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Susitna‐Watana Hydroelectric Project Document
ARLIS Uniform Cover Page
Title:
Riparian instream flow study, Study plan Section 8.6, 2014-2015 Study
Implementation Report SuWa 289
Author(s) – Personal:
Author(s) – Corporate:
R2 Resource Consultants
ABR, Inc. (Appendix A only)
AEA‐identified category, if specified:
November 2015; Study Completion and 2014/2015 Implementation Reports
AEA‐identified series, if specified:
Series (ARLIS‐assigned report number):
Susitna-Watana Hydroelectric Project document number 289
Existing numbers on document:
Published by:
[Anchorage : Alaska Energy Authority, 2015]
Date published:
November 2015
Published for:
Alaska Energy Authority
Date or date range of report:
Volume and/or Part numbers:
Study plan Section 8.6
Final or Draft status, as indicated:
Document type:
Pagination:
v, 64, iii, 25 pages
Related works(s):
Pages added/changed by ARLIS:
Notes:
Contents:
[Main report] -- Appendix A. Riparian vegetation groundwater/surface water study sampling design.
All reports in the Susitna‐Watana Hydroelectric Project Document series include an ARLIS‐
produced cover page and an ARLIS‐assigned number for uniformity and citability. All reports
are posted online at http://www.arlis.org/resources/susitna‐watana/
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Riparian Instream Flow Study
Study Plan Section 8.6
2014-2015 Study Implementation Report
Prepared for
Alaska Energy Authority
Prepared by
R2 Resource Consultants
November 2015
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page i November 2015
TABLE OF CONTENTS
1. Introduction ........................................................................................................................1
2. Study Objectives.................................................................................................................1
3. Study Area ..........................................................................................................................3
4. Methods and variances ......................................................................................................3
4.1. Literature Review of Dam Effects on Downstream Vegetation ........................3
4.2. Focus Area Selection─Riparian Process Domain Delineation ..........................4
4.3. Seed Dispersal and Seedling Establishment Studies .........................................4
4.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River
Valley Climate ................................................................................ 4
4.3.2. Seedling Establishment and Recruitment Study ............................. 4
4.4. River Ice Effects on Floodplain Vegetation .......................................................5
4.4.1. Variances ......................................................................................... 6
4.5. Floodplain Stratigraphy and Floodplain Development ......................................6
4.5.1. Variances ......................................................................................... 6
4.6. Riparian Floodplain Vegetation Groundwater and Surface Water Hydroregime
Study (i.e., Riparian GW/SW Study) .................................................................6
4.6.1. Variances ......................................................................................... 7
4.7. Riparian Vegetation Modeling Synthesis and Project Area Scaling .................7
4.7.1. Variances ......................................................................................... 7
5. Results .................................................................................................................................8
5.1. Literature Review of Dam Effects on Downstream Vegetation ........................8
5.2. Focus Area Selection─Riparian Process Domain Delineation ..........................8
5.3. Seed Dispersal and Seedling Establishment Studies .........................................8
5.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River
Valley Climate ................................................................................ 8
5.3.2. Seedling Establishment and Recruitment Study ............................. 8
5.4. River Ice Effects on Floodplain Vegetation .......................................................9
5.5. Floodplain Stratigraphy and Floodplain Development ....................................10
5.6. Riparian Floodplain Vegetation Groundwater and Surface Water Hydroregime
Study (i.e., Riparian GW/SW Study) ...............................................................10
5.7. Riparian Vegetation Modeling Synthesis and Project Area Scaling ...............11
6. Discussion..........................................................................................................................11
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page ii November 2015
6.1. Literature Review of Dam Effects on Downstream Vegetation ......................11
6.2. Focus Area Selection─Riparian Process Domain Delineation ........................11
6.3. Seed Dispersal and Seedling Establishment Studies .......................................12
6.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River
Valley Climate .............................................................................. 12
6.3.2. Seedling Establishment and Recruitment Study ........................... 12
6.4. River Ice Effects on Floodplain Vegetation .....................................................13
6.5. Floodplain Stratigraphy and Floodplain Development ....................................13
6.6. Riparian Floodplain Vegetation Groundwater and Surface Water Hydroregime
Study (i.e., Riparian GW/SW Study) ...............................................................13
6.7. Riparian Vegetation Modeling Synthesis and Project Area Scaling ...............14
7. Conclusion ........................................................................................................................14
7.1. Literature Review of Dam Effects on Downstream Vegetation ......................14
7.2. Focus Area Selection─Riparian Process Domain Delineation ........................14
7.3. Seed Dispersal and Seedling Establishment Studies .......................................14
7.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River
Valley Climate .............................................................................. 14
7.3.2. Seedling Establishment and Recruitment Study ........................... 14
7.4. River Ice Effects on Floodplain Vegetation .....................................................15
7.5. Floodplain Stratigraphy and Floodplain Development ....................................15
7.6. Riparian Floodplain Vegetation Groundwater and Surface Water Hydroregime
Study (i.e., Riparian GW/SW Study) ...............................................................15
7.6.1. Modifications to Study Plan.......................................................... 15
7.7. Riparian Vegetation Modeling Synthesis and Project Area Scaling ...............16
8. Literature Cited ...............................................................................................................17
9. Tables ................................................................................................................................18
10. Figures ...............................................................................................................................29
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iii November 2015
LIST OF TABLES
Table 5-1. Summary of the QC3 data files used in support of this SIR and its appendices that have
been delivered to GINA and are publically available (http://gis.suhydro.org/SIR/08-
Instream_Flow/8.6-Riparian_Instream_Flow/)..................................................................... 19
Table 5-2. Total Year 0+ Poplar, Willow, Undifferentiated Poplar/Willow and Alder Seedlings
Counted from 2013-2015. ..................................................................................................... 20
Table 5-3. Total Year 1+ Poplar, Willow, and Alder Seedlings Counted from 2013-2015. ....... 20
Table 5-4. Percent Substrate Cover along Transects. .................................................................. 21
Table 5-5. Percent Vegetation Cover along Transects. ................................................................ 22
Table 5-6. Tree age data for field samples collected in 2012 and 2013. Note that this data has not
been corrected for age to height of core above tree root collar. ............................................ 23
LIST OF FIGURES
Figure 3-1. Map depicting the Upper, Middle and Lower Segments of the Susitna River potentially
influenced by the Susitna-Watana Hydroelectric Project. .................................................... 30
Figure 5-1. Total Number of Year 0+ Seedlings by transect from July 2014 to September 2015.
............................................................................................................................................... 31
Figure 5-2. Total Number of Year 1+ Seedlings by transect from July 2014 to September 2015.
............................................................................................................................................... 32
Figure 5-3. Total Number of Year 0+ Seedlings at each plot in transect FA-104 STR 3. .......... 33
Figure 5-4. Total Number of Year 1+ Seedlings at each plot in transect FA-104 STR 3. .......... 34
Figure 5-5. Total Number of Year 0+ Seedlings at each plot in transect FA-128 STR 2. .......... 35
Figure 5-6. Total Number of Year 1+ Seedlings at each plot in transect FA-128 STR 2. .......... 36
Figure 5-7. Total Number of Year 0+ Seedlings at each plot in transect FA-138 STR 3. .......... 37
Figure 5-8. Total Number of Year 1+ Seedlings at each plot in transect FA-138 STR 3. .......... 38
Figure 5-9. Photo of transect in 2013 (left) and 2015 (right) of FA-113 STR11. ....................... 39
Figure 5-10. Elevation comparison of Transect FA-113 STR11. ................................................ 40
Figure 5-11. Photo of transect in 2013 (left) and 2015 (right) of FA-128 STR2. ....................... 41
Figure 5-12. Elevation comparison of Transect FA-128 STR2. .................................................. 42
Figure 5-13. Photo of transect in 2013 (left) and 2015 (right) of FA-138 STR3. ....................... 43
Figure 5-14. Elevation comparison of Transect FA-138 STR3. .................................................. 44
Figure 5-15. Ice scar wedge collection locations at FA-104 (Whiskers Slough). The downstream
extent of river ice floodplain tree interactions was observed at PRM 102.5, just upriver of the
confluence of the Susitna and Chulitna rivers. ..................................................................... 45
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Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iv November 2015
Figure 5-16. Ice scar wedge sample collection locations at FA-113 (Oxbow 1). ........................ 46
Figure 5-17. Ice scar wedge sample collection locations at FA-115 (Slough 6A). ..................... 47
Figure 5-18. Ma Ice scar wedge sample collection locations at FA-128 (Slough 8A). ............... 48
Figure 5-19. Tree ice scar and zone of floodplain ice influence, FA-104 (Whiskers Slough). ... 49
Figure 5-20. Tree ice scar and zone of floodplain ice influence, FA-113 (Oxbow 1). ................ 50
Figure 5-21. Tree ice scar and zone of floodplain ice influence, FA-115 (Slough 6A). ............. 51
Figure 5-22. Tree ice scar and zone of floodplain ice influence, FA-128 (Slough 8A). ............. 52
Figure 5-23. Tree ice scar and zone of floodplain ice influence, FA-138 (Gold Creek). ............ 53
Figure 5-24. Flow routing cross-section, tree ice survey, FA-104 (Whiskers Slough). .............. 54
Figure 5-25. Flow routing cross-section, tree ice survey, FA-104 (Whiskers Slough). .............. 55
Figure 5-26. Flow routing cross-section, tree ice survey, and plant communities FA-104 (Whiskers
Slough). ................................................................................................................................. 56
Figure 5-27. Tree core aging sample distribution within the Middle River Segment. Table 5-6
provides preliminary age, location and collection data for all sampled trees. ...................... 57
Figure 5-28. Preliminary tree age data for FA-104 (Whiskers Slough). ..................................... 58
Figure 5-29. Preliminary tree age data for FA-128 (Slough 8A). ................................................ 59
Figure 5-30. Penman-Monteith July 2013 evapotranspiration results for Matteuccia struthiopteris
at FA-104 (Whiskers Slough). .............................................................................................. 60
Figure 5-31. Isotopic compositions of precipitation, surface water, and groundwater samples
collected on the Susitna Middle River Segment in 2013. Global meteoric water line (GMWL)
and local meteoric water line (LMWL) are shown for reference. ........................................ 61
Figure 5-32. Two map layers for FA-113 (Oxbow 1) an FA-115 (Slough 6A) of all mapped
riparian areas that are wetted by the 100-year flood, and mapped riparian areas which remain
above the 100-year flood. ..................................................................................................... 62
Figure 5-33. Two map layers for FA-128 (Slough 8A) of all mapped riparian areas that are wetted
by the 100-year flood, and mapped riparian areas which remain above the 100-year flood. 63
Figure 5-34. Two map layers for FA-138 (Gold Creek) of all mapped riparian areas that are wetted
by the 100-year flood, and mapped riparian areas which remain above the 100-year flood. 64
APPENDICES
Appendix A: Riparian Vegetation Groundwater/Surface Water Study Sampling Design
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page v November 2015
LIST OF ACRONYMS AND SCIENTIFIC LABELS
Abbreviation Definition
2-D Two Dimensional
AEA Alaska Energy Authority
cfs cubic feet per second
DBH Diameter at Breast Height
ENRI University of Alaska Anchorage’s Environment and Natural Resources Institute
ET Evapotranspiration
FA Focus Area
FERC Federal Energy Regulatory Commission
GIS Geographic Information System
GPS Global Positioning System
GW Groundwater
ILP Integrated Licensing Process
ISR Initial Study Report
ITU Integrated Terrain Unit
LAI Leaf Area Index
LiDAR Light Detection and Ranging
LR Lower Susitna River Segment, PRM 102.4 to PRM 0
MR Middle Susitna River Segment, PRM 187.1 to PRM 102.4
PM Penman/Monteith
PRM Project River Mile
Project Susitna-Watana Hydroelectric Project, FERC No. 14241
QC Quality Control
RIFS Riparian Instream Flow Study 8.6
RSP Revised Study Plan
SIR Study Implementation Report
SW Surface Water
TM Technical Memorandum
TWG Technical Workgroup
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Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 1 November 2015
1. INTRODUCTION
This Riparian Instream Flow Study (RIFS), Section 8.6 of the Revised Study Plan (RSP) approved
by the Federal Energy Regulatory Commission (FERC) for the Susitna-Watana Hydroelectric
Project (Project), FERC Project No. 14241, focuses on the methods for assessing the effects of the
proposed Project and its operations on the floodplain plant communities in the Susitna River basin.
A summary of the development of this study, together with the Alaska Energy Authority’s (AEA)
implementation of it through the 2013 study season, appears in Part A, Section 1 of the Initial
Study Report (ISR) (AEA 2014) filed with FERC in June 2014 (AEA 2014). As required under
FERC’s regulations for the Integrated Licensing Process (ILP), the ISR describes AEA’s “overall
progress in implementing the Study Plan and schedule and the data collected, including an
explanation of any variance from the Study Plan and schedule.” (18 CFR 5.15(c)(1)).
Since filing the ISR in June 2014, AEA has continued to implement the FERC-approved Study
Plan for the RIFS. Major RIFS activities completed in 2014 and 2015 included:
Completion of literature review (Revised Study Plan [RSP] Section 8.6.3.1) in coordination
with Fluvial Geomorphology (Study 6.6) and preparation of a Technical Memorandum
(TM), filed with FERC November 14, 2014 (R2 and Tetra Tech 2014)
Completion of the second and third years of field surveys for the longitudinal willow-
cottonwood sexual reproduction seedling study (RSP Section 8.6.3.3.2)
Completion of a second season of aerial ice break-up observations and river ice scar
surveys in the Middle Susitna River Segment (MR) and Lower Susitna River Segment (LR)
of the Susitna River (RSP Section 8.6.3.4).
Continuation of field data collection for the Floodplain Stratigraphy and Floodplain
Development study (RSP Section 8.6.3.5) and Riparian GW/SW study (RSP Section
8.6.3.6)
On October 17, 2014, AEA held an ISR meeting for the Riparian Instream Flow Study.
In furtherance of the next round of ISR meetings and FERC’s Director’s Study Determination
expected in 2016, this Study Implementation Report (SIR) describes AEA’s overall progress in
implementing the RIFS from October 2013 through September 2015. Rather than a
comprehensive reporting of all field work, data collection, and data analysis since the beginning
of AEA’s study program, this report is intended to supplement and update the information
presented in Part A of the ISR for the RIFS efforts through September 2015. Th e SIR describes
the methods and results implemented in the 2014 and 2015 field efforts and discusses the results
in terms of the seven stated objectives of the RIFS (Study 8.6).
