate instream
habitat quality on a spatially-distributed basis rather than the cross-sectionally-based approach
used in traditional Instream Flow Incremental Methodology (IFIM) studies.
For the FA-IFS, an assessment of whether the current channel geometry and substrate
characterization used in evaluation of habitats will remain relatively unchanged over the period
of the license under both the pre- and post-Project conditions will be important. The
Geomorphology Study will determine the equilibrium status of each reach such that the
distribution of habitat conditions over the timeframe of the license (assumed to be 50 years,
corresponding to the maximum FERC licensing period) will be adequately reflected by existing
channel morphology. If it is determined that the river is not in a state of dynamic equilibrium, the
Geomorphology Study will provide projections of the direction and magnitude of the changes
under both existing and Project conditions. Changes in the relative occurrence of aquatic habitat
types and the associated surface area versus flow relationships that may occur as a result of the
Project will be an important outcome of these studies. As part of this evaluation, pre- and post-
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Project changes in channel dimensions (width and depth) and the proportion and distribution of
geomorphic features and habitat types will be estimated for each of the delineated reach types
using the channel classification system to be developed for the Susitna River. This will provide
the FA-IFS with an important part of the information required to evaluate the post-Project effects
on aquatic habitat. Other important information to be provided by the Fluvial Geomorphology
Modeling study for the Instream Flow Study includes the following:
• Identification of zones of substrate mobilization, deposition, and scour at the reach scale
for pre- and post-Project flow regimes.
• Potential changes in off-channel habitat connectivity due to aggradation and degradation.
• Pre- and post-Project changes in spatial and seasonal patterns of the fine sediment (wash
load) transport and the associated Project effects on turbidity.
• Changes in substrate composition in both the main channel and off-channel habitats.
• Pre- and post-Project large woody debris (LWD) recruitment and transport.
Riparian Instream Flow Study (Section 8.6): Riparian vegetation plays a large role in the
development of islands and off-channel habitats, primarily by protecting surfaces from erosion
and promoting sediment deposition. Vegetation can also contribute to channel narrowing by
encroaching onto bars and islands and riverward growth of banks through trapping of sediments.
Conversely, changes in the flow regime and/or ice processes can alter riparian vegetation
patterns, including the extent, species composition, and age-classes; thus, there is a feedback
mechanism between the two processes. As a result, the influence of riparian vegetation on the
morphology of the Susitna River is an important consideration in these studies. The R-IFS,
Geomorphology and Fluvial Geomorphology Modeling studies need to be closely coordinated
because of the interaction described above. The collaboration will begin with coordinated
selection of the Focus Area among the R-IFS, Ice Processes, Geomorphology and Fluvial
Geomorphology Modeling study teams. By analyzing the same Focus Areas in a coordinated
manner, the teams will develop an understanding of the interaction between the processes that
are responsible for creation and maintenance of the islands and off-channel habitats. Estimates of
the ages of island and floodplain surfaces from the Riparian Instream Flow Study based on
dendrochronology, combined with the inundation results from the 2-D modeling, will greatly
facilitate this effort by helping to identify rates of sediment deposition and reworking of these
surfaces. Similarly, profiling of deposited sediments in the riparian corridor to identify the types
of sediments that make up the floodplain will also contribute to the understanding of the physical
processes and development of the functional model for linkage of the geomorphology, riparian
vegetation, and ice processes.
The results of the fluvial geomorphology model along with applicable geomorphic principles
will be applied to interpret model results. An understanding of the geomorphology of the system
will also be used to provide a reality check on the extent of changes indicated by the modeling.
Examples of the linkage between the R-IFS and the Fluvial Geomorphology Modeling include
the following:
• Altering Manning’s n-values to represent establishment (increased n) or removal
(decreased n) of vegetation.
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• Application of shear stress parameter to determine the erodibility of banks and potential
influence of and on vegetation.
• Interpretation of flow and sediment transport patterns to determine areas of sediment
deposition within and adjacent to vegetation.
• More accurate water surface elevations and flow distributions from the local-scale 2-D
models than is provided by the 1-D models for periods when the flows only partially
inundate the riparian corridor.
• Estimation of the change in the rate of floodplain and island building under the with-
Project condition and between various operational scenarios. This can be accomplished
by scaling the historical rates of sedimentation developed from the R-IFS by the ratio of
the with-Project rate of sediment delivery to the floodplain surfaces to the existing rate.
The 2-D model will be applied to simulate sediment delivery to the floodplains and
islands.
• Use of geomorphic threshold relationships to understand the potential for removal of
vegetation by the flows and the potential for additional channel narrowing due to changes
in the vegetation patterns.
Ice Processes Study (Section 7.6): Ice processes influence both the channel morphology and
riparian vegetation. For example, ice can prevent vegetation from establishing on bars by
annually shearing off or uprooting young vegetation. Similarly, ice can scour vegetation from the
banks, increasing their susceptibility to erosion. In both examples these influences affect
channel morphology. Ice jams can also directly influence the channel morphology by diverting
flows onto floodplains where new channels can form, particularly when the downstream water
surface elevations are low, allowing the return flows to headcut back into the floodplain. Ice can
also move bed material that would normally not be mobilized by rafting large cobbles and
boulders.
There will be close collaboration between the Geomorphology and Ice Process studies to identify
the key physical processes that interact between the two. Working together to analyze the
conditions at the Focus Areas will be a key part of this collaboration. A significant portion of the
influences of ice processes on morphology are directly related to their effects on riparian
vegetation. Additionally, influences of ice processes beyond the riparian vegetation issues that
may be incorporated directly into the Fluvial Geomorphology Modeling may include the
following:
• Simulating the effects of surges from ice jam break-up on hydraulics, sediment transport,
and erosive forces using unsteady-flow 2-D modeling with estimates of breach
hydrographs.
• Simulating the effect of channel blockage by ice on the hydraulic and erosion conditions
resulting from diversion of flow onto islands and the floodplain.
• Use of the 2-D model output to assess shear stress magnitudes and patterns in vegetated
areas, and the likelihood of removal or scouring.
