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Susitna-Watana Hydroelectric Project Document
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Title:
Riparian instream flow study, Study plan Section 8.6 : Final study plan
SuWa 200
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Alaska Energy Authority
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Final study plan
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Susitna-Watana Hydroelectric Project document number 200
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[Anchorage : Alaska Energy Authority, 2013]
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July 2013
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Study plan Section 8.6
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59 p.
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Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Riparian Instream Flow Study
Study Plan Section 8.6
Final Study Plan
Alaska Energy Authority
July 2013
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-1 July 2013
8. INSTREAM FLOW STUDY: FISH, AQUATICS, AND RIPARIAN
8.6. Riparian Instream Flow 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 Riparian Instream Flow
Study, Section 8.6. RSP Section 8.6 focuses on providing a quantitative, spatially-explicit model
to predict potential impacts to downstream floodplain vegetation from Project operations.
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 8.6 was one of the 13 approved with
modifications. In its April 1 SPD, FERC recommended the following:
Seedling Establishment
-We recommend that the study plan be modified to require AEA to sample seedling
establishment following the initial spring peak flows (e.g., July) and again in September in
2013 and 2014. This is consistent with accepted methods (section 5.9(b)(6)), and would
provide information necessary to support the design of the project, assess environmental
effects, and evaluate proposed environmental measures.
Adequacy of MODFLOW and Xylem Water Isotopic Sampling to Establish
Groundwater/Hydroperiod Relationships
- We discuss the use of RIP-ET and our recommendations in Study 7.5 (groundwater).
- Consequently, we recommend that AEA consult with the TWG on the sampling design for
collecting plant xylem water; and file no later than June 30, 2013, the following:
1) A detailed description of the sampling sites, frequency, and schedule.
2) Documentation of consultation with the TWG, including how its comments were
addressed.
Soil Profile Sampling
- We recommend that the study plan be modified to specify that sediment grain size
measurements would be based on samples taken at soil horizons, rather than at equal depth
increments.
Vegetation Response Curves
- AEA would follow the methods of Henszey et al. (2004) to develop vegetation-flow response
curves. Prior to developing vegetation flow response curves, Henszey et al. (2004), and
more recently Orellana et al. (2012), evaluated a number of different water-level summary
statistics to determine which were most strongly correlated with plant frequency and were
thus most suitable for inclusion in the vegetation-flow response curves. Testing the statistics
for best fit, as recommended by FWS, is a commonly accepted practice (section 5.9(b)(6).
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We recommend that AEA do so in consultation with the riparian technical workgroup.
Methods of analysis should be reported in the initial and updated study reports.
Floodplain Vegetation Study Synthesis, Focus Area to Riparian Process Domain Model Scaling,
and Project Operations Effects Modeling
- We recommend AEA include a schedule and plan for [modeling] development in either the
initial or updated study report, as appropriate.
- We do not recommend that such models be provided to stakeholders. Stakeholders would
have an opportunity at various points in the ILP process (e.g., initial and updated study
reports, preliminary licensing proposal, final license application) to identify specific project
operation scenarios, which AEA would need to evaluate using the methods described in the
study plan.
Consultation on the interrelated riparian vegetation, riparian instream flow and riparian
groundwater/surface water (GW/SW) study plans was accomplished with TWG representatives
in two meetings; held April 23, 2013 and June 6, 2013. Licensing participants were provided the
opportunity to address technical details and comments and concerns regarding the study’s
approaches and methods.
The Riparian Instream Flow, Groundwater, and Riparian Vegetation Studies FERC
Determination Response Technical Memorandum (Riparian/GW TM) addresses FERC’s April 1
SPD request concerning the adequacy of MODFLOW and xylem water isotopic sampling. The
Riparian/GW TM was filed with FERC on June 30, 2013.
This Final Study Plan reflects FERC’s requested modifications regarding seedling establishment
(Section 8.6.3.3.2), soil profile sampling (Section 8.6.3.5), vegetation response curves (Section
8.6.3.6.2), and floodplain vegetation study synthesis, focus area to riparian process domain
model scaling, and project operations effects modeling (Section 8.6.3.7).
8.6.1. General Description of the Proposed Study
8.6.1.1. Riparian IFS Goal and Objectives
The goal of the 2013–2014 Riparian Instream Flow Study (hereafter Riparian IFS) is to provide a
quantitative, spatially-explicit model to predict potential impacts to downstream floodplain
vegetation from Project operational flow modification of natural Susitna River flow, sediment,
and ice process regimes. To meet this goal, a physical and vegetation process modeling
approach will be used (Figure 8.5-10). First, existing Susitna River groundwater and surface
water (GW/SW) flow, sediment and ice process regimes will be measured and modeled relative
to floodplain plant community establishment, recruitment, and maintenance requirements.
Second, predictive models will be developed to assess potential Project operational impacts to
floodplain plant communities and provide operational guidance to minimize these impacts.
Third, the predictive models will be applied spatially in a Geographic Information System (GIS)
to the riparian vegetation map produced by the Riparian Botanical Survey Study to produce a
series of maps of predicted changes under alternative operational flow scenarios.
The Riparian IFS approach and format have been written to address, and to parallel, the study
format proposed in the U.S. Fish and Wildlife Service (USFWS) Riparian IFS Request (May 31,
2012).
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Riparian IFS objectives are as follows:
1. Synthesize historic physical and biological data for Susitna River floodplain vegetation,
including 1980s studies, studies of hydro project impacts on downstream floodplain plant
communities, and studies of un-impacted floodplain plant community successional
processes.
2. Delineate sections of the Susitna River with similar environments, vegetation, and
riparian processes, termed riparian process domains, and select representative areas
within each riparian process domain, termed Focus Areas, for use in detailed 2013–2014
field studies.
3. Characterize seed dispersal and seedling establishment groundwater and surface water
hydroregime requirements. Develop a predictive model of potential Project operational
impacts to seed dispersal and seedling establishment.
4. Characterize the role of river ice in the establishment and recruitment of dominant
floodplain vegetation. Develop a predictive model of potential Project operational
impacts to ice processes and dominant floodplain vegetation establishment and
recruitment.
5. Characterize the role of erosion and sediment deposition in the formation of floodplain
surfaces, soils, and vegetation. Develop a predictive model of Project operations changes
to erosion and sediment deposition patterns and associated floodplain vegetation.
6. Characterize natural floodplain vegetation groundwater and surface water maintenance
hydroregime. Develop a predictive model to assess potential changes to natural
hydroregime and potential floodplain vegetation change.
7. Develop floodplain vegetation study, Focus Area to riparian process domain scaling and
Project operations effects modeling.
8.6.1.2. Riparian IFS Analytical Framework and Study Interdependencies
Figure 8.5-10 depicts the overall analytical framework of the Instream Flow Studies
commencing with the Reservoir Operations Model (ROM) that will be used to generate
alternative operational scenarios under different hydroregimes. The ROM will provide the input
data that will be used to predict hourly flow and water surface elevation data at multiple points
downstream, taking into account accretion and flow attenuation. A series of biological and
riverine processes studies will be completed to supplement the information collected in the
1980s, to define relationships between mainstem flow, riverine processes, and biological
resources. This will result in development of a series of flow-sensitive models (e.g., models of
selected anadromous and resident fish habitats by species and life stage, models to describe
invertebrate habitats, temperature model, ice process model, sediment transport model, turbidity
model, large woody debris (LWD) recruitment model, riparian vegetation groundwater and
surface water interaction model) that will enable the translation of effects of alternative Project
operations on the respective riparian processes and biological resources. While there is likely to
be a cumulative effect that translates throughout the entire length of the Susitna River, many of
the resource and process effects will be location- and habitat-specific (e.g., responses are
expected to be different in side sloughs versus mainstem versus side channel versus tributary
delta versus riparian habitats). Additionally, alternative Project operations will likely affect
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specific habitats and processes differently, both spatially and temporally. Therefore, the habitat
and process models will be spatially discrete (e.g., by site, reach) and yet able to be integrated
across the entire study area to allow for a holistic evaluation of each alternative operational
scenario. This will allow for an Integrated Resource Analysis of separate operational scenarios
that includes each resource element, the results of which can serve in a feedback capacity leading
to new or, modifications of, existing scenarios.
The Riparian IFS is an interdependent effort coordinated with a range of other study disciplines,
and these interdependencies are depicted in Figure 8.6-1. Studies providing input to the Riparian
IFS include Fish and Aquatics Instream Flow (see Section 8.5), Groundwater Study (see Section
7.5), Ice Processes Study (see Section 7.6), Fluvial Geomorphology Study (see Section 6.6), and
Riparian Vegetation Study (see Section 11.6). The Riparian IFS will provide data and results to
the Geomorphology Study (see Section 6.0), Ice Processes Study (see Section 7.6), Wildlife
Studies (see Section 10.0), River Productivity Study (see Section 9.8), Riparian Vegetation Study
(see Section 11.6), and to Project operational flow design. The Riparian IFS is a modeling effort
designed to evaluate potential Project operations effects on downriver floodplain plant
communities. The modeling design incorporates both floodplain plant community succession
models and physical process models (fluvial geomorphology, sediment transport, ice processes,
and groundwater and surface interaction. Together, the vegetation and physical models comprise
a hydrogeomorphic approach to modeling the physical floodplain boundary conditions
controlling the establishment, recruitment, and maintenance of characteristic riparian floodplain
plant communities (Figure 8.6-1and Figure 8.6-2). These vegetation and physical models
represent the core tools that will be used for assessing changes in floodplain physical
characteristics (flow, sediment and ice process regimes) and associated floodplain plant
community composition, succession, and spatial distribution under alternative Project
operational scenarios.
8.6.1.3. Existing Information and Need for Additional Information
Information for the study area includes, but is not limited to, 1) recent and historic aerial
photography; 2) riparian vegetation surveys and characterizations from recent and early 1980s
studies; 3) riparian vegetation succession conceptual models developed from the 1980s data as
part of the original Susitna Hydroelectric Project (SHP) Phase I vegetation mapping studies
conducted along the Susitna River from the downstream end of Devils Canyon to Talkeetna, and
4) vegetation succession studies conducted in the Susitna River floodplain between Gold Creek
and the Deshka River (McKendrick et al. 1982; UAFAFES 1985). The riparian sites visited in
the 1980s studies were re-sampled in 1992–1993 (Collins and Helm 1997; Helm and Collins
1997). Of primary importance to the Riparian IFS is the previous vegetation mapping and
successional dynamics studies by McKendrick et al. (1982), Collins and Helm (1997), and Helm
and Collins (1997). These previous works will serve to inform the development of a stratified
sampling protocol for both the Riparian IFS and Botanical Riparian Study vegetation surveys.
The riparian study modeling efforts will build upon the Collins and Helm (1997) riparian
vegetation succession conceptual model (Figure 8.6-2).
Although substantial data and information concerning riparian vegetation were collected in the
1980s, those data are approximately 30 years old and therefore additional information needs to
be collected to provide a contemporary understanding of the riparian conditions existing in the
Susitna River. Moreover, previous studies (McKendrick et al. 1982; Collins and Helm 1997;
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Helm and Collins1997) were largely descriptive of riparian vegetation composition, structure,
and forest succession, and as such, do not provide an analytical framework sufficient for
assessing potential impacts to floodplain vegetation that may result from Watana Dam
operations, nor do they provide the ability to model and develop alternative flow scenarios. In
addition, the configuration and proposed operations of the Project have changed and must be
evaluated within the context of the existing environmental setting. This includes consideration
of potential load-following effects on riparian ecosystems downstream of the Watana Dam site
(including the Lower River Segment, as appropriate). Therefore, additional riparian studies are
necessary to adequately address the effects of potential Project operations on the riparian
floodplain plant communities.
8.6.2. Study Area
The study area includes the Susitna River active floodplain that would be affected by the
operation of the Project downstream of Watana Dam. The active floodplain is the valley bottom
flooded under the current climate. The longitudinal extent of the formal Riparian IFS study area
currently extends to river mile (RM) 75. Determining how far downstream Project operational
effects will extend will depend largely on the results of the Open-water Flow Routing Model (see
Section 8.5.4.3), which is scheduled to be completed in Q1 2013. Thus, an initial assessment of
the downstream extent of Project effects will be developed in Q2 2013 with input from 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 (see Section 6.5), habitat mapping
(see Sections 6.5 and 9.9), operations modeling (see Section 8.5.4.2.2), and the Mainstem Open-
water Flow Routing Model (see Section 8.5.4.3). The assessment will guide the need to extend
studies into the Lower River Segment and if needed, will identify which geomorphic reaches will
be subject to detailed instream flow analysis in 2013. Results of the 2013 studies would then be
used to determine the extent to which Lower River Segment studies should be adjusted in 2014.