2. STUDY OBJECTIVES
As stated in ISR Study 8.6, the goal of the RIFS is to provide a quantitative, spatially explicit
model to predict potential impacts to downstream floodplain vegetation from Project operational
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FERC Project No. 14241 Page 2 November 2015
flow modification of the natural Susitna River flow, sediment, and ice regimes. To meet this goal,
a physical and vegetation process modeling approach is being applied. First, existing Susitna River
groundwater (GW) and surface water (SW) flow, sediment, and ice regimes are being measured
and modeled relative to floodplain plant community establishment, recruitment, and maintenance
requirements. Second, predictive models are being developed to assess potential Project
operational impacts to floodplain plant communities and to provide operational guidance to
minimize these impacts. Third, the predictive models are being applied spatially in a Geographic
Information System (GIS) to the riparian vegetation map produced by the Riparian Vegetation
Study (Study 11.6) to produce a series of maps of predicted changes under alternative operational
flow scenarios.
Seven RIFS objectives were established in RSP Section 8.6.1 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 (RSP Section 8.6.3.1).
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 Areas1 (RSP Section 8.6.3.2).
3. Characterize seed dispersal and seedling establishment GW and SW hydroregime
requirements. Develop a predictive model of potential Project operational impacts to seed
dispersal and seedling establishment (RSP Section 8.6.3.3).
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 process regimes and dominant floodplain vegetation establishment and recruitment
(RSP Section 8.6.3.4).
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 (RSP
Section 8.6.3.5).
6. Characterize natural floodplain vegetation GW and SW maintenance hydroregime.
Develop a predictive model to assess potential changes to natural hydroregime and
potential floodplain vegetation (RSP Section 8.6.3.6).
7. Develop floodplain vegetation study synthesis, scaling of Focus Areas to riparian process
domains, and Project operations effects modeling (RSP Section 8.6.3.7).
1 Focus Areas are intensive study areas representing specific sections of the Middle Segment of the Susitna River that will be
investigated across resource disciplines to provide for an overall understanding of interrelationships of river flow dynamics on the
physical, chemical, and biological factors that influence fish habitat (AEA 2012).
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FERC Project No. 14241 Page 3 November 2015
3. STUDY AREA
As established in RSP Section 8.6.2, the RIFS study area includes the Susitna River active
floodplain that would be affected by the operation of the Project downstream of the proposed
Watana Dam site (PRM 187.1). The active floodplain is the valley bottom flooded under the
current climate. The lateral extent of the Riparian Vegetation Study (Study 11.6) area was defined
by the extent of the riverine physiographic region generated by the Susitna River. Riverine
physiography includes: 1) those areas of the valley bottom, including off-channel water bodies,
that are directly influenced by regular (0–25 year) to irregular (25–100 year) overbank flooding;
and 2) those areas of the valley bottom influenced indirectly by GW associated with the Susitna
River. The riverine physiographic map has undergone review and refinement by the principal
investigators leading the RIFS, Riparian Vegetation Study (Study 11.6), and associated physical
processes studies (GW Study 7.5, Ice Processes Study 7.6, and Fluvial Geomorphology Modeling
Study 6.6). The longitudinal extent of the study area for the RIFS has been defined in coordination
with the Riparian Vegetation Study 11.6, Fluvial Geomorphology Modeling Study 6.6, and GW
Study 7.5. The study area includes those riparian areas downstream of the Project proposed dam
Site to a point at which the effects of altered stage and flow effects expected in the Susitna River
would not be ecologically significant (i.e., the expected hydraulic alterations would be overridden
by the input from other rivers and/or the effects of tidal fluctuations from Cook Inlet). Following
the completion of the Open-water Flow Routing Model in Q1 2013 and after receiving input from
the Technical Workgroup (TWG), the downstream extent of the study areas for the riparian studies,
including the Riparian Vegetation Study, was extended to Project River Mile [PRM] 29.9 (R2
2013). As established in the Study Plan, the Susitna River is characterized by three segments
(Figure 3-1). The RIFS study area includes the MR, which extends from the proposed dam Site at
PRM 187.1 downstream to the Three Rivers Confluence at PRM 102.4, and a portion of the LR,
which extends from the Three Rivers Confluence to PRM 29.9 just below the confluence with the
Yentna River (Figure 3-1).
4. METHODS AND VARIANCES
The RIFS is divided into seven study components listed in Section 3. This section provides an
update of activities related to each of the objectives that have occurred following reporting
provided in the June 2014 ISR. The June 2014 ISR reports on work that occurred through October
2013. The SIR reports on work completed after October 2013 which was not included in the June
2014 ISR. Only objectives for which work has been completed in this period are discussed in
detail in this SIR; others are cross-referenced back to the methods and results in the ISR.
4.1. Literature Review of Dam Effects on Downstream Vegetation
AEA prepared a TM which combined the RIFS (Study 8.6) and Geomorphology Studies (Studies
6.5 and 6.6) reviews of the scientific literature concerning downstream effects of dams titled Dam
Effects on Downstream Channel and Floodplain Geomorphology and Riparian Plant
Communities and Ecosystems−Literature Review (R2 and Tetra Tech 2014), filed with FERC
November 14, 2014. The objective of the TM was to synthesize studies of hydro project impacts
on downstream floodplain plant communities, studies of un-impacted floodplain plant community
successional processes, and historic physical and biologic data for the Susitna River floodplain
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FERC Project No. 14241 Page 4 November 2015
vegetation, including 1980s studies (RSP Section 8.6.3.1). As such, this literature review
summarizes reported study results and findings, presented as general background information, to
inform potential responses of the Susitna River channel, floodplain and riparian ecosystem to
Project operational flow modifications. The literature review was presented in three sections: 1)
introduction, including nature and scope of the question, theoretical framework, riverine─riparian
ecosystems, and definition of dams and hydroregulation; 2) review of 1980s Susitna River riparian
studies; and 3) review of literature concerning dam effects on downstream channel and floodplain
geomorphology and riparian plant communities and ecosystems. An annotated, searchable
bibliography summarizing more than 110 peer-reviewed articles was provided in Appendix A of
the TM.
The results of this study task provide a state-of-the-science background to the Project regarding
reported peer reviewed, and non-peer reviewed, literature concerning dam effects on downstream
channel and floodplain geomorphology and riparian plant communities and ecosystems.
4.2. Focus Area Selection─Riparian Process Domain Delineation
Study 8.6 ISR, Part A, Section 4.2 describes the approach and methodology used to develop the
riparian process domain map and RIFS Focus Area selection process. As described in Study 8.6
ISR, Part A, Section 4.2, AEA implemented the methods associated with this study element in
accordance with the Study Plan. There has been no substantive activity on this element since
completion of the June 2014 ISR. No updates to the preliminary riparian process delineation
mapping were completed in 2014.
4.3. Seed Dispersal and Seedling Establishment Studies
In this study task, dominant woody species seed dispersal and seedling establishment hydrologic
requirements will be determined through field surveys and GW and SW interaction measurement
and modeling. The study task has two subtasks: 1) seed dispersal, hydrology, and local Susitna
River valley climate synchrony study task, and 2) seedling establishment study task. As described
in Study 8.6 ISR, Part A, Section 4.3, AEA implemented the methods associated with this study
element in accordance with the Study Plan.
4.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River Valley
Climate
Methods for the seed dispersal study task are described fully in Study 8.6 ISR, Part A,
Section 4.3.1. No additional field efforts or data analyses were completed for this study objective
subsequent to the ISR.
4.3.2. Seedling Establishment and Recruitment Study
The goal of the seedling establishment and recruitment study task is to identify, measure, and
model potential impacts of Project operational changes to the GW, SW, sediment, and ice regimes,
and to assess the effects of these impacts on seedling establishment and recruitment within the
active channel margin / floodplain environment. As described in Study 8.6 ISR, Part A, Section
4.3.2, AEA implemented the methods associated with this study element in accordance with the
Study Plan.
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FERC Project No. 14241 Page 5 November 2015
As described in the Study 8.6 ISR, Part A, Section 4.3.2 willow and poplar seedling establishment
data (2013-2015) was collected. Methods and results of the 2013 data collection effort are
provided in Study 8.6 ISR, Part A, Section 4.3.2.1 and 5.3.2.1. Methods and preliminary results
of the three year willow and poplar seedling establishment data are described below.
Second year seedling establishment study task sampling efforts occurred from July 29, 2014
through August 4, 2014 and from August 30, 2014 through September 4, 2014. Third year seedling
establishment study task sampling efforts occurred from July 21, 2015 to July 25, 2015 and August
28, 2015 to September 3, 2015. The methods used in the 2014 and 2015 study were identical to
the 2013 field effort described in Study 8.6 ISR, Part A, Section 4.3.2.1.1. Using transects and
plot locations established in 2013 (Study 8.6 ISR, Part A, Section 4.3.2.1.1.), 0.25-square-meter
(2.7-square-foot) quadrats were laid out at 1-meter (3.3-foot) intervals along randomly located
transects along a baseline established parallel to the channel. Transects established in 2013 we re
relocated in 2014 and again in 2015. Transects extended normal to the channel from lowest extent
of seedling occurrence (typically the edge of water) to full vegetative canopy cover in adjacent
floodplain forest or shrub community. Nearly all the transect rebar pins placed in 2013 were
relocated during the 2014 and 2015 efforts. Several sites had significant erosion or deposition at
one end of the transect so rebar mid-points were used to start or end transects. Within each plot,
second year seedlings were counted to ascertain longitudinal survival from 2013-2015. Poplar and
willow first-year germinants/seedlings were counted to estimate abundance and density of new
recruit cohort in 2014 and again 2015. In addition to counting target woody seedlings, all
herbaceous plant cover within the plots was estimated. Aerial percent cover and stem heights for
tree or shrub seedlings were measured. At each 0.25-square-meter (2.7-square-foot) quadrat the
following data were collected in 2014 and 2015:
Sediment texture was recorded as percent cover of quadrat gravel or cobble vs. percent
cover by sand or silt.
Depth to gravel/cobble layer was measured using a 2-meter (6.6 feet) tile probe
(AMS, Inc.).
Elevation of each quadrat was surveyed with a level. Transect quadrat points were
surveyed to the intermediate benchmark set in 2013 and tied into the Project datum.
4.3.2.1. Variances
AEA implemented the methods as described in the Study Plan with exception of methods for
documentation of clonal reproduction for willow and cottonwood recruitment as described in
Study 8.6 ISR, Part A, Section 4.3.2.2.
4.4. River Ice Effects on Floodplain Vegetation
In this study task, multiple lines of evidence are being used to evaluate how vegetation responds
to the influence of ice shearing in the Susitna River floodplain, including observations of ice
vegetation impacts (distribution map and dendrochronologic ages of tree ice-scars), gravel
floodplain deposit evidence, results from the Ice Processes modeling (Study 7.6), and historic
accounts (anecdotal and recorded) of ice dam generated flood events. As described in Study 8.6
ISR, Part A, Section 4.4, AEA implemented the methods associated with this study element in
accordance with the Study Plan.
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Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 6 November 2015
Observations of ice effects on floodplains have been completed in 2012, 2013, 2014, and 2015.
Methods and results of the 2012 and 2013 data collection efforts are summarized in Study 8.6 ISR,
Part A, Section 4.4.1 and 5.4.1. Maps showing tree ice scar observations from 2013 field efforts
are provided in Study 8.6 ISR, Part A, Figure 5.4.4 and 5.4.5.
In 2014, additional field observations were made but were limited to spring break-up observations
from a helicopter, and an aerial and boat-based Lower River ice scar reconnaissance survey to
determine the downstream extent of ice scars.
In 2015, Middle River tree ice scar mapping was completed by helicopter and use of a jet dinghy
to access shallow water areas previously inaccessible by jet boat. Surveys were conducted from
PRM 187 to PRM 102 with coverage including Middle River mainstem channel, secondary
channels and side sloughs. Mapping was conducted using a Trimble Geo 7x with added laser
rangefinder and mounted external antenna. As in 2013 surveys, the 2015 survey protocol was to
make observations at approximately 0.2 mile intervals. If scars were present, the nearest tree with
an ice-scar was surveyed using the laser. If no ice-scarred trees were visible, the floodplain surface
elevation was surveyed. Tree ice-scar measurements included: 1) height of tree ice-scar; 2) height
of floodplain surface at the base of the tree; 3) height of floodplain above the water surface; and
4) horizontal location of the tree or floodplain surface. In 2015, the jet dinghy and helicopter
allowed access to channel reaches that were previously mapped as inaccessible in 2013. In
addition, areas which were marked with no ice scars in 2013 were resampled on foot and by boat
to confirm or revise the 2013 determinations. All Global Positioning System (GPS) location data
were post-processed with differential corrections using Trimble software and mapped on aerial
photographs.
4.4.1. Variances
AEA implemented the methods as described in the Study Plan with no variances.
4.5. Floodplain Stratigraphy and Floodplain Development
Methods and results of the 2013 data collection efforts are summarized in Study 8.6 ISR, Part A,
Section 4.5.1 and 5.5.1. As described in Study 8.6 ISR, Part A, Section 4.5, AEA implemented
the methods associated with this study element in accordance with the Study Plan.
4.5.1. Variances
AEA implemented the methods as described in the Study Plan with no variances.
4.6. Riparian Floodplain Vegetation Groundwater and Surface Water
Hydroregime Study (i.e., Riparian GW/SW Study)
Installation methods and locations followed methods described in Study 8.6 ISR, Part A,
Section 4.6.1 for 2013 field efforts. As described in Study 8.6 ISR, Part A, Section 4.6, AEA
implemented the methods associated with this study element in accordance with the Study Plan.
During the 2014 field season, field work was restricted to collecting continuous sap velocity
measurements using sap flow sensors. In 2014, however, the number of total sensors was reduced
in several trees. The total number of sensors and sensor types differed between the two years for
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given trees and thus data is reported in two separate databases. Methods and results of the 2013
data collection effort are provided in Study 8.6 ISR, Part A, Sections 4.6.2.4 and 5.6.3.
Stomatal conductance and leaf area index (LAI) measurements were collected in 2013, as
components of the Penman/Monteith (PM) equation, to be used to produce transpiration curves for
herbaceous and wood shrubs. Methods are provided in Study 8.6 ISR, Part A, Section 4.6.2.4.
Additional limited data analysis has occurred since the June 2014 ISR. Specifically, a preliminary
PM model was developed with 2013 results using the standard FAO Penman/Monteith approach
to calculate evapotranspiration (ET) on an hourly basis (Allen et al. 1998). As described in Study
8.6 ISR, Part A, Section 4.6, AEA implemented the methods associated with this study element in
accordance with the Study Plan. No additional field efforts occurred in 2014 or 2015 on stomatal
conductance or LAI, sediment, plant and water isotope or root depth sampling.
Preliminary surface water modeling was completed using a riparian floodplain mapping exercise
utilizing a water surface plane from the Fluvial Geomorphology Modeling Study (Study 6.6). This
geomorphology model was run for a 100-year flood (~98,000 cubic feet per second [cfs] at the
Gold Creek Gage) from ~PRM 154 to PRM 103, and the resulting water surface plane was overlaid
atop the 2013-2014 Light Detection and Ranging (LiDAR) digital elevation model. A map of the
extent of flooding caused by the 100-year flood was obtained by subtracting the elevation of the
underlying terrain from this 100-year water surface plane.
