HomeMy WebLinkAbout3.1Grant Lk Geomorphology Final Report June 2014 FINAL
Grant Lake Hydroelectric Project (FERC No. 13212)
Water Resources – Geomorphology
Final Report
Prepared for
Kenai Hydro, LLC
Prepared by
P. Pittman
Element Solutions
June 2014
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 i June 2014
TABLE OF CONTENTS
1 Introduction ..............................................................................................................................1
2 Study Objectives.......................................................................................................................5
2.1. Grant Lake Shoreline Erosion Study ...................................................................................5
2.2. Grant Creek Spawning Substrate Recruitment Study ..........................................................5
3 Study Area ................................................................................................................................5
3.1. Grant Lake Geomorphic Setting ..........................................................................................5
3.2. Grant Creek Geomorphic Conditions and Processes ...........................................................6
4 Methods .....................................................................................................................................6
4.1. Methods to Evaluate Grant Lake Shoreline Erosion............................................................6
4.2. Methods to Evaluate Grant Creek Geomorphic Response ..................................................8
5 Results .....................................................................................................................................15
5.1. Grant Lake Shoreline Geomorphic Conditions and Processes Results .............................15
5.2. Grant Creek Geomorphic Conditions and Assessment Results .........................................17
5.2.1. Grant Creek Geomorphic Setting and Conditions ............................................. 17
5.2.2. Quantitative Sediment Characterization Summary ............................................ 22
6 Conclusions .............................................................................................................................29
6.1. Grant Lake Shoreline Erosion Study Conclusions .............................................................29
6.2. Grant Creek Spawning Substrate Recruitment Study Conclusions ...................................30
7 Variances from FERC-Approved Study Plan and Proposed Modifications ....................32
8 References ...............................................................................................................................33
Appendices
Appendix 1: Grant Lake Shoreline Geomorphology Site Photos
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 ii June 2014
List of Tables
Table 4.1-1: Relative erodability integrating erosion susceptibility with wave energy potential. 8
Table 5.2-1. Surface (Wolman grid) sampling (frequency-by-numbers) results. ......................... 22
Table 5.2-2. Subsurface volume (bulk) sampling (frequency-by-weight (volume)) results. ........ 24
Table 5.2-3. Summary of incipient motion calculations at 385 cfs. ............................................ 28
Table 6.2-1. Potential geomorphic responses from Project operational conditions. .................... 31
List of Figures
Figure 1.0-1. Natural resources study area. ................................................................................... 3
Figure 4.1-1. Grant Lake geomorphology relative shoreline erosion. ........................................... 9
Figure 4.2-1. Grant Lake geomorphology relative sample sites. ................................................. 11
Figure 5.2-1. Grant Creek stream profile generated from LiDAR (2002). Vertical axis is in feet
NAVD 88 and horizontal axis is in feet as measured from the outlet at Grant Creek. ......... 18
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 iii June 2014
Acronyms and Abbreviations
AEIDC Arctic Environmental Information Data Center
cfs cubic feet per second
DLA Draft License Application
EPA Environmental Protection Agency
FERC Federal Energy Regulatory Commission
GIS Geographic Information System
KHL Kenai Hydro, LLC
LA License Application
mm millimeter
MW megawatt
NAVD 88 North American Vertical Datum of 1988
NGVD 29 National Geodetic Vertical Datum of 1929
NOI Notice of Intent
OHWM ordinary high water mark
PAD Pre-Application Document
PM&E protection, mitigation and enhancement
Project Grant Lake Hydroelectric Project
USFS U.S. Department of Agriculture, Forest Service
USGS U.S. Department of the Interior, Geological Survey
WSE water surface elevation
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 iv June 2014
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FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 1 June 2014
Water Resources – Geomorphology
Final Report
Grant Lake Hydroelectric Project (FERC No. 13212)
1 INTRODUCTION
On August 6, 2009, Kenai Hydro, LLC (KHL) filed a Pre-Application Document (PAD; KHL
2009), along with a Notice of Intent (NOI) to file an application for an original license, for a
combined Grant Lake/Falls Creek Project (Federal Energy Regulatory Commission [FERC] No.
13211/13212 [“Project” or “Grant Lake Project”]) under Part I of the Federal Power Act (FPA).
On September 15, 2009, FERC approved the use of the Traditional Licensing Process (TLP) for
development of the License Application (LA) and supporting materials. As described in more
detail below, the Project has been modified to eliminate the diversion of water from Falls Creek
to Grant Lake. The Project will be located near the community of Moose Pass, Alaska in the
Kenai Peninsula Borough, approximately 25 miles north of Seward, Alaska and just east of the
Seward Highway (State Route 9).
The Water Resources Study Plan (Plan) was designed to address information needs identified in
the PAD, during the TLP public comment process, and through early scoping conducted by
FERC. The following study report presents the results of the geomorphological components of
the Plan along with previously existing information relative to the scope and context of potential
effects of the Project. This information will be used to analyze Project impacts and propose
protection, mitigation, and enhancement (PM&E) measures in the draft and final LA’s for the
Project.
The Project is located near the community of Moose Pass, approximately 25 miles north of
Seward and just east of the Seward Highway. It lies within Section 13 of Township 4 North,
Range 1 West; Sections 1, 2, 5, 6, 7, and 18 of Township 4 North, Range 1 East; and Sections
27, 28, 29, 31, 32, 33, 34, 35, and 36 of Township 5 North, Range 1 East, Seward Meridian (U.S.
Geological Survey [USGS] Seward B-6 and B-7 Quadrangles).
The proposed Project would be composed of an intake structure at the outlet to Grant Lake, a
tunnel, a surge tank, a penstock, and a powerhouse. It would also include a tailrace detention
pond, a switchyard with disconnect switch and step-up transformer, and an overhead or
underground transmission line. The preferred alternative would use approximately 15,900 acre-
feet of water storage during operations between pool elevations of approximately 692 and up to
703 feet North American Vertical Datum of 1988 (NAVD 88)1.
1 The elevations provided in previous licensing and source documents are referenced to feet mean sea level in
NGVD 29 [National Geodetic Vertical Datum of 1929] datum, a historical survey datum. The elevations presented
in the Grant Lake natural resources study reports are referenced to feet NAVD 88 datum, which results in an
approximate +5-foot conversion to the NGVD 29 elevation values.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 2 June 2014
An intake structure would be constructed approximately 500 feet east of the natural outlet of
Grant Lake. An approximate 3,200-foot-long, 10-foot diameter horseshoe tunnel would convey
water from the intake to directly above the powerhouse at about elevation 628 feet NAVD 88.
At the outlet to the tunnel a 360-foot-long section of penstock will convey water to the
powerhouse located at about elevation 531 feet NAVD 88. An off-stream detention pond will be
created to provide a storage reservoir for flows generated during the rare instance when the units
being used for emergency spinning reserve are needed to provide full load at maximum ramping
rates. The tailrace would be located in order to minimize impacts to fish habitat by returning
flows to Grant Creek upstream of the most productive fish habitat.
Two concepts are currently being evaluated for water control at the outlet of Grant Lake. The
first option would consist of a natural lake outlet that would provide control of flows out of
Grant Lake. A new low level outlet would be constructed on the south side of the natural outlet
to release any required environmental flows when the lake is drawdown below the natural outlet
level. The outlet works would consist of a 48-inch diameter pipe extending back into Grant
Lake, a gate house, regulating gate, controls and associated monitoring equipment. The outlet
would discharge into Grant Creek immediately below the natural lake outlet.
In the second option, a concrete gravity diversion structure would be constructed near the outlet
of Grant Lake. The gravity diversion structure would raise the pool level by a maximum height
of approximately 2 feet (from 703 to 705 feet NAVD 88), and the structure would have an
overall width of approximately 120 feet. The center 60 feet of the structure would have an
uncontrolled spillway section with a crest elevation at approximately 705 feet NAVD 88.
Similar to the first option, a low level outlet would be constructed on the south side of the natural
outlet to release any required environmental flows when the lake is drawn down below the
natural outlet level. The outlet works would consist of a 48-inch diameter pipe extending back
into Grant Lake, a gate house a regulating gate, controls, and associated monitoring equipment.
The outlet would discharge into Grant Creek immediately below the diversion structure.