During the 1980s studies, the Susitna River was characterized into three segments extending
above and below the two proposed dam sites. After researching potential Project configurations,
AEA is proposing a single dam configuration at the Watana Dam site at RM 184. The proposed
study characterizes the Susitna River as three segments (Figure 8.5-9). The Upper River
Segment represents that portion of the watershed above the Watana Dam site at RM 184; the
Middle River Segment (extending from RM 184 downstream to the Three Rivers Confluence at
RM 98.5); and the Lower River Segment (extending from the confluence of Chulitna and
Talkeetna rivers (Three Rivers) to Cook Inlet (RM 0). Potential Project effects to the Upper
River Segment above the Watana Dam site are addressed in Section 9.0, Fish and Aquatic
Resources; Section 10.0, Wildlife Resources; Section 11.0, Botanical Resources; and other
studies. Potential Project effects to the Upper River Segment will not be addressed in the
Instream Flow Study. The study area of the Instream Flow Study is focused on the two lower
segments of the river, the Middle River Segment and the Lower River Segment.
The Middle River Segment encompasses approximately 85 miles between the proposed Watana
Dam site (at RM 184) and the Three Rivers Confluence, located at RM 98.5. The river flows
from Watana Canyon into Devils Canyon, the narrowest and steepest gradient reach on the
Susitna River. In Devils Canyon, constriction creates extreme hydraulic conditions including
deep plunge pools, drops, and high velocities. The Devils Canyon rapids appear to present a
partial barrier hindering upstream passage at some flow conditions to the migration of
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anadromous fish; only a few adult Chinook salmon have been observed upstream of Devils
Canyon. Downstream of Devils Canyon, the middle Susitna River widens but remains
essentially a single channel with stable islands, occasional side channels, and sloughs. For
purposes of the study, the Middle River Segment was further divided into eight reaches.
The Lower River Segment consists of an approximate 98-mile section between the Chulitna
River confluence and Cook Inlet (RM 0). An abrupt change in channel form occurs where the
Chulitna River joins the Susitna River near the town of Talkeetna. The Chulitna River drains a
smaller area than the Middle River Segment at the confluence, but drains higher elevations
(including Denali and Mount Foraker) and many more glaciers. The annual flow of the Chulitna
River is approximately the same as the Susitna River at the confluence, though the Chulitna
contributes much more sediment than the Susitna. For several miles downstream of the
confluence, the Susitna River becomes braided, characterized by unstable, shifting gravel bars
and shallow subchannels. For the remainder of its course to Cook Inlet, the Susitna River
alternates between single channel, braided, and meandering planforms with multiple side
channels and sloughs. Major tributaries drain the western Talkeetna Mountains (the Talkeetna
River, Montana Creek, Willow Creek, Kashwitna River), the Susitna lowlands (Deshka River),
and the Alaska Range (Yentna River). The Yentna River is the largest tributary in the Lower
River Segment, supplying about 40 percent of the mean annual flow at the mouth.
Further refinements to the classification system being applied to the Susitna River have been
made since the Proposed Study Plan (PSP), but the major divisions associated with the middle
and lower segments have been retained. However, these are now incorporated into a more
refined hierarchical classification system that scales from relatively broad to more narrowly
defined categories as follows:
Segment → Geomorphic Reach → Mainstem Habitat Type → Mesohabitat Types
(Main channel only) → Off-channel Habitat Types.
The highest level category is termed Segment and refers to the Middle River Segment and the
Lower River Segment.
The Geomorphic Reach level is next and consists of eight categories (MR-1 through MR-8) for
the Middle River Segment and four categories (LR-1 through LR-6) for the Lower River
Segment. The geomorphic reach breaks were based in part on the following five factors: 1)
planform type (single channel, island/side channel, braided); 2) confinement (approximate extent
of floodplain, off-channel features); 3) gradient; 4) bed material / geology; and 5) major river
confluences.
This is followed by Mainstem Habitat Types, which include the same categories applied during
the 1980s studies – Main Channel, Side Channel, Side Slough, Upland Slough, Tributary Mouth,
and Tributary.
The next level in the hierarchy is Mesohabitat Type, which at this time is reserved for
classifying main channel habitats into categories of Riffle, Pool, Run, and Glide.
The last level in the hierarchy is referred to as Off-channel Habitats consisting of a number of
descriptive categories and quantitative indices including Turbid/Clear, Beaver Presence (Y/N),
Gross Area (Off-channel Habitats), Shoreline Length (includes both Main Channel and Off-
Channel Habitats). These are more fully described in the Fish and Aquatics Instream Flow
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Study (see Section 8.5), with further information provided in both the Geomorphic Study Plan
(see Section 6.0), and the Habitat Characterization Study Plan.
8.6.3. Study Methods
The Riparian IFS will first develop a process-based model of riparian vegetation succession and
dynamics driven by riverine hydrogeomorphic processes. The modeling approach will use
geomorphic, hydraulic, ice process, and GW/SW interaction models coupled with riparian
vegetation succession models based upon riparian vegetation surveys and previous Susitna River
riparian forest research (Helm and Collins 1997). Objectives of the modeling approach are as
follows:
1. Measure and model riparian vegetation physical process relationships under the
natural flow, sediment, and ice regimes.
2. Model potential impacts to riparian vegetation resulting from proposed Project
operational changes to natural flow, sediment, and ice regimes.
3. Provide guidance for Project operation scenarios to minimize potential riparian
vegetation impacts.
The Riparian IFS methods section is presented in the following format addressing each of the
seven Project components and objectives. First, each study component and associated objectives
are described. Second, study methods, with appropriate literature citations, are presented. Third,
Data Input to the Riparian IFS from other Project studies, and Data Output from Riparian IFS to
other Project studies, are detailed. Fourth, expected work products are presented. The Riparian
IFS Project schedule is presented in Section 8.6.9 (Table 8.6-1) and a glossary of relevant terms
is presented in the Glossary of Terms and Acronyms - Instream Flow.
8.6.3.1. Synthesize Historic Physical and Biologic Data for Susitna River Floodplain
Vegetation, Including 1980s Studies, Studies of Hydro Project Impacts on
Downstream Floodplain Plant Communities, and Studies of Un-impacted
Floodplain Plant Community Successional Processes
The goal of this study is to critically review and synthesize historic Susitna River riparian
vegetation studies within the context of physical process investigations conducted in the 1980s
including ice processes, sediment transport, GW/SW, and herbivory. Studies of downriver
floodplain vegetation response to hydroregulation on other hydro projects (both North American
and circum-polar) will be incorporated into the review to develop a current state-of-the-science
analysis of potential Project operational flow effects to Susitna River riparian floodplain
vegetation. Additionally, studies of un-impacted temperate and boreal floodplain plant
community successional processes will be incorporated into the study as appropriate. Study
objectives, methods and expected results are summarized in Table 8.6-2.
The objectives of this study task are as follows:
1. Conduct a critical review of previous Susitna River 1980s floodplain vegetation studies.
2. Place potential Susitna River Project operational effects within context of studies from
other hydroregulated rivers in North America.
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3. Review, and include relevant findings of, current research concerning temperate and
boreal floodplain forest succession and dynamics under natural flow regimes.
8.6.3.1.1. Methods
A critical literature review of all appropriate Susitna 1980s studies, historic and current hydro
project floodplain effects studies, and temperate and boreal floodplain forest scientific literature
will be conducted. The synthesis of findings will focus on elements relevant to evaluating
potential Project operation effects on downstream floodplain vegetation. An annotated,
searchable bibliography will be developed.
8.6.3.1.2. Data Input From Other Studies
Data input from other studies will include 1980s Susitna River floodplain study literature, hydro
project studies of downstream floodplain vegetation, and studies of un-impacted temperate and
boreal floodplain plant community succession.
8.6.3.1.3. Data Output to Other Studies
Output to other studies will include data for Geomorphology and Ice Processes studies, literature
review findings concerning Susitna River riparian vegetation and physical process, identification
of critical issues from hydro project floodplain vegetation impact analyses, and relevant findings
from natural flow regime floodplain vegetation research.
The results of this study will also provide Project operational design guidance.
8.6.3.1.4. Work Products
1. ISR chapter with an annotated, searchable, bibliographic appendix.
2. Product deliverable date: Q4 2013.
8.6.3.2. Focus Area Selection−Riparian Process Domain Delineation
Floodplain plant communities within mountain river corridors are dynamic in that channel and
ice processes annually disturb floodplain vegetation resulting in the characteristic patchwork of
floodplain vegetation composition, structure, and age together reflecting time since most recent
vegetation disturbance (Naiman et al. 1998). Vegetation disturbance can be defined as those
processes that remove or otherwise impact plant communities and soils, often setting the system
back to an earlier successional state. Floodplain vegetation disturbance types found within the
study area include channel migration (erosion and depositional processes), ice processes
(shearing impacts, flooding, and freezing), herbivory (beaver, moose, and hare), wind, and, to an
infrequent extent, fire. Floodplain disturbance regimes (type, magnitude, frequency, duration
and timing) vary systematically throughout river networks and, therefore, their geographic
distribution may be mapped (Montgomery 1999).
Process domains define specific geographic areas in which various geomorphic processes govern
habitat attributes and dynamics (Montgomery 1999). Within the mountain river network,
temporal and spatial variability of channel, ice, and sediment disturbance processes can be
classified and mapped, allowing characterization of specific riparian process domains with
similar suites of floodplain disturbance types. The riparian process domain approach is
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hierarchical in structure allowing for river network stratified sampling to statistically describe
elements and processes within each process domain. Riparian study sites, including those
located within Focus Areas, will be selected to capture the variability in floodplain vegetation
types, and geomorphic terrains, within each riparian process domain. The number of Focus
Areas necessary to capture process domain variability will be determined through a power
analysis. The hierarchical stratification of the Susitna River Study Area into riparian process
domains will facilitates both representative sampling and the ‘scaling-up’ of Focus Area
modeling results to the larger Study Area.
The issue of pseudoreplication (Hurlbert 1984), and number of adequate sample sites necessary
to perform robust statistical analyses, is addressed in the hierarchical riparian process domain
sampling design and integration of the Riparian Botanical Survey design. Focus Area sites will
be representative of specific riparian process domains and their channel / floodplain
characteristics (ice process domains, channel plan form, channel slope, channel confinement).
Focus Area physical and vegetation processes will be modeled and floodplain vegetation-flow
response relationships statistically described in probabilistic models (Rains et al. 2004). The
Riparian Botanical Survey (see Section 11.6 for vegetation statistical sampling protocols) is
designed to provide Study Area -wide representative sample replicates of floodplain vegetation,
soils, and alluvial terrain relationships. Furthermore, the surface water flood regime for the
Study Area will be modeled, and mapped, providing flow regime plant community relationship
analysis replicates throughout the greater Study Area, in addition to those modeled at each Focus
Area. The riparian process domain and Study Area -wide sampling of the Riparian Botanical
Survey are specifically designed to address the question of pseudoreplication. Study
interdependencies are presented in Figure 8.6-3. Study objectives, methods and expected results
are summarized in Table 8.6-3.
The objectives of the Focus Area selection and riparian process domain delineation are as
follows:
1. Develop a riparian process domain stratification of the Study Area.
2. Select Focus Areas representative of each riparian process domain for physical process
and vegetation survey sampling and modeling.
8.6.3.2.1. Methods
Riparian process domain delineation, and riparian Focus Area selection is an iterative process
(Figure 8.6-3 and Figure 8.6-4). First, in Q1 21013 the results of the 2012 geomorphology study
and channel classification (Section 6.6), ice processes study (Section 7.6), riparian botanical
survey (Section 11.6) will be used to classify channel, floodplain and floodplain vegetation
types. The Lower River (RM 0 to RM 98), the Middle River (RM 98 to RM 184), and the Upper
River to the Maclaren River confluence (RM 184 to RM 260) were delineated into large-scale
geomorphic river segments (few to many miles) with relatively homogeneous characteristics,
including channel width, entrenchment, ratio, sinuosity, slope, geology/bed material,
single/multiple channel, braiding index, and hydrology (inflow from major tributaries) for the
purposes of stratifying the river into study segments (Figure 8.5-11 and Figure 8.5-12). This
type classification data will be used in a spatially constrained cluster analysis process (Brenden
et al. 2008) to group Study Area channel reaches and segments into riparian process domains.
Second, process domain type variability will be statistically described and a power analysis
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performed to determine the number of Focus Areas necessary to capture process domain
variability in the stratified sampling approach. Third, candidate Focus Areas previously
identified through the expert-opinion process for both Aquatic and Riparian IFS will be reviewed
(Figures 8.5-13 through 8.5-22). Fourth, results of the cluster analysis, power analysis and
expert-opinion process will be presented to the TWG for final selection of Focus Areas.
Additionally, ice process floodplain vegetation interactions will be measured thorough tree ice-
scar mapping to be conducted in Q2 and Q3 2013. A preliminary tree ice-scar survey was begun
in October 2012. Additional tree ice-scar mapping is being conducted by snow machine in Q4
2012. The preliminary 2012 tree ice-scar mapping data will be processed, mapped and presented
with the results of the riparian process domain and Focus Area selection analyses results to the
TWG in Q1 2013.
When the ice process mapping is completed in Q4 2013, the riparian process domain analysis
and Focus Area selection process will be performed a second time to assess whether additional
Focus Areas are necessary to measure and model ice process effects on floodplain vegetation. If
the results of this analytical process conclude that additional Focus Areas are necessary they will
be selected with input from the TWG for 2014 field sampling.