Next, this 100-year flood extent was laid over top of the riparian floodplain map, which was
delineated for the Riparian Vegetation Study (Study 11.6) from approximately PRM 108 to the
proposed Dam Site (PRM 187.1). The riparian floodplain map was then further delineated into
wet and dry sections, based on whether or not a given area overlapped with the 100-year flood
extent. The result produced two map layers from ~PRM 154 to PRM 108: 1) mapped riparian
areas that are wetted by the 100-year flood, and 2) mapped riparian areas which remain above the
100-year flood.
4.6.1. Variances
AEA implemented the methods as described in the Study Plan with no variances.
4.7. Riparian Vegetation Modeling Synthesis and Project Area
Scaling
As described in Study 8.6 ISR, Part A, Section 4.7, AEA implemented the methods associated
with this study element in accordance with the Study Plan. An RIFS TWG Meeting was held on
April 29 and 30, 2014 (http://www.susitna-watanahydro.org/meetings/past-meetings/) in which an
integrated modeling proof of concept and Project effects metrics were presented and discussed.
4.7.1. Variances
AEA implemented the methods as described in the Study Plan with no variances.
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5. RESULTS
Field data that has been QA/QC’d, and used in developing: 1) ISR Study 8.6 and 2) SIR Study 8.6
are available on the GINA website at the links below.
http://gis.suhydro.org/isr/08-Instream_Flow/8.6-Riparian_Instream_Flow/
http://gis.suhydro.org/SIR/08-Instream_Flow/8.6-Riparian_Instream_Flow/
See Table 5-1 for a listing of data files pertaining to this SIR on the GINA website.
5.1. Literature Review of Dam Effects on Downstream Vegetation
AEA prepared and submitted to FERC a TM titled Dam Effects on Downstream Channel and
Floodplain Geomorphology and Riparian Plant Communities and Ecosystems−Literature Review
(R2 and Tetra Tech 2014). This study objective has been met.
5.2. Focus Area Selection─Riparian Process Domain Delineation
No additional work has been completed on this study task after the June 2014 ISR. Refer to Study
8.6 ISR, Part A, Section 5.2.
5.3. Seed Dispersal and Seedling Establishment Studies
5.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River Valley
Climate
No additional work has been completed on this study task since the June 2014 ISR. Refer to Study
8.6 ISR, Part A, Section 5.3.1.
5.3.2. Seedling Establishment and Recruitment Study
In 2013, across all transects, more than 45,000 first year (0+) poplar and willow seedlings were
counted. Since the June 2014 ISR, additional seedling establishment surveys have been conducted.
In July of 2014, the first round of seedling sampling recorded 383 poplar, 23 willow, 13,398
undifferentiated poplar/willow, and 78 alder year 0+ seedlings and 493 poplar, 1,329 willow, and
25 alder year 1+ seedlings (Table 5-2). During the second round of sampling in September 2014,
5,586 poplar, 411 willow, 51 undifferentiated poplar/willow, and 10 alder year 0+ seedlings and
235 poplar, 1,083 willow, and 5 alder year 1+ seedlings were recorded.
General survival rates between July and September sampling events for year 0+ poplar and willow
year seedlings was 44%, and year 0+ alder was 12%. Survival rates of year 1+ seedlings in 2014
were 48%, 39%, and 20% for poplar, willow, and alder respectively (Table 5-2 and Table 5-3).
During the July 2015 survey, 6,715 poplar, 1,731 willow, 32 undifferentiated poplar/willow, and
947 alder year 0+ seedlings were recorded. In addition, 989 poplar, 2,476 willow, and 140 alder
year 1+ seedlings were recorded. Surveys conducted along these transects in September 2015
recorded 1,604 poplar, 1,400 willow, 11 undifferentiated poplar/willow, and 1,133 alder year 0+
seedlings and 410 poplar, 961 willow, and 43 alder year 1+ seedlings. General year 0+ seedling
survival rates between July and August 2015 were 24%, 81%, and 34% for poplar, willow, and
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differentiated poplar/willow respectively, Establishment of alder seedlings appears to continue
later in the growing season as alder year 0+ seedlings increased by 86 seedlings between July and
September 2015. Average Year 1+ seedling survival rates were 42%, 39%, and 31% for poplar,
willow, and alder respectively (Table 5-2 and Table 5-3).
Survival trends were highly variable among all tree species and between transects. Total seedling
counts observed at individual transects in 2014 and 2015 for Year 0+ and Year 1+ seedlings are
shown in Figure 5-1 and Figure 5-2. Figure 5-3 through Figure 5-8 provide examples of seedling
survivals across specific transects within Focus Areas FA-104 (Whiskers Slough), FA-128 (Slough
8A), FA-138 (Gold Creek) (FA-104 STR 3, FA-128 STR 2, and FA-138 STR 3).
Throughout the course of the study, plot elevation remained fairly consistent for most transects.
However, sediment erosion, whether by ice plowing or sheer stress, and sediment deposition was
observed at a number of transects. Examples of transect elevation comparisons from 2013 through
2015 are presented in Figures 5-9 through Figure 5-14. In addition to plot elevation surveys, depth
to cobble and GW elevation were measured during July 2014 and in both July and September of
2015.
Ocular estimates of surface substrate (sand/silt versus gravel/cobble) and vegetation leaf cover
(herbaceous and woody) were conducted at each plot during each sampling period. Substrate
varied among transects and geomorphic locations. However, silt and sands were the overall
dominate substrates along seedling transects. Cobble/Gravel was predominantly found along
lower elevations of transects (Table 5-4). Overall vegetation cover varied across transects. Both
herbaceous and woody vegetation cover increased along higher elevations along transects
(Table 5-5). Additional statistical analyses will be conducted following the completion of all
interrelated studies to assess the relative importance of environmental factors on seedling survival.
5.4. River Ice Effects on Floodplain Vegetation
On May 2, 2014, a 1-day ice break-up aerial reconnaissance and photographic survey, was
conducted by helicopter to observe ice-floodplain vegetation interactions. The 2014 thermal
breakup provided the opportunity to observe conditions that were very different from the 2013
dynamic river breakup where numerous ice dams were observed. The helicopter flight was
conducted by flying the Susitna River mainstem from Talkeetna (PRM 102) to the proposed Dam
Site at PRM 187.1. On May 2, 2014, slowly melting ice was observed throughout the main
channel, and no main channel ice dams were observed except at Whiskers Slough PRM 104. The
PRM 104 ice dam caused significant backwater flooding throughout the Whiskers Slough
floodplains, with ice tree interactions occurring along the river banks.
Additional tree ice scar wedges were sampled during field surveys on August 5-7, 2014 for
dendrochronologic analysis at FA-113 (Oxbow 1) and FA-115 (Slough 6A), a reach known
historically for ice dam formations, and on September 3-5, 2014 at FA-104 (Whiskers Slough) and
FA-128 (Slough 8A). Figure 5-15 through Figure 5-18 summarize the locations of tree ice scar
wedge samples collected in Focus Areas in 2013 and 2014. Figure 5-19, Figure 5-20, Figure 5-
21, Figure 5-22, and Figure 5-23 show the compilation of all tree ice scars observed relative to the
zone of floodplain ice influence at each Focus Area.
A determination of the geographic extent of tree ice scar occurrence along the Lower Susitna River
main channel was independently conducted by the RIFS study team, September 2014, and Fluvial
Geomorphology Modeling Study (Study 6.6) study team, August 2014, leads by jet boat from the
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Three Rivers Confluence (PRM 102.4) to Little Willow Creek (PRM 54.5). The first Susitna River
main channel tree ice scar was mapped at PRM 102.5, September 2014, immediately upriver of
the confluence of the Susitna and Chulitna rivers (Figure 5-15, see inset). Neither study lead
observed any tree ice scars from the Three Rivers Confluence to the confluence of Little Willow
Creek.
Tree ice scar mapping was also completed from PRM 102 to PRM 187 during late September
2015. Focus Area examples of mapped tree ice scars and the reach scale lateral extent of river ice
floodplain influence are depicted in Figure 5-19 [FA-104 (Whiskers Slough)], Figure 5-20 [FA-
113 (Oxbow 1)], Figure 5-21 [FA-115 (Slough 6A)], Figure 5-22 [FA-128 (Slough 8A)], and
Figure 5-23 [FA-138 (Gold Creek)]. The vertical extent of ice dam back-water flooding relative
to the open water 2-year event (approximately 50,000 cfs) and the 100-year event (100,000 cfs) is
illustrated in Figure 5-24, Figure 5-25, and Figure 5-26. These examples show that the highest
surface water elevations on the MR of the Susitna River are associated with ice dam back-water
flooding.
5.5. Floodplain Stratigraphy and Floodplain Development
Field data collection on floodplain formation was conducted in 2013, 2014, and 2015. Methods
and results of the 2013 data collection efforts are summarized in ISR Study 8.6, Section 4.5.1 and
5.5.1.
Since the June 2014 ISR, field data collection was limited to a September 22-28, 2014 riparian
sediment sampling survey that was conducted along the Susitna River corridor downriver from the
proposed Dam Site. Sediment cores were collected for sediment isotope geochronological analysis
at 38 sites along the MR between PRM 104 and 144.
Tree-core samples for tree age characterization were collected at all Integrated Terrain Unit (ITU)
plots in coordination with the Riparian Vegetation Study (Study 11.6) as reported in the June 2014
ISR. Preliminary tree core aging data was completed after the June 2014 ISR for all samples.
Results are provided in Table 5-6. Locations of these samples are summarized in Figure 5-27.
Preliminary tree age data for FA-104 (Whiskers Slough) and FA-128 (Slough 8A) are presented
in Figure 5-28 and Figure 5-29.
Sediment core 210Pb and 137Cs laboratory geochronology analyses were conducted in 2014;
however, the results will not be presented until final analyses and interpretation is conducted.
5.6. Riparian Floodplain Vegetation Groundwater and Surface Water
Hydroregime Study (i.e., Riparian GW/SW Study)
In 2014, a full season of sap flow measurements with associated GW well data was collected for
a suite of floodplain trees and shrubs. As described above, in 2014, the number of total sensors
was reduced relative to 2013 protocols in several trees. Results of the 2013 data collection effort
are provided in ISR Study 8.6, Sections 5.6.3.
Stomatal conductance and LAI measurements were collected in 2013, as components of the
Penman/Monteith (PM) equation, to be used to produce transpiration curves for herbaceous and
wood shrubs. Results from the 2013 field season are provided in ISR Study 8.6, Section 5.6.3. A
preliminary PM model shows the July 2013 evapotranspiration results for Matteuccia
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struthiopteris at FA-104 (Whiskers Slough) (Figure 5-30). All sap flow instrumentation was
removed from the field in September 2015.
During the 2013 field effort, the RIFS field team collected 370 soil samples, 661 plant samples,
and 100 water samples during June, July, and September for stable isotope analysis of oxygen18
and deuterium. Raw samples were delivered to University of Alaska Anchorage’s Environment
and Natural Resources Institute (ENRI) Stable Isotope Lab beginning in August 2013, and
cryogenic vacuum extraction of plant and soil samples began in February 2014. Results of the
2013 data collection effort are provided in ISR Study 8.6, Sections 5.6.1. Complete modeling
could not be done without the additional data; however, after the June 2014 ISR a preliminary
model of July 2013 proportional plant water uptake by soil depth for plants species at FA-128
(Slough 8A) in open alder cover type was prepared (Figure 5-31).
The surface water modeling floodplain mapping exercise utilizing a water surface plane from the
Fluvial Geomorphology Modeling Study (Study 6.6) effort produced two map layers from ~PRM
154 to PRM 108: 1) mapped riparian areas that are wetted by the 100-year flood, and 2) mapped
riparian areas which remain above the 100-year flood. Figure 5-32, Figure 5-33, and Figure 5-34
show results of this analysis at FA-113 (Oxbow 1) and FA-115 (Slough 6A), FA-128 (Slough 8A),
and FA-138 (Gold Creek).
5.7. Riparian Vegetation Modeling Synthesis and Project Area
Scaling
A Technical Work Group (TWG) meeting was held April 29-30, 2014 in which elements of the
conceptual model of riparian floodplain vegetation were discussed. Presentations from RIFS
(Study 8.6), Riparian Vegetation (Study 11.6), GW (Study 7.5), Ice Processes (Study 7.6), and
Fluvial Geomorphology Modeling (Study 6.6) studies are available on the Project website
(http://www.susitna-watanahydro.org/meetings/past-meetings/). In these meetings, a conceptual
design and formulation of dynamic spatially-explicit floodplain vegetation models were presented
for simulating floodplain vegetation response to Project operation modification of the natural flow,
sediment and ice processes regimes. The outcome of further modeling synthesis and Project area
scaling efforts are to provide guidance to Project operations to minimize modeled floodplain
vegetation effects. No additional work has been completed on this study task after the ISR. Refer
to ISR Study 8.6, Section 5.7.
6. DISCUSSION
6.1. Literature Review of Dam Effects on Downstream Vegetation
This study task is complete. Refer to Study 8.6 ISR, Part A, Section 6.1 and the November 15,
2014 TM titled Literature Review of Dam Effects on Downstream Vegetation (R2 and Tetra Tech
2014).
6.2. Focus Area Selection─Riparian Process Domain Delineation
No additional work has been completed on this study task since that reported in the June 2014 ISR.
Refer to Study 8.6 ISR, Part A, Section 6.2.
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6.3. Seed Dispersal and Seedling Establishment Studies
6.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River Valley
Climate
No additional work has been completed on this study task since that reported in the ISR. Refer to
Study 8.6 ISR, Part A, Section 6.3.1.
6.3.2. Seedling Establishment and Recruitment Study
Fluvial processes are essential component of riparian plant successional changes on floodplain
surfaces. Seasonal changes in water level control sediment transport, GW elevation, soil moisture,
silt deposition, and seedling burial and scouring. All these things have been well established in
directly affecting the success of riparian seedling establishment. To date, seedling establishment
study has met the objectives outlined in the Study Plan by completing three years of seedling
establishment counts two times during the growing season to capture the long-term seedling
survival for a river system that has an average bimodal summer discharge. Throughout this study,
established seedling transects were visited two times during the growing season where seedling
survival counts, floodplain elevations, depth of sediment layer, and GW/SW elevations were all
recorded.
Across all sampling years, seedling survivorship varied across Focus Areas, geomorphic features,
and transects. In general, all three years consistently showed large mortality rate for year 0+
seedlings between the two sampling events. Early seedling establishment occurs on moist alluvial
surfaces following the peak in the hydrograph. Based on field observations, large numbers of year
0+ mortality was a result of desiccation do to drying surfaces as river stage decreases . However,
trends show an increase of year 1+ seedlings survival from July 2014 through September 2015.