Figure 1.0-1 displays the global natural resources study area for the efforts undertaken in 2013
and 2014 along with the likely location of Project infrastructure and detail related to land
ownership in and near the Project area. Further discussions related to specifics of the
aforementioned Project infrastructure along with the need and/or feasibility of the diversion dam
will take place with stakeholders in 2014 concurrent with the engineering feasibility work for the
Project. Refined Project design information will be detailed in both the Draft License
Application (DLA) and any other ancillary engineering documents related to Project
development. The current design includes two Francis turbine generators with a combined rated
capacity of approximately 5.0 megawatts (MW) with a total design flow of 385 cubic feet per
second. Additional information about the Project can be found on the Project website:
http://www.kenaihydro.com/index.php.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 5 June 2014
2 STUDY OBJECTIVES
The Grant Lake and Grant Creek Fluvial Geomorphology Study consisted of two independent
study components: a Grant Lake shoreline erosion study and a Grant Creek spawning substrate
recruitment study. The goals of the studies were to provide supporting information on the
potential resource impacts of the Project that were identified during development of the PAD,
public comment, and FERC scoping for the LA. The objectives of the studies are described
below.
2.1. Grant Lake Shoreline Erosion Study
The primary study objective of the Grant Lake shoreline erosion study was to provide a basis for
predicting and assessing potential lake shore erosion in Grant Lake as a result of general
reservoir operations. Operations will affect the timing, duration and range of water surface
elevations (WSE), and thus change the Grant Lake shoreline geomorphic conditions. The Grant
Lake shore geomorphic study was a qualitative inventory of shoreline conditions that affect
erosion potential based on professional judgment.
2.2. Grant Creek Spawning Substrate Recruitment Study
The primary objective of the Grant Creek spawning substrate recruitment study was to provide a
basis for predicting and assessing potential changes to material movement, sedimentation, and
gravel recruitment that may occur in Grant Creek with proposed operational management,
especially as related to the long-term maintenance of fish spawning substrate. Operation of the
Project would alter the flow regime and create a situation where some amount of flow will
bypass the canyon reach. The Grant Creek spawning substrate study combines quantitative and
qualitative elements.
3 STUDY AREA
The Project vicinity is near the town of Moose Pass, Alaska, approximately 25 miles north of
Seward, just east of the Seward Highway (State Route 9). The specific geomorphology
assessment study area includes Grant Lake shoreline and Grant Creek within the lower portion of
the Grant Lake watershed.
3.1. Grant Lake Geomorphic Setting
Grant Lake is an approximately 6-mile long, 1,600 acre (2.5 square mile) lake located in a
68,000 acre (44 square mile) watershed within the Chugach Mountains of Kenai Range east of
Moose Pass. Inlet Creek is the predominant stream in the upper portion of the watershed and
drains melting alpine glaciers and snow from the nearby mountains into Grant Lake at the
eastern end of the lake. Grant Lake itself sits in the lower portion of the watershed, capturing
over 95 percent of the watershed area.
Grant Lake is located in a deep glacially-carved basin flanked by the high bedrock peaks of Lark
and Solars Mountains. Grant Lake encompasses two almost separate bathymetric lake basins
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 6 June 2014
that are separated by a shallow submerged ridge at a narrow “neck” that connects the two basins
at right angles (EBASCO 1984). The upper basin is oriented primarily east-west, whereas the
lower basin is oriented primarily north-south. Much of the overall shoreline littoral zone is steep
bedrock. The deepest point within the lower basin is approximately 262 feet deep and the upper
basin is 283 feet deep (EBASCO 1984).
3.2. Grant Creek Geomorphic Conditions and Processes
The Grant Creek watershed occupies approximately 44 square miles with a majority of its
watershed bound by the steep mountains of the Kenai Range. Grant Creek itself is
approximately 5,800 feet long and flows west from the outlet of Grant Lake to the “narrows”
between Upper and Lower Trail lakes. Grant Creek has a mean annual flow of 200 cubic feet
per second (cfs), with an average gradient of 200 feet per mile. In its upper half, Grant Creek
passes through a steep bedrock canyon with three substantial waterfalls. In its lower half, Grant
Creek becomes less steep with boulder and cobble dominant alluvial substrate. Grant Creek is a
high energy stream with a wide variability in flow regime.
4 METHODS
4.1. Methods to Evaluate Grant Lake Shoreline Erosion
The methods to conduct the shoreline erodibility assessment of Grant Lake consisted of both a
desktop analysis using existing information and a field evaluation of conditions observed along
the shoreline by boat at a relatively high lake stage (approximately 2 feet of water depth over the
outlet to Grant Creek which is estimated to be 703 feet NAVD 88). For the field evaluation, it
was assumed that the Project WSE would be approximately 3 to 5 feet higher than at the time of
our site visit on August 24, 2013 assuming water depths at the invert would be a maximum of 3
to 5 feet deep. Minimum Project WSE would be 692 feet NAVD 88, or approximately 11 feet
lower than at the time of our field visit. The desktop analysis utilized integrating previous
studies and information, including bathymetric mapping, LiDAR, digital orthographic photos,
and geologic mapping. Spatial information was evaluated and findings were mapped in a
Geographic Information System (GIS). The analysis drew upon a number of assumptions as
described below.
For conditions and impacts to the littoral zone at elevations that were submerged at the time of
the field visit, it was assumed that the geomorphic units identified and mapped at the shoreline
near the ordinary high water mark (OHWM) were the same in the submerged areas to at least the
depth of the proposed managed WSE. The rationale for this assumption is that most of the steep
shoreline was bedrock, or landforms that result from hill-slope process deposition (e.g. alluvial
fan), continue downslope. In two instances, the landforms did not fit this model (at both distal
ends of the lake), in these instances, the extent of geomorphic unit was inferred based upon the
assumption that the unit continued in submerged areas to at least the bathymetric break in slope.
In both instances, the bathymetric break in slope occurred below the proposed minimum WSE.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 7 June 2014
Methods
The erodibility assessment was initiated with a GIS desktop analysis. The analysis included
remotely mapping the geomorphic features of the Grant Lake shoreline area. This was
accomplished by evaluating a combination of spatial data sets in conjunction with historic
studies and information and making an informed geological interpretation. The data sets that
were used included:
2002 Aerial Photos of Grant Lake: USFS, 1996-2004, 2-5 meter, Black/White, UTM 6
NAD 27
Google Earth oblique view aerial photos
4-foot contours generated from 2002 LiDAR using GIS: Aero-Metric Inc., 2008, 10-foot
resolution, format: LiDAR point cloud data 1.1.
Surface Geology Maps (EBASCO 1984)
The interpretation of landforms involved analysis of slope/relief, shape, contributing upland area,
fluvial/non-fluvial influence, vegetation, texture and previous geological assessments. A
“Geomorphic Unit” was developed based on geomorphic process for the landforms along the
shoreline and each Geomorphic Unit was mapped within 200-foot buffer from the shoreline in
GIS. The following Geomorphic Units were established for this analysis:
Alluvial Deltaic Deposits
Alluvial Fan Deposits
Beach/Littoral Deposits
Colluvial Deposits
Landslide Deposits
Bedrock
The depositional units were characterized based on typical sediment size and character of
depositional material (layered strata versus massive consolidated strata, sorted versus unsorted
sediment) with the rationale that smaller sediment size and layered strata were relatively more
susceptible to erosion than larger sediment sizes and massive consolidated deposits. As a result,
a relative erodibility of the geomorphic unit was generated such that the aforementioned units are
listed from most susceptible to erosion to least susceptible. The geomorphic units in the area
buffering the shoreline were field validated. Photographs of “type-sections” of geomorphic units
are provided in Appendix 1. Mapping of geomorphic units is shown in Figure 4.1-1.
Wind generated waves are likely the predominant erosional process acting on the Grant Lake
shoreline during present conditions. To evaluate the wind-generated wave erosion potential, an
overlay of relative fetch potential was applied with the rationale that larger waves had more
energy and were more effective at eroding the shoreline area than were smaller waves. Field
observations of wave run-up potential were made during the boat-based survey and documented
with photographs.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 8 June 2014
Evaluation
The evaluation was initiated by compiling all existing spatial information into a GIS-based
platform. The geomorphic units were integrated with the fetch parameters to determine relative
erodibility (Table 4.1-1). The resulting relative erodibility was mapped in GIS.
Table 4.1-1. Relative erodability integrating erosion susceptibility with wave energy potential.