• Use of the 2-D model output to assess shear stress magnitudes and patterns in
unvegetated areas, and the likelihood of direct scour of the boundary materials.
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• Application of the 2-D model to investigate whether ice jams are a significant contributor
to floodplain and island deposition as a result of ice jams inundating these features and
causing sedimentation.
Water Quality Modeling (Section 5.6): The Fluvial Geomorphology Modeling Study will have
two primary areas of interaction with the Water Quality Modeling Study. The first involves the
determination of reservoir sediment trap efficiency. The EFDC model that is being used for
studying the water quality of the reservoir, Middle and Lower Susitna River Segments will be
used to perform a determination the final determination of reservoir sediment traps efficiency.
This will provide a more accurate determination of the fine sediment settling than use us the
empirical equations that are described in Section 6.5.4.8.2.1 that will be used for the initial
estimate of trap efficiency. The Geomorphology Study will provide the Water Quality Modeling
study with the sediment inflow to the reservoir based on the sediment supply analysis conducted
in Section 6.5.4.3. The second are of interaction is the routing of fine sediment, silt and clay,
downstream. Both the 1-D bed evolution model form this study and the EFDC model from the
water quality will route fine sediments in the Middle Susitna River Segment and upper portion of
the Lower Susitna River Segment. The water quality models interested in the fine sediment in
order to estimate the Project effects on turbidity, while the Fluvial Geomorphology Modeling
Study is primarily interested in fine sediment in terms of the Project effects on areas of
deposition in the main channel, off-channel and floodplain areas. The results of each model in
terms of fine sediment transport results will be compared to insure consistency.
6.6.4.3.2.3. Information Required
The following available existing information will be needed to conduct this component of the
modeling study:
• Study plans for other studies
The following additional information will need to be obtained to conduct this component of the
modeling study:
• Locations of sites for other studies
• Lists of output required for other studies, including list of key habitat indicators.
• Output formats required for other studies
• Schedule dates for providing output
6.6.4.3.3. Study Products
The products of this component of the modeling study will include summarized results from the
1-D and 2-D sediment-transport modeling in an appropriate format. This will include the values
of variables that are taken directly from the models (Table 6.6-6) and variables or indicators that
are computed from a combination of the direct model output and other available information
using appropriate relationships outside the direct context of the model (Table 6.6-7).
Although the desired format of the model output is not known at this time, the formatted
products could include the following:
• Spreadsheets summarizing predicted hydraulic conditions.
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• Spreadsheets summarizing the sediment-transport results at various times during the 1-D
mobile boundary sediment-transport simulations.
• ArcGIS shapefiles, and where necessary, spreadsheets, representing the predicted
hydraulic conditions (velocity magnitude and direction, water depth, shear stress
magnitude and direction, etc.) at various times during the 2-D modeling simulation at
each of the Focus Areas.
• ArcGIS shapefiles, and where necessary, spreadsheets, representing the sediment-
transport results (predicted change in bed elevation, sediment size, etc.) at various times
during the 2-D modeling simulation at each of the Focus Areas.
6.6.5. Consistency with Generally Accepted Scientific Practice
A wide range of temporal scale processes, unknown initial and forcing conditions, unresolved
heterogeneities, and unanticipated mechanisms make geomorphic prediction challenging and
problems of scale important (Wilcock and Iverson 2003). Fluvial geomorphologic analyses
typically involve focusing on a variety of spatial scales at which landforms have characteristic
features (Grant et al. 1990; Rosgen 1996; Thomson et al. 2001). These scales generally
reference the river channel width (W) due to the similarity of forms among systems of different
absolute size that are governed by the same underlying processes (Pasternack 2011). For
example, the analysis could include an assessment at the watershed scale, river segment scale
(103-104 W), morphologic or reach scale (100-101 W), and Focus Area local scale (10-1-100 W).
As discussed in more detail below, the Geomorphology Modeling Study will require both reach-
scale (1-D modeling) and Focus Area local-scale (2-D modeling) analyses. Synthesis of the
reach-scale and local scale analyses will therefore be necessary to identify potential Project-
induced changes in the relative occurrence of aquatic habitat types and associated surface area
versus flow relationships. In addition to the results of the hydraulic and sediment transport
modeling, this synthesis will require application of fluvial geomorphic relationships to develop a
comprehensive and defensible assessment of potential Project effects. Examples of this type of
integrated analysis that have been successfully performed by the Project team include instream
flow, habitat, and recreation flow assessments to support relicensing of Slab Creek Dam in
California; a broad range of integrated geomorphic assessments and modeling to assist the Platte
River Recovery Implementation Program in Central Nebraska; and ongoing work to support the
California Department of Water Resources and Bureau of Reclamation to design restoration
measures for the San Joaquin River in the Central Valley of California downstream of Friant
Dam.
1-D and 2-D models are commonly used tools to assess hydraulic and sediment transport
conditions in rivers 1. The potential models that are described in the model selection section have
been in use by the engineering and geomorphic community for many years (in some cases, many
decades) for evaluating both existing/baseline conditions and predicting the likely effects of
proposed changes in flow regime, sediment supply, and other natural and anthropogenic factors.
All of the proposed models have been developed using scientifically-sound relationships to
describe the physical processes that are important to the analysis. The proposed modeling steps,
1 The March 2008 Edition of the American Society of Civil Engineers Journal of Hydraulic Engineering was
entirely dedicated to the practice and challenges associated with sediment transport modeling.
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that include initial reconnaissance to understand the study reach, field data collection to obtain
quantitative information necessary to build the model inputs files, calibration steps to ensure
model results are consistent with field conditions, and modifications to the model input to
represent the range of potential future conditions, are commonly employed by practitioners and
researchers. Results from the application of these types of models have provided significant
technical basis for FERC licensing of numerous projects through the U.S. and similar licensing
throughout the world.