8.6.3.2.2. Data Inputs from Other Studies
The Geomorphology Study has provided the geomorphic reach classification and stratification.
The Ice Process Study will provide further modeling and observational data for refining riparian
process domains.
8.6.3.2.3. Data Output to Other Studies
The riparian process domain map will be provided to geomorphology, riparian botanical, ice
processes, and fish and wildlife studies.
8.6.3.2.4. Work Products
1. ISR chapter, describing the approach and methodology used to develop the riparian
process domain map and Focus Area selection process.
2. Map of Susitna River riparian process domains and Focus Area locations.
Final Focus Areas, of riparian study concern, selection will be finished with input from the
Technical Workgroup (TWG) in Q2 2013.
8.6.3.3. Characterize Seed Dispersal and Seedling Establishment Groundwater and
Surface Water Hydroregime Requirements. Develop Predictive Model of
Potential Project Operational Impacts to Seedling Establishment
Floodplain plant seed dispersal and seedling establishment are critical processes in floodplain
plant community succession that may be affected by hydroproject operations (Braatne et al.
1996; Cooper et al. 1999; Rood et al. 2003). In this study dominant woody species seed
dispersal and seedling establishment hydrologic requirements will be determined through field
surveys and groundwater and surface water interaction measurement and modeling. The study
has two subtasks: (1) seed dispersal, hydrology, and local Susitna River valley climate synchrony
study, and (2) seedling establishment study.
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8.6.3.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River Valley Climate
Susitna River pioneer riparian tree and shrub species in the family Salicaceae, Balsam poplar
(Populus balsamifera), and willows (Salix spp.) are adapted to seasonal snowmelt-driven spring
peak flows, in terms of timing of seed dispersal, newly deposited mineral colonization substrates,
and concordant near-surface floodplain groundwater conditions, all necessary conditions for
poplar and willow seedling establishment and recruitment (Figure 8.6-5; Braatne et al. 1996;
Mahoney and Rood 1998; Mouw et al. 2012). Project operations may result in a reduction of
June/July peak flows, and associated floodplain groundwater conditions, necessary to dispersal
and establishment of cottonwood and willow trees and shrubs. The timing of snowmelt spring
flows, and of tree and shrub seedling release and dispersal, is critical to successful establishment
and maintenance of riparian floodplain forests (Figure 8.6-6; Braatne et al. 1996; Mahoney and
Rood 1998). An empirical model, the “Recruitment Box Model” that captures cottonwood and
willow seed dispersal, flow response and recruitment requirements has been successfully
demonstrated on rivers throughout North America (Figure 8.6-6; Mahoney and Rood 1998; Rood
et al. 2003). The model characterizes seasonal flow pattern, associated river stage (elevation),
and flow ramping necessary for successful cottonwood and willow seedling establishment
(Figure 8.6-5 and Figure 8.6-6). A recruitment box model for balsam poplar and select willow
species for the Susitna River will be developed. Study interdependencies are presented in Figure
8.6-7. Study objectives, methods and expected results are summarized in Table 8.6-4.
Objectives of the seed dispersal, hydrology, and climate synchrony study are as follows:
1. Measure cottonwood and select willow species seed dispersal timing.
2. Model local Susitna River valley climate, and associated seasonal peak flows, relative to
cottonwood and willow seed dispersal.
3. Develop a recruitment box model of seed dispersal timing, river flow regime, and
cottonwood and willow seed dispersal and establishment.
8.6.3.3.1.1. Methods
To evaluate the natural synchrony of balsam poplar, and select willow species (Salix alaskensis
and S. barclayi) seed release, and Susitna River natural flow regime, the following tasks will be
undertaken: (1) conduct a two-year survey of seed release of balsam poplar and select willow
species (Q2-3 2013; Q2-3 2014), (2) develop a ‘degree-day’ climate model for the onset of seed
release relative to local temperature conditions using methods developed by Stella et al. (2006),
and (3) analyze the historic climate and Susitna River flow regime relationship. The results of
this study will identify flow regime timing conditions necessary to support riparian cottonwood
and willow establishment on the Susitna River.
Four floodplain sites near existing meteorological stations in the Middle and Lower Susitna
(Figure 8.6-8) will be selected for balsam poplar and select willow species seed release surveys.
At each site, 10 to 15 dominant female balsam poplar trees and willows will be surveyed weekly
during the months of June, July, and the first two weeks of August, 2013–2014. Seed release
will be measured during each survey by counting open catkins for each tree or shrub using
methods developed by Stella et al. (2006). Floodplain riparian plant community characteristics
will be sampled for each floodplain seed dispersal site using the riparian botanical survey
vegetation sampling techniques (see Section 11.6). Tree data and seed release timing will be
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analyzed using protocols developed by Stella et al. (2006). At all field sites, local air
temperature measurements will be collected from adjacent weather monitoring stations (Figure
8.6-8). A degree-day model using seed release observations and continuous temperature records
from the monitoring stations will be developed (Stella et al. 2006).
A recruitment box model (Figure 8.6-6; Mahoney and Rood 1998; Rood et al. 2003) will be
developed to evaluate the potential effects of various proposed spring operational flows on
cottonwood and willow establishment.
8.6.3.3.1.2. Data Input From Other Studies
The IFS Flow Routing (see Section 8.6) and Geomorphology (see Section 6.6) studies will
provide flow modeling (frequency, magnitude, duration, and seasonal timing) for development of
the “recruitment box model” of seed dispersal timing and flood regime.
8.6.3.3.1.3. Data Output to Other Studies
The modeling results of the synchrony study will be used to guide Project operations design such
that seasonal flow regime supports identified cottonwood and willow seeding establishment
requirements.
8.6.3.3.1.4. Work Products
1. ISR and USR chapters detailing study methods, results, and conclusions.
2. Degree-day model of peak seed release window using seed release observations and
continuous temperature records from each floodplain sample site.
3. Recruitment box model of cottonwood and select willow species.
4. Model of peak runoff / seed release temporal synchrony for operational flow guidelines.
5. Model of critical summer flow regime necessary to support seedling establishment.
The seed dispersal study fieldwork will be conducted in Q2 and Q3 during both 2013 and 2014.
Model development will be conducted during Q1-4 2014.
8.6.3.3.2. Seedling Establishment and Recruitment Study
Riparian vegetation in mountain river networks is adapted to a dynamic physical disturbance
regime including flooding, summer desiccation, erosion, sediment burial, ice shearing and
freezing, wind, herbivory and, infrequently, fire (Naiman et al. 1998). Seedling establishment,
survival, and recruitment are critical phases in the development of floodplain plant communities
within this dynamic physical environment (Walker and Chapin 1986; Walker et al. 1986;
Karrenberg et al. 2002; Muow et al. 2009, 2012; Rood et al. 2007). The goal of the seedling
establishment and recruitment study is to identify, measure, and model potential impacts of
Project operational changes to the groundwater, surface water, sediment, and ice regimes, and to
assess the effects on seedling establishment and recruitment within the active channel margin /
floodplain environment.
Identifying the spatial locations, and groundwater, surface water, and sediment requirements
under which new cohorts of dominant riparian plant seedlings establish, survive, and recruit on
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the Susitna River floodplain is a critical element in evaluating potential floodplain vegetation
effects of Project operational alterations of the natural flow and sediment regimes. River ice
seedling interactions, an additional critical physical disturbance factor, will be investigated in the
ice process modeling study (see Section 8.6.3.4.2).
Seedling recruitment in the Susitna floodplain occurs not only on new flood-deposited sediments
along channel and floodplain margins—the primary sites of balsam poplar, willow, thinleaf alder
(Alnus tenuifolia), and Sitka alder (Alnus sinuata) colonization—but also on sediment deposits
within the developing and mature floodplain forest (Helm and Collins 1997). Helm and Collins
(1997) noted that within the floodplain forest, white spruce (Picea glauca) and paper birch
(Betula papyrifera) seedlings were found to establish, and recruit, on mineral soils associated
with both floodplain surface sediment deposits, ice-influenced sediment deposits, and tree wind
throw mound soils. Also, during the 2012 Riparian Botanical Survey, white spruce and paper
birch seedlings were observed growing on mounds of gravel and sand apparently pushed onto the
floodplain interior by ice flows.
Study interdependencies are presented in Figure 8.6-9. Study objectives, methods and expected
results are summarized in Table 8.6-5.
A two year study using woody seedling dendrochronology to date the year of seedling year of
establishment is adequate to characterize seedling establishment hydrologic conditions. Seedling
year of establishment will be used, with the historic discharge record, to model the flood regime
at the sample site 1-D or 2-D hydraulic models.
While not included within this study plan, to address a USFWS request, AEA will conduct a
longitudinal three-year second-peak seedling cohort establishment and survival analysis to
inform the adaptive management components of future Project instream flow regimes. This
analysis is described in the Three-Year Seedling Cohort Longitudinal Establishment and
Survival Analysis. Specifically, the objective of the analysis is to identify, and measure, seedling
and flow regime characteristics in a longitudinal seedling cohort analysis as compared to the
two-year study.
The seedling cohort establishment analysis will be initiated in summer 2013 and carried through
for three years 2014 to 2016; final results will be presented in a technical memorandum to be
prepared Q4 2016. The technical memorandum is not necessary for the environmental analysis
supporting AEA’s License Application because the anticipated results are not necessary to assess
overall Project effects. Instead, AEA anticipates relying upon the technical memorandum for
adaptive management of future Project operations.
Objectives of the seedling recruitment study are as follows:
1. Map the spatial locations of seedlings of dominant woody riparian species including
balsam poplar, white spruce, paper birch, thinleaf and Sitka alder, feltleaf willow, and
Barclay’s willow throughout the Focus Area, and Riparian Vegetation Study sites, active
channel margins, and floodplain.
2. Use a stratified random sampling approach, with variable plot sizes (Mueller-Dombois
and Ellenburg 1974), to sample mapped seedling polygons.
3. Identify seedlings to species, and measure seedling heights and density.
4. Describe and measure seedling site soil characteristics (see Section 8.6.3.7 for methods).
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5. Measure and model seedling site GW/SW hydroregimes.
6. Measure seedling xylem water source through isotopic analysis (see Section 8.6.3.6 for
methods).
7. Investigate ice process seedling site interactions through empirical observations and ice
process modeling.
8. Develop a probabilistic model of seedling hydrologic, sediment, and ice regime
processes.
8.6.3.3.2.1. Methods
Dominant riparian woody species will be sampled in this study, including balsam poplar, white
spruce, paper birch, thinleaf and Sitka alder, feltleaf willow, and other willow species. In
addition to the target woody seedlings, all herbaceous seedlings within the woody species
seedling plots will be identified and measured. Seedling establishment sampling will occur at
times following the initial spring peak flows (e.g., July) and again in September in 2013 and
2014.
Seedlings are defined as those plants established within the current year of sampling, and all
plants with stems < 1m in height. At select Riparian Botanical Survey reaches, and at all Focus
Areas, seedling patches will be mapped and sampled using a stratified random sampling protocol
to obtain statistically representative samples of select woody species (Elzinga et al. 1998;
Mueller-Dombois and Ellenberg 1974).
The survey sampling approach is as follows. First, a helicopter survey of each reach will be
conducted to locate and map observable seedling areas. Second, four to eight transects will be
placed systematically throughout the reach normal to main channel, extending across the
adjacent floodplain intersecting observed seedling sites. Each transect will be traversed and all
remotely observed, and newly identified on-the-ground seedling locations will be mapped with
GPS. Third, seedling site polygon boundaries will be mapped with GPS. Fourth, seedling
patches will be sampled using a stratified random approach to locate sample plots. Seedling
species will be identified, or collected for herbarium identification, and abundance (density) and
height measured using variable plot size and shapes (Elzinga et al. 1998; Mueller-Dombois and
Ellenberg 1974). Fifth, at each plot two to three seedlings of each species will be excavated and
rooting depth measured. Excavated woody seedlings will be aged at the root collar in the
laboratory and annual rings counted to provide seedling age. Substrate texture and depth to
cobbles will be described and measured in soil pits excavated to 50 cm in depth or to
gravel/cobble refusal layer. Sixth, a sub-sample of Focus Area site seedlings will be used for
xylem isotopic analyses to identify source of water (see Section 8.6.3.6). Results of seedling
mapping and characterization will be used to assess groundwater, surface water, and ice regime
relationships using 1-D / 2-D, MODFLOW and ice process modeling results from the
Groundwater, Geomorphology, and Ice Processes studies.
A probabilistic model of seedling and GW/SW, sediment, and ice regime will be developed
using techniques and methods described in Franz and Bazzaz (1977), Rains et al. (2004),
Henszey et al. (2004), Baird and Maddock (2005), and Maddock et al. (2012).
The results of the Focus Area modeling will be scaled-up to the riparian process domains using
spatially explicit GIS models as described in Section 8.6.3.7.
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8.6.3.3.2.2. Data Input from Other Studies
Data input will include groundwater, surface water, and sediment regime characteristics of
seedling sites developed in the Groundwater (Section 7.5) and Fluvial Geomorphology (Section
6.6) studies. The Ice Processes Study (Section 7.6) will provide modeled ice influence vertical
and horizontal zones.