We believe this is partly due to the fact there has only been one significant peak flow event over
the course of the study, which occurred in late August of 2013. This event was observed to have
scoured out many year 0+ seedlings between the first and second sampling. In addition, both 2014
and 2015 experienced mild thermal breakups, reducing the severity of back water flooding and ice
scouring attributed to more dynamic breakups. The impacts of high water events and ice to
seedling survival are also evident through erosion and sediment deposition observed along
transects.
By standardizing seedling survival by elevation and incorporating shear stress and GW elevation
into the analysis, the results of the seedling establishment study task will model spatially where
seedling establishment will occur with Project operations flow regimes. The effects metric to be
developed will be a spatially explicit projection of potential seedling encroachment, or mortality
due to erosion, throughout the Project area. The results of the seedling study task, and metrics
developed in collaboration with the Fluvial Geomorphology Modeling Study (Study 6.6), will be
a key element in the Fluvial Geomorphology Modeling Study team’s 50+ year alluvial terrain
model projection. The results, and vegetation encroachment or erosion metrics, will predict where
and to what extent vegetation encroachment along the channel margins is likely to occur.
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6.4. River Ice Effects on Floodplain Vegetation
The objective of the ice effects vegetation study task is to quantitatively describe the role and
degree of influence ice processes have on the composition, abundance, age, and spatial pattern of
riparian vegetation along the Susitna River.
The data that has been collected throughout the three years of field efforts will provide the
necessary data to meet study objectives outlined in the Study Plan. During this time, a large
dendrochronology effort was undertaken in 2013 to map out the age of various floodplain surfaces.
In addition, a complete map of the Middle River provides the location and elevation in which ice
interacts with vegetation. Ice scar wedge samples collected at certain Focus Areas, provide a
historic record of large ice events. The data of this study while be integrated into the hydrological
models and the results will be used to assess how floodplain vegetation pattern and process may
change with Project operation alterations of the natural ice process regime. Finally, the riparian
vegetation process analysis will support the projected Project impacts analysis providing metrics
for wildlife habitat studies.
6.5. Floodplain Stratigraphy and Floodplain Development
The Floodplain Stratigraphy and Floodplain Development (RSP Section 8.6.3.5) study task results
will be used to measure the Project operations impacts on riparian vegetation establishment,
maintenance, and succession. The sediment isotope sedimentation rate analyses will be used to
develop change metrics for the Fluvial Geomorphology Modeling Study (Study 6.6) floodplain
evolution model. The results metrics will be utilized in the Riparian Vegetation Study (Study 11.6)
and wildlife habitat studies. Additional sediment core data was collected and preliminary tree age
data were determined subsequent to the ISR. No additional analyses have been completed on this
study task since that reported in the June 2014 ISR. Refer to Study 8.6 ISR, Part A, Section 6.3.5.
6.6. Riparian Floodplain Vegetation Groundwater and Surface Water
Hydroregime Study (i.e., Riparian GW/SW Study)
It is widely accepted that a river’s hydroregime can have many effects on the existence of certain
riparian plant species. Changes in river hydrology can affect the composition and distribution of
riparian species. The goal of the Riparian Floodplain Vegetation Groundwater and Surface Water
Hydroregime Study (RSP Section 8.6.3.6) was to collect the necessary data to be able to
statistically model relationships between individual riparian plant species, floodplain plant
community types, and natural GW/SW hydroregime.
The study is progressing toward meeting objectives set in the Study Plan to collect the necessary
data needed to build transpiration curves for MODFLOW modeling and is awaiting associated
Quality Control (QC) level data from inter-related studies. In 2013 and 2014, both field and
analytical progress to build transpiration curves for MODFLOW modeling were accomplished
through the collection of sap flow measurements across a full growing season and the construction
of preliminary PM models for dominant herbaceous species. In addition, a large number of water
isotope samples have been analyzed providing the necessary data needed to understand both the
general location riparian plant species uptake water from and the relative amount of water taken
from each source.
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The final results of the riparian GW/SW study task will be used to predict potential changes in the
hydrological cycle during Project operations and its possible impacts to the composition of
floodplain vegetation communities. By identifying the physical hydrological boundaries which
help maintain current Susitna River floodplain conditions, the results from this study task are
designed to form the basis for recommended flow prescriptions necessary to support floodplain
vegetation establishment, recruitment, and maintenance.
6.7. Riparian Vegetation Modeling Synthesis and Project Area
Scaling
The TWG meeting was held April 29-30, 2014 in which elements of the conceptual model of
riparian floodplain vegetation were discussed. No additional work has been completed on this
study task since that reported in the June 2014 ISR. Refer to Study 8.6 ISR, Part A, Section 5.7.
7. CONCLUSION
The following conclusions are presented sequentially by study section.
7.1. Literature Review of Dam Effects on Downstream Vegetation
The Literature Review of Dam effects on Downstream Vegetation (RSP Section 8.6.3.1) has been
completed and submitted to FERC November 14, 2014.
7.2. Focus Area Selection─Riparian Process Domain Delineation
Initial analyses have been accomplished. Preliminary riparian process domain delineation and
RIFS Focus Area selection was completed using an iterative process starting with a
multidisciplinary approach, statistical analyses, and analysis of Viereck Level III vegetation types
and type abundance along digitized transects. The final riparian process domain delineation will
be completed for the MR and LR in a final statistical analysis incorporating final tree ice scar
mapping data, ice process modeling results, and open-water floodplain inundation frequency
modeling results.
7.3. Seed Dispersal and Seedling Establishment Studies
7.3.1. Synchrony of Seed Dispersal, Hydrology, and Local Susitna River Valley
Climate
Field data collection and preliminary climate day model analysis was accomplished in 2014. An
additional year’s worth of seed dispersal data is necessary to complete the study. Final synchrony
modeling will be conducted once final fieldwork is accomplished.
7.3.2. Seedling Establishment and Recruitment Study
Three years (2013, 2014, and 2015) of seedling survival sampling was finished in September 2015.
Next steps to finalize the study are to: (1) incorporate Fluvial Geomorphology Two-Dimensional
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(2-D) bed shear stress modeling results for all sample transects, and (2) complete the statistical
analysis of the field data and modeling results.
7.4. River Ice Effects on Floodplain Vegetation
Tree ice scar field mapping was finished in September 2015. Next steps to finalizing the study
include: (1) analysis of tree ice scar map and dendrochronologic data throughout the MR,
(2) quantitatively compare ice-influenced and non-ice-influenced floodplain plant communities to
assess the role and degree of ice process influence, and (3) comparison analysis of Ice Process
Study river modeling results with the empirical tree ice scar mapping.
7.5. Floodplain Stratigraphy and Floodplain Development
Sediment stratigraphy field work was completed in 2013, 2014 & 2015. Final laboratory isotope
analysis has not yet been completed.. Final steps to finish the study include: (1) analysis of Fluvial
Geomorphology Study channel migration study results with Riparian Vegetation Study vegetation
map and RIFS dendrochronologic analyses, (2) analysis of sediment isotope study results with
open water floodplain frequency model and tree ice scar study area mapping, (3) incorporation of
Riparian Vegetation Study successional models with results of Fluvial Geomorphology channel
and floodplain evolution models, and (4) assess/model how Project operation induced changes in
sediment transport and soil development will affect floodplain development and plant community
succession.
7.6. Riparian Floodplain Vegetation Groundwater and Surface Water
Hydroregime Study (i.e., Riparian GW/SW Study)
In 2013 and 2014, both field and analytical progress to build transpiration curves for MODFLOW
modeling were accomplished through the collection of tree sap flow measurements across a full
growing season and the construction of preliminary Penman Monteith models for dominate
herbaceous species. In addition, a large number of water isotope samples have been analyzed
providing the necessary isotope data needed to understand both riparian plant species water sources
and the relative amount of water taken from each source. Final steps to finish the study include:
(1) laboratory analysis of plant, soil and water isotope samples, (2) additional year of GW samples
at Focus Areas, (3) additional root depth sampling, and (4) GW/SW analysis and modeling.
7.6.1. Modifications to Study Plan
During the April 2014 RIFS TWG Meeting it was discussed that further evapotranspiration (ET)
measurements were not necessarily warranted given that the Susitna Valley region is not a
precipitation limited region. Therefore a second year of sap-flow and stomatal conductance
measurements will not be conducted. ET modeling will use the results of 2013 -2014
measurements.
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7.7. Riparian Vegetation Modeling Synthesis and Project Area
Scaling
A TWG meeting was held April 29-30, 2014 in which a synthesis of the various elements of the
riparian floodplain vegetation conceptual model were presented representing RIFS (Study 8.6),
Riparian Vegetation (Study 11.6), GW (Study 7.5), Ice Processes (Study 7.6), and Fluvial
Geomorphology Modeling (Study 6.6) studies. Conceptual design and formulation of dynamic
spatially-explicit floodplain vegetation models and projects effects metrics for simulating
floodplain vegetation response to Project operation modification of the natural flow, sediment and
ice processes regimes were presented. No additional work has been completed on this study task
since that reported in the June 2014 ISR.
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 17 November 2015
8. LITERATURE CITED
Alaska Energy Authority (AEA). 2012. Revised Study Plan. Susitna-Watana Hydroelectric
Project, FERC Project No. 14241 Submittal: December 14, 2012. http://www.susitna-
watanahydro.org/study-plan.
Alaska Energy Authority (AEA). 2014. Initial Study Report. Susitna-Watana Hydroelectric
Project, FERC Project No. 14241 Submittal: June 3, 2014. http://www.susitna-
watanahydro.org/type/documents/
Allen, R.G., Pereira, L.S., Raes, D., Smith M.D. 1998. Crop Evapotranspiration – Guidelines for
Computing Crop Requirements - Irrigation and Drainage. Paper no. 56. In: FAO ed. FAO,
Rome, Italy.
R2 Resource Consultants (R2). 2013a. Selection of Focus Areas and Study Sites in the Middle
and Lower Susitna River for Instream Flow and Joint Resource Studies – 2013 and 2014.
Susitna-Watana Hydroelectric Project, FERC No. P-14241 Submittal: March 1, 2013,
Attachment C, Joint Resource Study Technical Memorandum. Prepared for Alaska Energy
Authority, Anchorage, Alaska. http://www.susitna-watanahydro.org/wp-
content/uploads/2013/09/TechMemoSelectionOfFocusAreas.pdf.
R2 Resource Consultants (R2). 2013b. Adjustments to Middle River Focus Areas. Susitna-
Watana Hydroelectric Project, FERC No. P-14241 Submittal: May 31, 2013, Study 8.5
Technical Memorandum. Prepared for Alaska Energy Authority, Anchorage, Alaska.
http://www.susitna-watanahydro.org/wp-content/uploads/2013/09/8.5B.pdf.
R2 Resource Consultants (R2) and Tetra Tech. 2014. Dam Effects on Downstream Channel and
Floodplain Geomorphology and Riparian Plant Communities and Ecosystems−Literature
Review. Susitna-Watana Hydroelectric Project, FERC No. P-14241 Submittal: November
14, 2014, Attachment H, Study 6.6 and Study 8.6 Technical Memorandum. Prepared for
Alaska Energy Authority, Anchorage, Alaska. http://www.susitna-watanahydro.org/wp-
content/uploads/2014/11/08.6_RIFS_R2_TM_IFSRiparianGeomorphLitReview.pdf.
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 18 November 2015
9. TABLES
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 19 November 2015
Table 5-1. Summary of the QC3 data files used in support of this SIR and its appendices that have been delivered to GINA and are publically available
(http://gis.suhydro.org/SIR/08-Instream_Flow/8.6-Riparian_Instream_Flow/).
Component1 Data File Name Description
2 SIR_8_6_RIFS_ProcessDomains_20151106.shp GIS shapefile of riparian process domains
3 SIR_8_6_RIFS_SeedReleaseDatabase_20151106.xlsx
Excel file with single year of willow and poplar seed release
observation data
3 SIR_8_6_RIFS_SeedlingEstablishmentStudyDatabase_20151106.xlsx
Excel file with willow, alder, poplar seedling establishment data for
2013-2015 field seasons
4 SIR_8_6_RIFS_IceScarDatabase_20151106.xlsx Excel file with ice scar observation data from 2013-2015
6 SIR_8_6_RIFS_VegetationGWSW_20151106.xlxs Riparian GW/SW study sap flow data
6 SIR_8_6_RIFS_ PorometerandLAIDatabase_20151106.xlsx Riparian GW/SW study porometer and LAI field data
6 SIR_8_6_RIFS_GWSW_WaterIsotopeDatabase_20151106.xlsx Riparian GW/SW study water isotope sample data
3, 5, 6 SIR_8_6_RIFS_StudyLocations_20151106.xlsx Riparian study site locations as point features
3, 5, 6 SIR_8_6_RIFS_StudyTransects_20151106.shp GIS shapefile of riparian study transect locations
Notes:
Component 1: Literature Review of Dam Effects on Downstream Vegetation (RSP Section 8.6.4.1)
Component 2: Focus Area Selection−Riparian Process Domain Delineation (RSP Section 8.6.4.2)
Component 3: Seed Dispersal and Seedling Establishment (RSP Section 8.6.4.3)
Component 4: River Ice Effects on Floodplain Vegetation (RSP Section 8.6.4.4)
Component 5: Floodplain Stratigraphy and Floodplain Development (RSP Section 8.6.4.5)
Component 6: Riparian GW/SW Hydroregime (RSP Section 8.6.4.6)
Componen 7: Riparian Vegetation Modeling Synthesis and Project Area Scaling (RSP Section 8.5.4.7)
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
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FERC Project No. 14241 Page 20 November 2015
Table 5-2. Total Year 0+ Poplar, Willow, Undifferentiated Poplar/Willow and Alder Seedlings Counted from 2013-2015.
Sum Poplar
Year 0+
Sum Willow
Year 0+
Sum of Poplar/Willow
Seedling Year 0+
Sum of Alder
Year 0+ Totals
August 2013 41553 7643 0 0 49196
September 2013 11498 4882 0 3 16383
July 2014 383 23 13398 78 13882
September 2014 5586 411 51 10 6058
July 2015 6715 1731 32 947 9425
September 2015 1604 1400 11 1133 4148
Table 5-3. Total Year 1+ Poplar, Willow, and Alder Seedlings Counted from 2013-2015.
Sum Poplar
Year 1+
Sum Willow
Year 1+
Sum of Alder
Year 1+ Totals
August 2013 Did not sample Did not sample Did not sample Did not sample
September 2013 Did not sample Did not sample Did not sample Did not sample
July 2014 493 1329 25 1847
September 2014 235 1083 5 1323
July 2015 989 2476 140 3605
September 2015 410 961 43 1414
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
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FERC Project No. 14241 Page 21 November 2015
Table 5-4. Percent Substrate Cover along Transects.