One-Dimensional Modeling at the Reach Scale: Potential 1-D models that are being considered`
for this study include the U.S. Army Corps of Engineers HEC-RAS (version 4.1; USACE
2010a), the Bureau of Reclamation’s SRH-1D (version 2.8; Huang and Greimann 2011), DHI’s
MIKE 11 (version 2011; DHI 2011a), and Mobile Boundary Hydraulics’ HEC-6T (version
5.13.22_08; MBH 2008). Based on the information above and experience with these models, the
Geomorphology Study team tentatively proposes to use HEC-6T for the reach-scale sediment
transport analysis. This proposal is based on confidence gained that HEC-6T is capable of
effectively and efficiently modeling the processes that are important for this scale of geomorphic
analysis. HEC-6T has been successfully applied to model the sediment-transport conditions in a
wide range of river systems for a variety of studies. The study team is currently using the model
to evaluate sediment augmentation for habitat restoration purposes in the Central Platte River in
Nebraska (Tetra Tech 2010). It was successfully used to evaluate the effects of seismic retrofit
options for San Clemente Dam on sediment-transport through the reservoir and in the
downstream Carmel River (Mussetter Engineering, Inc. 2008).
Two-Dimensional Modeling at the Local Scale: Potential 2-D models that are being considered
for this study include the U.S. Bureau of Reclamation’s SRH2-D version 3 (Lai 2008; Greimann
and Lai 2008), USACE’s Adaptive Hydraulics (ADH) version 3.3 (USACE 2010b), USGS’s
MD_SWMS modeling suite (McDonald et al. 2005; Nelson et al. 2010), and DHI’s MIKE 21
version 2011 (DHI 2011b) River2D modeling suite (University of Alberta 2002; University of
British Columbia 2009). The selection of the 2-D model will be coordinated with the other
pertinent studies and the licensing participants. In addition to the User’s Manuals that are
available with each of the potential models, a number of standalone references are also available
that provide guidance for development and application of the 2-D models, or highlight successful
application of 2-D geomorphologic modeling. For example, Pasternack (2011) includes an entire
chapter that provides instruction for 2-D model development, and separate chapters for SRH-2D
model execution and interpretation of SRH-2D model results. Conaway and Moran (2004)
present successful application of MD_SWMS to modeling sediment-transport conditions in
Alaskan rivers. MD_SWMS has also been successfully used to model sediment-transport and
Island formation in a gravel bed portion of the Snake River (McDonald et al. 2005).
6.6.6. Schedule
A schedule for the Fluvial Geomorphology Modeling Study has been developed, and indicates
the Model Development, Coordination, and Calibration study component will be completed by
the end of the second quarter 2014; the Model Existing and with-Project Conditions study
component will be completed by the end of the fourth quarter 2014; and Coordination on Model
Output study component will be completed by the end of the fourth quarter 2014. The Initial
Study Report (ISR) and the Updated Study Report (USR) explaining the actions taken and data
collected to date will be due within one and two years, respectively, of FERC’s Study Plan
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Determination. A more specific breakdown of the anticipated schedule is presented in Table 6.6-
8.
6.6.7. Relationship with Other Studies
A flow chart describes study interdependencies (Figure 6.6-4) and outlines the information and
products required from other studies and the timing of delivery to successfully complete the
Fluvial Geomorphology Modeling Study on schedule. In the study interdependencies chart, the
studies providing input are listed in the five sided boxes at the top of the chart. The sections of
the corresponding study’s RSP which develop and provide the information are shown in
parentheses. The rectangular boxes below the five sided boxes list the major information and
products that the other studies will provide to the Fluvial Geomorphology Modeling Study. The
primary studies that the Fluvial Geomorphology Modeling Study will require information from
are listed below and in Table 6.6-9.
• Geomorphology Study (Section 6.5)
o Geomorphic Reach delineation
o Sediment transport rating curves and sediment balance
o Identification of key physical processes
• Fish and Aquatics Instream Flow Study (Section 8.5)
o Collaboration on Focus Area selection
o Identification of specific areas of interest with focus areas
o Velocity and transect measurements for hydraulic calibration
• Riparian Instream Flow Study (Section 8.6)
o Floodplain sedimentation rates
o Soil samples
• Groundwater Study (Section 7.5)
o Level logger information
• Characterization and Mapping of Aquatic Habitats Study (Section 9.9)
o Assistance in identifying tributaries to study
o Identification of specific areas of interest with focus areas
• Ice Processes Study (Section 7.6)
o Identification of ice influences
• Reservoir Operations Modeling (Engineering)
o Project outflow for alternative scenarios
• Mainstem (Open-water) Flow Routing Model (Section 8.5.4.3)
o Cross-sections
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o Measured water surface elevations from level loggers
o Hourly flows for alternative scenarios throughout the study area
• Water Quality Modeling Study (Section 5.6)
o Reservoir trap efficiency for existing conditions and alternative scenarios
• Glacial and Runoff Changes Study (Section 7.7)
o Potential increase in sediment supply from glacial surge
The USGS will provide the extended hydrologic record for 11 gage locations for a period of 61
years. This information will be used as the hydrologic record for analysis of existing stream flow
characteristics and will also provide the flows to be used by the Reservoir Operations Study
(Engineering) and the Mainstem (Open-water) Flow Routing Model (Section 8.5.4.3) to generate
flow conditions in the Middle and Lower Susitna River Segments for the with-Project conditions.
The timing of delivery of each type of information or study product to be provided to the
Geomorphology study is the provided in parentheses by quarter and year. For example, “(Q4-
12)” indicates the information will be provided in the fourth quarter of 2012. Table 6.6-9
provides these interdependencies in tabular form including the study providing the information
and which area of the Fluvial Geomorphology Modeling Study requires the information or study
product.
The chart indicates which areas of the Fluvial Geomorphology Modeling Study require the
information. The Fluvial Geomorphology Modeling Study areas are identified in the blue
ellipses and include:
• Field Data Collection
• 1-D, 2-D and tributary delta model development and calibration
• 1-D, 2-D and tributary delta modeling of baseline and alternative scenarios
• Integration of reach- and local-scale modeling and geomorphic analysis
The flow chart also shows products and information the Fluvial Geomorphology Modeling Study
will provide to other studies and the timing of their delivery. Table 6.6-10 provides these study
interdependencies in tabular form including the area of the Fluvial Geomorphology Modeling
Study providing the information and which study requires the information or study product. The
products and information the Fluvial Geomorphology Modeling Study will provide are identified
in the rectangles below the study area ellipses. The quarter and year that the products and
information will be provided to other studies is indicated in the parentheses adjacent to each
item. At the bottom of the chart, the studies that require the information from the Fluvial
Geomorphology Modeling Study are listed in the five sided boxes. In parentheses adjacent to
each study is the section of the RSP that the product or information will support. The primary
studies requiring information from the Fluvial Geomorphology Modeling Study are listed below.