8.6.3.3.2.3. Data Output to Other Studies
Data output will include groundwater, surface water, and sediment regime seedling requirements
to Floodplain Vegetation Study Synthesis, Focus Area to Riparian Process Domain Scaling and
Model Project Operations Effects Section 8.6.3.7 and Project operations design.
8.6.3.3.2.4. Work Products
1. ISR and USR chapters detailing study methods, results, and conclusions.
2. Probabilistic seedling hydrologic, sediment, and ice regime model.
The seedling establishment and recruitment study fieldwork will be conducted in Q2 and Q3
during both 2013 and 2014. Results analysis will be conducted during Q1-4 2014.
8.6.3.4. Characterize the role of river ice in the establishment and recruitment of
dominant floodplain vegetation. Develop predictive model of potential Project
operational impacts to ice processes and dominant floodplain vegetation
establishment and recruitment.
Although the role of fluvial disturbance (erosion and sediment deposition) in the development of
floodplain vegetation has been well investigated (Naiman et al. 1998; Rood et al. 2007), the role
of river ice processes has seen little study (Engstrom et al. 2011; Prowse and Beltaos 2002;
Prowse and Culp 2003; Rood et al. 2007). The results of river ice disturbance of floodplain
vegetation have been observed in the Susitna River, and reported anecdotally, in Helm and
Collins (1997). The 2012 Riparian Botanical Survey Team observed extensive evidence of ice
disturbance to floodplain trees, and soils, in the form of tree ice-scars, mechanically disturbed
soil stratigraphy, and floodplain gravel deposits throughout the Middle and Lower Susitna River
surveys (Figure 8.6-10, Figure 8.6-11, and Figure 8.6-12).
Impacts of ice-related processes to riparian habitat typically occur during break-up when ice
scours channel and floodplain surfaces (Prowse and Culp 2003). During break-up, ice
accumulation in meander bends can create ice dams elevating backwater surfaces, forcing
meltwater to bypass the bend and scour a new meander cutoff, generating new side channels
(Prowse and Culp 2003). Elevated backwater, resulting from ice dams, may also float ice blocks
onto and through vegetated floodplain surfaces, causing mechanical shearing effects including
tree ice-scarring and abrasion, removal of floodplain vegetation, and disturbance of floodplain
soils (Engstrom et al. 2011; Rood et al. 2007; Prowse and Culp 2003).
8.6.3.4.1. Empirical Studies of River Ice and Floodplain Vegetation
Given the paucity of studies concerning river ice and floodplain vegetation interactions, multiple
lines of evidence will be used to inform a final research study design to address the question of
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vegetation response to ice shearing influence on the Susitna River floodplain. First, ice
vegetation impacts (tree ice-scars) will be observed, mapped, and aged (using dendrochronologic
techniques), and gravel floodplain deposits will be mapped throughout the Study Area to develop
a Study Area map of river ice floodplain vegetation interaction domains. Preliminary tree ice-
scar mapping was begun during the 2012 Riparian Botanical Survey, and early October 2012
Focus Area reconnaissance. Mapping will continue in Q2 and Q3 2013 and throughout the 2013
and 2014 riparian field seasons. Second, local residents will be interviewed (e.g., Mike Wood,
who lives across from Whiskers Slough) concerning their knowledge of spatial locations of
historic ice dams, years of significant ice occurrence, and other anecdotal historical information
concerning ice on the Susitna River. From these two sources of information, a map will be
created of Susitna River ice process floodplain vegetation effect domains. The ice process map
will be used to: (1) inform riparian process domain delineation (see Section 8.6.3.2) and (2)
develop a floodplain vegetation study to compare floodplains affected by ice with those un-
impacted by ice, similar to the approach of Engstrom et al. (2011).
Floodplain vegetation surveys will be conducted to quantitatively measure (stratified random
sampling of mapped floodplain vegetation ice shear process zones) and statistically describe and
compare vegetation characteristics associated with floodplains experiencing ice shear events and
floodplain vegetation without observed ice influence. The vegetation study design will build on
the design and results of Engstrom et al. (2011) where they studied and assessed the effects of
anchor ice on riparian vegetation. Engstrom and others found that species richness was higher at
sites affected by anchor ice than at sites where anchor ice was absent, suggesting that ice
disturbance plays a role in enhancing plant species richness (Engstrom et al. 2011).
The objective of the ice effects vegetation study will be to quantitatively describe floodplain
plant community composition, abundance, age, and spatial pattern to assess the role and degree
of influence ice processes have on Susitna River floodplain vegetation. The results of the study
will be used to assess how floodplain vegetation pattern and process may change with Project
operation alterations of the natural ice process regime. The final study design will be completed
in Q2-3 2013, as additional tree ice-scar field data become available.
8.6.3.4.2. Ice Process Modeling Studies
The ice process study will develop and calibrate a dynamic thermal and ice processes model (see
Section 7.6 for details). The model will provide maps of ice cover progression and decay, ice
cover extent and thickness, and effects of Project operational flow fluctuation on ice cover
development and stability. Additionally the model will provide flow routing capability. Ice and
flow routing effects on floodplain vegetation and channel morphology will be assessed. The Ice
Processes study will also provide videography of ice formation and ice break-up at a number of
locations throughout the Study Area. The ice process modeling study will provide the riparian
ice vegetation study with estimated horizontal and vertical zones of ice formation, ice thickness,
and floodplain impact zones. Model output will be used in conjunction with the empirical survey
data to (1) empirically test model output with mapped riparian domains of ice floodplain
vegetation interaction, and (2) model changes in locations and types of ice formation processes
due to Project operational flow regime. Together, the empirical mapped ice influence zones,
empirical studies of vegetation / ice interactions, and modeling confirmation and prediction will
be used to understand and predict the influence of Project operational flows on ice and floodplain
vegetation interactions.
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Study interdependencies are presented in Figure 8.6-13. Study objectives, methods and expected
results are summarized in Table 8.6-6.
The objectives of the ice processes floodplain vegetation interaction and modeling study are as
follows:
1. Develop an integrated model of ice process interactions with floodplain vegetation.
2. Conduct primary research to identify the effects of ice on floodplain vegetation within
mapped Susitna River ice floodplain impact zones.
3. Provide Project operational guidance on potential effects of operations flow on ice
formation and floodplain vegetation development.
8.6.3.4.2.1. Methods
1. Mapping of ice floodplain vegetation interactions and soil disturbance throughout the
Study Area.
2. Interviews of local Susitna River residents concerning knowledge of ice dam locations
and ice process effects.
3. Comparative quantitative vegetation study of ice effects on identified ice floodplain
impact and un-impacted zones. Methods will build on those presented in Engstrom et al.
(2011).
4. Final ice vegetation field sampling methodology will be developed in Q2, Q3 2013 as
tree ice-scar field data become available and ice effect domains are delineated.
5. Integration of ice process modeling results with empirical ice vegetation mapping and ice
vegetation interaction studies.
8.6.3.4.2.2. Data Input From Other Studies
Data inputs including ice process modeling results concerning spatial location of ice, vertical
extent of ice, and potential ice dam locations will be available beginning Q4 2013 extending
through Q4 2014.
8.6.3.4.2.3. Data Output to Other Studies
Data outputs will include Project operation guidance on minimizing alteration of ice processes
and subsequent effects to floodplain vegetation.
8.6.3.4.2.4. Work Products
1. ISR and USR chapters detailing study methods, results, and conclusions.
The river ice seedling establishment and recruitment study fieldwork will be conducted in Q2
and Q3 during both 2013 and 2014. Results analysis and technical memorandum, or chapter,
will be conducted during Q1-4 2014.
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8.6.3.5. Characterize the role of erosion and sediment deposition in the formation of
floodplain surfaces, soils, and vegetation. Develop a predictive model of
Project operations changes to erosion and sediment deposition pattern and
associated floodplain vegetation.
The dynamic of channel migration—sediment transport, and resulting floodplain erosion and
sediment depositional patterns—is a critical physical process directly affecting floodplain soil
development, and vegetation establishment, recruitment, and spatial location, throughout alluvial
segments of the river network (Richards et al. 2002). The life history strategies and
establishment requirements of floodplain plant species are adapted to natural flow and sediment
regimes (Braatne et al. 1996; Naiman et al. 1998; Karrenberg et al. 2002). As such, alterations of
natural hydrologic and sediment regime seasonal timing, magnitude, frequency, and duration
may have effects on plant species establishment, survival, and recruitment (Braatne et al. 1996).
The goal of this study is to characterize the role of erosion and sediment deposition in evolution
of floodplain plan form, soil development, and trajectory of plant community succession,
especially vegetation establishment stage. This study, in coordination with the Fluvial
Geomorphology Study (see Section 6.6), will investigate the geomorphic evolution of the Study
Area floodplain with an emphasis on floodplain sediment deposition, stratigraphy, soil
development, and associated plant community succession. Historic sediment deposition rates
will be measured throughout the Study Area river network and variations in floodplain forming
processes will be assessed. Finally, a predictive model will be developed with the Fluvial
Goemorphology Study (see Section 6.6) to assess Project operational effects on hydrologic and
sediment regimes, and effects on soil and floodplain plant community development.
In a river that meanders through a wide valley, such as the Susitna River, erosion on one side of
the channel will be balanced by deposition on the opposite site as the river migrates laterally.
Disturbance to riparian habitat on the eroding bank will be balanced by opportunities for
recruitment on the point bar. This type of geomorphic process maintains the characteristic range
of floodplain surface elevations and vegetation age classes contributing to the diversity of
floodplain vegetation composition and structure (Naiman et al. 1998). The rate of channel
migration may be impacted by Project operations with secondary impacts on the riparian
community. The Fluvial Geomorphology Study will assess Project alterations to downstream
channel bed and floodplain surface elevations through sediment transport modeling and analyses.
These potential changes will be provided to the Riparian IFS. Development of the study design,
modeling, and methods has been coordinated closely with Geomorphology, Ice Processes, and
Riparian Vegetation study teams (Figure 8.6-1).
The fluvial geomorphology modeling approach (see Section 6.6) is based upon (1) 1-D / 2-D
modeling of river discharge and stage, (2) 1-D / 2-D sediment transport model, (3) geomorphic
reach analyses (aerial photographic analyses of historic channel change), and (4) flow routing
model.
Study interdependencies are presented in Figure 8.6-14. Study objectives, methods and expected
results are summarized in Table 8.6-7.
The objectives of the study are as follows:
1. Measure the rates of channel migration, and floodplain vegetation disturbance or
turnover, throughout the Study Area.
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2. Measure the rates of sediment deposition, and floodplain development, throughout the
Study Area.
3. Assess / model how Project operations will effect changes in the natural sediment
regime, floodplain depositional patterns, and soil development throughout the Study
Area.
4. Assess / model how Project operations changes in sediment transport and soil
development will affect floodplain plant community succession.
8.6.3.5.1. Methods
1. Floodplain soils and stratigraphy will be sampled throughout the Study Area using a
stratified random approach, including pits located in all Focus Areas.
2. Floodplain soil pits will be excavated from the surface to gravel / cobble layer (historic
channel bed) and soil stratigraphy will be described and measured using standard NRCS
field techniques (Schoeneberger et al. 2002). Standard sediment grain size sieve analysis
will be conducted on samples taken at soil horizons.
3. Direct dating of fluvial sediments will be conducted using isotopic techniques, including,
but not limited to, 137Cs and 210Pb measurements as described in Stokes and Walling
(2003).
4. Dendrochronologic techniques (Fritts 1976) will be used to age trees and current
floodplain surfaces at each soil pit.
Woody species will be sampled, and aged, at all mapped Focus Area plant communities,
including seedlings, to determine year of origin. Standard dendrochronologic techniques will be
applied for tree and shrub sampling and growth ring measurements (Fritts 1976).
For each Focus Area mapped stand, two to three trees and shrubs per species will be sampled for
age determination. Tree and shrub samples will be taken with either an increment borer or by
cutting the shrub or sapling stem and removing a stem section for laboratory analysis. Increment
cores (two per tree) will be collected from each tree. For each tree sampled, floodplain sediment
will be excavated to uncover the stem root collar and depth of sediment aggradation will be
measured for further age estimation. Woody species seedlings for each dominant species will be
excavated, heights measured, stems sectioned at the root collar, and annual rings measured under
a dissecting microscope. A regression analysis will be conducted to assess the relationship
between stem age and seedling height. The results will be used to add additional years to trees to
account for height of core sample above the root collar.
Tree cores will be taken as close to the ground surface as possible, generally 30 centimeters or
less above ground surface. Total height of tree core sample above the root collar will be
calculated and used to estimate additional years to estimate tree year of origin. Increment cores
will be mounted on pieces of 1-inch by 2-inch wood and sanded with variable grades of
sandpaper following standard methods described in Fritts (1976). Ring width measurements will
be made, and annual years counted, for both the tree cores and stump sections using a dissecting
microscope. Individual trees will be cross-dated, if possible, using standard methods (Fritts
1976).