Distance
along
Transect
(cm)
FA-104 STR3 FA-128 STR2 FA-138 STR3
Average Sand/Silt
Cover
Average
Gravel/Cobble Cover
Average Sand/Silt
Cover
Average Gravel/Cobble
Cover
Average Sand/Silt
Cover
Average Gravel/Cobble
Cover
Percent
Cover % StdDev
Percent
Cover % StdDev
Percent
Cover % StdDev
Percent
Cover % StdDev
Percent
Cover % StdDev
Percent
Cover % StdDev
50 24.7 28.2 75.3 28.2 36.7 49.3 63.3 49.3 35.0 28.3 70.8 29.1
150 25.0 22.6 75.0 22.6 58.3 44.0 50.0 43.6 25.2 12.9 79.0 15.4
250 16.2 9.3 83.8 9.3 66.7 48.0 40.0 50.5 17.6 8.3 85.3 10.3
350 51.7 13.7 48.3 13.7 61.7 45.4 46.0 46.2 45.8 25.0 54.2 25.0
450 19.2 10.7 80.8 10.7 61.7 42.2 46.0 42.2 92.5 9.9 7.5 9.9
550 37.5 28.9 62.5 28.9 68.3 45.8 38.0 48.2 70.8 35.3 29.2 35.3
650 66.7 32.5 33.3 32.5 78.3 29.9 26.0 31.3 73.3 34.4 26.7 34.4
750 95.8 10.2 4.2 10.2 88.3 16.0 14.0 16.7 77.5 12.5 22.5 12.5
850 100.0 0.0 0.0 0.0 80.0 25.3 24.0 26.1 97.2 4.0 3.4 4.2
950 93.3 16.3 3.3 8.2 97.5 4.2 3.0 4.5 85.8 14.3 14.2 14.3
1050 53.3 34.3 46.7 34.3 86.7 20.7 16.0 21.9 100.0 0.0 0.0 0.0
1150 93.0 12.9 5.0 12.2 92.5 16.0 9.0 17.5 99.7 0.8 0.4 0.9
1250 99.2 2.0 0.0 0.0 100.0 0.0 0.0 0.0 99.7 0.8 0.4 0.9
1350 100.0 0.0 0.0 0.0 100.0 0.0 0.0 0.0 99.5 1.2 0.6 1.3
1450 100.0 0.0 0.0 0.0 91.7 20.4 10.0 22.4 100.0 0.0 0.0 0.0
1550 100.0 0.0 0.0 0.0 68.3 45.8 38.0 48.2 100.0 0.0 0.0 0.0
1650 44.0 43.8 56.0 43.8 100.0 0.0 0.0 0.0
1750 67.5 19.9 32.5 19.9 100.0 0.0 0.0 0.0
1850 80.0 25.3 0.0 0.0 100.0 0.0 0.0 0.0
1950 55.0 34.5 45.0 34.5 100.0 0.0 0.0 0.0
2050 100.0 0.0 0.0 0.0 100.0 0.0 0.0 0.0
2150 100.0 0.0 0.0 0.0 100.0 0.0 0.0 0.0
2250 100.0 0.0 0.0 0.0 99.2 2.0 0.0 0.0
2350 100.0 0.0 0.0 0.0
2450 100.0 0.0 0.0 0.0
2550 100.0 0.0 0.0 0.0
2650 100.0 0.0 0.0 0.0
2750 97.5 6.1 2.5 6.1
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
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FERC Project No. 14241 Page 22 November 2015
Table 5-5. Percent Vegetation Cover along Transects.
Location
along
Transect (cm)
FA-104 STR3 FA-128 STR2 FA-138 STR3
Herbaceous Plant
Cover Woody Plant Cover Herbaceous Plant
Cover Woody Plant Cover Herbaceous Plant
Cover Woody Plant Cover
Percent
Cover % StdDev
Percent
Cover % StdDev
Percent
Cover % StdDev
Percent
Cover % StdDev
Percent
Cover % StdDev
Percent
Cover % StdDev
50 0.2 0.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
150 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
250 0.0 0.0 0.0 0.0 0.4 0.9 0.0 0.0 0.0 0.0 0.0 0.0
350 3.8 2.6 0.0 0.0 0.4 0.9 0.0 0.0 4.3 1.2 0.0 0.0
450 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 28.8 25.0 7.5 11.7
550 0.2 0.3 0.0 0.0 0.0 0.0 0.0 0.0 20.7 19.9 0.0 0.0
650 3.2 2.6 0.0 0.0 0.0 0.0 0.0 0.0 6.8 4.8 0.0 0.0
750 0.2 0.4 17.5 14.4 0.0 0.0 0.0 0.0 20.7 12.1 0.0 0.0
850 3.8 5.8 3.3 5.2 0.0 0.0 0.0 0.0 21.5 20.2 0.0 0.0
950 8.7 4.5 16.8 14.5 0.0 0.0 0.0 0.0 17.7 7.4 0.0 0.0
1050 9.8 4.7 0.0 0.0 0.0 0.0 0.0 0.0 18.5 11.5 0.7 1.2
1150 6.6 5.3 60.0 47.0 0.0 0.0 0.0 0.0 32.2 25.2 2.7 4.1
1250 13.0 4.0 5.8 12.0 2.0 4.5 0.0 0.0 20.7 10.4 0.0 0.0
1350 4.3 3.7 29.2 30.7 1.4 2.2 0.0 0.0 15.2 6.0 23.3 27.5
1450 2.5 2.7 88.3 13.7 9.0 6.5 0.0 0.0 16.4 8.5 15.0 36.7
1550 0.8 2.0 105.8 12.8 21.4 20.5 19.0 20.7 16.8 9.4 26.7 41.8
1650 3.1 4.4 74.2 37.5 20.9 16.2 35.0 41.7
1750 2.8 2.6 39.2 47.6 18.3 9.8 15.5 24.8
1850 10.9 8.2 26.7 38.8 16.8 10.2 51.7 37.6
1950 0.3 0.4 12.2 21.5 8.7 5.7 11.3 11.8
2050 4.6 4.6 53.3 37.8 32.0 19.5 13.3 32.7
2150 15.1 11.7 65.0 38.3 17.7 12.5 15.8 22.9
2250 11.0 8.2 83.3 16.3 17.8 10.6 36.7 25.0
2350 10.2 7.6 60.0 33.5
2450 8.0 4.8 87.5 17.8
2550 11.0 6.9 78.3 24.0
2650 9.4 4.7 84.7 16.4
2750 1.5 2.1 84.2 22.9
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
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FERC Project No. 14241 Page 23 November 2015
Table 5-6. Tree age data for field samples collected in 2012 and 2013. Note that this data has not been corrected for age to
height of core above tree root collar.
Tree Species
Tree
Diameter
at Breast
Height
(DBH)
(cm) Latitude Longitude
Height
of core
above
collar
(cm)
Year of
establishment
2013
Age
(years)
Values not corrected for
height of core above collar
Alnus incana ssp. tenuifolia 13.1 62.37592382 -150.1736146 32 1988 25
Alnus incana ssp. tenuifolia 12.8 62.3785855 -150.170866 20 1991 22
Alnus incana ssp. tenuifolia 8.8 62.3785855 -150.170866 45 1997 16
Alnus incana ssp. tenuifolia 12.3 62.51826681 -150.1285175 44 1963 50
Alnus incana ssp. tenuifolia 15.2 62.51826681 -150.1285175 20 1957 56
Alnus incana ssp. tenuifolia 11 62.49722312 -150.1034488 34 1959 54
Alnus incana ssp. tenuifolia 16.1 62.527667 -150.114712 41 1973 40
Alnus incana ssp. tenuifolia 17.2 62.527667 -150.114712 45 1976 37
Alnus incana ssp. tenuifolia 6.3 62.385278 -150.164847 20 1990 23
Alnus incana ssp. tenuifolia 11.3 62.385278 -150.164847 120 1991 22
Alnus incana ssp. tenuifolia 7 62.25121577 -150.1473657 24 1996 17
Alnus incana ssp. tenuifolia 11.6 62.47195059 -150.1175162 27 1983 30
Alnus incana ssp. tenuifolia 10.8 62.47195059 -150.1175162 111 1984 29
Alnus incana ssp. tenuifolia N/A 62.325479 -150.140126 N/A 2001 12
Betula papyrifera 51 62.37652 -150.16694 34 1899 114
Betula papyrifera 30.8 62.37342124 -150.1651724 23 1910 103
Betula papyrifera 40.7 62.78558104 -149.6584431 19 1951 62
Betula papyrifera 15.4 62.78558104 -149.6584431 18 1960 53
Betula papyrifera 19 62.37592382 -150.1736146 16 1978 35
Betula papyrifera 24.5 62.37592382 -150.1736146 29 1894 119
Betula papyrifera 32.5 62.37740189 -150.1745112 22 1912 101
Betula papyrifera 25.9 62.37740189 -150.1745112 36 1923 90
Betula papyrifera 15.5 62.38078809 -150.1741396 67 1938 75
Betula papyrifera 22.9 62.38078809 -150.1741396 37 1903 110
Betula papyrifera 35.6 62.38032877 -150.1661723 51 1921 92
Betula papyrifera 34.6 62.38032877 -150.1661723 52 1941 72
Betula papyrifera 34.1 62.38226775 -150.1643814 40 1917 96
Betula papyrifera 39 62.38226775 -150.1643814 45 1932 81
Betula papyrifera 33.3 62.38377624 -150.1536686 47 1870 143
Betula papyrifera 14.5 62.51826681 -150.1285175 22 1977 36
Betula papyrifera 17.7 62.51826681 -150.1285175 27 1977 36
Betula papyrifera 9.5 62.51860083 -150.126904 12 1980 33
Betula papyrifera 34.2 62.3849093 -150.1491894 24 1955 58
Betula papyrifera 51 62.3849093 -150.1491894 21 1921 92
Betula papyrifera 37 62.3855192 -150.1489759 75 1956 57
Betula papyrifera 30.3 62.3855192 -150.1489759 38 1957 56
Betula papyrifera 25 62.3878462 -150.150655 24 1953 60
Betula papyrifera 18.6 62.3878462 -150.150655 23 1955 58
Betula papyrifera 48.3 62.530895 -150.114009 57 1918 95
Betula papyrifera 31 62.5248715 -150.1228237 47 1899 114
Betula papyrifera 27 62.5248715 -150.1228237 21 1888 125
Betula papyrifera 48.7 62.5246056 -150.124250 45 1892 121
Betula papyrifera 38.7 62.531976 -150.113418 40 1923 90
Betula papyrifera 44.5 62.531976 -150.113418 38 1876 137
Betula papyrifera 54 62.526997 -150.115877 45 1877 136
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
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FERC Project No. 14241 Page 24 November 2015
Tree Species
Tree
Diameter
at Breast
Height
(DBH)
(cm) Latitude Longitude
Height
of core
above
collar
(cm)
Year of
establishment
2013
Age
(years)
Values not corrected for
height of core above collar
Betula papyrifera 44 62.526997 -150.115877 45 1912 101
Betula papyrifera 27.3 62.522653 -150.117096 39 1968 45
Betula papyrifera 21.6 62.522653 -150.117096 20 1961 52
Betula papyrifera 20.1 62.520321 -150.130267 26 1876 137
Betula papyrifera 22.3 62.520321 -150.130267 50 1880 133
Betula papyrifera 24.5 62.521097 -150.129336 26 1912 101
Betula papyrifera 21.9 62.521097 -150.129336 28 1943 70
Betula papyrifera 37.4 62.522758 -150.126772 37 1888 125
Betula papyrifera 41.2 62.522758 -150.126772 41 1884 129
Betula papyrifera 38.6 62.388893 -150.163350 45 1886 127
Betula papyrifera 34.2 62.388893 -150.163350 48 1892 121
Betula papyrifera 27.4 62.390361 -150.157489 24 1911 102
Betula papyrifera 30.7 62.390361 -150.157489 23 1871 142
Betula papyrifera 46.5 62.387701 -150.148731 50 1933 80
Betula papyrifera 39.5 62.387701 -150.148731 50 1932 81
Betula papyrifera 47 62.51899324 -150.1252551 22 1930 83
Betula papyrifera 42.2 62.69704 -149.835744 22 1966 47
Betula papyrifera 24 62.468811 -150.121384 1905 108
Pinus glauca 32 62.51826681 -150.1285175 40 1809 204
Pinus glauca 42 62.3849093 -150.1491894 19 1826 187
Pinus glauca 42.5 62.376507 -150.169146 40 1837 176
Pinus glauca 27.8 62.38078809 -150.1741396 21 1841 172
Pinus glauca 33.1 62.514191 -150.114209 27.5 1846 167
Pinus glauca 33.7 62.520321 -150.130267 36 1848 165
Pinus glauca 28.1 62.387701 -150.148731 39 1852 161
Pinus glauca 51.2 62.38124122 -150.1568733 33 1858 155
Pinus glauca 54.9 62.376507 -150.169146 50 1858 155
Pinus glauca 36 62.387701 -150.148731 48 1862 151
Pinus glauca 38.4 62.38226775 -150.1643814 29 1865 148
Pinus glauca 46.5 62.530895 -150.114009 51 1865 148
Pinus glauca 16.4 62.513867 -150.115286 31 1865 148
Pinus glauca 18 62.521097 -150.129336 26 1866 147
Pinus glauca 49.6 62.667012 -149.906416 33 1869 144
Pinus glauca 20.5 62.521097 -150.129336 27 1870 143
Pinus glauca 31.3 62.38377624 -150.1536686 23 1874 139
Pinus glauca 17.5 62.518987 -150.116599 27 1874 139
Pinus glauca 30 62.388893 -150.16335 28 1876 137
Pinus glauca 34.8 62.388893 -150.16335 40 1878 135
Pinus glauca 31.1 62.468811 -150.121384 1878 135
Pinus glauca 38 62.5080139 -150.1088219 43 1879 134
Pinus glauca 54 62.38124122 -150.1568733 23 1884 129
Pinus glauca 40 62.028985 -150.133263 33 1884 129
Pinus glauca 31.1 62.520321 -150.130267 25 1885 128
Pinus glauca 24.8 62.508235 -150.109330 25 1885 128
Pinus glauca 26.7 62.518987 -150.116599 22 1889 124
Pinus glauca 15 62.51507128 -150.1140557 16 1890 123
Pinus glauca 28.3 62.522758 -150.126772 22 1892 121
Pinus glauca 22.5 62.513253 -150.114524 32 1898 115
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
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FERC Project No. 14241 Page 25 November 2015
Tree Species
Tree
Diameter
at Breast
Height
(DBH)
(cm) Latitude Longitude
Height
of core
above
collar
(cm)
Year of
establishment
2013
Age
(years)
Values not corrected for
height of core above collar
Pinus glauca 35.2 62.5080139 -150.1088219 36 1903 110
Pinus glauca 32.7 62.38226775 -150.1643814 28 1905 108
Pinus glauca 16.9 62.522758 -150.126772 22 1905 108
Pinus glauca 27.9 62.38070855 -150.1590193 15 1906 107
Pinus glauca 30.6 62.509115 -150.109170 37 1906 107
Pinus glauca 16.3 62.38377624 -150.1536686 48 1907 106
Pinus glauca 26.5 62.38112412 -150.1616836 42 1908 105
Pinus glauca 48.2 62.33495132 -150.1397751 29 1912 101
Pinus glauca 26.9 62.390361 -150.157489 32 1912 101
Pinus glauca 35.9 62.5246056 -150.1242497 34 1913 100
Pinus glauca 18 62.37740189 -150.1745112 27 1915 98
Pinus glauca 35.2 62.38132244 -150.1581059 32 1915 98
Pinus glauca 26.5 62.507907 -150.108986 30 1923 90
Pinus glauca 42 62.51899324 -150.1252551 3 1929 84
Pinus glauca 21.8 62.38078809 -150.1741396 23 1939 74
Pinus glauca 31.9 62.3878462 -150.150655 22 1939 74
Pinus glauca 11.3 62.471290 -150.109410 29 1939 74
Pinus glauca 39.4 62.531976 -150.113418 45 1940 73
Pinus glauca 14.7 62.47132732 -150.1094839 32 1942 71
Pinus glauca 37.3 62.3849093 -150.1491894 35 1942 71
Pinus glauca 28 62.59631775 -150.0316515 27 1944 69
Pinus glauca 22.2 62.51507128 -150.1140557 22 1945 68
Pinus glauca 23 62.37341847 -150.165286 20 1946 67
Pinus glauca 25.6 62.5248715 -150.1228237 16 1949 64
Pinus glauca 25.6 62.59631775 -150.0316515 28 1950 63