The information they will require is identified in Table 6.6-10 (Note: Table 6.6-6 and 6.6-7
provide a detailed list of 1-D and 2-D model output and other information the Fluvial
Geomorphology Modeling and Geomorphology Studies will provide to other studies):
• Geomorphology Study (Section 6.5)
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• Fish and Aquatics Instream Flow Study (Section 8.5)
• Riparian Instream Flow Study (Section 8.6)
• Characterization and Mapping of Aquatic Habitats Study (Section 9.9)
• Groundwater Study (Section 7.5)
• River Recreation Flow and Access Study (Section 12.7)
• Water Quality Modeling Study (Section 5.6)
6.6.8. Level of Effort and Cost
Initial estimates of the costs to perform the components of the Fluvial Geomorphology Modeling
Study are provided in Table 6.6-11. The total effort for the Fluvial Geomorphology Modeling
Study is estimated to cost between approximately $2.3 million and $2.8 million.
6.6.9. Literature Cited
Acres. 1983. Before the Federal Energy Regulatory Commission Application for License for
Major Project Susitna Hydroelectric Project. Volume 5A, Exhibit E, Chapters 1 & 2.
Prepared for Alaska Power Authority.
Alaska Energy Authority (AEA). 2010. Railbelt Large Hydro Evaluation Preliminary Decision
Document. Prepared by the Alaska Energy Authority (AEA).
Alaska Power Authority (APA). 1984. Susitna Hydroelectric Project Economic and Financial
Update. Draft Report dated February 27, 1984. Prepared by the Alaska Power Authority
(APA).
Ashton, William S., and R&M Consultants, Inc. 1985. Lower Susitna River Aggradation Study:
Field Data Final Report. Anchorage, Alaska: Alaska Power Authority.
Bovee, K.B., 1982. A guide to stream habitat analysis using the instream flow incremental
methodology. Instream Flow Information Paper No. 12. FWS/OBS-82/26. U.S. Fish and
Wildlife Service, Office of Biological Services, Fort Collins, Colorado.
Bovee, K., B.L. Lamb, J.M. Bartholow, C.B. Stalnaker, J. Taylor, and J. Henriksen. 1998.
Stream habitat analysis using the instream flow incremental methodology. U.S.
Geological Survey, Biological Resources Division Information and Technology Report
USGS/BRD-1998-0004.
Brabets, T.P, 1997, Geomorphology of the Lower Copper River, Alaska: U.S. Geological Survey
Professional Paper 1581, 89 p.
Conaway, J.S., and Moran, E.H., 2004, Development and calibration of two-dimensional
hydrodynamic model of the Tanana River near Tok, Alaska: U.S. Geological Survey
Open-File Report 2004-1225, 22 p.
DHI, 2011a. MIKE 11 A modeling system for Rivers and Channels User Guide. December.
DHI, 2011b. MIKE 21 Flow Model Hydrodynamic Module User Guide. June.
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Grant, G.E., Swanson, F.J., and Wolman, M.G., 1990. Pattern and origin of stepped-bed
morphology in high-gradient streams, Western Cascades, Oregon. Geophysical Society
of America Bulletin 102 (3), pp. 340-352.
Greimann, B. and Y. Lai, 2008. Two-Dimensional Total Sediment Load Model Equations,
ASCE J Hyd Div, 134:8, pp. 1142-1146.
HDR 2011, Watana transportation access study, Project No. 82002. Draft report prepared for the
Alaska Department of Transportation and Public Facilities. November 29, 2011.
Holly, F.M., Jr., J.C. Yang, and M. Spasojevic, 1985. Numerical Simulation of Water and
Sediment Movement in Multiply-Connected Networks of Mobile Bed Channels. Prepared
for Harza-Ebasco Susitna Joint Venture. Iowa City, Iowa: The University of Iowa.
Horritt, M.S., P.D. Bates, M.J. Mattinson, 2006. Effects of mesh resolution and topographic
representation in finite volume models of shallow water fluvial flow, J Hydrology, vol
329, Issues 1-2, September, pp 306-314.
Huang, J., Greimann, B.P., and Bauer, T., 2006. Development and Application of GSTAR-1D,
Federal Interagency Sedimentation Conference in Reno, NV, April 2-6.
Huang, J.V. and Greimann, B.P., 2011. SRH-1D 2.8 User’s Manual, Sedimentation and River
Hydraulics – One Dimension, Version 2.8, U.S. Department of Interior, Bureau of
Reclamation, Technical Service Center, Sedimentation and River Hydraulics Group. 227
pp.
Lai, Y.G., 2008. SRH-2D version 2: Theory and User’s Manual, Sedimentation and River
Hydraulics – Two-Dimensional River Flow Modeling, U.S. Department of Interior,
Bureau of Reclamation, November, 113 p.
Mobile Boundary Hydraulics (MBH) Software, Inc., 2010. Sedimentation in Stream Networks
(HEC-6T), User Manual, March 16, 388 pp.
MBH, 2008. Sedimentation in Stream Networks (HEC-6T), User Manual, Version 5.13.22_08.
McDonald, R.R., Nelson, J.M., and Bennett, J.P., 2005, Multi-dimensional surface-water
modeling system user’s guide: U.S. Geological Survey Techniques and Methods, 6-B2,
136 p.
McDonald, R., Nelson, J., Kinzel, P., and Conaway, J., 2005. Modeling Surface-Water Flow and
Sediment Mobility with the Multi-Dimensional Surface-Water Modeling System
(MD_SWMS). U.S. Geological Survey Fact Sheet 2005 – 3078, 6 p.