Relative
Fetch
Distance
Geomorphic Unit
Alluvial
Deltaic Alluvial Fan Beach Colluvium
Landslide
(bedrock) Bedrock
Short Moderate Moderate Moderate Low Low Low
Medium Moderate-
High Moderate-High Moderate-High Moderate-Low Moderate-Low Low
Long High High High Moderate Moderate Low
The integration of the relative erodibility susceptibility of the Geomorphic Units with the fetch
distance to determine relative erodibility along the shoreline relies upon the following
assumptions:
1. As the fetch increases the wave size increases, and therefore the wave-generated
erosional processes increase with fetch
2. The geomorphology/geology within each mapped unit was assumed to be consistent
throughout that individual unit.
In addition to wind-generated wave erosion potential, erosion due to changes in base elevation
which could cause stream incision of streams that outlet along the shoreline during lower lake
WSE conditions was considered.
4.2. Methods to Evaluate Grant Creek Geomorphic Response
General Methods
The methods identified in the study plan to evaluate the sediment transport effecting salmon
spawning substrate conditions following operational scenarios, included the following tasks:
1. assessment of the substrate at existing spawning areas including aspects of embeddedness
and substrate size composition;
2. quantification of material transport conditions under the existing and projected flow
regimes; and
3. qualitative geomorphic assessment of existing sediment supply conditions.
Figure 4.2-1 refers to the study area and sampling locations.
Developed For:
Drawing Scale:
GRANT LAKE HYDROELECTRIC PROJECT - FERC PROJECT #P-13212
GRANT LAKE NATURAL RESOURCES STUDY
FIGURE 4.1-1: GRANT LAKE GEOMORPHOLOGYRELATIVE SHORELINE EROSION
±
0 620 1,240 1,860 2,480310
Feet
THE SONNA BUILDING910 MAIN ST. SUITE 258BOISE, ID 83702
OFFICE: 208.342.4214FAX: 208.342.4216
REV DESCRIPTIONBYDATE SCALE:
FIGURE 4.1-1
ISSUED DATE
CHECKED
DRAWN
DESIGNED
"!±b "!±b
"!±b
"!±b
"!±b
"!±b
"!±b
"!±b
"!±b
"!±b "!±b
"!±b
"!±b
"!±b
"!±b
"!±b
"!±b
GRANT CREEK(Outlet)
INL
E
T
C
R
E
E
K
(Lower Basin)(Upper Basin)GRANT LAKE
LARK MOUNTAIN
LandslideScarp
LandslideScarp(Recent)
SOLARS MOUNTAIN
9
8
7
6
54
3
2117
16
15
14
13
12
1110
Legend
"!±b Photo Points
Shoreline Geomorphology
Geomorphic Units
Alluvial Deltaic Deposit
Alluvial Fan Deposit
Beach Deposit
Bedrock
Colluvium
Landslide
Shoreline Erodiblity Potential
Relative Erodability
High
Moderate-High
Moderate
Moderate-Low
Low
Mapping and Geologic
Interpretation by
Paul Pittman
1812 Cornwall Ave
Bellingham, WA 98225
info@elementsolutions.org
Developed For:
Drawing Scale:
GRANT LAKE HYDROELECTRIC PROJECT - FERC PROJECT #P-13212
GRANT LAKE NATURAL RESOURCES STUDY
FIGURE 4.2-1: GRANT CREEKGEOMORPHOLOGY SAMPLE SITES
±
0 140 280 420 56070
Feet
THE SONNA BUILDING910 MAIN ST. SUITE 258BOISE, ID 83702
OFFICE: 208.342.4214FAX: 208.342.4216
REV DESCRIPTIONBYDATE SCALE:
FIGURE 4.2-1
ISSUED DATE
CHECKED
DRAWN
DESIGNED
GRANT LAKE
REACH 1 REACH 2 REACH 3
REACH 4
REACH 5
REACH 6
C anyon R each (Reaches 5 & 6)Upper Trail Lake
LowerTrailLakeThe NarrowsAnatomosing Reach (Reaches 2 - 4)
Alluvial FanDistributary Reach
#1#2#3#4
#5#6
#7
#8
Legend
Sediment Sample Sites
Sample Type
Bulk and Wolman
Wolman
Grant Creek Lower-Flow Channel
Grant Creek Higher Flow Channels
Grant Creek Alluvial Plain
Lakes
Mapping and Geologic
Interpretation by
Paul Pittman
1812 Cornwall Ave
Bellingham, WA 98225
info@elementsolutions.org
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 13 June 2014
Assumptions
The general operational scenario for the Project would result in bypassing some amount of flow
from the canyon reach and the potential for an alteration of the natural flow regime. The
specifics of the alteration cannot be detailed yet as ongoing work from an engineering feasibility
standpoint and further discussions with stakeholders related to instream flows are needed prior to
accurately defining the operational flow regime. What is certain is that the current natural flows
would be modified as a result of Project operations and it is likely that peak flows would be
decreased as a result of operations. For this assessment, in lieu of specific operational
parameters that are yet to be worked out with stakeholders, an assumed operational peak flow of
approximately 385 cfs (based upon general design parameters) was used.
The focus of this study was on the potential impacts to the spawning-size range of sediment. The
following species of concern are documented to use Grant Creek for spawning: Chinook
(Oncorhynchus tshawytscha), sockeye (Oncorhynchus nerka), coho (Oncorhynchus kisutch),
rainbow trout (Salmo gairdneri Oncorhynchus mykiss) and Dolly Varden (Salvelinus malma
malma). The range of documented preferred spawning sediment size classes that encompass
these species can typically range from 5- 50 cm, with rainbow trout preferring the smaller
substrate range and Chinook utilizing the larger substrate range (Russell 1974; Jones 1975;
Suchanek et al. 1984; Milhous 1998; Bovee 1982; Swan 1989; Kondolf 1993). While these are
the literature referenced “preferred” substrate size ranges, utilization of sediment sizes beyond
this range does occur in reality. This is likely the case in Grant Creek, where sediment is
typically larger than the stated preferred size classes. Although there is great variability in
spawning substrate size preference between individual fish, different species and different river
systems, the general size range is limited at the upper end by a substrate size that a particular fish
has the physical ability to dislodge and at the lower range by a substrate size that reduces egg
survivability during incubation. Substrate size alone is not a useful predictor of spawning
potential (Geist and Dauble 1998).
Surface Sampling Methods
Surface sampling, also referred to as Wolman or frequency-by-numbers, was conducted on May
10, 2013 to characterize surface substrate size at various bedforms often utilized for spawning.
Subsurface sampling methods utilized a random point sampling method to collect and measure
surface sediment B-axis dimensions. Measurements were made using a Wolman template for a
100-stone count in areas of probable spawning. The grid spacing and measurement area was
determined by field conditions such that the sample area was isotropic in the horizontal
directions.
Subsurface Bulk Sampling Methods
Subsurface bulk sampling, also referred to as frequency-by-weight, was conducted on May 10,
2013 to characterize subsurface substrate size at anticipated spawning areas. Subsurface methods
utilized field and laboratory sieving technics at four sampling sites in Reaches 1-4 downstream
of the canyon to characterize subsurface conditions. The sampling sites were established at or
near locations historic spawning or anticipated spawning at established instream flow monitoring
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 14 June 2014
sites in order to integrate the instream flow modeling outputs into the sediment transport
equation. Based upon professional judgment, fewer sampling sites were needed due to the
homogeneity of the substrate and field conditions. The sampling sites were spatially referenced
for future monitoring.
Subsurface bulk samples were collected in areas assumed to have a high probability for salmon
spawning based on the surface substrate size conditions and channel bed form (point or lateral
bars that were immediately above the wetted channel margin at a flow of approximately 50 cfs).
The surface armoring was removed as sample locations to the depth of at least one stone depth of
the maximum surface stone diameter. Sieving many subsamples of a large sample volume was
used to reduce bias and account for the large grain size observed at Grant Creek (Church et al.
1987). The largest grain size present in the sample is used as a basis for the sample volume
following the reasoning that the largest particles will be the fewest in number and, therefore,
least well represented. Because of the large grain sizes present at the site, it was infeasible to
remove the full sample for laboratory measurement; therefore field sieving methods were used.
The subsurface material was field sieved and weighed on site using the 2 percent criterion of
Church et al. (1987) as the largest stone exceeded 90 mm which yielded individual sediment
sample weights in excess of 450 pounds (200 kilograms). Sediment passing the 45 mm screen
was sieved at a lab. A total of 4 bulk sample measurements were conducted in the Project reach.