Pinus glauca 36 62.51860527 -150.1209339 27 1950 63
Pinus glauca 41.4 61.77902572 -150.1922578 24 1951 62
Pinus glauca 15.7 62.47132732 -150.1094839 34 1952 61
Pinus glauca 24.1 62.470725 -150.109568 21 1952 61
Pinus glauca 29.5 62.37652 -150.16694 28 1955 58
Pinus glauca 14 62.49838393 -150.103414 30 1955 58
Pinus glauca 21.2 62.470542 -150.109408 24 1955 58
Pinus glauca 14.2 62.49722312 -150.1034488 23 1956 57
Pinus glauca 48 62.59631775 -150.0316515 36 1958 55
Pinus glauca 20.1 62.471589 -150.109154 26 1958 55
Pinus glauca 11.4 62.49722312 -150.1034488 22 1959 54
Pinus glauca 20 62.37420226 -150.1637481 12 1960 53
Pinus glauca 27.5 62.37592382 -150.1736146 29 1960 53
Pinus glauca 19.9 62.470928 -150.109483 23 1962 51
Pinus glauca 7.2 62.470878 -150.109531 26 1962 51
Pinus glauca 8.6 62.49838393 -150.103414 30 1963 50
Pinus glauca 11.8 62.37625969 -150.162004 12 1964 49
Pinus glauca 25.3 62.5246056 -150.1242497 23 1965 48
Pinus glauca 21.5 62.662034 -149.927085 25 1965 48
Pinus glauca 19.9 62.3855192 -150.1489759 19 1966 47
Pinus glauca 10.9 62.7203859 -149.7799213 18 1968 45
Pinus glauca 54.4 61.77902572 -150.1922578 49 1969 44
Pinus glauca 17 62.662034 -149.927085 33 1972 41
2014-2015 STUDY IMPLEMENTATION REPORT RIPARIAN INSTREAM FLOW STUDY (8.6)
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FERC Project No. 14241 Page 26 November 2015
Tree Species
Tree
Diameter
at Breast
Height
(DBH)
(cm) Latitude Longitude
Height
of core
above
collar
(cm)
Year of
establishment
2013
Age
(years)
Values not corrected for
height of core above collar
Pinus glauca 11.8
on ice jam island near PRM 134 -
exact lat/long not known 25 1973 40
Pinus glauca 21 62.37341847 -150.165286 15 1975 38
Pinus glauca 8 62.508864 -150.109662 26 1978 35
Pinus glauca 13.1 62.509709 -150.116485 23 1980 33
Pinus glauca 10.3 61.62133462 -150.3692625 26 1981 32
Pinus glauca 4.5 62.659675 -149.939883 38 1987 26
Pinus glauca 12.2 61.62133462 -150.3692625 22 1990 23
Pinus glauca 5.1 62.25104585 -150.1438387 27 1993 20
Pinus glauca 6 62.659990 -149.939938 27 1993 20
Pinus glauca 10.3 61.62166252 -150.3682398 26 1995 18
Pinus glauca 30.6 62.667012 -149.906416 38 tree older than 1825 N/A
Pinus glauca 41.5 62.51826681 -150.1285175 46 tree older than 1855 N/A
Pinus glauca 18.6 62.37740189 -150.1745112 24 tree older than 1860 N/A
Pinus glauca 33.9 62.509709 -150.116485 42 tree older than 1864 N/A
Pinus glauca 46.4 62.37342124 -150.1651724 20 tree older than 1870 N/A
Pinus glauca 30.3 62.664702 -149.910262 34 tree older than 1880 N/A
Pinus glauca 40.4 62.37592382 -150.1736146 29 tree older than 1890 N/A
Pinus glauca 27.9 62.3855192 -150.1489759 22 tree older than 1890 N/A
Pinus glauca 43.7 62.5248715 -150.1228237 42 tree older than 1894 N/A
Pinus glauca 57.1 62.3878462 -150.150655 55 tree older than 1895 N/A
Pinus glauca 34.9 62.38070855 -150.1590193 72 tree older than 1915 N/A
Pinus glauca 30.6 62.390361 -150.157489 7 tree older than 1915 N/A
Pinus glauca 27.6 62.38112412 -150.1616836 19 tree older than 1920 N/A
Pinus glauca 31.1 62.531976 -150.113418 35 tree older than 1920 N/A
Pinus glauca 51 62.767403 -148.832306 42 tree older than 1925 N/A
Pinus glauca 27.1 62.508475 -150.109498 31 tree older than 1925 N/A
Pinus glauca 28.9 62.38132244 -150.1581059 28 tree older than 1935 N/A
Pinus glauca 34.6 62.33495132 -150.1397751 18 tree older than 1940 N/A
Pinus glauca 9 62.509686 -150.109773 35 tree older than 1975 N/A
Populus balsamifera 39.9 62.49838393 -150.103414 44 1924 89
Populus balsamifera 4.9 62.49804354 -150.1054514 27 2005 8
Populus balsamifera 11 62.25121577 -150.1473657 31 1996 17
Populus balsamifera 11 62.25121577 -150.1473657 29 1993 20
Populus balsamifera 11 62.25332578 -150.1618839 33 1988 25
Populus balsamifera 11.5 62.325479 -150.140126 28 1987 26
Populus balsamifera 12 62.323834 -150.135411 31 1984 29
Populus balsamifera 16.5 62.25332578 -150.1618839
22 or
24 1990 23
Populus balsamifera 18.5 62.699886 -149.847921 26 1992 21
Populus balsamifera 20 62.509261 -150.116294 22 1993 20
Populus balsamifera 20.1 61.94982257 -150.1143957 39 1966 47
Populus balsamifera 20.2 62.6593104 -149.9403894 28 1978 35
Populus balsamifera 22 62.38132244 -150.1581059 42 1847 166
Populus balsamifera 23.3 62.509261 -150.116294 48 1991 22
Populus balsamifera 23.5 62.02789 -150.13635 32 1983 30
Populus balsamifera 23.9 61.94982257 -150.1143957 31 1971 42
Populus balsamifera 27.1 62.37341847 -150.165286 42 1929 84
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Tree Species
Tree
Diameter
at Breast
Height
(DBH)
(cm) Latitude Longitude
Height
of core
above
collar
(cm)
Year of
establishment
2013
Age
(years)
Values not corrected for
height of core above collar
Populus balsamifera 27.2 62.3734185 -150.165286 18 1987 26
Populus balsamifera 27.7 62.38070855 -150.1590193 98 1825 188
Populus balsamifera 27.8 62.324453 -150.136971 28 1979 34
Populus balsamifera 28 62.3734185 -150.165286 17.5 1990 23
Populus balsamifera 28.2 62.49722312 -150.1034488 28 1954 59
Populus balsamifera 31.5 62.6593104 -149.9403894 23 1979 34
Populus balsamifera 32 62.49722312 -150.1034488 25 1954 59
Populus balsamifera 33.1 62.49838393 -150.103414 55 1954 59
Populus balsamifera 36 62.37734682 -150.1612654 50 1957 56
Populus balsamifera 37.5 62.38132244 -150.1581059 35 1847 166
Populus balsamifera 37.8 62.25104585 -150.1438387 27 1974 39
Populus balsamifera 37.8 62.78558104 -149.6584431 22.5 1957 56
Populus balsamifera 39.2 62.47132732 -150.1094839 27 1922 91
Populus balsamifera 39.7 62.78558104 -149.6584431 9 1955 58
Populus balsamifera 41.5 62.38112412 -150.1616836 63 1883 130
Populus balsamifera 43.7 62.47132732 -150.1094839 42 1924 89
Populus balsamifera 43.8 62.5086294 -150.1097566 55 1906 107
Populus balsamifera 44 61.62133462 -150.3692625 72 1970 43
Populus balsamifera 45.2 62.7203859 -149.7799213 31 1946 67
Populus balsamifera 45.8 62.37341847 -150.165286 64.5 1923 90
Populus balsamifera 46.6 62.37341847 -150.165286 48 1912 101
Populus balsamifera 47.8 62.38124122 -150.1568733 29 1855 158
Populus balsamifera 48.4 62.7203859 -149.7799213 44 1948 65
Populus balsamifera 48.5 62.5086294 -150.1097566 37 1908 105
Populus balsamifera 48.5 62.38112412 -150.1616836 43 1874 139
Populus balsamifera 48.8 62.5080139 -150.1088219 46 1866 147
Populus balsamifera 49 62.662034 -149.927085 35 1965 48
Populus balsamifera 52.5 62.38124122 -150.1568733 22 1860 153
Populus balsamifera 53.6 61.62133462 -150.3692625 35 1947 66
Populus balsamifera 55 62.37625969 -150.162004 28 1920 93
Populus balsamifera 57.3 61.62166252 -150.3682398 54 1971 42
Populus balsamifera 57.5 62.5080139 -150.1088219 NA 1864 149
Populus balsamifera 58 62.59631775 -150.0316515 47 1915 98
Populus balsamifera 58.4 62.662034 -149.927085 51 1951 62
Populus balsamifera 60.5 62.522653 -150.117096 38 1907 106
Populus balsamifera 63.2 62.523692 -150.11616 47 1939 74
Populus balsamifera 67.5 61.62133462 -150.3692625 60 1971 42
Populus balsamifera 69.3 61.77902572 -150.1922578 125 1857 156
Populus balsamifera N/A 62.699886 -149.847921 25 1991 22
Populus balsamifera N/A 62.358338 -150.146652 N/A 1991 22
Populus balsamifera N/A 62.604274 -150.026936 N/A 1977 36
Populus balsamifera N/A 62.35726 -150.147113 N/A 1972 41
Populus balsamifera N/A 62.604274 -150.026936 N/A 1926 87
Populus balsamifera 56.5 62.59631775 -150.0316515 38 tree older than 1953 N/A
Populus balsamifera 67.8 62.523692 -150.11616 65 tree older than 1936 N/A
Populus balsamifera 86.6 62.667012 -149.906416 34 tree older than 1901 N/A
Populus balsamifera 75.5 62.667012 -149.906416 34 tree older than 1835 N/A
Populus balsamifera 62.357899 -150.14821 tree older than 1990 N/A
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Tree Species
Tree
Diameter
at Breast
Height
(DBH)
(cm) Latitude Longitude
Height
of core
above
collar
(cm)
Year of
establishment
2013
Age
(years)
Values not corrected for
height of core above collar
Salix alba 10.5 62.25121577 -150.1473657 46 1994 19
Salix alba 10.3 62.25121577 -150.1473657 10 1993 20
Salix alba
Cored
Shrub 62.70048545 -149.8467152 15 1991 22
Salix alba unknown 62.671843 -149.894408 NA 1974 39
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10. FIGURES
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Figure 3-1. Map depicting the Upper, Middle and Lower Segments of the Susitna River potentially influenced by the Susitna-Watana Hydroelectric Project.
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Figure 5-1. Total Number of Year 0+ Seedlings by transect from July 2014 to September 2015.
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Figure 5-2. Total Number of Year 1+ Seedlings by transect from July 2014 to September 2015.
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Figure 5-3. Total Number of Year 0+ Seedlings at each plot in transect FA-104 STR 3.
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Figure 5-4. Total Number of Year 1+ Seedlings at each plot in transect FA-104 STR 3.
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Figure 5-5. Total Number of Year 0+ Seedlings at each plot in transect FA-128 STR 2.
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Figure 5-6. Total Number of Year 1+ Seedlings at each plot in transect FA-128 STR 2.
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Figure 5-7. Total Number of Year 0+ Seedlings at each plot in transect FA-138 STR 3.
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Figure 5-8. Total Number of Year 1+ Seedlings at each plot in transect FA-138 STR 3.
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Figure 5-9. Photo of transect in 2013 (left) and 2015 (right) of FA-113 STR11.
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Figure 5-10. Elevation comparison of Transect FA-113 STR11.
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Figure 5-11. Photo of transect in 2013 (left) and 2015 (right) of FA-128 STR2.
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Figure 5-12. Elevation comparison of Transect FA-128 STR2.
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Figure 5-13. Photo of transect in 2013 (left) and 2015 (right) of FA-138 STR3.
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Figure 5-14. Elevation comparison of Transect FA-138 STR3.
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Figure 5-15. Ice scar wedge collection locations at FA-104 (Whiskers Slough). The downstream extent of river ice floodplain tree interactions was observed at PRM 102.5,
just upriver of the confluence of the Susitna and Chulitna rivers.
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Figure 5-16. Ice scar wedge sample collection locations at FA-113 (Oxbow 1).
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Figure 5-17. Ice scar wedge sample collection locations at FA-115 (Slough 6A).
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Figure 5-18. Ma Ice scar wedge sample collection locations at FA-128 (Slough 8A).
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Figure 5-19. Tree ice scar and zone of floodplain ice influence, FA-104 (Whiskers Slough).
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Figure 5-20. Tree ice scar and zone of floodplain ice influence, FA-113 (Oxbow 1).
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Figure 5-21. Tree ice scar and zone of floodplain ice influence, FA-115 (Slough 6A).
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Figure 5-22. Tree ice scar and zone of floodplain ice influence, FA-128 (Slough 8A).