Mussetter Engineering, Inc., 2008. Flood Inundation Mapping, Flood Hazard Evaluation, and
Downstream Impact Analysis of the Carmel River Reroute and Removal Option for the
San Clemente Dam Seismic Retrofit Project, California. Prepared for California Coastal
Conservancy and MWH Americas, Inc. February.
Mussetter, R.A., Harvey, M.D. and Sing, E.F., 1995. Assessment of dam impacts on
downstream channel morphology. In Lecture Series, U.S. Committee on Large Dams,
San Francisco, California, May 13-18, pp. 283-298.
Mussetter, R.A. and Harvey, M.D., 1996. Geomorphic and hydraulic characteristics of the
Colorado River, Moab, Utah: Potential impacts on a uranium tailings disposal site. Proc.
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Conference on Tailings and Mine Waste, '96, Colorado State University, January 16-19,
1996, Balkema, Rotterdam, pp. 405-414.
Nelson, J.M., Y. Shimizu, H. Takebayashi, and R.R. McDonald, 2010. The international river
interface cooperative: public domain software for river modeling, 2nd Joint Federal
Interagency Conference, Las Vegas, June 27 to July 1.
Parker, G., 1990. The “Acronym” series of Pascal programs for computing bedload transport in
gravel rivers. University of Minnesota, St. Anthony Falls Hydraulic Laboratory, External
Memorandum No. M-220.
Pasternack, G B., 2011. 2D Modeling and Ecohydraulic Analysis, Land, Air, and Water
Resources, University of California at Davis, 158 pp.
Rosgen, D.L., 1996. Applied River Morphology. Wildland Hydrology, Pagosa Springs.
Ruark, M., Niemann, J., Greimann, B., and Arabi (2011). “Method for Assessing Impacts of
Parameter Uncertainty in Sediment Transport Modeling Applications,” Journal of
Hydraulic Engineering, ASCE, Vol. 137, No. 6, pp. 623-636.
Smiarowski, A, 2010. The evaluation of a two-dimensional sediment transport and bed
morphology model based on the Seymour River. Master Thesis, University of British
Columbia.
Tetra Tech, 2010. DRAFT Hydraulic and Sediment-transport Modeling for the Platte River
Sediment Augmentation Feasibility Study, Nebraska. Prepared for the Platte River
Recovery Implementation Program, September.
Tetra Tech, 2012. Technical Memorandum: Fluvial Geomorphology Modeling. Prepared for
AEA.http://www.susitnaWatanahydro.org/documents/AEA_SuWa_FluvialModelingTech
Memo20120518_Draft.pdf
Thomson, J.R., Taylor, M.P., Fryirs, K.A., and Brierley, G.J., 2001. A geomorphological
framework for river characterization and habitat assessment. Aquatic Conservation-
Marine and Freshwater Ecosystems 11 (5), pp. 373-389.
University of Alberta, 2002. River2D, two-dimensional depth averaged model of river
hydrodynamics and fish habitat, introduction to depth averaged modeling and user's
manual, September.
University of British Columbia, 2009. River2D – Morphology, R2DM, user manual for version
5.0, July
URS. 2011. AEA Susitna Water Quality and Sediment Transport Data Gap Analysis Report.
Prepared by Tetra Tech, URS, and Arctic Hydrologic Consultants. Anchorage, Alaska. 62
pp. Appendixes.
U.S. Army Corps of Engineers (USACE), 1993. HEC-6, Scour and Deposition in Rivers and
Reservoirs, User’s Manual, Hydrologic Engineering Center, Davis, California.
USACE, 2010a. HEC-RAS, River Analysis System. Users Manual, Version 4.1, Hydrologic
Engineering Center, Davis, California.
USACE, 2010b. Adaptive Hydraulics User Manual Version 3.3. U.S. Army Corps of Engineers
Waterways Experiment Station, Vicksburg, Mississippi.
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Wilcock, P.R. and Crowe, J.C., 2003. Surface-based transport model for mixed-size sediment.
Journal of Hydraulic Engineering, ASCE, v. 129, no. 2, February, pp. 120-128.
Wilcock, P.R. and R.M. Iverson. 2003, Prediction in Geomorphology, in Prediction in
Geomorphology, edited by Wilcock, P.R. and R.M. Iverson, American Geophysical
Monograph.
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6.6.10. Tables
Table 6.6-1. Schedule for the downstream study limit determination process for the Fluvial Geomorphology Modeling
Study.
Step in Downstream Geomorphology Study Limit Determination Date
RM 75 downstream geomorphology modeling limit proposal in RSP December 2012
Recon. level assess. of Project effects in the L. Susitna River Segment and flow routing model results January 2013
Tech. memorandum on recon. level assessment of Project effects in the Lower Susitna River
Segment January 2013
TWG meeting for confirmation of downstream geomorphology modeling limit Feb / Mar 2013
1-D bed evolution modeling and 2013 Geomorphology Study results and tech memo January 2014
TWG meeting(s) to reevaluate and confirm or adjust downstream modeling limits Feb / Mar 2014
Collect additional data if need identified (Summer 2014) Summer 2014
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Table 6.6-2. Evaluation of potential 1-D bed evolution models.
Evaluation Criteria Models
HEC-RAS SRH-1D MIKE 11 HEC-6T
General
Proprietary/cost (if applicable) ○ ○ ● / $8,000 ● / $3,000
Full or quasi unsteady for sediment
transport simulation Quasi Both Full Quasi
Ice for fixed bed ● ○ ○ ○
Ice for moveable bed ● ○ ○ ○
# of transport equations supported 7 13 10 18
Supports user defined transport equation ○ ○ ○ ●
Closed loop capability ○1 ● ● ●
Experience with model: High (H);
Moderate (M); Low (L) H L M H
Model Size Limitations
# of cross-sections NL NL NL 5,000
# of hydrograph ordinates 40,000 NL NL NL
# of sediment sizes 20 8 NL 20
Sediment Sizes Supported
Wash load (silts, clays) ● ● ● ●
Considers settling and resuspension ● ● ● ●
Sand ● ● ● ●
Gravel and cobble ● ● ● ●
Notes: ● = Yes; ○ = No; NL = No Limit 1 Not currently available, but in development.