Embeddedness Measuring Methods
The embeddedness sampling included measurements of approximately 50 stones of surface
substrate of a particle size range that falls within the range of spawning substrate sizes for
species using Grant Creek. Measurements of particle diameter (Dt) in the vertical direction and
depth of embedment (De) were made of stones in the approximately D50 size class to achieve
the Embeddedness Ratio. Embeddedness measurements were made at two sample sites in which
Wolman counts were conducted.
Surface Marker Observation Methods
Surface marking methods were employed to field evaluate the presence or absence of sediment
transport resulting from flows experienced in the 2013 season and to use to test sediment
incipient motion calculations. Two areas of in situ surface substrate were marked at Sample Site
1 in which a Wolman Count and Bulk Sampling was performed. Substrate marking was
accomplished by painting two one-meter square areas just above the low flow wetted margins
adjacent to the Bulk Sample sites in situ conditions. These painted areas were inundated with
higher flows (>100 cfs) and reevaluated following three months of high flow conditions to
identify if thresholds of bed mobility were reached and compare to the modeling results.
Hydrology, Hydraulics and Incipient Motion Analysis Methods
Sediment transport analysis integrates the proposed maximum operation flows (385 cfs) and
2013 measurements of hydraulic characteristics at select sites utilizing the instream flow
modeling outputs. Incipient motion particle size analysis was the method selected to determine
the threshold of mobility for particles of various sizes given the proposed hydraulic condition.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 15 June 2014
Incipient motion particle size analysis was used to estimate the particle size that is anticipated to
be transported at proposed operational flow (~350 cfs) and compare it to the spawning substrate
size range to determine the impacts to the spawning substrate size range under the operational
flow regime. A certain degree of sediment transport is necessary to maintain spawning substrate
quality (Kondolf 1993). The incipient motion equation and literature-referenced calibration
estimates were used to estimate the incipient motion particle size. The equation is:
τ* =
τo
(γs – γw) Ds
Where:
τ* = Dimensionless Shield’s parameter
τo = Channel bed shear, pounds per square foot (psf)
γs = Unit weight of sediment, assumed to be 165 pounds per cubic foot (pcf)
γw = Unit weight of water, 62.4 pcf
Ds = Size of sediment at incipient motion, feet
The values of the dimensionless Shield’s parameter depend upon the size and shape of the
substrate. A Shield’s parameter value of 0.03 was considered for the Grant Creek calculation
based on previous work by Inter-Fluve in the Cooper Lake Hydroelectric Project (FERC No.
2170; Inter-Fluve 2004) relicensing analyses, which referenced a study for small platy sediment
forms (Mantz 1977). However, a range of different Shield parameter values were considered
based upon the heterogeneity of the substrate shape and based on field observations and
professional judgment.
Geomorphic Field Assessment
A qualitative geomorphic assessment of the sediment supply for Grant Creek was conducted on
August 24, 2013. Analysis was based on observations from the field, understanding of the Grant
Lake watershed, known geological conditions, and professional interpretation of observed
geomorphic processes.
5 RESULTS
5.1. Grant Lake Shoreline Geomorphic Conditions and Processes Results
The results of the geomorphic shoreline mapping are shown on Figure 4.1-1. The shoreline
conditions of Grant Lake are influenced by geologic conditions, geomorphic processes, and
climate. Alluvial, colluvial and mass wasting processes, including avalanche, deliver sediment
to the shoreline area and deposits of sediment locally bound the shoreline. The upper basin
receives the dominant sediment load being transported to the lake via hill-slope and fluvial
processes.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 16 June 2014
While most geologic and geomorphic processes effecting the littoral zone occur at relatively
slow rates, evidence of large mass wasting events in Grant Lake were observed, which can create
punctuated change along shorelines and stream channels, including rapid change in sediment
supply, shoreline boundary changes, and large pressure generated waves, and erosion. It is
hypothesized that the alluvial plain morphology of Grant Creek was influenced by a relatively
recent landslide generated wave originating from Grant Lake. Large mass wasting events can
have dramatic effect on the landscape.
Natural Influences on Grant Lake WSEs and Littoral Conditions
Grant Lake shoreline geomorphology is influenced by climate and seasonal variability. The lake
remains ice free for approximately half of the year. During the ice-free period, WSEs fluctuate
in response to snow melt, glacial melt, and precipitation. Wind generated wave processes erode,
rework, deposit, and transport sediment in the littoral zone during the ice-free periods. The
narrow confined valleys flanking the lake control wind direction and intensity. Wind direction
from east or west will have the greatest effect on the upper lake basin whereas this wind
direction will have little effect on the lower lake basin. Conversely, wind directions from north
or south will have the greatest effect on the lower lake basin and only negligible effect on the
upper lake basin. Because the lake orientation is divided by a 90 degree “bend” approximately
mid-point, the effective maximum fetch is only approximately 3-miles. The largest wind-
generated waves will be at the shorelines at the end of the fetch runs. The near shore
bathymetric conditions also effect wave height and run up potential.
The highest WSEs typically occur in the summer months when snow melt and precipitation
probability are highest or episodically in fall when transient snow and precipitation occur. WSE
of Grant Lake is controlled by the Grant Creek outlet elevation (703 feet NAVD 88) and the
hydrologic inputs from the watershed. The ordinary high WSE of the lake is at approximately
703 feet NAVD 88 based on previous estimates (EBASCO 1984). The OHWM has apparent
elevation increases where wind generated wave run up occurs, including at the outlet at Grant
Creek.
Grant Lake WSE is lowest in the winter months when the watershed is frozen, virtually halting
hydrologic input. During ice-on conditions, the effect of wind generated waves is likely
negligible except during ice break-up conditions. Anecdotal information would suggest that the
lake WSE can fluctuate by several feet between high and low water. It is not known if the WSE
drops below the elevation of the outlet control. If so, it is possible that some continued outlet of
water occurs from the fractured or jointed bedrock present at the outlet. The presence of
hydraulic loss at the outlet sill would also explain the fairly steady low flow rates observed in
Grant Creek throughout the winter months when hydrologic inputs into Grant Creek are
negligible.
Project Operations Influencing Grant Lake WSEs
Two design alternatives that affect the Grant Lake WSEs are being considered; one that allows
for approximately 11 feet of WSE fluctuation but maintains the existing outlet elevation, and one
that increases the outlet elevation by 2 feet and allows for 13 feet of WSE fluctuation. For this
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 17 June 2014
analysis, the more extreme of the two alternatives was considered since it will have the greatest
influence on shoreline geomorphology. Table 5.1-1 provides a summary of the proposed
operational changes to WSE.
The alternative to raise the natural outlet invert by 2 feet would be accomplished by constructing
a concrete gravity diversion structure at the outlet of Grant Lake. The gravity diversion structure
would raise the pool level by a maximum height of approximately 2 feet, and the structure would
have an overall width of approximately 120 feet. The center 60 feet of the structure would have
an uncontrolled spillway section with a crest elevation estimated at approximately 705 feet
NAVD 88. A low level outlet would be constructed on the south side of the natural outlet to
release any required environmental flows when the lake is drawn down below the natural outlet
level. The outlet works would consist of a 48-inch diameter pipe extending back into Grant
Lake, a gate house a regulating gate, controls, and associated monitoring equipment. The outlet
would discharge into Grant Creek immediately below the diversion structure.
The primary release of water from Grant Lake for hydroelectric generation would be a concrete
intake tower structure located approximately 500 feet east of the natural outlet of Grant Lake and
adjacent to the shore. The intake would allow for drawdown of Grant Lake to elevation of
approximately 692 feet NAVD 88. The intake can be designed to allow the Project to draw
water near the surface at various levels of storage, if deemed necessary.
5.2. Grant Creek Geomorphic Conditions and Assessment Results
5.2.1. Grant Creek Geomorphic Setting and Conditions
The Grant Lake watershed is situated on the Kenai Peninsula within the Kenai Mountain Range.
Metasedimentary and Metavolcanic rocks from the Valdez Group (Mesozoic Era) dominate the
bedrock geology of the Grant Lake watershed and the Project area (Tysdal and Case 1979). The
Valdez group within the watershed is composed primarily of greywacke, slate, and sandy slates
(EBASCO 1984). The watershed has several faults and fracture zones that cut through it
(Hartman and Johnson 1978; EBASCO 1984).