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8.6.3.5.2. Data Input From Other Studies
Geomorphology Study (see Section 6.6) will provide for all Focus Areas: (1) historic channel
migration rates, floodplain vegetation disturbance or turnover rate; (2) flood frequency,
magnitude, duration, and timing; (3) sediment transport and depositional spatial model.
Instream Flow Study (IFS) flow routing: Study Area -wide flood frequency, magnitude, duration,
and timing.
The Riparian Botanical Survey (see Section 11.6) will conduct the sediment and soils fieldwork
including stratigraphic description, strata measurements, and floodplain sediment dating for all
Focus Areas and Study Area -wide sampling.
8.6.3.5.3. Data Output to Other Studies
To Geomorphology Study: (1) dating of floodplain stratigraphy and surfaces using direct isotopic
and dendrochronologic techniques, and (2) floodplain stratigraphic descriptions and grain size
analyses.
To Section 8.6.3.7 Floodplain Vegetation Study Synthesis, Focus Area to Riparian Process
Domain Scaling and Project Operations Effects Modeling: (1) dating of floodplain stratigraphy
and surfaces using direct isotopic and dendrochronologic techniques, and (2) floodplain
stratigraphic descriptions and grain size analyses.
8.6.3.5.4. Work Products
1. ISR and USR chapters detailing study methods, results, and conclusions.
Fieldwork will be conducted in Q2 and Q3 during both 2013 and 2014. Analyses will be
conducted during Q2-4 2013 and Q1-4 2014.
8.6.3.6. Characterize natural floodplain vegetation groundwater and surface water
maintenance hydroregime. Develop a predictive model to assess potential
Project operational changes to natural hydroregime and floodplain
vegetation.
Water sources for the establishment and maintenance of floodplain vegetation include
precipitation, groundwater, and surface water (Cooper et al. 1999; Rood et al. 2003). Identifying
both floodplain plant water sources and the GW/SW hydroregime associated with critical
riparian plant species life stages is necessary to (1) characterize natural floodplain vegetation
establishment and maintenance hydrologic requirements, and (2) evaluate effects of Project
operations on these hydroregimes and associated plant communities.
The goal of the floodplain vegetation GW/SW interaction modeling effort is to statistically
characterize the relationship between floodplain groundwater and surface water hydroregime and
associated floodplain plant communities and to use this model to predict Project operation effects
on floodplain vegetation throughout the Study Area. This investigation will (1) characterize
dominant floodplain woody plant species establishment and maintenance life stage water sources
through stable isotope analyses of groundwater, soil water, and xylem water; (2) develop a
floodplain GW/SW model; and (3) develop floodplain vegetation-flow response models.
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Riparian woody species establishment has been associated with both surface water flooding and
precipitation (Braatne et al 1996; Cooper et al. 1999; Rood et al. 2003). Riparian floodplain
vegetation maintenance relies to a large extent on groundwater as a water source (Cooper et al.
1999; Rood et al., 2003; Henszey et al. 2004). Floodplain groundwater depths have been
demonstrated to control floodplain plant community composition, species richness, and structure
(Henszey et al. 2004; Baird et al. 2005; Mouw et al. 2009). Project operations will alter, on a
seasonal basis, the flows in the Susitna River, and on a shorter time scale, flows associated with
potential load-following operations potentially affecting floodplain shallow aquifer water
elevations. The results of this study will be scaled-up from the Focus Areas, to their respective
riparian process domains, to provide a model of the entire Study Area.
8.6.3.6.1. Groundwater and Surface Water Interaction Modeling
A physical model of GW/SW interactions will be developed for all Focus Area sites to model
floodplain plant community GW/SW relationships. Developing conceptual model and numerical
representations of the GW/SW interactions, coupled with important processes in the unsaturated
zone, will help evaluate natural variability in the Susitna River riparian floodplain plant
communities, and assesses how various Project operations may potentially result in alterations of
floodplain plant community types, as well as improve the understanding of what controlled
fluctuations of flow conditions would result in minimal riparian changes.
Regional and local groundwater flow systems are important to floodplain vegetation (Figure
8.6-15). Seasonal river stage fluctuations generate transient GW/SW interactions at a local scale
under and adjacent to the river, including side channels, side sloughs, and upland sloughs (Figure
8.6-16 and Figure 8.6-17). A typical system representing several types of surface water features
is shown in the Whiskers Slough proposed Focus Area (Figure 8.6-16). This plan view shows
both the potential orientation of mainstem and side channel surface water features, along with
typical riparian floodplain plant community types found in the Middle River Segment of the
Susitna River. A schematic cross-section of a typical profile across the river floodplain from
main channel through floodplain, secondary channel and adjacent hillslope is shown in Figure
8.6-18. This figure depicts the relative relationships between surface water stage levels,
groundwater levels, land surface elevations, and riparian floodplain plant community types.
Developing conceptual model and numerical representations of the GW/SW interactions,
coupled with important processes in the unsaturated zone, will help evaluate natural variability in
the Susitna River floodplains, and how various Project operations could result in alterations of
floodplain plant community types, as well as improve the understanding of what Project
operational fluctuations of flow conditions would result in minimal riparian changes.
8.6.3.6.2. Floodplain Vegetation-GW/SW Regime Functional Groups
Floodplain vegetation−GW/SW regime functional groups are assemblages of plants that have
established and developed under similar GW/SW hydrologic regimes. Metrics will be developed
for quantitatively describing the relationship between floodplain plant communities and the
GW/SW hydroregime. Probabilistic response curves will be developed for select plant species
and all riparian plant community types using techniques described in Rains et al. (2004) and
Henszey et al. (2004). Water-level summary statistics will be tested for best fit with input from
the TWG. The results of the response curve analyses will be used to develop floodplain
vegetation-GW/SW regime functional groups (Merritt et al. 2010; Rains et al. 2004). These
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techniques and analyses will form the basis for development of a statistically modeled
relationship between individual riparian species, floodplain plant community types, and natural
GW/SW hydroregime that will be used to analyze potential effects of Project operations on
Susitna River floodplain plant communities. These floodplain vegetation-GW/SW regime
statistical relationships will provide a defensible basis for recommended flow prescriptions
necessary to support floodplain vegetation establishment, recruitment, and maintenance
throughout the Study Area.
The physical modeling and spatial mapping of riparian vegetation conducted in the Botanical
Riparian Study will be integrated to analyze the extent and characteristics of riparian vegetation
change under various simulated Project operational flows (Pearlstine et al. 1985).
Study interdependencies are presented in Figure 8.6-19. Study objectives, methods and expected
results are summarized in Table 8.6-8.
8.6.3.6.3. Methodology
In response to FERC’s study plan determination, the methodology of this section has been
supplemented with the June 30, 2013 Instream Flow, Groundwater, and Riparian Vegetation
Studies Technical Memorandum (Riparian/GW TM).
MODFLOW (USGS 2005), the most widely used groundwater model in the U.S. and worldwide,
will be used. Additionally, RIP-ET (riparian−evapotranspiration MODFLOW package;
Maddock et al. 2012), developed to help better represent plant transpiration processes in the
unsaturated zone, will be utilized to more accurately calculate evapotranspiration, separating out
plant transpiration from evaporation processes.
Focus Area GW / SW sampling is designed to measure, and model, GW/SW hydroregime for all
floodplain plant community types and successional stages including plant establishment, plant
recruitment, and mature forest vegetation. The sampling approach and design will include
transects and arrays of groundwater wells and surface water stage stations (Figure 8.6-16 and
Figure 8.6-17). Complete sampling design details can be found in the Groundwater Study,
Section 7.5.
The groundwater and surface water data collection period will begin early July 2013 and
continue through September 2014. This will include the fall 2013 winter transition period,
winter 2013–2014 conditions, spring 2014, and summer 2014. Physical weather and climate
conditions are not the same from year to year, so data collected during summer 2013 cannot be
combined with data from 2014.
Field data on riparian plant communities will be collected in coordination with Riparian
Vegetation Study (see Section 11.6). Riparian floodplain plant community and soils sampling
approach and design is detailed in the Riparian Vegetation Study Section 11.6.
Woody species source of water will be directly determined from stable isotope analyses of
groundwater, soil water, precipitation, and xylem water hydrogen and oxygen. Xylem water has
been demonstrated to reflect isotopic composition of the source water taken up by roots
(Flanigan and Ehleringer 1991; Dawsen and Ehleringer 1991). Stable isotope analysis of
deuterium (2H) and oxygen (18O) ratios will be conducted for dominant woody species using
standard methods (Cooper et al. 1999; Flanigan and Ehleringer 1991; Dawsen and Ehleringer
1991).
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It is critical to measure the depth of the root zone of dominant floodplain plants for accurately
modeling groundwater, capillary fringe, and floodplain plant relationships. The rooting depth of
dominant floodplain plants will be measured through excavation of trenches within each Focus
Area floodplain plant community type in coordination with soil stratigraphic excavations and
well point soil pits. Depth and width of dominant plant root systems will be measured, sketched,
and photographed. Excavation plot elevations will be surveyed. Additionally, a riverbank
survey will be conducted by boat to utilize recently exposed root systems for measurement. The
riverbank survey will provide a much greater sample size than possible through trench
excavations alone. Root zone excavation and riverbank root zone survey data will be statistically
summarized to provide individual plant species and plant community type root zone depth
characterization for use in GW/SW modeling
The riparian vegetation GW/SW interactions study approach and design will be integrated with
the findings of the riparian plant community succession, geomorphology, and ice processes
modeling to characterize physical processes and riparian plant community relationships. The
results of these studies will be used to assess (1) changes to physical processes due to dam
operations, and (2) response of riparian plant communities to operations alterations of natural
flow and ice processes regimes.
The results of the Focus Area modeling will be scaled-up to the riparian process domains as
described in Section 8.6.3.7 Floodplain Vegetation Study Synthesis, Focus Area to Riparian
Process Domain Scaling and Project Operations Effects Modeling
The detailed GW/SW interaction study approach and methods are presented in the Groundwater
Study, Section 7.5.
8.6.3.6.4. Data Input from Other Studies
The Groundwater Study Section 7.5 will provide GW / SW interaction modeling results
including a range of GW/SW regime seasonal statistics including frequency, timing and duration
of surface-water and groundwater levels. Groundwater monitoring data will be provided to the
Riparian IFS in real time throughout Q3, Q4 2013 and Q1-Q4 2014. MODFLOW results and
report will be provided in Q3 and Q4 2014.
8.6.3.6.5. Data Output to Other Studies
Modeling results will be provided to: Riparian Vegetation Study Section 11.6; Fluvial
Geomorphology Study Section 6.6; Wildlife Study Section 10.0; and Floodplain Vegetation
Study Synthesis, Project operations design Section 8.6.3.7.
8.6.3.6.6. Work Products
1. ISR and USR chapters detailing study methods, results, and conclusions summarizing
Focus Area GW /SW modeling results including quantification of frequency, timing and
duration of surface water and groundwater levels required to establish, maintain and
promote floodplain and riparian plant communities. Fieldwork will be conducted Q2-Q4
2013 and Q2-Q4 2014.
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8.6.3.7. Floodplain Vegetation Study Synthesis, Focus Area to Riparian Process
Domain Model Scaling and Project Operations Effects Modeling.
The results of floodplain vegetation and soils mapping, forest succession models, seed dispersal
study, seedling establishment studies, ice processes study, floodplain erosion and sediment
transport study, and groundwater and surface water interaction study will be integrated into a
conceptual ecological model of Susitna River floodplain vegetation and physical processes,
including flow, sediment and ice process regimes. The results of these studies will be used to
develop a dynamic floodplain vegetation model for simulating floodplain vegetation response to
Project operation modification of the natural flow, sediment and ice processes regimes (Franz
and Bazzaz 1976; Benjankar et al. 2011; Springer et al. 1999).
Fluvial Geomorphology Section 6.6, Ice Processes Section 7.6, and Groundwater Section 7.5
modeling studies will provide modeling results of both existing conditions and Project operation
scenarios. Together riparian botanical forest succession models (see Section 11.6), floodplain
vegetation GW/SW flow response curve analyses and physical process models (geomorphology,
groundwater, ice processes) will be used to model floodplain vegetation transition dynamics
(Walker and del Moral 2008) resulting from Project operation scenarios.
Study interdependencies are presented in Figure 8.6-20. Study objectives, methods and expected
results are summarized in Table 8.6-9.
Study objectives are to:
1. Develop conceptual ecological model of Susitna River floodplain vegetation
establishment and recruitment based on synthesis of Riparian Vegetation Study and
Riparian IFS results.
2. Scale-up results of Focus Area floodplain vegetation and physical process modeling
results to riparian process domains.
3. Develop a dynamic spatially-explicit floodplain vegetation model for simulating
floodplain vegetation response to Project operation modification of the natural flow,
sediment and ice processes regimes.
4. Develop spatially explicit maps of modeled Project operations effects throughout the
Study Area.