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Table 6.6-3. Evaluation of potential 2-D bed evolution models.
Evaluation Criteria Model
SRH-2D ADH SToRM MIKE 21 River2D
General
Proprietary/cost (if applicable) ○ ○ ○ ● / $20,000 ○
Unsteady flow capability ● ● ● ● ●
Ice for fixed bed ○ ○ ○ ● ●
Ice for moveable bed ○ ○ ○ ● ●
Number of transport equations
supported 4 2 ○1 10 2
Supports user defined transport
equation ○ ● ○1 ● ○
Relative execution speed:
Fast (F), Slow (S) F S F F S
Model stability: High (H), Moderate
(M), Low (L) H M M H H
Experience with model: High (H),
Moderate (M), Low (L) H M L L M
Moveable boundary simulation ● ● ○1 ● ●
Grid Structure/Model Formulation
Finite element (FE)/
Finite Volume (FV) FV FE FV/FE FV/FE FE
Grid structure: Flexible Mesh (FM) FM FM FM FM FM
Model Size Limitations
# of grid elements 16,000 Unlimited Unlimited Unlimited >100,000
Sediment Sizes Supported
Wash load (silts, clays) ○ ● ○1 ● ○
Considers settling ○ ● ○1 ● ○
Sand ● ● ○1 ● ●
Gravel and cobble ● ● ○1 ● ●
Notes: ● = Yes; ○ = No; U = Unknown, currently investigating capabilities; NL = No Limit 1 Not currently available, but in development.
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Table 6.6-4. Summary of model parameter precedencies for water resources models to be applied in the Susitna-Watana licensing effort.
Model Study Section Software Program Precedence (Parameters that the model results will be adopted for as the governing values)
Operations Model Engineering HEC
ResSim
Project releases (discharge from the dam including spills) and reservoir pool elevations. The model will be refined
throughout the study period to reflect any changes in project configuration and as operations scenarios are
developed. (Available Q4 2012 )
Initial Flow Routing Model
(Hydrologic Routing) Engineering HEC
ResSim
Discharge, stage and other hydraulic parameters such as velocity and depth from RM 184 to RM 84 until the
Mainstem Open-Water Flow Routing Model is developed (Q1 2013)
Mainstem Open-Water Flow
Routing Model (Hydraulic
Routing)
8.5 HEC-RAS
Discharge, stage and other 1-D hydraulic parameters such as velocity and depth from RM 184 downstream to RM
74 once the model is developed (Q1 2013 version 1) during open water periods. Model will be updated with
additional cross-section from 2013 fieldwork (Q4 2013 ver. 2) and finalized (Q4 2104 ver. 3). Provides boundary
conditions to 2-D Bed Evolution Model.
Susitna River Ice Processes
Model (Hydraulic Routing) 7.6 River 1D
Discharge, stage, and other 1-D hydraulic parameters such as velocity and depth from RM 184 to RM 100 during
periods of ice formation, ice cover and ice break-up once model is developed (Q4 2013 ver. 1, Q4 2014 ver. 2). The
model will also provide water temperature, ice extents and ice thickness for the same period.
Susitna River Ice Processes
Model – Focus Areas 7.6 River 1D
River 2D
Hydraulic conditions, water temperature, ice extents and ice thickness within the focus areas during periods of ice
formation, ice cover and ice break-up.
Susitna River Water Quality
Model 5.6 EFDC Water temperature during the open water period and other water quality parameters year round from RM 184 to RM
26
1-D Bed Evolution Model
(Hydraulics and Sediment
Transport)
6.6 TBD1
(Q2 2013)
One-dimensional sediment transport characteristics, bed aggradation/degradation and substrate gradation in the
main channel from RM 184 to RM 74. May be used to determine these parameters for localized off-channel habitat
within focus areas. Mainstem Open-Water Hydraulic Routing Model will take precedence for 1-D hydraulics.
2-D Bed Evolution Model
(Hydraulics and Sediment
Transport)
6.6 TBD2
(Q2 2013)
Detailed two-dimensional hydraulic and sediment transport characteristics, bed aggradation/degradation and
substrate gradation within the focus areas. Will provide two-dimensional velocity and depth for FA-IFS within focus
area where applied during the open water period. Boundary condition of downstream water surface elevation and
upstream inflow supplied by Mainstem Open-Water Flow Routing Model
Notes:
1 Candidate Models: HEC-RAS, HEC-6T, SRH-1D, MIKE-11
2 Candidate Models: SRH-2D, MIKE-21, SToRM, ADH, River-2D
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Table 6.6-5. Potential Focus Areas in the Middle and Lower Susitna River Segments.
Feature Downstream RM
Upstream RM Geomorphic Reach Reach
Type
Below Dam 182.0
(184.7)1
183.0
(185.7) 1
MR-1 SC2
MR2-wide 170.7
(173.6) 1
172.5
(175.4) 1
MR-2 SC2
MR2-narrow 168.5
(171.6) 1
170.0
(173.0) 1
MR-2 SC2
Portage Cr 148.3
(151.8) 1
148.8
(152.3) 1
MR-5 SC2
Slough 21 141.0
(144.4) 1
142.1
(145.7) 1
MR-6 SC3
Indian R 138.4
(141.8) 1
140.0
(143.4) 1
MR-6 SC3
Slough 11 135.3
(138.7) 1
136.6
(140.0) 1
MR-6 SC3
Slough 8A 124.2
(128.1) 1
126.1
(129.7) 1
MR-6 SC3
Slough 6A 111.8
(115.3) 1
113.0
(116.5) 1
MR-7 SC2
Whiskers Slough 101.0
(104.8) 1
102.2
(106.0) 1
MR-8 MC1
Notes:
1 Values in parenthesis are Project River Miles (PRM)
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Table 6.6-6. Primary output variables for which values are taken directly from the 1-D and 2-D mobile-boundary models and relevance to other studies.