The most recent and prevailing influence on the geomorphology of the Grant Lake Watershed
was the Pleistocene glaciations. Major continental glaciers have occupied portions of Kenai
Peninsula at least four times over the past 1.6 million, the most recent ending approximately
11,000 years ago. The most recent major glaciation was the Naptwne Glaciation which occurred
in the late Pleistocene, ending in the early Holocene (approximately 11,000 years ago) (Wilson et
al 2012). The Grant Lake Watershed has been influenced by continental glaciers for much of its
glacial history however the most recent glacial stade, the Elemendorf Stade, included mostly
advances of Alpine glaciers that were concurrent with the continental glaciers. These glacial
stades and interglacial periods have greatly altered the landscape by eroding bedrock, carving out
the lake basin, steepening the valley walls, and depositing minor amounts of sediments. Glaciers
have, for the most part, retreated to the upper limits of the watershed and only a few small alpine
glaciers and snow fields are present today.
Grant Creek drains Grant Lake. It is a steep mountain stream with several falls, a narrow
canyon, and a steep alluvial plain (Figures 4.2-1 and 5.2-1). In its upper half, the stream passes
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 18 June 2014
through a narrow bedrock canyon with three substantial waterfalls. The lower half of Grant
Creek is a broader alluvial plain with a decreased stream gradient. It is likely that a faulting zone
has facilitated the development of Grant Creek and the deep canyon that is associated with it.
Grant Creek follows the Grant Creek Fault which has likely caused a shearing zone that has
weakened the rock in this area and allowed the erosive power of Grant Creek flows to quicken
the erosion of the canyon (EBASCO 1984). Additional linear features have also been identified
in the watershed and several of these features are located on the ridgeline just west of Grant Lake
and are in line with the abandoned relict drainage outlets that were formed when the lake level
was higher. Grant Lake is in the process of lowering as it erodes the outlet sill and continues to
incise the canyon.
Figure 5.2-1. Grant Creek stream profile generated from LiDAR (2002). Vertical axis is in feet NAVD
88 and horizontal axis is in feet as measured from the outlet at Grant Creek.
Geomorphic interpretation of the alluvial plain landform indicates that relatively large
hydrologic event(s) that are much larger than the historically observed hydrology have occurred
and formed the broader alluvial plain. Substantial channel “rill” and fan topography near the
canyon outlet and large alluvial transported boulders across a broad alluvial fan suggests a
massive flow with sediment transport and deposition. The scale of the event(s) that formed the
Canyon
Grant Lake
Trail Lake
2.6%
1.5%
Alluvial Plain
6.4%
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 19 June 2014
alluvial plain is likely substantially larger than snow-melt/rain flows where the largest recorded
flow was 2,140 cfs (EBASCO 1984). It is hypothesized that the “event” was the result of an
impact to Grant Lake that sent a surge of water over the Grant Creek outlet at the south end of
Grant Lake. The event could have been a landslide or earthquake initiated seiche or an ice-jam
dam break flood. The presence of very large sediment particles in the channel and on the alluvial
plain that are beyond the transport capacity of the observed stream are relict of this event.
The alluvial plain channel has predominant substrate size that ranges from boulder to cobble and
decreases from boulder-dominant substrate into a cobble-dominant substrate in the downstream
direction (EBASCO 1984). The Grant Creek alluvial plain is bound by bedrock topography.
The alluvial plain stream channel is approximately 25 feet at bankfull width on average, whereas
the width of the alluvial plain is substantially larger than the bankfull and active channel which
suggests that Grant Creek has historically occupied and eroded the alluvial plain margins.
Three generalized geomorphic channel form reaches currently exist in Grant Creek; the Canyon
Reach, the Anastomosing Reach, and the Alluvial Fan Distributary Reach. The Canyon Reach
(Reaches 5 and 6) is a confined bedrock channel and the primary source of sediment recruitment
for Grant Creek. The channel in this section is steep and bedrock lined with limited sediment
storage, both in volume and temporal duration. Most sediment is stored in the Canyon Reach
sediment wedges formed behind boulder obstructions. Extremely large flows are capable of
mobilizing these wedges and net incision into the bedrock is the trend. A series of headcuts
(falls) are migrating up the stream in the direction of Grant Lake. In geologic time, these
headcuts will migrate to Grant Lake and the lake water surface will drop to the new control
elevation.
The Anastomosing Reach is within the partially confined alluvial plain and is net depositional
zone with periods of incision occurring during low sediment input rates. Loss in hydraulic
confinement and a change in gradient allow for sediment deposition within this reach when
sediment input rates are high and transport capacity is low. It is anticipated that these conditions
are episodic and driven by upper watershed conditions (hydrologic or geologic events)
coinciding with a large sediment supply stored within the canyon reach. A low flow, primary
channel carries the predominant flow and a series of side channel and floodplain channels are
wetted at various flow conditions. The anastomosing reach changes relatively rapidly in both
horizontal and vertical orientation depending upon the sediment load and is a more dynamic
geomorphic reach than the Canyon Reach. Horizontal movements result from either lateral
channel erosion or avulsion. It is anticipated the alluvial deposits overlay a bedrock base and
that there is a robust hyporheic-ground water interaction, and that there is minimal hydrologic
loss in this reach. The Anastomosing Reach channel and bedforms are sensitive to changes in
flow regime and sediment load. Loss of side channel connectivity will result in a single thread
channel, which decreases hydraulic complexity, concentrates stream power, and often results in
increased channel incision.
The Alluvial Fan Distributary Reach is an unconfined, net depositional reach. Distributary
channel networks that disperse flow to Lower Trail Lake and the Narrows are accessed at a wide
range of flows. The Alluvial Fan Distributary Reach is likely the most dynamic reach in Grant
Creek with respect to horizontal and vertical channel movements and avulsions. The reach is
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 20 June 2014
very sensitive to disturbances, particularly sediment supply and flow regime changes. Hydraulic
complexity in The Alluvial Fan reach is hydraulically less complex than the Anastomosing
Reach and it is probable that there is a slight hydrologic loss experienced in this reach.
The Anastomosing Reach of Grant Creek likely provides the greatest overall ecological function
and salmonid productivity relative to the other reaches. The rationale for this hypothesis is that
the reach has:
the greatest hydraulic complexity;
the greatest wetted channel length at moderate flows
a more balanced wetted perimeter to depth at moderate flows;
a higher probability of maintaining low and hyporheic connectivity in the winter;
is more stable than the Alluvial Fan Reach; and
lower velocity and stream power than the Canyon Reach.
Sediment Supply and Transport Influences on Grant Creek Geomorphology
A small amount of suspend and dissolved sediment load from the upper watershed reaches Grant
Creek. However, Grant Lake acts to arrest all bedload sediment transport from the upper
watershed area. Therefore, the sediment supply for Grant Creek, excluding the throughput
suspended sediment load, is the canyon reach. With the majority of the sediment source for
Grant Creek being derived from the canyon walls, the geological formations present along this
length of stream channel play a critical role. The primary process for generating new bedload
sediment in Grant Creek are the erosional forces that incise the canyon causing wall undermining
and mass wasting (rock fall) from the canyon walls and exposing the geology to freeze-thaw and
other surface erosion processes.
While Grant Creek within the alluvial plain exhibits net deposition over time, it is under
“normal” hydrologic conditions a supply limited stream, meaning that the sediment transport
capacity of the stream is greater than the sediment supply to the stream. A supply limited stream
tends to migrate less laterally and vertically than a transport limited stream, and channel form is
more “stable”. Supply limited streams also tend to be armored, incised, and exhibit a straight
versus meandering channel form.
Sediment Form Influences on Grant Creek Geomorphology
Of the three geological formations present along the creek channel, the greywacke is the more
resistant rock type, whereas the sandy slate and slate are more friable and tend to supply the
majority of sediment to the stream bed. The greywacke units control the base elevation in Grant
Lake by creating the outlet sills and forming waterfalls. In time, erosion of the greywacke and
head-cut retreat of the canyon would lower Grant Lake.