5. Provide guidance to environmental analysis of Project operations.
8.6.3.7.1. Methods
The results of the Focus Area modeling will be scaled-up to the riparian process domains using
spatially explicit GIS-based models (Benjankar et al. 2011; Chacon-Moreno et al. 2007). The
goal is to model both natural riparian flow-response functional groups and natural Susitna River
physical process regimes to measure and map Project operational impacts to floodplain
vegetation and riparian ecosystem processes throughout the Study Area. Recent developments in
GIS, Li DAR-driven digital terrain models (DEMs), and geo-spatial analytical tools (ARCMAP,
ESRI) have provided modelers the capacity to use the results of reach-scale analyses to scale-up
to larger geospatially defined areas or domains (Benjankar et al. 2011; Chacon-Moreno et al.
2007). Modeling riparian vegetation response, over a 185-mile Susitna River valley, to
alterations of natural flow regimes, is inherently a geospatial analytical problem. Current state-
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of-the-art and science practice will be utilized to integrate modeling of physical processes (HEC-
RAS, MODFLOW), and riparian vegetation-flow response functional groups with GIS
geospatial analysis and display (ARCMAP, HEC-GEORAS).
The objectives of the Focus Area scaling model are as follows:
1. Scale-up Focus Area modeling results to riparian process domains.
2. Assess potential impacts of Project operational flows on downriver floodplain plant
communities and ecosystem processes.
3. Provide guidance to environmental analysis of Project operations.
8.6.3.7.2. Work Products
1. ISR chapter detailing the schedule and plan for model development.
2. USR chapter detailing study methods, results, and conclusions summarizing: (1)
floodplain vegetation study synthesis, physical process modeling studies, and vegetation
succession models, (2) scaling results of floodplain and physical process Focus Area to
riparian process domain modeling, and (3) spatially explicit maps of modeled Project
operations effects throughout the Study Area.
The modeling synthesis and Project operations modeling will be conducted Q4 2013 and Q1-Q2
2015. Modeling, results analysis, and USR chapter, will be developed in Q2 through Q4 2014
and Q1-2 2015.
8.6.4. Consistency with Generally Accepted Scientific Practice
The proposed Riparian IFS, including methodologies for data collection, analysis, modeling,
field schedules, and study durations, is consistent with generally accepted practice in the
scientific community. The Riparian IFS is consistent with common approaches used for other
FERC proceedings and references specific protocols and survey methodologies, as appropriate.
Specifically, riparian vegetation mapping and measurement, the classification of riparian plant
communities, and dendrochronologic techniques will follow standard methods generally
accepted by the scientific community. Proposed GW/SW models have been widely used
throughout the discipline (Baird and Maddock 2005; Maddock et al. 2012; Franz and Bazzaz
1977; Rains et al. 2004).
Current state-of-the-art and science practice will be utilized to integrate modeling of physical
processes and riparian vegetation-flow response guilds with GIS geospatial analysis and display
(Benjankar et al. 2011; Chacon-Moreno et al. 2007; Van de Rijt et al. 1996).
8.6.5. Schedule
The schedule for completing all components of the Riparian IFS is provided in Table 8.6-1.
Licensing participants will have opportunities for study coordination through regularly scheduled
meetings, reports, and, as needed, technical subcommittee meetings. Reports will be prepared at
the end of 2013 (Initial Study Report) and 2014 (Updated Study Report) for each of the study
components. Licensing participants will have the opportunity to review and comment on these
reports. Workgroup meetings are planned to occur on at least a quarterly basis, and workgroup
subcommittees will meet or have teleconferences as needed.
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8.6.6. Level of Effort and Cost
The Riparian Instream Flow Study is planned as a 2+ year effort, with field sampling conducted
spring through summers and fall of 2013–2014. The Initial Study Report will be delivered in
late 2013 and updated in early 2015.
Riparian Instream Flow Study elements and their estimated levels of effort include the following:
1. Spring/summer 2013 fieldwork investigating eight or more Focus Areas. Field effort will
involve approximately two teams of two ecologists one to two weeks per Focus Area to
map and sample riparian vegetation.
$400,000
2. Spring/summer 2014 fieldwork investigating up to eight Focus Areas. Field effort will
involve approximately a team of three ecologists one to two weeks per study site to map
and sample riparian vegetation.
$310,000
3. Modeling forest succession and physical processes (GW/SW, hydraulic, ice processes,
operational flow simulations).
$440,000
4. Statistical analyses and report development, meetings, and presentations.
$440,000
5. GW/SW interaction study.
Costs provided in Groundwater Study, Section 7.5.
The total approximate effort/cost is $1.6 million (not including costs for riparian GW/SW
interaction study instrumentation, field installation and monitoring, and MODFLOW modeling).
Details and level of field effort will be based upon approved of overall study objectives and
design. Field surveys will be conducted for 40 to 50 days in each year, depending on the needs
for additional ground-verification data. The Riparian IFS Study will involve extensive, office-
based activities including remote sensing interpretation, physical modeling, vegetation modeling,
statistical modeling, geospatial analyses, and study report preparation.
The final types and level of physical process modeling will be determined in coordination with
the Instream Flow, Geomorphology, Ice Processes, Botanical Riparian, and Groundwater Study
teams. Estimated study costs are subject to review and revision as additional details are
developed.
8.6.7. Literature Cited
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and application for groundwater models. Journal of Hydrology 312: 176-190.
Benjankar, R., G. Egger, K. Jorde, P. Goodwin and N.F. Glenn. 2011. Dynamic floodplain
vegetation model development for the Kootenai River, USA. Journal of Environmental
Management 92: 3058-3070.
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Braatne, J.H., S.B. Rood and P.E. Heilman. 1996. Life history, ecology, conservation of
riparian cottonwoods in North America. In: Biology of Populus and its Implications for
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processes in a Venezuelan flooding savanna. Ecottopicos 20: 55-73.
Collins, W.B., and D.J. Helm. 1997. Moose, Alces alces, habitat relative to riparian succession
in the boreal forest, Susitna River, Alaska. Canadian Field-Naturalist 111: 567–574.
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Helm, D.J., and W.B. Collins. 1997. Vegetation succession and disturbance on a boreal forest
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riparian grassland species along the Platte River in Central Nebraska, USA. Wetlands 24:
665-687.
Hurlbert, S.H. 1984. Pseudoreplication and the design of ecological field experiments.
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former tidal area: a vegetation-type response model based on DCA and logistic regression
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8.6.8. Tables
Table 8.6-1. Schedule for implementation of the Riparian Instream Flow Study.
Activity 2012 2013 2014 2015
1 Q 2 Q 3 Q 4 Q 1 Q 2 Q 3 Q 4 Q 1 Q 2 Q 3 Q 4 Q 1 Q 2 Q
Refine and Finalize Study Plan
Focus Area Study Site Selection ------ ------ --
Critical review of 1980s Susitna River data; current scientific research concerning
hydro project floodplain vegetation effects; and unimpacted, natural floodplain
vegetation research
Finalize Riparian Groundwater / Surface Water Field Design ------ ------ ---
Implement Riparian Groundwater / Surface Water Installation and Sampling
Riparian Vegetation: Field data collection
Seed dispersal study
Tree ice-scar mapping
Focus Area vegetation mapping and sampling
Dendrochronology sampling
Soil sampling
Sediment Dating: Sampling and Analysis
Develop groundwater / surface water models
Develop vegetation flow-response models
Develop riparian scaling model: reach to riparian process domain
Develop vegetation Project operational flow-response model
Riparian vegetation impact analyses
Alternative operational scenarios
Reporting Δ ▲
Legend:
Planned Activity Δ Initial Study Report
----- Follow up activity (as needed) ▲ Updated Study Report
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-31 July 2013
Table 8.6-2. 8.6.3.1 Floodplain Vegetation and Physical Process Regimes Critical Review, Synthesis and Lessons Learned.
STUDY OBJECTIVES
1. Conduct a critical review of previous Susitna River 1980s floodplain vegetation studies.
2. Conduct a critical review, and synthesis of relevant findings, of circumpolar, temperate and boreal regions, scientific research
concerning dam effects on downriver floodplain plant communities.
3. Conduct critical review, and synthesis of relevant current scientific research, concerning temperate and boreal floodplain forest
succession and dynamics under natural flow regimes.
METHODS
1. Search libraries and internet for relevant scientific literature.
2. Develop annotated, searchable bibliography.
3. Develop critical review paper with thematic format:
a. first, identify critical floodplain ecological processes effected by dams,
b. second, compare Project dam operations under current design and compare with scientific literature reported effects,
c. third, identify potential alternative operation scenarios to limit effects.
EXPECTED RESULTS
1. State of the science review of scientific findings concerning dam effects on downriver floodplain plant communities.
2. Summary of expected effects of Project operations on Susitna River floodplain plant communities and ecosystems.
3. Set of guidelines for limiting Project operations effects based on current science.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-32 July 2013
Table 8.6-3. 8.6.3.2 Focus Area Selection−Riparian Process Domain Delineation
STUDY OBJECTIVES
1. Develop a riparian process domain stratification of the Study Area.
2. Select Focus Areas representative of each riparian process domain for physical process and vegetation survey sampling and
modeling.
METHODS
1. Riparian process domain delineation, and riparian Focus Area selection is an iterative process.
2. In Q1 21013 the results of the 2012 geomorphology study and channel classification (Section 6.6), ice processes study (Section
7.6), riparian botanical survey (Section 11.6) will be used to classify channel, floodplain and floodplain vegetation types.
3. Constrained cluster analysis will be performed on channel, floodplain and vegetation types.
4. Process domain type variability will be statistically described and a power analysis performed to determine the number of Focus
Areas necessary to capture process domain variability in the stratified sampling approach.
5. Candidate Focus Areas previously identified through the expert-opinion process for both Aquatic and Riparian IFS will be reviewed.
6. Results of the cluster analysis, power analysis and expert-opinion process will be presented to the TWG for final selection of Focus
Areas.
7. Ice process mapping results, completed in Q4 2013, will be used in a second round of riparian process domain analysis and Focus
Area selection.
8. Results of second iterative analysis will be used to assess whether additional Focus Areas are needed to capture ice process
effects for 2014 field sampling.
EXPECTED RESULTS
1. Hierarchical stratification of Susitna River Study Area into riparian process domains.
2. Statistically robust selection of representative riparian process domain Focus Areas.
3. Study Area floodplain vegetation and physical process sampling and characterization necessary to support model scaling of Focus
Area study results to riparian process domain.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-33 July 2013
Table 8.6-4. 8.6.3.3.1 Synchrony of Seed Dispersal, Hydrology, and Local Susitna River Valley Climate
STUDY OBJECTIVES
1. Measure cottonwood and select willow species seed dispersal timing.
2. Model local Susitna River valley climate, and associated seasonal peak flows, relative to cottonwood and willow seed dispersal.
3. Develop a recruitment box model of seed dispersal timing, river flow regime, and cottonwood and willow seed dispersal and
establishment.
METHODS
1. Conduct a two-year field survey of seed release of balsam poplar and select willow species.
2. Develop a ‘degree-day’ climate model for the onset of seed release relative to local temperature conditions using methods
developed by Stella et al. (2006).
3. Analyze the historic climate and Susitna River flow regime relationship.
EXPECTED RESULTS
1. Degree-day model of peak seed release window using seed release observations and continuous temperature records from each
floodplain sample site.
2. Recruitment box model of cottonwood and select willow species.
3. Model of peak runoff / seed release temporal synchrony for operational flow guidelines.
4. Model of critical summer flow regime necessary to support seedling establishment.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-34 July 2013
Table 8.6-5. 8.6.3.3.2 Seedling Establishment and Recruitment Study
STUDY OBJECTIVES
1. Map the spatial locations dominant woody riparian seedlings including balsam poplar, white spruce, paper birch, thinleaf and Sitka
alder, feltleaf willow, and Barclay’s willow throughout the Focus Area, and Riparian Vegetation Study sites, active channel margins,
and floodplain.
2. Use a stratified random sampling approach, with variable plot sizes (Mueller-Dombois and Ellenburg 1974) to sample mapped
seedling polygons.
3. Identify seedlings to species, and measure seedling heights and density.
4. Describe and measure seedling site soil characteristics (see Section 8.6.3.7 for methods).
5. Measure and model seedling site GW/SW hydroregimes.
6. Measure seedling xylem water source through isotopic analysis (see Section 8.6.3.6 for methods).
7. Investigate ice process seedling site interactions through empirical observations and ice process modeling.
8. Develop a probabilistic model of seedling hydrologic, sediment, and ice regime processes.
METHODS
1. Survey sampling approach is as follows.
2. First, a helicopter survey of each reach will be conducted to locate and map observable seedling areas.
3. Second, four to eight transects will be placed systematically throughout the reach normal to main channel, extending across the
adjacent floodplain intersecting observed seedling sites. Each transect will be traversed and all remotely observed, and newly
identified on-the-ground seedling locations will be mapped with GPS.
4. Third, seedling site polygon boundaries will be mapped with GPS.
5. Fourth, seedling patches will be sampled using a stratified random approach to locate sample plots. Seedling species will be
identified, or collected for herbarium identification, and abundance (density) and height measured using variable plot size and
shapes (Elzinga et al. 1998; Mueller-Dombois and Ellenberg 1974).
6. Fifth, at each plot two to three seedlings of each species will be excavated and rooting depth measured. Excavated woody
seedlings will be aged at the root collar in the laboratory and annual rings counted to provide seedling age. Substrate texture and
depth to cobbles will be described and measured in soil pits excavated to 50 cm in depth or to gravel/cobble refusal layer.