Variable Description of Model Output Spatial Resolution Relevance to Other Studies
1-D mobile-boundary model
Water-surface profiles Steady-state water-surface profiles for all discharges Cross-section Geomorphology
Cross-sectionally averaged hydraulic
conditions
Flow depth, velocity, bed shear stress, channel top
width Cross-section FA-IFS, R-IFS, Geomorphology
Bed material load transport rates Transport rates by grain size fraction Cross-section Geomorphology
Bed material (i.e., substrate) gradations Change in surface layer bed gradations by cross-
section over time (0, 25, 50 years) Cross-section FA-IFS, Geomorphology
Bed elevation Changes in bed elevation with time Cross-section, longitudinal profile FA-IFS, R-IFS, Geomorphology,
GW
2-D mobile-boundary model
Water-surface elevations Steady and unsteady water-surface elevations Grid element FA-IFS, R-IFS, Geomorphology,
GW
Depth-averaged hydraulic conditions Flow depth , velocity (magnitude and direction), bed
shear stress Grid element FA-IFS, R-IFS, Geomorphology,
GW
Flow distribution among multiple channels
(including side channels)
Discharge in each branch (including side channels)
over range of flows; changes associated with bed
evolution model results
Channel width FA-IFS, R-IFS, Geomorphology,
GW
Bed material load transport rates Transport rates by grain size fraction, including supply
to and transport through side channels Grid element FA-IFS, R-IFS, Geomorphology,
GW
Bed material (i.e., substrate) gradations Change in substrate gradations by grid element over
time, including side channels and side sloughs Grid element FA-IFS, R-IFS, Geomorphology,
GW
Bed elevation
Changes in bed elevation with time, including side
channels and side sloughs. Evolution of mouths and
spawning areas of particular interest
Grid element FA-IFS, R-IFS, Geomorphology,
GW
Breaching flows Magnitude, frequency and duration of flows overtopping
control at the head of side channels Grid element →side channel width FA-IFS, Geomorphology
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Table 6.6-7. Key variables needed for the impact assessments for which results are obtained through additional analysis of predictions taken directly from the 1-D and 2-
D mobile-boundary models.
Variable Description Spatial Resolution Relevance to Other Studies
1-D mobile-boundary model
Wash load transport rates Correlations between wash load transport rates and
discharge Gage locations WQ, R-IFS
Overbank sedimentation rates Rate of sediment delivery into overbanks and vertical
accretion rates Reach-averaged R-IFS, Geomorphology
Breaching flows Magnitude, frequency and duration of flows overtopping
control at the head of side channels Site R-IFS, Geomorphology
Side channel connectivity Frequency, duration and inundation extent of backwater
flows into side channels Site R-IFS
Bed Material Motion Thresholds (aka
Incipient Motion Analysis)
Frequency and duration of flows sufficient to cause
general mobilization of bed material
Cross-section and/or reach-
averaged FA-IFS, Geomorphology
Bed material transport capacity rating
curves
Bed material transport capacity (total and by-size
fraction) as a function of discharge
Cross-section and/or reach-
averaged Geomorphology
Effective Discharge Magnitude and frequency of flows that transport the
most sediment over defined period of time Reach-averaged Geomorphology
Bank erosion rates Estimated rate of erosion into main and side channel
banks
Cross-section and/or reach-
averaged R-IFS, Geomorphology
LWD recruitment Quantities of LWD delivered to mainstem and side
channels due to bank erosion Reach R-IFS, Geomorphology
Deposition rates at tributary mouths Evolution of tributary mouth fans/bars over time Geomorphology unit FA-IFS, Geomorphology
Hydraulic conditions at tributary mouths Potential effect of changes in tributary mouths and
effects on fish passage into tributaries Geomorphology unit FA-IFS, Geomorphology
2-D mobile-boundary model
Weighted-useable-area versus discharge
curves
Hydraulic conditions (velocity, depth, substrate size)
provided to FA-IFS for WUA estimates Grid element→ Habitat unit FA-IFS, Geomorphology
Overbank sedimentation rates Rate of sediment delivery into overbanks and vertical
accretion rates Grid element R-IFS, Geomorphology
Bed Material Motion Thresholds (aka
Incipient Motion Analysis)
Frequency and duration of flows sufficient to cause
general mobilization of bed material Grid element→ Habitat unit FA-IFS, Geomorphology
Bank erosion rates Changes in bank shear stress and bank energy index
(BEI) Model reach R-IFS, Geomorphology
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Variable Description Spatial Resolution Relevance to Other Studies
Changes in side channel, side slough and
upland slough geometry Evolution of channel width and depth Grid element →side channel width FA-IFS, R-IFS,
Geomorphology
Fine sediment interactions in spawning
areas
Potential for infiltration and flushing of fines from
spawning substrate, including side channels and side
sloughs
Grid element→ Habitat unit FA-IFS, R-IFS,
Geomorphology
LWD recruitment Changes in bank erosion rates that could affect LWD
recruitment Grid element FA-IFS, R-IFS,
Geomorphology
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Table 6.6-8. Schedule for implementation of the Fluvial Geomorphology Modeling Study.
Activity 2012 2013 2014 2015
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1
Selection of 1-D and 2-D Models ●
Selection of Focus Areas ●
Coordination w/ Other Studies on Modeling Needs Including Focus Areas ●
2013 Field Data Collection / Supplemental Field Data Collection 2014 ● / ●
Coordinate with Other Studies on Processes Modeled ●
1-D Model Development and Calibration
Perform 1-D Modeling of Existing Conditions and Initial Project Run ●
Reevaluate Downstream Study Limits Based on 1-D Results ●
2-D Model Development and Calibration
Perform 2-D Modeling of Existing Conditions ●
Perform 1-D Modeling of Alternative Scenarios ●
Perform 2- Modeling of Alternative Scenarios ●
Post Process and Provide Model Results to Other Studies ●
Interpretation of Channel Change and Integration with Other Studies ●
Initial Study Report /Updated Study Report Δ ▲
Legend: Planned Activity
● Technical Memorandum or Interim Product
Δ Initial Study Report
▲ Updated Study Report
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Table 6.6-9. Information and products required by the Fluvial Geomorphology Modeling Study from other studies.