The sediment being recruited to Grant Creek is angular, with the slate having a “platy” particle
morphology (A-axis and B-axis are similar, disproportionately small C-axis) and the greywacke
having long “blocky or brick-like” particle morphology (large A-axis, similar disproportionately
small B and C-axes). The high stream power in the canyon and the relatively short transport
distance from the sediment source in the canyon to the depositional areas downstream results in
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 21 June 2014
relatively large grain size with high degree of angularity of the particles compared to other
streams of similar discharge with a greater spatial extent of bedload sediment inputs. Blocky and
platy sediment morphologies with the same B-axes dimensions have different volumes (think of
a dinner plate versus a watermelon that both have similar B-axis diameter), and therefore a
different surface area to mass, which effects transport characteristics. Angular sediment also
transports across the channel bed (rolling and saltating) and entrains differently than does
rounded. The particle morphology of Grant Creek likely increases the armoring qualities of the
bed and thus adds to the overall stability of the channel form.
Hydrologic Influences on Grant Creek Sediment Transport and Geomorphology
The hydrology of Grant Creek is predominantly driven by the cycle of melting snow and
precipitation in the summer and frozen watershed conditions in the winter. Historic hydrologic
monitoring was conducted by a U.S. Department of the Interior, Geological Survey (USGS)
operated gage between 1947 and 1959 and subsequent modeling indicates that Grant Creek has a
mean annual flow of ~198 cfs (AEIDC 1983). Grant Creek was gauged in the spring of 2013
and a flow range of approximately 16 to 1,005 cfs was documented. The months of June through
August typically produce the highest mean monthly flows (approximately 450 to 500 cfs)
(AEIDC 1983). The highest measured flow was 2,140 cfs (EBASCO 1984). Recurrence
intervals have not been calculated for this watershed.
It is the bankfull and peak flows that dominate the fluvial geomorphic processes at Grant Creek.
The stream bed is comprised of large sediment particles and the bed is armored, so only the
larger flows are able to mobilize the bed armoring, transport sediment en masse, and reorganize
bedforms. The sustained flows offered by snow melt conditions allow for a longer duration of
time for which to organize the substrate, construct and arrange the geomorphic channel bed
structures, and allow channel form development.
A larger, but unmonitored hydrologic event likely occurred on Grant Creek in September 2012
when many other gauged streams in the vicinity of Grant Creek experienced flows of record.
Some residual high water marks on Grant Creek were observed which showed that the 2012
event was larger than the highest 2013 flow. Using the existing stage gage and rating curve to
estimate the flows, the 2012 flow was likely between approximately 1,500 and 2,000 cfs. The
September 2012 flow was short duration and occurred late in the season and winter conditions
set in soon after, therefore reducing the amount of time for flows following the event to process
the transported sediment and adapt to the modified channel bed forms. As a result, the 2013
higher flow season responded to the disturbances from the 2012 event and there were several
channel changes, including recapture of some floodplain channels, an avulsion, and partial
abandonment of previously occupied low flow channels. The primary driver for these changes
was likely a redistribution of bedload sediment and localized vertical channel bed changes,
which affected localized WSEs. The observation shows that the channel form and bed forms and
the interaction with the floodplain and floodplain side channels are dynamic, and thus habitat
that relies on the availability, extent, and quality of substrate are related to sediment transport
processes.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 22 June 2014
Non-climate driven hydrologic events likely occur within Grant Creek. The Grant Creek
watershed is within an active seismic area and a large scale landslide, avalanche or earthquake
caused seiche could occur. In the event that a large scale landslide did occur and deliver large
volumes of material rapidly into Grant Lake, then large waves or seiches could propagate
throughout the lake basin and into Grant Creek. It is probable that the hydrograph from one of
these events, although brief in nature, would be substantially greater in magnitude than climate
driven hydrographs.
5.2.2. Quantitative Sediment Characterization Summary
The Grant Creek channel bed is vertically stratified with at least two distinct layers; armored or
pavement layer, and subsurface (Table 5.2-1). A sub-pavement layer was not distinct. The
surface is highly armored which is enhanced by angular particle forms and the surface has low
embeddedness and is relatively low in fine grained sediment. The subsurface is well-graded
cobble and gravel with sand and nominal fines (less than 1 percent of sediment by volume is 1
mm (medium sand) or smaller). The subsurface material is anticipated to be easily remobilized
when the armoring is removed.
Table 5.2-1. Surface (Wolman grid) sampling (frequency-by-numbers) results.
Sample ID - Description Diameter Statics Size (mm)
1A - Point/lateral bar
D16 30
D50 59
D84 115
D-Maximum >520
1B – In channel adjacent 1A point/lateral bar
D16 55
D50 154
D84 524
D-Maximum >600
2 – Riffle (side channel)
D16 16
D50 48
D84 110
D-Maximum >520
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Table 5.2-1, continued…
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 23 June 2014
3 – Glide (side channel)
D16 58
D50 118
D84 183
D-Maximum >520
4A – Upper Riffle (in channel)
D16 40
D50 78
D84 122
D-Maximum >520
4B – Lower Riffle (in channel)
D16 62
D50 133
D84 190
D-Maximum >520
5 – Run (in channel)
D16 51
D50 121
D84 209
D-Maximum >520
6 – Riffle (in channel)
D16 49
D50 111
D84 177
D-Maximum >520
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Table 5.2-1, continued…
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 24 June 2014
7 – Point bar
D16 35
D50 77
D84 145
D-Maximum >256
8 – Point bar
D16 51
D50 83
D84 151
D-Maximum >520
Surface Analysis Results Summary
In summary, the wetted low-flow channel areas are substantially coarser and more armored than
are the lateral and point bars (Table 5.2-2). No trend in surface sediment decrease moving in the
downstream direction was observed. It is hypothesized that local hydraulics and the two distinct
particle forms (platy and blocky) influences particle size to transport relationship and deposition
more than channel gradient in this turbulent system. The instream D50 is generally larger than
literature referenced “preferred” spawning substrate size; however, in the case of Grant Creek the
spawning species are utilizing the areas with large, armored surface substrate.
Table 5.2-2. Subsurface volume (bulk) sampling (frequency-by-weight (volume)) results.
Sample ID - Description Diameter Statics Size (mm)
1 – Point bar/lateral bar
D16 20
D50 52
D84 133
D-Maximum >128
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Table 5.2-2, continued…
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 25 June 2014
2 – Riffle in side channel D16 17
D50 21
D84 38
D-Maximum >128
7 – Point bar D16 17
D50 28
D84 98
D-Maximum >256
8 – Point bar D16 31
D50 74
D84 147
D-Maximum >256
Subsurface Analysis Results Summary
The subsurface is less coarse than the surface, except at Sample Site 1, where the subsurface had
a higher percentage by size class of large particles and yet a similar D50 size. It is hypothesized
that the subsurface in Sample Site 1 represented a hyperconcentrated flow deposit as it lacked
sorting and imbrication structure that was apparent in the other subsurface sample sites.
Subsurface sediment was overall well-graded cobble and gravel with sand with minimal fines.
Similar to the surface analysis, there was not a general trend in decreasing D50 particle size in
the downstream direction because of the influence of localized hydraulics and relict
hyperconcentrated lag deposits. It should be noted that inaccuracies in bulk sampling can be
pronounced in bimodal distributions containing large clasts and where lag deposits from hyper-
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 26 June 2014
concentrated/dam outburst type alluvial deposits are found, as is the interpreted conditions of
Grant Creek.
Embedment Results
Field observations of embeddedness resulting from fine-grained sediment deposition in the
interstitial spaces of the surface armoring were found to be extremely low. The reasons for this
are hypothesized to be that: the Grant Creek system is relatively starved of fine sediment and that
the current flow regime transports most fines through the system as throughput, and the low
sediment delivery rate and high flows result in armored condition.
General clast-to-clast embedment was difficult to measure because of the particle forms,
particularly platy, and the generally well armored conditions. Qualitatively, clast-to-clast
embedment appeared relatively high because of armoring. Because of the high percentage of
imbricated platy sediment particles, there is low confidence in the values measured, and
therefore it is our opinion that quantitative results are not reliable. However, it is not anticipated
that the operational scenario will not increase the deposition of fines in the stream, therefore
there should not be an increase in fines filling the interstitial spaces of the surface sediment
within the spawning reach.