7. Sixth, a sub-sample of Focus Area site seedlings will be used for xylem isotopic analyses to identify source of water (Section
8.6.3.6).
8. Seedling establishment model will be developed using techniques and methods described in Franz and Bazzaz (1977), Rains et al.
(2004), Henszey et al. (2004), Baird and Maddock (2005), and Maddock et al. (2012).
EXPECTED RESULTS
1. Probabilistic model of seedling establishment requirements based on GW/SW interaction model, sediment transport model, and ice
regime model.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-35 July 2013
Table 8.6-6. 8.6.3.4 Characterize the role of river ice in the establishment and recruitment of dominant floodplain
vegetation.
STUDY OBJECTIVES
1. Develop an integrated model of ice process interactions with floodplain vegetation.
2. Conduct primary research to identify the effects of ice on floodplain vegetation within mapped Susitna River ice floodplain impact
zones.
3. Quantitatively describe and compare ice influenced and non-ice-influenced floodplain plant community composition, abundance,
age, and spatial pattern to assess the role and degree of influence ice processes have on Susitna River floodplain vegetation.
4. Provide Project operational guidance on potential effects of operations flow on ice formation and floodplain vegetation development.
METHODS
1. Multiple lines of evidence will be used to inform a final research study design to address the question of vegetation response to ice
shearing influence on the Susitna River floodplain.
2. First, ice vegetation impacts (tree ice-scars) will be observed, mapped, and aged (using dendrochronologic techniques), and gravel
floodplain deposits will be mapped throughout the Study Area to develop a Study Area map of river ice floodplain vegetation
interaction domains.
3. Second, local residents will be interviewed (e.g., Mike Wood, who lives across from Whiskers Slough) concerning their knowledge of
spatial locations of historic ice dams, years of significant ice occurrence, and other anecdotal historical information concerning ice
on the Susitna River.
4. From these two sources of information, a map will be created of Susitna River ice process floodplain vegetation effect domains.
5. Floodplain vegetation surveys will be conducted to quantitatively measure (stratified random sampling of mapped floodplain
vegetation ice shear process zones) and statistically describe and compare vegetation characteristics associated with floodplains
experiencing ice shear events and floodplain vegetation without observed ice influence. The vegetation study design will build on
the design and results of Engstrom et al. (2011) where they studied and assessed the effects of anchor ice on riparian vegetation.
Engstrom and others found that species richness was higher at sites affected by anchor ice than at sites where anchor ice was
absent, suggesting that ice disturbance plays a role in enhancing plant species richness (Engstrom et al. 2011).
EXPECTED RESULTS
1. Ice processes domain and floodplain ice interaction geographic, and elevation, map to inform floodplain ice interaction vegetation
study design and ice processes modeling, Section 7.6.
2. Develop a floodplain vegetation ice processes interaction study to compare ice disturbed and un-disturbed floodplains, similar to the
approach of Engstrom et al. (2011),
3. The results of the study will be used to assess how floodplain vegetation pattern and process may change with Project operation
alterations of the natural ice process regime. The final study design will be completed in Q2-3 2013, as additional tree ice-scar field
data become available.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-36 July 2013
Table 8.6-7. 8.6.3.5 Characterize the role of erosion and sediment deposition in the formation of floodplain surfaces, soils,
and vegetation.
STUDY OBJECTIVES
1. Measure the rates of channel migration, and floodplain vegetation disturbance or turnover, throughout the Study Area.
2. Measure the rates of sediment deposition, and floodplain development, throughout the Study Area.
3. Assess / model how Project operations will effect changes in the natural sediment regime, floodplain depositional patterns, and soil
development throughout the Study Area.
4. Assess / model how Project operations changes in sediment transport and soil development will affect floodplain plant community
succession.
METHODS
1. Floodplain soils and stratigraphy will be sampled throughout the Study Area using a stratified random approach, including pits
located in all Focus Areas.
2. Floodplain soil pits will be excavated from the surface to gravel / cobble layer (historic channel bed) and soil stratigraphy will be
described and measured using standard NRCS field techniques (Schoeneberger et al. 2002). Standard sediment grain size sieve
analysis will be conducted on samples taken at soil horizons..
3. Direct dating of fluvial sediments will be conducted using isotopic techniques, including, but not limited to, 137Cs and 210Pb
measurements as described in Stokes and Walling (2003).
4. Dendrochronologic techniques (Fritts 1976) will be used to age trees and current floodplain surfaces at each soil pit.
EXPECTED RESULTS
1. Dating of floodplain stratigraphy and surfaces using direct isotopic and dendrochronologic techniques for development of floodplain
evolution model,
2. Floodplain stratigraphic descriptions and grain size analyses for development of floodplain evolution model and sediment transport
modeling.
3. Measurement of rate of channel migration disturbance of floodplain vegetation. Measurement of rate of floodplain turnover or
disturbance.
4. Model of how Project operations will effect soil development.
5. Model of alteration of riparian seedling establishment floodplain surfaces and floodplain vegetation succession.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-37 July 2013
Table 8.6-8. 8.6.3.6 Characterize natural floodplain vegetation groundwater and surface water maintenance
hydroregime.
STUDY OBJECTIVES
1. Characterize dominant floodplain woody plant species establishment and maintenance life stage water sources through stable
isotope analyses of groundwater, soil water, and xylem water.
2. Measure groundwater and surface water regime at Focus Areas (GW: depth seasonally; SW: river stage)
3. Develop a floodplain GW/SW interaction model (water level frequency, magnitude, depth, duration, timing, interaction response).
4. Develop floodplain vegetation-flow response models.
5. Model Project operational flow effects on floodplain plant communities.
METHODS
1. Focus Area GW / SW sampling for all floodplain plant community types and successional stages including plant establishment, plant
recruitment, and mature forest vegetation.
2. Sampling design will include transects and arrays of groundwater wells and surface water stage stations see Groundwater Study
Section 7.5 for details.
3. Riparian floodplain plant community and soils sampling approach and design is detailed in the Riparian Vegetation Study Section
11.6.
4. Woody species source of water will be directly determined from stable isotope analyses of groundwater, soil water, precipitation, and
xylem water hydrogen and oxygen.
5. The rooting depth of dominant floodplain plants will be measured through excavation of trenches within each Focus Area floodplain
plant community type in coordination with soil stratigraphic excavations and well point soil pits.
6. Probabilistic response curves will be developed for select plant species and all riparian plant community types using techniques
described in Rains et al. (2004) and Henszey et al. (2004).
EXPECTED RESULTS
1. Probabilistic response curves for select plant species and all riparian plant community types.
2. Floodplain vegetation-GW/SW regime functional groups.
3. Statistically modeled relationship between individual riparian species, floodplain plant community types, and natural GW/SW
hydroregime.
4. Model of potential effects of Project operations on Susitna River floodplain plant communities.
5. Basis for recommended flow prescriptions necessary to support floodplain vegetation establishment, recruitment, and maintenance.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-38 July 2013
Table 8.6-9. 8.6.3.7 Floodplain Vegetation Study Synthesis, Focus Area to Riparian Process Domain Model Scaling and
Project Operations Effects Modeling
STUDY OBJECTIVES
Study objectives are to:
1. Develop conceptual ecological model of Susitna River floodplain vegetation establishment and recruitment based on synthesis of
Riparian Vegetation Study and Riparian IFS results.
2. Scale-up results of Focus Area floodplain vegetation and physical process modeling results to riparian process domains.
3. Develop a dynamic spatially-explicit floodplain vegetation model for simulating floodplain vegetation response to Project operation
modification of the natural flow, sediment and ice processes regimes.
4. Develop spatially explicit maps of modeled Project operations effects throughout the Study Area.
5. Provide guidance to environmental analysis of Project operations.
METHODS
1. Develop a dynamic spatially-explicit floodplain vegetation model for simulating floodplain vegetation response to Project operation
modification of the natural flow, sediment and ice processes regimes (Franz and Bazzaz 1976; Benjankar et al. 2011; Springer et al.
1999).
2. Fluvial geomorphology Section 6.6, ice process Section 7.6, and groundwater Section 7.5 modeling studies will provide modeling
results of both existing conditions and Project operation scenarios.
3. Riparian botanical forest succession models synthesis.
4. Floodplain vegetation (individual plant species and community types) GW/SW flow response curve analyses and physical process
models (geomorphology, groundwater, ice processes) will be used to model floodplain vegetation transition dynamics at riparian
process domain scale.
5. Focus Area modeling will be scaled-up to the riparian process domains using spatially explicit GIS models.
EXPECTED RESULTS
1. Conceptual ecological model of Susitna River floodplain vegetation establishment and recruitment floodplain vegetation.
2. Dynamic spatially-explicit floodplain vegetation model for simulating floodplain vegetation response to Project operation modification
of the natural flow, sediment and ice processes regimes.
3. Riparian process domain scale model of floodplain vegetation and physical processes.
4. Spatially explicit maps of modeled Project operations floodplain vegetation effects throughout the Study Area.
5. Project operations guidance to minimize modeled floodplain vegetation effects.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-39 July 2013
8.6.9. Figures
Figure 8.6-1. Study interdependencies for Riparian Instream Flow Study.
IFS F & A 8.5
IFS Riparian 8.6
Groundwater
7.5
Ice Processes
7.6
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
Groundwater 7.5 Ice Processes
7.6
Project Area Riparian
Vegetation & Soils
Mapping &
Quantitative
Description
(Q 4, 2013; Q4 2014)
Site Selection
Riparian Process Domain
Modeling Needs
Field Data Sharing
(Q 4-2012, Q1-2013)
Groundwater / Surface
Water Interaction
Study Model
•Groundwater Depth
•Seasonal Statistics
•Project operational
effects
(Q3-4, 2014)
Geomorphic Processes
Sediment Supply Regime
Hist. Channel Change
Flood Freq. & Flow Duration
(Q4, 2013; Q3-4, 2014)
Ice dam regime and river
network location
Ice / floodplain interactions
(Q3-4, 2014)
STUDY INTERDEPENDENCIES FOR RIPARIAN INSTREAM FLOW STUDY SECTION 8.6
Vegetation
Sampling,
Dendrochronology,
Seed Dispersal,
Seedling
Recruitment
(Q2-4, 2013; Q2-4,
2014)
Scaling Model
−from Reach to
Riparian Process
Domain
Geomorphology
6.0
Potential Changes in Floodplain
Vegetation Habitats & Plant
Community Succession:
-Relative Spatial Distribution
-Types of projected change
(Q4, 2013; Q1, 2015)
Vegetation Flow-
Response & Physical
Process Regime
Modeling (Flooding,
Sediment, Ice,
Channel, Climate)
Ice Processes
7.6
River
Productivity
9.8
Project Operational
Flow Design
Sediment Dating
(dendrochronology &
Isotopic/Radiogenic)
(Q4, 2013; Q4 2014)
Dendrochronology
(tree ice scar)
(Q4, 2013; Q4 2014)
Seed Dispersal,
Hydrology,
Climate
Synchrony Model
Riparian
Botanical
11.6
Wildlife
10.0
Geomorphology
Large Woody
Debris 6.5.4.9
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FERC Project No. 14241 Page 8-40 July 2013
Figure 8.6-2. Helm and Collins (1997) Susitna River floodplain forest succession. Note: model depicts typical floodplain
forests found in the Susitna River Middle River and Three Rivers Confluence segments.
AlderEarly
Shrub
Young
Poplar
Old
Poplar
Poplar
Spruce
Birch-
Spruce
Shrubby
Birch
Spruce
Barren
Active Channel
Logging
BeaverFlooding
Ice Scour
Advance
Wind
>200 yr170 yr100-150 yr50-90 yr20-50 yr0-15 yr
BeaverIce Scour
Susitna River Floodplain Forest Succession
(after Helm and Collins 1997)
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-41 July 2013
Figure 8.6-3. Riparian Process Domain Delineation 8.6.3.2.
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
Ice Processes
7.6
Project Area wide collection
of location data for:
1.tree ice-scars,
2.shrub scars,
3.floodplain ice gravel
and soil shearing
4.plant community types.
(Q 4, 2013; Q4 2014)
Geomorphic river segment
and reach classification
(Q4, 2012)
Modeling ice dam regime
and river network location
Ice / floodplain interactions.
(Q3-4, 2014)
Annual ice formation and
break-up videography
surveys (Q2,Q4 2012; Q1-2,
Q3-4 2013; Q1-2, Q3-4 2013;
Q1-2, Q3 2014)
RIPARIAN PROCESS DOMAIN DELINEATION 8.6.3.2
1.Riparian process domain GIS
cluster analysis. (Q1, Q4
2013)
2.Systematic Project Area
survey of tree ice-scar
locations and tree scar
dendrochronology. (Q2, Q3
2013)
3.Iterative riparian process
domain map generation.
(Q2-4, 2013; Q2-4, 2014)
1.Iterative riparian process domain
map generation. (Q2-4 2013; Q4
2014)
2.Ice / floodplain interaction map.