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Figure 5-23. Tree ice scar and zone of floodplain ice influence, FA-138 (Gold Creek).
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Figure 5-24. Flow routing cross-section, tree ice survey, FA-104 (Whiskers Slough).
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Figure 5-25. Flow routing cross-section, tree ice survey, FA-104 (Whiskers Slough).
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Figure 5-26. Flow routing cross-section, tree ice survey, and plant communities FA-104 (Whiskers Slough).
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Figure 5-27. Tree core aging sample distribution within the Middle River Segment. Table 5-6 provides preliminary age, location and collection data for all sampled trees.
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Figure 5-28. Preliminary tree age data for FA-104 (Whiskers Slough).
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Figure 5-29. Preliminary tree age data for FA-128 (Slough 8A).
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Figure 5-30. Penman-Monteith July 2013 evapotranspiration results for Matteuccia struthiopteris at FA-104 (Whiskers
Slough).
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Figure 5-31. Isotopic compositions of precipitation, surface water, and groundwater samples collected on the Susitna Middle River Segment in 2013. Global meteoric
water line (GMWL) and local meteoric water line (LMWL) are shown for reference.
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Figure 5-32. Two map layers for FA-113 (Oxbow 1) an FA-115 (Slough 6A) of all mapped riparian areas that are wetted by the 100-year flood, and mapped riparian areas
which remain above the 100-year flood.
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Figure 5-33. Two map layers for FA-128 (Slough 8A) of all mapped riparian areas that are wetted by the 100-year flood,
and mapped riparian areas which remain above the 100-year flood.
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Figure 5-34. Two map layers for FA-138 (Gold Creek) of all mapped riparian areas that are wetted by the 100-year flood,
and mapped riparian areas which remain above the 100-year flood.
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APPENDIX A: RIPARIAN VEGETATION GROUNDWATER / SURFACE
WATER STUDY SAMPLING DESIGN
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Riparian Instream Flow Study
Study Plan Section 8.6
2014-2015 Study Implementation Report
Appendix A
Riparian Vegetation Groundwater / Surface Water
Study Sampling Design
Prepared for
Alaska Energy Authority
Prepared by
R2 Resource Consultants, Inc.
ABR, Inc.
November 2015
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TABLE OF CONTENTS
1. Introduction ........................................................................................................................1
2. Riparian Vegetation GW/SW Study Areas .....................................................................1
3. Methods ...............................................................................................................................2
3.1. Hydrology Observations and Modeling .............................................................2
3.1.1. Groundwater and Surface Water Measurements ............................ 2
3.1.2. Groundwater and Surface Water Modeling .................................... 2
3.2. Riparian Vegetation Sampling Methods ............................................................3
3.2.1. Sample Design ................................................................................ 3
3.3. Groundwater and Surface Water Direct Gradient Analyses ..............................4
4. Literature Cited .................................................................................................................5
5. Tables ..................................................................................................................................6
6. Figures ...............................................................................................................................16
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LIST OF TABLES
Table 1. Middle River wells........................................................................................................... 7
Table 2. Middle River vegetation. ................................................................................................. 9
Table 3. Lower River wells and vegetation. ................................................................................ 13
Table 4. Existing gage stations. ................................................................................................... 14
LIST OF FIGURES
Figure 1. Riparian process domains, Focus Areas and riparian study sites. ................................ 17
Figure 2. Lower River riparian transects locations. ..................................................................... 18
Figure 3. FA-104 (Whiskers Slough) Riparian and aquatic well locations. Inset: Ecotype overlay
of riparian well transect......................................................................................................... 19
Figure 4. FA-115 (Slough 6A) Riparian and aquatic well locations. Inset: Ecotype overlay of
riparian well transect. ............................................................................................................ 20
Figure 5. FA-128 (Slough 8A) Riparian and aquatic well locations. Inset: Ecotype overlay of
riparian well transect. ............................................................................................................ 21
Figure 6. FA-138 (Gold Creek) Riparian and aquatic well locations. Inset: Ecotype overlay of
riparian well transect. ............................................................................................................ 22
Figure 7. FA-115 (Slough 6A) Primary riparian well transect with ecotype overlay, well locations,
and groundwater and surface water. ..................................................................................... 23
Figure 8. FA-128 (Slough 8A) Upper riparian well transect with ecotype overlay, well locations,
and groundwater and surface water. ..................................................................................... 23
Figure 9. FA-115 (Slough 6A) Primary riparian transect with ecotypes and rapid vegetation
transect (RVT) locations. ...................................................................................................... 24
Figure 10. Riparian vegetation transect point-intercept sampling schematic. ............................. 25
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LIST OF ACRONYMS AND SCIENTIFIC LABELS
Abbreviation Definition
AEA Alaska Energy Authority
ELS Ecological Land Survey
FA Focus Area
FERC Federal Energy Regulatory Commission
GW Groundwater Study 7.5
GW/SW Groundwater/Surface Water
ISR Initial Study Report
ITU Integrated Terrain Unit
LiDAR Light Detection and Ranging
PRM Project River Mile
Project Susitna-Watana Hydroelectric Project
RIFS Riparian Instream Flow Study 8.6
RIP Riparian Vegetation Study 11.6
RSP Revised Study Plan
RVT Rapid Vegetation Transect
TM Technical Memorandum
TWG Technical Workgroup
USFWS United States Fish & Wildlife Service
USGS United States Geological Survey
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1. INTRODUCTION
The Alaska Energy Authority (AEA) is preparing a License Application that will be submitted to
the Federal Energy Regulatory Commission (FERC) for the Susitna-Watana Hydroelectric Project
(Project) using the Integrated Licensing Process. The Project is located on the Susitna River, an
approximately 300-mile long river in the South-central Region of Alaska. The Project’s dam site
will be located at Project River Mile (PRM) 187.1. The Project construction and operation would
have an effect on the flows downstream of the dam site, the degree of which will ultimately depend
on final Project design and operations.
Seasonal changes to the Susitna River hydro regime due to Project operations may include lower
discharges during the summer reservoir refill period and higher discharges during the winter
relative to current hydrologic conditions. In addition to these seasonal changes, the Project may
be operated in a load-following mode to meet energy demands on an hourly basis. During load-
following operations, the amount of water released from the reservoir would cycle daily according
to energy demands such that higher volumes would be released during peak-load hours relative to
off-peak hours. Seasonal and daily/hourly changes to Susitna River hydrology would influence
downstream aquatic and riparian resources and processes related to floodplain groundwater depths
and surface water floodplain inundation. To address potential downstream effects of Project
operations AEA has developed, and FERC approved, a riparian groundwater vegetation study plan
(detailed in Groundwater Study [GW] 7.5. Revised Study Plan [RSP] Section 7.5.4.4, Riparian
Instream Flow Study 8.6 [RIFS] RSP Section 8.6.3.6 [AEA 2012], and Riparian Instream Flow,
Groundwater, and Riparian Vegetation Studies FERC Determination Response submitted to the
FERC July 1, 2013[R2 et al. 2013]).
During the October 17, 2014 RIFS and Riparian Vegetation Study 11.6 (RIP) Initial Study Report
(ISR) Meeting, Bob Henszey, U.S. Fish & Wildlife Service (USFWS), and Greg Auble, U.S.
Geological Survey (USGS), requested a detailed accounting of riparian vegetation groundwater
and surface water (GW/SW) sampling design be presented to the Technical Workgroup (TWG)
for review. This Technical Memorandum (TM) has been developed to present details concerning
riparian vegetation GW/SW sampling design broadly described in RSP Section 8.6.3.6
Characterize Natural Floodplain Vegetation Groundwater and Surface Water Maintenance
Hydroregime. The TM details include: 1) riparian vegetation GW/SW sampling design, and 2)
number and locations of riparian vegetation sample plots. The riparian vegetation GW/SW
sampling design builds on the RIFS (RSP Section 8.6) and RIP (RSP Section 11.6) designs, and
the Riparian Instream Flow, Groundwater, and Riparian Vegetation Studies FERC Determination
Response (R2 et al. 2013).
2. RIPARIAN VEGETATION GW/SW STUDY AREAS
As established in RSP Sections 8.6 and 11.6, and the June 2013 FERC Determination Response
(R2 et al. 2013), riparian GW/SW study sites are located at Focus Areas (FA) FA-104 (Whiskers
Slough), FA-115 (Slough 6A), FA-128 (Slough 8A), and FA-138 (Gold Creek) (Figure 1), and
four Lower River transect sites (Figure 2). Additional satellite riparian vegetation plot locations
for under- or non-represented ecotypes will be determined prior to the next study year. New
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floodplain water body surface water gages were deployed in 2013 to be utilized in the lateral
gradient hydrologic domain analysis and may be used in the next study year for satellite riparian
vegetation plot locations.
3. METHODS
The Riparian Vegetation Sampling design covering Project Area and Focus Area vegetation
mapping and plant community characterization has been presented in the Riparian Vegetation
Study (RSP Section 11.6.4). Riparian Vegetation GW/SW study hydrologic measurements and
modeling designs have been presented in RIFS RSP Section 8.6.3.6 and GW RSP Section 7.5.4.4.
Both an overview of riparian vegetation GW/SW sampling methods and additional details
concerning riparian vegetation GW/SW sampling design have been developed since submittal of
the RSP.
3.1. Hydrology Observations and Modeling
3.1.1. Groundwater and Surface Water Measurements
Water surface elevations are measured at both groundwater stations and surface-water stations
within each of the Focus Areas. Groundwater depths are measured at wells located in FA-104
(Whiskers Slough), FA-115 (Slough 6A), FA-128 (Slough 8A), and FA-138 (Gold Creek).
GW/SW measurements are used to develop groundwater statistics used in the riparian vegetation
frequency response curve analyses (Henszey et al. 2004). These data from the various stations,
including those associated with specific transects for analysis of GW/SW interactions, cover the
range of hydrologic conditions from summer through fall freeze-up, winter, and spring snowmelt
and breakup.
In 2014, 42 additional staff gages were installed in various Focus Areas and other locations to
provide data for lateral hydrologic gradient analyses. A subset of these gages may be utilized to
capture additional satellite riparian vegetation sample plots for the riparian vegetation GW/SW
study.
3.1.2. Groundwater and Surface Water Modeling
Groundwater measurements will be used to generate seasonal water-depth statistics for the riparian
vegetation response curve analyses (Henszey et al. 2004; Rains et al. 2004). Response curve
analysis details can be found in RSP Section 8.6.3.6.2 and follow Henszey et al. 2004
methodology. Surface water floodplain inundation frequency maps will be generated for the entire
study area using 1-D HEC-RAS model with RAS-MAPPER software. Two-dimensional modeling
will be utilized to generate flood frequency inundation maps for the Focus Areas as discussed in
the Fluvial Geomorphology Modeling Study RSP Section 6.6.
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3.2. Riparian Vegetation Sampling Methods
3.2.1. Sample Design
Three sampling designs are currently being employed for the riparian vegetation study as described
in Study 11.6 ISR, Part A, Section 3.2.1.1. These include Ecological Land Survey (ELS) plot
sampling at Focus Areas, ELS plot sampling at Non-Focus Area (i.e., Satellite Areas), and
Integrated Terrain Unit (ITU) plot sampling along ITU mapping transects.
A fourth sample design will be employed for the purposes of the riparian vegetation GW/SW
study. Rapid vegetation transects (RVT) will be utilized to sample vegetation frequency along
GW transects for use in developing riparian ecotype and plant species response curves as detailed
in RIFS RSP Section 8.6.3.6.2 (Figures 3-8).
3.2.1.1. Rapid Vegetation Transects
A minimum of 5 RVTs will be placed in each ecotype along each GW well transect in addition to
any intensive sample plots (Figures 3-5). The RVTs will be evenly distributed along elevation
gradients of each ecotype as determined by Light Detection and Ranging (LiDAR) digital elevation
model and Focus Area GW transect location. Figure 9 displays a conceptual example of the
placement of RVTs in ecotypes along the GW transect in FA-115 (Slough 6A). RVTs will be 25
meters in length and oriented perpendicular to the associated GW transect. Along each RVT,
vegetation will be measured at sampling points spaced one meter apart (25 points total) using the
point-intercept method (Figure 10). Point-intercept sampling at each point along RVTs will be
conducted using the same methods used for points along vegetation sampling lines in ELS plots
as described in Study 11.6 ISR, Part A, Section 4.2.5. Each RVT will be considered the sampling
unit. ELS plots at Focus Areas will be used in addition to RVTs to model plant frequency response
curves along GW gradients.
3.2.1.2. Sample Size for Groundwater Wells, Vegetation Plots, and Gaging Stations
Table 1 provides the sample size for GW wells in each ecotype and Focus Area. There are 22
existing aquatic resource wells, 37 existing riparian resource wells, and 5 proposed riparian
resource wells for a total of 64 GW wells located in 13 ecotypes.
Table 2 provides the total number of planned and completed ELS plots and planned RVTs by
ecotype and study location in the Middle Susitna River. The table also displays the spatial extent
(acres) and percent of the total area of each Focus Area for each ecotype. There are 132 planned
ELS plots, 40 completed ELS plots, and 75 planned RVTs for a total of 247 vegetation plots in 17
ecotypes.
Table 3 displays the number of existing riparian GW wells and RVTs in the Lower Susitna River.
There are 10 existing GW wells and 30 planned RVTs.
Table 4 displays the sample size for existing gage stations by ecotype, study area, and purpose.
There are 7 existing gaging stations with the purpose of monitoring GW and 35 existing gaging
stations with the purpose of monitoring SW for a total of 42 gaging stations in 13 ecotypes.
Note that Table 2 does not include completed and planned ITU vegetation mapping plots as they
are not utilized in the riparian vegetation GW/SW study. ITU mapping plots include:
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Completed ITU mapping plots: 322
Planned ITU mapping plots: 210
Total: 532
3.3. Groundwater and Surface Water Direct Gradient Analyses
A direct gradient analysis (Whittaker 1967) will be used to characterize the relationship between
GW/SW gradients and plant community composition throughout the study area as described in
RSP Section 8.6. Non-linear models will be used to fit plant species response curves to water-
level gradients ranging from shallow GW to standing water as described in Henszey et al. (2004).
Groundwater summary statistics (e.g., 7 or 10 day high water average depth) and riparian plant
frequency measurements will be used in the analysis. One-dimensional and 2-D hydraulic models
will generate floodplain inundation curves to be utilized in a direct gradient analysis of current
distribution of floodplain vegetation relative to frequency and duration of inundation using the
gaging period of record data. Surface water direct gradient methods will follow those used by
Auble et al. (1994), Franz and Bazzaz (1977); and Rains et al. (2004).
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4. LITERATURE CITED
Auble, G.T., J.M. Friedman and M.L. Scott. 1994. Relating riparian vegetation to present and
future stream flows. Ecological Application 4:544-554.