Source of Product or Information Information or Product to be Provided Timing
Information or Products Required for: Field Data Collection
Fish and Aquatics Instream Flow Study (Section 8.5)
Riparian Instream Flow Study (Section 8.6)
Groundwater Study (Section 7.5)
Ice Processes Study (Section 7.6)
Characterization and Mapping of Aquatic Habitats
Study (Section 9.9)
Collaboration on Focus Area selection Q1-13
Collaboration on modeling needs Q2-13
Sharing of field data
Q3-13 Locations of specific interest within the Focus Areas
Information or Products Required for: 1-D, 2-D and Tributary Delta Model Development and Calibration
Geomorphology Study (Section 6.5)
Sediment supply Q4-12 &
Q4-13
Historical channel change Q1-13
Identify physical processes Q4-13
Initial estimates of reservoir sediment trap efficiency Q3-13
Q3-13 Flood frequency and flow duration
Water Quality Modeling Study (Section 5.6) Reservoir sediment trap efficiency for alt. scenarios Q2-14
Glacial and Runoff Change Study (Section 7.7) Potential increase in sediment supply from glacial
surge
Q1-14
Mainstem (Open-water) Flow Routing Model (Section
8.5.4.3)
Tributary inflows and accretions Q3-13
Reservoir Operations (Engineering) Base case annual hydrographs for representative
years
Q3-13
Mainstem (Open-water) Flow Routing Model (Section
8.5.4.3)
Base case continuous record daily flows (50 years) Q3-13
Information or Product Required for: 1-D, 2-D and Tributary Delta Model Baseline and Alternative Scenarios Analysis
Mainstem (Open-water) Flow Routing Model (Section
8.5.4.3)
Tributary inflows and accretions Q3-13
Reservoir Operations (Engineering)
Base case annual hydrographs for representative
years
Q3-13
Alt. scenarios annual hydrographs for representative
yrs
Q4-14
Mainstem (Open-water) Flow Routing Model (Section
8.5.4.3)
Base case continuous record daily flows (50 years) Q3-13
Alt. scenarios continuous record daily flows (50 years) Q4-14
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Source of Product or Information Information or Product to be Provided Timing
Information or Product Required for: Integration of Reach- & Local-Scale Modeling and Geomorphic Analysis
Geomorphology (Section 6.5)
Bed material mobilization and effective discharge Q4-13 &
Q4-14 Assessment Project effects on geomorphic processes
and threshold relationships
Ice Processes (Section 7.6) Geomorphic influences from ice Q4-13
Riparian Instream Flow Study (Section 8.6) Historical floodplain sedimentation rates Q1-14
Vegetation age classes Q1-14
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Table 6.6-10. Information and products the Fluvial Geomorphology Modeling Study will provide to other studies.
Study the Product or Information is Provided to Information or Product to be Provided Timing
Information or Products Provided by: Field Data Collection
Geomorphology Study (Section 6.5)
Fish and Aquatics Instream Flow Study (Section 8.5)
Riparian Instream Flow Study (Section 8.6)
Water Quality Modeling Study (Section 5.6)
Cross-section and bathymetry
Q4-13
ADCP velocity and depths
Bed and bank material sample results
Geomorphic site assessments
Locations of specific interest within the Focus Areas
Information or Products Provided by: 1-D, 2-D and Tributary Delta Model Development and Calibration
1-D, 2-D and Tributary Delta Model Baseline and
Alternative Scenarios (Section 6.6.4.2)
Calibrated 1-D bed evolution model Q4-13
Calibrated 2-D bed evolution model Q2-14
Tributary delta model for selected tributaries Q1-14
Information or Products Provided by: 1-D, 2-D and Tributary Delta Model Baseline and Alternative Scenarios Analysis
Water Quality Modeling Study (Section 5.6) Changes in fine sediment load for turbidity modeling Q4-14
Geomorphology Study (Section 6.5)
Fish and Aquatics Instream Flow Study (Section 8.5)
Riparian Instream Flow Study (Section 8.6)
Groundwater Study (Section 7.5)
Bed aggradation and degradation - reach scale
Q4-14
Change in substrate size – reach scale
Changes in erosion and deposition patterns
Changes in bed material load transport
Hydraulic parameters: velocity depth and water
surface elevations (WSE)
Information or Products Provided by: Integration of Reach- & Local-Scale Modeling and Geomorphic Analysis
(see Tables 6.6-6 and 6.6-7 for detailed list of information)
Riparian Instream Flow Study (Section 8.6)
Potential changes in channel morphology Q4-14 Groundwater Study (Section 7.5)
Recreation and Aesthetics Study (Section 12)
Fish and Aquatics Instream Flow Study (Section 8.5)
Potential changes in habitat: maintenance and
evolution
Q4-14 Potential changes in habitat: relative distribution
Potential changes in habitat: areas for specific types
Potential changes in habitat: connectivity of off-
channel
Riparian Instream Flow Study (Section 8.6) Changes in floodplain sedimentation rates Q4-14
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Table 6.6-11. Fluvial Geomorphology Modeling Study costs.
Component Task/Subtask Estimated Cost Range
Bed Evolution Model
Development, Coordination
and Calibration
Development of Bed Evolution
Modeling Approach and Model
Develop Approach $50,000
Develop Model $400,000 to $500,000
Field Data Collection $900,000 to $1,100,000
Coordination with other Studies on Processes Modeled $50,000
Calibration/Validation of Model $200,000 to $300,000
Model Existing and with-
Project Conditions
Model Existing Conditions (one scenario) $200,000 to $300,000
Model with-Project Conditions (three scenarios) $250,000 to $350,000
Coordination on Model Output / Study Integration $150,000 to $200,000
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6.6.11. Figures
Figure 6.6-1. Example of coarse mesh applied to the Whiskers Slough potential Focus Area, Middle Susitna River Segment, Geomorphic Reach MR-8
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Figure 6.6-2. Example of fine mesh applied to the Whiskers Slough proposed Focus Area, Middle Susitna River Segment, Geomorphic Reach MR-8
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Figure 6.6-3. Locations of proposed Middle Susitna River Segment Focus Areas.
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Figure 6.6-4. Study interdependencies for the Fluvial Geomorphology Modeling Study