(Q4 2013; Q4 2014)
Ice Processes
9.8
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
Riparian IFS
Scaling &
Project
Effects
Modeling
8.6.3.7
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
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FERC Project No. 14241 Page 8-42 July 2013
Figure 8.6-4. Riparian Focus Area Selection 8.6.3.2.
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
Project Area wide collection
of location data for:
1.tree ice-scars,
2.shrub scars,
3.floodplain ice gravel
and soil shearing ,
4.plant community types.
(Q 4, 2013; Q4 2014)
Geomorphic river segment
and reach classification
(Q4, 2012)Team expert-opinion
selection of candidate Focus
Areas (Q3-4 2012)
RIPARIAN FOCUS AREA SELECTION 8.6.3.2
Technical Work Group
Focus Area selection
meetings (Q1 -2
2013; Q1 2014)
Selected riparian Focus Areas
(Q1 2013; Q1 2014)
Groundwater
7.5
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
IFS F & A 8.5
IFS Riparian 8.6
Geomorphology 6.0
Groundwater 7.5
Ice Processes 7.6
1.Riparian focus area
and process domain
GIS cluster analyses.
2.Preliminary riparian
focus area selection
& stratified sampling
design .
(Q1 2013; Q1 2014)
Riparian IFS
Scaling &
Project
Effects
Modeling
8.6.3.7
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
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FERC Project No. 14241 Page 8-43 July 2013
Figure 8.6-5. Cottonwood (Populus) life history stages: seed dispersal and germination, sapling to tree establishment. Cottonwood typically germinates on newly created
bare mineral soils associate with lateral active channel margins and gravel bars. Note proximity of summer baseflow and floodplain water table (Braatne et al. 1996).
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
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Figure 8.6-6. The riparian “Recruitment Box Model” describing seasonal flow pattern, associated river stage (elevation),
and flow ramping necessary for successful cottonwood and willow seedling establishment (from Amlin and Rood 2002;
Rood et al., 2005). Cottonwood species (Populus deltoides), willow species (Salix exigua). Stage hydrograph and seed
release timing will vary by region, watershed, and plant species.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
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FERC Project No. 14241 Page 8-45 July 2013
Figure 8.6-7. Seed Dispersal, Hydrology and Climate Synchrony Study8.6.3.3.1.
Flow Routing 6.5
Historic peak flow
hydrograph analyses
(Q2-Q4, 2014)
SEED DISPERSAL, HYDROLOGY AND CLIMATE SYNCHRONY STUDY 8.6.3.3.1
Model of Poplar and willow seed
dispersal, hydrology and climate
(Q4 2014)
Riparian IFS
Scaling &
Project
Effects
Modeling
8.6.3.7
Project
Operation
Design
1. Seed dispersal field
surveys (Q2 2013; Q2
2014).
2. Hydrologic analyses,
3. Climate modeling.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
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FERC Project No. 14241 Page 8-46 July 2013
Figure 8.6-8. Susitna Study Area meteorological station locations.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
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FERC Project No. 14241 Page 8-47 July 2013
Figure 8.6-9. Seedling Establishment & Recruitment Study 8.6.3.3.2.
River ice
floodplain
vegetation study
8.6.3.4
Fluvial
Geomorphology
6.6
Preliminary map of ice /
floodplain vegetation
interaction zones.
(Q 2-3 2013)
1.Focus Area sediment
transport modeling.
2.Focus Area hydrograph
analyses.
Groundwater / Surface
Water Interaction Study
Model
•Measure and model
frequency, magnitude,
duration & timing of surface
& groundwater flux
•Model project operational
GW/SW effects
(Q3-4, 2014)
SEEDLING ESTABLISHMENT & RECRUITMENT STUDY 8.6.3.3.2
Probabilistic model of seedling
establishment GW/SW hydrologic,
and soil/sediment requirements .
Riparian
Botanical
11.6
Groundwater
7.5
1.Map seedling zones
2.Sample seedlings and
soil.
3.Monument 3-year
cohort sample plots
4.Analyze seedling hydro-
regime conditions
5.Develop probabilistic
models.
(Q3-4 2013; Q3-4 2014)
Riparian IFS
Scaling &
Project
Effects
Modeling
8.6.3.7
3-year Seedling
cohort
establishment
and survival
study
Project
Operation
Design
1.Cohort establishment (survival
for three years) study results.
2.Refined Probabilistic model of
seedling establishment GW/SW
hydrologic, and soil/sediment
requirements .
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FERC Project No. 14241 Page 8-48 July 2013
Figure 8.6-10. Cottonwood tree ice-scar. Floodplain located immediately above Three Rivers Confluence.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-49 July 2013
Figure 8.6-11. Cottonwood forest tree ice-scars. Floodplain located immediately above Three Rivers Confluence.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-50 July 2013
Figure 8.6-12. Floodplain ice deposited gravel piles. Floodplain in braided reach below Three Rivers Confluence.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
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FERC Project No. 14241 Page 8-51 July 2013
Figure 8.6-13. River Ice-Floodplain Vegetation Establishment and Recruitment 8.6.3.4.
Riparian
Botanical
11.6
Botanical survey mapping
of:
1.tree ice-scars,
2.shrub scars,
3.floodplain ice gravel
and soil shearing ,
4.plant community types.
(Q 4, 2013; Q4 2014)
1.Seasonal ice formation and
break-up videography (Q4
2012, Q1-2, 4 2013; Q1-2, 4
2014)
2.Summary of 1980’s ice process
studies.
3.Ice process modeling results
(Q4 2014)
RIVER ICE− FLOODPLAIN VEGETATION ESTABLISHMENT AND RECRUITMENT 8.6.3.4
1.Using ice process domain map,
develop quantitative study
comparing ice influenced and non-
ice-influenced floodplain plant
community establishment and
recruitment.
2.Characterize role, and degree of
influence ,of ice processes in Susitna
River floodplain vegetation.
1.Vegetation study design (Q2 2013).
2.Characterization of ice process effects on
floodplain vegetation (Q4 2014).
Riparian IFS
8.6.3.2,
8.6.3.3
Riparian
Botanical
11.6
Ice Processes 7.6
Ice Processes 7.6
1.Tree ice scar and gravel
deposit mapping (Q3-4
2012; Q1-3 2013; Q1-3
2014).
2.Interview local Susitna
residents about ice dam
locations (Q1-2 2013).
3.Develop iterative map of
river ice floodplain
vegetation interaction
domains (Q2 & Q4 2013;
Q4 2014).
Riparian IFS
Scaling &
Project
Effects
Modeling
8.6.3.7
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-52 July 2013
Figure 8.6-14. Floodplain Erosion, Sediment Deposition & Floodplain Vegetation Study 8.6.3.5.
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
1.Floodplain sediment &
stratigraphy descriptions.
2.Floodplain soils analyses.
3.Floodplain isotopic
sediment dating.
4.Plant community mapping.
(Q 4, 2013; Q4 2014)
1.Focus Areas (FA) channel migration
rates.
2.FA’s floodplain disturbance rates.
3.FA’s flood frequency, magnitude,
duration, timing hydrograph and
modeling analyses.
4.2-D sediment transport and
floodplain sediment deposition
modeling.
(Q3-4, 2013; Q3-4 2014)
Project Area wide 1-D
hydraulic modeling of
historic flood frequency,
magnitude, duration and
timing (Q4 2013).
FLOODPLAIN EROSION, SEDIMENT DEPOSITION & FLOODPLAIN VEGETATION STUDY 8.6.3.5
1.FA sediment deposition rate
characterization and mapping.
2.FA sediment and soil development
rate analyses.
3.Floodplain and floodplain vegetation
development conceptual model.
(Q4 2014)
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
Flow Routing
Modeling IFS 8.5
1.Dendrochronologic studies (tree /
floodplain dating) (Q4 2013; Q4
2014).
2.Floodplain sediment deposition
rate analyses (Q4 2013; Q4
2014).
3.Analyses of floodplain plant
community types & sediment
characteristics. (Q4 2013; Q4
2014)
Riparian IFS
Scaling &
Project
Effects
Modeling
8.6.3.7
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-53 July 2013
Figure 8.6-15. Riverine hydrologic landscape (Winter 2001).
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-54 July 2013
Figure 8.6-16. Whiskers Slough typical Focus Area groundwater / surface water study design illustrating monitoring well and stage recorder transect locations. Typical
floodplain plant community types found in the middle segment of the Susitna River are shown.
Spruce/Birch
Poplar/Spruce/Birch
Poplar/Spruce
Balsam Poplar
Willow/Alder/Wet Meadow
Willow/Wet Meadow
0 500 1,000
Feet
Monitoring Wells
Soil Temperature
Soil Moisture
Stage RecordersMeteorology Station (ET)Sampling Transects
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-55 July 2013
Figure 8.6-17. General schematic of a riparian Focus Area floodplain channel complex bounded by the Susitna River,
side slough, and side channel.
Three typical riparian plant communities are depicted (A, B, C). Two transects of groundwater wells and stage stations
are shown to help measure hydraulic interactions between the groundwater system and adjacent hydrologic boundaries
at surface-water features. Additional wells are located to help define (1) the orientation of the groundwater table across
the study area, and (2) conditions at specific plant community locations (e.g., seedling establishment zones). Surface-
water stage stations are located to capture main channel, side channel and side slough stage variability. A meteorological
station is located in the central study area. Each groundwater well location may include additional subsurface and
riparian sensor measurements.
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-56 July 2013
Figure 8.6-18. (A) Transect profile view of typical monitoring well and stage recorder locations looking downriver. (B)
Gold Creek Gauge Station, Susitna River April through September 2005-2009.
Water
Table Alder WillowWillowAlder WillowBalsam PoplarWhite Spruce/ Paper BirchPoplar/Alder White Spruce Paper BirchWells, Soil Temperature, Soil Moisture
Stage Recorder
Stage
Recorder
Stage
Recorder
Flood Levels
Fluctuating
Water Table
Regional
Groundwater
Gradient and
Fluctuations
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-57 July 2013
Figure 8.6-19. Floodplain Vegetation Groundwater & Surface Water Study 8.6.3.6.
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
Groundwater 7.5
Focus Area
Vegetation mapping & survey
sampling
Soils mapping &
characterization
(Q 4, 2013; Q4 2014)
Groundwater / Surface Water
Interaction Study Model
•Measure and model
frequency, magnitude,
duration & timing of surface &
groundwater flux
•Model project operational
GW/SW effects
(Q3-4, 2014)
Focus Area
Surface water flow regime
modeling
•Stage/discharge regime
•1D/2D model
(Q4, 2013; Q3-4, 2014)
FLOODPLAIN VEGETATION GROUNDWATER & SURFACE WATER STUDY 8.6.3.6
Probabilistic floodplain vegetation
GW/SW regime response curves (Q4
2013; Q4 2014)
Analysis of floodplain vegetation
water sources (Q4 2013, Q4 2014)
Vegetation flow-
response & GW/SW
modeling .
Isotopic analysis of
floodplain vegetation
water sources
(Q4, 2013; Q2-4 2014;
Q1 2015)
Riparian IFS
Scaling &
Operations
Modeling
8.6.3.7
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-58 July 2013
Figure 8.6-20. Floodplain Vegetation Study Synthesis, Focus Area to Riparian Process Domain Scaling & Project Operations Effects Modeling 8.6.3.7.
Riparian
Botanical
11.6
Fluvial
Geomorphology
6.6
Riparian Process
Domain Map
8.6.3.2
Ice Processes
7.6
1.Study Area
floodplain
vegetation
mapping.
2.Forest
succession
models
(Q 4 2014)
Project riparian
process domain map
(Q4 2013)
Geomorphic Processes
Sediment Supply Regime
Hist. Channel Change
Flood Freq. & Flow Duration
(Q4 2014)
Ice process modeling
1.existing conditions
2.project operations
scenarios
(Q4 2014)
FLOODPLAIN VEGETATION STUDY SYNTHESIS, FOCUS AREA TO RIPARIAN PROCESS
DOMAIN SCALING & PROJECT OPERATIONS EFFECTS MODELING 8.6.3.7
Spatially explicit
mapping of
modeled
Operations
scenarios floodplain
vegetation effects.
Q1-2 2015
Floodplain
erosion and
sediment
deposition
vegetation
model
8.6.3.5
1.Ecological model of
Susitna River floodplain
vegetation establishment
and recruitment.
2.Floodplain vegetation
Operations effects
simulation model.
Q1-2 2015
Seed Dispersal,
hydrology
climate model
8.6.3.3
Project
Operational Flow
Design
Sediment
transport &
deposition rates
(Q4 2014)
Seed dispersal
timing and flow
regime
requirements
(Q4 2014)
Seedling
establishment
study
8.6.3.3.2
Seedling
establishment
flow & sediment
regimes
requirements
(Q4 2014)
Floodplain ice
process
interaction
zones
(Q4 2014)
River ice effects
floodplain
vegetation study
8.6.3.4
Floodplain plant
community GW/SW
regime
requirements
(Q4 2014)
Floodplain
vegetation
GW/SW
interaction
model 8.6.3.6
FINAL STUDY PLAN RIPARIAN INSTREAM FLOW STUDY 8.6
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 8-59 July 2013