Sediment Incipient Motion Analysis Results
Grant Creek is an example of a complex system for the following reasons:
Grant Creek is a high gradient, boulder dominated stream with turbulent flow. Bedform
and channel bank irregularity, in addition to instream boulder and bedrock structures,
create turbulence with secondary flow influences that can be much more influential on
sediment transport than in planer bed conditions. Attempts to calculate or measure shear
stress values in mountain rivers are complicated by the channel bed roughness and the
associated turbulence and velocity fluctuations (Wohl, 2000).
Sediment particle shapes are unique and vary from referenced calibrated models. The
sediment shapes present in the Grant Creek are angular platy particles and angular blocky
or “brick” shaped particles. These two shapes will each mobilize and transport
differently relative to each other. These two shapes are different from the assumed
particle shape used to develop and calibrate models, which are spherical shapes.
Spherical particle shapes will have a different transport characteristic than either platy or
brick shapes. In addition, each particle form will lay and organize differently on the
channel bed and each has a different mass to B-axis ratio; therefore, incipient motion
will be different for each particle represented in Grant Creek as well as different than
predicted by equations developed using spherical models.
Sediment transport rates at Grant Creek are very low. There are three phases of sediment
transport associated with very low bedload transport rates, also known as marginal
transport. Incipient motion and net transport rates in these systems are very sensitive to
changing hydraulic conditions and bed material moves only partially; thus entrainment is
size-selective (Hassan et al. 2005; Wilcock and McArdell 1993).
The Grant Creek channel bed is locally armored. Sediment transport characteristics,
specifically incipient particle motion, in armored gravel-bed rivers is often controlled by
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 27 June 2014
patches of fine sediment and bedforms (e.g. Garcia et al. 1999). Bedload transport
characteristics vary from the initiation of particle movement to the point when the
breakup of the armor layer occurs when the channel becomes unstable at the reach scale.
Inter-particle relationships are not represented in model assumptions, so hiding effect and
“patches”, which can have significant influence on particle movement are not considered.
A given particle will move only when the shear stress acting on it is greater than the resistance of
the particle to movement. The magnitude of shear stress required to move a given particle is
known as the critical shear stress. The resistance of the particles to movement, and thus its
entrainment, will vary depending on its size, its size relative to surrounding particles, how it is
oriented, and the degree to which it is embedded. The size of the particle will influence the
weight of the particle. The size of the particles relative to surrounding particles will affect the
amount of shear stress the particle is exposed to via the “hiding” factor. Orientation of the
particle will affect the force required to roll the particle along the bed. Packing or embeddedness
will affect the amount of shear stress that the particle is exposed to.
The substrate particle forms, as previously described, are distinctly different and literature
supporting Shield parameter values for both platy and blocky particle forms is extremely limited.
It is hypothesized that platy particle forms in a cohesionless, heterogeneous particle shape planer
bed will mobilize in lower flows and be more easily entrained than will blocky particle forms of
similar B-axis dimensions in the same flow conditions if the platy particles are loose and
unorganized. However, if the platy sediment has become highly imbricated in a more
homogeneous particle shape grouping, thus increasing particle-to-particle contact forces and
decreasing fluid forces acting on a given surface area (skin friction), then the platy particle will
require a higher flow to initiate mobilization than the blocky sediment. Based on the lack of
strongly imbricated, homogenous surface present at Grant Creek, it is anticipate that the platy
particles will be mobilized more easily than the long axis blocky particles. It should also be
noted that Grant Creek channel bed is, for the most part, not planer, thus bed shear stress is
primarily associated with form drag rather than skin friction on individual particles, which is the
force that moves particles.
The incipient motion calculation estimated that the proposed maximum operational flow (385
cfs) will likely initiate mobilization of surface sediment within the preferred spawning substrate
range (10 mm – 50 mm). At 385 cfs, it is anticipated that substrate mobility will be partial,
limited to only smaller particles and that movement of particles will be intermittent, localized,
and primarily from the deeper channel areas or where turbulence is high. Mobilization of
particles will also depend upon the degree of armoring, bedform, and particle shape. Table 5.2-3
is a summary of the estimated upper particle size threshold being mobilized at 385 cfs.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 28 June 2014
Table 5.2-3. Summary of incipient motion calculations at 385 cfs.
Sample Site τ(blocky) τ(platy)
τb
(pounds/sf)
Ds(blocky)
mm
Ds(platy)
mm
D50
surface
mm
D50
subsurface
mm
1 0.06 0.03 1.85 92 183 59 52
2 0.06 0.03 0.79 39 79 48 21
7 0.06 0.03 1.32 65 131 77 28
8 0.06 0.03 1.12 55 111 83 74
Average 62.8 126 67 44
Field observations, marker analysis, and professional judgment would suggest that the predicted
particle sizes are high for the platy particle forms using the Shield’s parameter of 0.03. It also is
possible that the values obtained for the blocky substrate are too high as well. These outputs
predict that there would be substantial bedload movement at a 385 cfs flow. Very little bedload
sediment transport appeared to be occurring at flows near the proposed operational flow.
Additionally, flows near the proposed operational flow also coincided with spawning activity.
The point bar at Sample Site 1 had only experienced minor sediment transport even with the
1000 cfs flows, so it is unlikely that widespread surface sediment breakup occurred at 1000 cfs
flows. However, channel bed changes and resulting WSE changes occurred in 2013 occurred
following the higher flows; therefore, some degree of local bedload transport does occur with
flows between 350 cfs and 1,000 cfs.
Sediment Delivery Potential Results
Sediment delivery and transport in Grant Creek is divided between two transport characteristics;
suspended sediment load and bedload sediment. Suspended sediment load passes through Grant
Creek with very little deposition in the alluvial reach as a result of the steep stream gradient,
turbulence and low sediment load. The primary source of suspended sediment is from the glacial
headwaters. Much of the suspended sediment load settles out into Grant Lake. The suspended
sediment that passes through Grant Lake is extremely fine and has a very low settling rate, which
also decreases the potential for deposition to occur within Grant Creek.
There are four primary sources of bedload sediment in Grant Creek; lakeshore littoral sediment
input, canyon reach input, channel bed and channel bank remobilization (bank erosion, incision),
and mechanical breakdown of instream sediment during mobilization. Field investigation
determined that the bedload sediment supply in Grant Creek is extremely limited and that the
canyon is the predominant source of bedload sediment. Bedload sediment delivery arrives
episodically, either from a rock fall within the canyon, or a littoral contribution resulting from a
large wind storm occurring at high lake WSEs. Remobilization of channel bank and channel bed
sediment can provide a sediment input to lower reaches, but does not recharge or replenish the
whole stream system. Large hydrologic events are necessary to mobilize and transport sediment
from the canyon and deliver the sediment to the lower reaches as well as to mechanically
breakdown instream sediment.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 29 June 2014
6 CONCLUSIONS
6.1. Grant Lake Shoreline Erosion Study Conclusions
The analysis utilized methods prescribed in the Study Plan previously developed by KHL and
resource agencies and finalized in March 2013. Since operational WSE changes have not yet
been fully defined, the shoreline erosional change was difficult to completely determine.
Additionally, because of the presence of snow and ice occurring during low WSE, it was not
feasible to conduct a low lake WSE analysis. As a result, the analysis relied upon the previously
described conditions and available information. Lastly, the geomorphic analysis does not
include a geotechnical evaluation of existing slope stability or changes in slope stability resulting
from changes in Grant Lake WSE.
The anticipated impacts to shoreline erosion potential from the proposed operational WSE
fluctuation are likely to be relatively minor over the long term for the following reasons:
Proposed operational conditions only increase the WSE fluctuation range by a maximum
of 2 feet above existing natural lake WSE fluctuations
Most of the change in WSE range is a decreased WSE that occurs in winter during ice-on
conditions when wave and stream erosion processes are less active.
The shoreline littoral area is predominantly bedrock or coarse, angular boulders with a
low susceptibility to erosion.
Influence of wind-generated waves in Grant Lake is not a substantial erosional process
because the open fetch was limited to a maximum of approximately 3 miles, and
therefore wind wave heights were limited. In the areas where fetch was greatest and
bathymetric conditions favored high wave run up, only a slight increase in OHWM
elevation demonstrating that maximum wind-wave heights were estimated to be a
maximum of approximately 5 feet at Inlet Creek and 3 feet at Grant Creek outlet.
In the areas where erosion potential was greatest, only minimal erosion; in part because
of the depositional nature of the geomorphic units these areas and the apparent high
depositional rate. With the exception of the Beach geomorphic unit, all other areas are
actively delivering sediment to the shoreline area at rates that are greater than the erosion
potential.