Alaska Energy Authority (AEA). 2012. Revised Study Plan. Susitna-Watana Hydroelectric
Project, FERC Project No. 14241 Submittal: December 14, 2012. http://www.susitna-
watanahydro.org/study-plan.
Franz, E.H. and F.A. Bazzaz. 1977. Simulation of vegetation response to modified hydrologic
regimes: a probabilistic model based on niche differentiation in a floodplain forest.
Ecology 58:176-183.
Henszey, R.J., K. Pfeiffer, and J.R. Keough. 2004. Linking surface and ground-water levels to
riparian grassland species along the Platte River in Central Nebraska, USA. Wetlands 24:
665-687.
Rains, M.C., J.F. Mount, and E.W. Larsen. 2004. Simulated changes in shallow groundwater and
vegetation distributions under different reservoir operations scenarios. Ecological
Applications 14:192-207.
R2 Resource Consultants (R2), Geo-Scientific Watersheds (GWS), and ABR. 2013. Riparian
Instream Flow, Groundwater, and Riparian Vegetation Studies FERC Determination
Response. Susitna-Watana Hydroelectric Project, FERC No. 14241 Submittal: July 1,
2013, Studies 8.5, 7.5, and 11.6 Technical Memorandum. Prepared for the Alaska Energy
Authority, Anchorage, Alaska. http://www.susitna-watanahydro.org/wp-
content/uploads/2014/04/AEA-July-1-2013-Filing-of-Rip-IFS-Groundwater-and-Rip-
Veg-TM.pdf.
Whittaker, R.H. 1967. Gradient analysis of vegetation. Biological Reviews of the Cambridge
Philosophical Society 49:207-264.
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5. TABLES
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Table 1. Middle River wells.
Ecotype Focus Area
Existing
Aquatic Wells
Existing
Riparian Wells
Planned
Riparian Wells Grand Total
Lowland Organic-rich Bluejoint-Herb Meadow FA-115 1 1
Lowland Organic-rich Bluejoint-Herb Meadow Total 1 1
Riverine Gravelly Wormwood-Horsetail Barrens and Partially Vegetated FA-138 1 1
Riverine Gravelly Wormwood-Horsetail Barrens and Partially Vegetated
Total 1 1
Riverine Loamy Ostrich Fern Meadow
FA-104 3 3
FA-115 3 3
FA-138 2 2
Riverine Loamy Ostrich Fern Meadow Total 2 6 8
Riverine Loamy Spruce-Birch Forest FA-104 1 1 1 3
FA-115 3 3
Riverine Loamy Spruce-Birch Forest Total 1 4 1 6
Riverine Sandy Alder-Willow Tall Shrub FA-115 1 1
FA-128 1 4 5
Riverine Sandy Alder-Willow Tall Shrub Total 2 4 6
Riverine Sandy Balsam Poplar Sapling-Alder-Willow Tall Shrub
FA-104 3 2 5
FA-128 4 4
FA-138 2 2
Riverine Sandy Balsam Poplar Sapling-Alder-Willow Tall Shrub Total 9 2 11
Riverine Sandy Bluejoint-Herb Meadow FA-104 1 1
FA-115 1 1
Riverine Sandy Bluejoint-Herb Meadow Total 1 1 2
Riverine Sandy Pole-sized Balsam Poplar Forest FA-104 1 1
Riverine Sandy Pole-sized Balsam Poplar Forest Total 1 1
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Ecotype Focus Area
Existing
Aquatic Wells
Existing
Riparian Wells
Planned
Riparian Wells Grand Total
Riverine Sandy Timber-sized Balsam Poplar Forest
FA-104 1 1 2
FA-115 1 1
FA-128 1 6 7
Riverine Sandy Timber-sized Balsam Poplar Forest Total 2 7 1 10
Riverine Sandy-Loamy Balsam Poplar Large Tree Forest
FA-104 1 1
FA-128 1 5 6
FA-138 1 1
Riverine Sandy-Loamy Balsam Poplar Large Tree Forest Total 3 5 8
Riverine Sandy-Loamy Spruce-Balsam Poplar Forest
FA-104 1 1
FA-115 1 1
FA-128 2 2
FA-138 1 1
Riverine Sandy-Loamy Spruce-Balsam Poplar Forest Total 1 3 1 5
Riverine Wet Sedge-Forb Marsh FA-104 1 1
FA-115 1 1
Riverine Wet Sedge-Forb Marsh Total 1 1 2
Upland Loamy Spruce-Birch Forest FA-104 2 2
FA-115 1 1
Upland Loamy Spruce-Birch Forest Total 3 3
Grand Total 22 37 5 64
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Table 2. Middle River vegetation.
Ecotype
Study
Location
Focus
Area
Spatial
Extent
(acres)
% of Total
Focus
Area
Planned
ELS Plots
Complete
d ELS
Plots
Planned
Rapid Veg
Transects Total
Lowland Loamy Birch Forest FA-115 6.7 1.4% 2 2
Lowland Loamy Birch Forest Total 2 2
Lowland Organic-rich Bluejoint-Herb Meadow FA-115 11.3 2.3% 1 1 5 7
Lowland Organic-rich Bluejoint-Herb Meadow Total 1 1 5 7
Riverine Gravelly Wormwood-Horsetail Barrens and Partially Vegetated
FA-104 7.8 1.2% 2 2
FA-115 17.6 3.6% 1 1 2
FA-128 39.4 6.3% 5 5
FA-138 29.5 7.9% 2 2
Satellite
Area -- -- 1 1 2
Riverine Gravelly Wormwood-Horsetail Barrens and Partially
Vegetated Total 9 4 13
Riverine Loamy Birch Forest FA-115 8.8 1.8% 2 2
Riverine Loamy Birch Forest Total 2 2
Riverine Loamy Large Umbel Meadow
FA-138 6.4 1.7% 1 1
Satellite
Area -- -- 3 2 5
Riverine Loamy Large Umbel Meadow Total 4 2 6
Riverine Loamy Ostrich Fern Meadow
FA-104 23.8 3.7% 2 2 5 9
FA-115 37.5 7.6% 2 5 7
FA-138 7.7 2.1% 4 4
Satellite
Area -- -- 4 4
Riverine Loamy Ostrich Fern Meadow Total 12 2 10 24
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Ecotype
Study
Location
Focus
Area
Spatial
Extent
(acres)
% of Total
Focus
Area
Planned
ELS Plots
Complete
d ELS
Plots
Planned
Rapid Veg
Transects Total
Riverine Loamy Spruce-Birch Forest
FA-104 182.0 28.3% 5 2 7
FA-115 47.7 9.6% 3 2 5
FA-128 7.7 1.2% 5 5
Riverine Loamy Spruce-Birch Forest Total 8 4 5 17
Riverine Sandy Alder-Willow Tall Shrub
FA-115 4.4 0.9% 5 5
FA-128 92.9 15.0% 7 5 12
FA-138 26.9 7.3% 2 5 7
Satellite
Area -- -- 1 1
Riverine Sandy Alder-Willow Tall Shrub Total 10 15 25
Riverine Sandy Balsam Poplar Sapling-Alder-Willow Tall Shrub
FA-104 37.7 5.9% 1 3 5 9
FA-115 7.2 1.5% 1 1 2
FA-128 39.9 6.4% 5 5 10
FA-138 22.7 6.1% 1 5 6
Satellite
Area -- -- 1 1 2
Riverine Sandy Balsam Poplar Sapling-Alder-Willow Tall Shrub Total 9 5 15 29
Riverine Sandy Bluejoint-Herb Meadow
FA-104 15.5 2.4% 2 2
FA-115 13.4 2.7% 2 3 5 10
Satellite
Area -- -- 4 4
Riverine Sandy Bluejoint-Herb Meadow Total 8 3 5 16
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Ecotype
Study
Location
Focus
Area
Spatial
Extent
(acres)
% of Total
Focus
Area
Planned
ELS Plots
Complete
d ELS
Plots
Planned
Rapid Veg
Transects Total
Riverine Sandy Pole-sized Balsam Poplar Forest
FA-104 10.5 1.6% 1 3 5 9
FA-115 14.1 2.9% 4 4
FA-128 45.2 7.3% 5 5
FA-138 20.2 5.5% 1 5 6
Satellite
Area -- -- 2 2
Riverine Sandy Pole-sized Balsam Poplar Forest Total 13 3 10 26
Riverine Sandy Spruce Forest
Satellite
Area -- -- 4 4
Riverine Sandy Spruce Forest Total 4 4
Riverine Sandy Timber-sized Balsam Poplar Forest
FA-104 22.1 3.4% 4 5 9
FA-115 55.9 11.3% 3 1 5 9
FA-128 30.1 4.8% 4 5 9
FA-138 68.2 18.4% 5 5 10
Satellite
Area -- -- 1 1
Riverine Sandy Timber-sized Balsam Poplar Forest Total 13 5 20 38
Riverine Sandy-Loamy Balsam Poplar Large Tree Forest
FA-104 2.5 0.4% 5 5
FA-115 32.3 6.5% 4 4
FA-128 159.6 25.7% 8 5 13
FA-138 30.4 8.2% 2 2
Satellite
Area -- -- 2 2
Riverine Sandy-Loamy Balsam Poplar Large Tree Forest Total 16 10 26
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Ecotype
Study
Location
Focus
Area
Spatial
Extent
(acres)
% of Total
Focus
Area
Planned
ELS Plots
Complete
d ELS
Plots
Planned
Rapid Veg
Transects Total
Riverine Sandy-Loamy Spruce-Balsam Poplar Forest
FA-104 33.7 5.2% 1 4 5 10
FA-115 46.1 9.3% 5 5
FA-128 159.6 25.7% 4 5 9
FA-138 42.5 11.5% 2 2
Satellite
Area -- -- 2 2
Riverine Sandy-Loamy Spruce-Balsam Poplar Forest Total 14 4 10 28
Riverine Wet Sedge-Forb Marsh
FA-115 6.2 1.2% 1 5 6
FA-138 10.9 2.9% 2 5 7
Satellite
Area -- -- 2 1 3
Riverine Wet Sedge-Forb Marsh Total 4 2 10 16
Upland Loamy Spruce-Birch Forest FA-104 158.1 24.6% 3 3 5 11
FA-115 6.6 1.3% 2 5 7
Upland Loamy Spruce-Birch Forest Total 3 5 10 18
Grand Total 132 40 125 297
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Table 3. Lower River wells and vegetation.
Ecotype Transect Existing Wells
Planned Rapid Veg
Transects
Riverine Sandy Alder-Willow Tall Shrub LR1 1 3
LR4 3 9
Riverine Sandy Alder-Willow Tall Shrub Total 4 12
Riverine Sandy Balsam Poplar Sapling-Alder-Willow Tall Shrub LR4 1 3
Riverine Sandy Balsam Poplar Sapling-Alder-Willow Tall Shrub Total 1 3
Riverine Sandy Pole-sized Balsam Poplar Forest LR1 1 3
LR2 1 3
Riverine Sandy Pole-sized Balsam Poplar Forest Total 2 6
Riverine Sandy Rose-Willow Low Shrub LR3 1 3
Riverine Sandy Rose-Willow Low Shrub Total 1 3
Riverine Sandy Timber-sized Balsam Poplar Forest LR2 1 3
LR3 1 3
Riverine Sandy Timber-sized Balsam Poplar Forest Total 2 6
Grand Total 10 30
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Table 4. Existing gage stations.
Purpose
Ecotype Study Location Groundwater Surface Water
Grand
Total
Riverine Circumneutral Beaver Pond
FA-115 2 2
FA-138 1 1
FA-141 1 1
Satellite Area 2 2
Riverine Circumneutral Beaver Pond Total 6 6
Riverine Circumneutral Glacial River
FA-104 2 1 3
FA-115 2 2
FA-128 2 2 4
FA-138 1 2 3
FA-144 1 1
Riverine Circumneutral Glacial River Total 5 8 13
Riverine Complex
FA-144 1 1
Satellite Area 1 1
Riverine Complex Total 2 2
Riverine Gravelly Wormwood-Horsetail Barrens and Partially Vegetated
FA-128 1 1
FA-138 2 2
FA-144 1 1
Riverine Gravelly Wormwood-Horsetail Barrens and Partially Vegetated
Total 4 4
Riverine Loamy Birch Forest Satellite Area 1 1
Riverine Loamy Birch Forest Total 1 1
Riverine Loamy Ostrich Fern Meadow FA-115 1 1
Satellite Area 1 1
Riverine Loamy Ostrich Fern Meadow Total 2 2
Riverine Loamy Spruce-Birch Forest Satellite Area 1 1
Riverine Loamy Spruce-Birch Forest Total 1 1
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Purpose
Ecotype Study Location Groundwater Surface Water
Grand
Total
Riverine Sandy Alder-Willow Tall Shrub
FA-128 1 1 2
FA-138 1 1
FA-141 1 1
Satellite Area 1 1
Riverine Sandy Alder-Willow Tall Shrub Total 1 4 5
Riverine Sandy Balsam Poplar Sapling-Alder-Willow Tall Shrub FA-128 1 1
Riverine Sandy Balsam Poplar Sapling-Alder-Willow Tall Shrub Total 1 1
Riverine Sandy Bluejoint-Herb Meadow
FA-115 1 1
Satellite Area 2 2
Riverine Sandy Bluejoint-Herb Meadow Total 3 3
Riverine Sandy Timber-sized Balsam Poplar Forest FA-144 1 1
Riverine Sandy Timber-sized Balsam Poplar Forest Total 1 1
Riverine Sandy-Loamy Spruce-Balsam Poplar Forest FA-138 1 1
Satellite Area 1 1
Riverine Sandy-Loamy Spruce-Balsam Poplar Forest Total 1 1 2
Riverine Slough FA-104 1 1
Riverine Slough Total 1 1
Grand Total 7 35 42
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6. FIGURES
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Figure 1. Riparian process domains, Focus Areas and riparian study sites.
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Figure 2. Lower River riparian transects locations.
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Figure 3. FA-104 (Whiskers Slough) Riparian and aquatic well locations. Inset: Ecotype overlay of riparian well transect.
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Figure 4. FA-115 (Slough 6A) Riparian and aquatic well locations. Inset: Ecotype overlay of riparian well transect.
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Figure 5. FA-128 (Slough 8A) Riparian and aquatic well locations. Inset: Ecotype overlay of riparian well transect.
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Figure 6. FA-138 (Gold Creek) Riparian and aquatic well locations. Inset: Ecotype overlay of riparian well transect.
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Figure 7. FA-115 (Slough 6A) Primary riparian well transect with ecotype overlay, well locations, and
groundwater and surface water.
Figure 8. FA-128 (Slough 8A) Upper riparian well transect with ecotype overlay, well locations, and
groundwater and surface water.
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Figure 9. FA-115 (Slough 6A) Primary riparian transect with ecotypes and rapid vegetation transect (RVT)
locations.
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Figure 10. Riparian vegetation transect point-intercept sampling schematic.