It is anticipated the WSE fluctuations under proposed operational conditions will
decrease the duration of time that the WSE holds at any one elevation, especially peak
WSE levels, therefore decreasing the frequency of wave events occurring at any one
elevation and reducing the effects of wave erosion at any one shoreline elevation.
Because of the limited extent of littoral transport observed in the field, the effects on the
Beach geomorphic unit and other isolated pocket beaches is anticipated to be relatively
minor. It should be noted that an interruption of limited littoral-transported sediment
supply to Grant Creek will occur following the construction of the gravity diversion
structure (if this option is selected), but it is anticipated that the sediment volumes and
delivery rates are relatively small and only occur episodically and likely infrequently.
The impacts of erosion along the shoreline from an elevated lake WSE above the current
OHWM will be most dramatic in the first few years as loose and fine grained sediment
are “winnowed” from the shoreline deposits by wave action leaving behind an armored
shore. In some areas shoreline retreat and temporary vertical bluffs are expected,
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FERC No. 13212 30 June 2014
particularly in the more erodible alluvial deposits. This impact will be greatest in low-
sloping shorelines, fine-grained depositional areas, and areas with greater fetch, Inlet
Creek in particular will see the greatest shoreline changes. In addition, the vegetation
along the shoreline that is functioning to bind soils and slopes together with root mass
will lose this function as the vegetation in the inundated and dies. It is possible that the
shoreline will take up to a decade to recover from the initial disturbance created by the
increased WSE.
The areas most susceptible to erosion from stream incision caused by decreases in base
elevation are the alluvial deposits (Alluvial Deltaic and Alluvial Fan geomorphic units).
The potential effects of channel incision will be the steepening of stream gradient,
coarsening of streambed sediments, straightening of stream channels, decreased
floodplain connectivity, increased instream flow velocities and depths, and bank
steepening and retreat.
The potential for ice jams exists in Grant Lake, particularly at the narrow, shallow sill mid-way
down the lake and at Grant Creek outlet. The temporary elevation increase of WSE and resulting
shoreline erosion is possible during these potential episodes, as is the potential stream erosion in
Grant Creek resulting from an ice jam break. While landslides and ice-jams can be significant
geomorphic processes, the recurrence interval and magnitude is unknown, but likely infrequent.
The greatest ongoing potential for geomorphic impact is the potential incision of the inlet
streams at the shoreline margin, Inlet Creek at the east end of the lake in particular. The effects
of impact is lessened since these streams do not possess populations of any fish species other
than the potential for the stickleback and sculpin known to be the only two species that inhabit
Grant Lake. The degree of impact will be limited by the timing of high flows in combination
with the extent and duration of low lake WSE conditions. As lake WSE increases, the
probability and extent of stream incision impacts decreases.
6.2. Grant Creek Spawning Substrate Recruitment Study Conclusions
The analysis utilized methods prescribed in the Study Plan previously developed by KHL and
resource agencies and finalized in March 2013. In general, bedload transport is not a simple
exercise to measure or predict. There is a high degree of uncertainty and low degree in output
confidence in uncalibrated bedload transport modeling. A collaborative approach to addressing
these potential issues is recommended.
Grant Creek is a complex, steep stream that demonstrated a wide range of variability both with
the substrate and bedform conditions and transport is not adequately captured using referenced
Shield’s parameter values (Yager 2012). Regardless, the proposed operational conditions have
the potential to have a geomorphic response as summarized in Table 6.2-1.
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Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 31 June 2014
Table 6.2-1. Potential geomorphic responses from Project operational conditions.
Proposed Change Potential Geomorphic Response
Decreased frequency and
magnitude of Grant
Creek peak flows
Reduced shear stress potential resulting in decreased net sediment transport
potential
Decreased movement potential for large sediment material
Continued sediment transport of smaller and intermediate sediment sizes from
the surface or subsurface following bioturbation (specifically spawning)
Decreased potential for armor remobilization
Increased relative armoring trend over time resulting from smaller particle
“winnowing” (migrating in a downstream direction)
Decreased remobilization of sub-surface sediment except in spawning areas
Increased potential for channel stability (decreased lateral migration, net
increase for channel incision potential)
Increased potential for development of a single-thread channel
Loss of floodplain connectivity
Decreased potential for scour and organization of depositional channel bed
forms
Decreased bedform quantity and associated loss of hydraulic complexity
Decreased sediment supply resulting from lateral migration
Decreased frequency and
duration of Grant Creek
low flows
Decreased potential for fine-grained sediment deposition
Flow bypass of the
canyon reach
Reduced sediment supply availability
Decreased ice-jam dam outburst potential
Decreased potential for slope instability in canyon reach
Decreased potential for bedrock outlet control degradation (erosion) and long-
term Grant Lake WSE reduction
Of the potential geomorphic responses listed above, the following geomorphic responses are
anticipated to have impacts to spawning substrate. Many of the geomorphic response and the
resulting impacts to spawning substrate are anticipated to occur incrementally over time
measured in years and decades. It is anticipated that there will be high potential for:
An increased coarsening of surface bedload sediment as the sediment supply decreases
from a bypass of the Canyon Reach and smaller surface sediment is transported out of the
reach by operational flow. As a result, there is likely to be degradation spawning
substrate quantity and quality resulting from this geomorphic response.
Increased armoring and pavement depth in spawning areas as subsurface fines are
mobilized and winnowed out of the system following bioturbation pavement breakup
(from spawning). As a result, there is likely to be a degradation of spawning substrate
quality resulting from this geomorphic response.
Decreased geomorphic channel form complexity (loss of side-channel and floodplain
connectivity, development of a single-thread channel) resulting from decreased sediment
supply will increase primary channel incision and stream velocity. As a result, there will
likely be a decrease in spawning substrate quantity resulting from this geomorphic
response.
Decreased quantity of channel bedforms (riffles and bars) resulting from decreased
sediment supply and decreased sediment transport with a reduced flow regime. As a
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Grant Lake Hydroelectric Project Kenai Hydro, LLC
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result, there will likely be a decrease in hydraulic complexity that is expected to degrade
spawning substrate quality and reduce its availability resulting from this geomorphic
response.
It is the conclusion of this analysis that there will be an ecological impact related to the
anticipated geomorphic responses resulting from operational conditions. There is a direct
relationship between stream flow and sediment transport and aquatic habitat availability and
quality (Pitlick and Wilcock 2001). Bedload sediment supply in combination with a variable
flow regime creates and modifies channel bedforms, controls sediment transport and storage,
affects surface texture through selective transport, influences channel migration, and has a direct
influence on aquatic habitat. The flux rate of coarse material combined with high flow
magnitude and duration create an important component of sediment mass balance and
geomorphic response in a stream and modification of these variables and can have ecological
significance both for salmonid spawning, juvenile rearing, and invertebrate production. While a
variable flow regime is vital to creating and maintaining spawning substrate, it is possible that
some moderation of the Grant Creek flow range under certain management scenarios could
provide some positive impacts to redd survival.
Geomorphic bedform features create hydraulic processes that support ecologic function, in
particular channel and bedform complexity create hydraulic conditions favorable for spawning
and rearing habitat by creating interstitial flow pathways between surface water, hyporheic, and
ground water zones (Geist et al. 1998). Geomorphic bedforms are created, organized and
destroyed by flow variability, higher flows that mobilize bedforms are particularly important in
this process. Salmonid spawning tends to occur at the transitions between pools and riffles
associated with lateral bar deposition (Bjornn and Reiser 1991; Church and Jones 1982).
A management scenario that integrates some degree of flow variability to provide flows of
sufficient peak and duration to enable spawning substrate mobilization and organization could be
utilized to offset some of the impacts to substrate quality. Additionally, a management scenario
that allows periodic, sediment flushing flows through the canyon reach could provide for
recruitment and transport of the sediment necessary to maintain spawning substrate quantity in
the lower reaches. This management scenario would have to be coordinated with reservoir level
and habitat utilization period(s). Another alternative could be to develop a sediment nourishment
program to replace the lost sediment recruitment opportunity created from the canyon bypass.
7 VARIANCES FROM FERC-APPROVED STUDY PLAN AND PROPOSED
MODIFICATIONS
There were three variances from the FERC and agency-approved study plan that occurred in the
geomorphology analysis. One is that a dataset for the embeddedness assessment task was not
provided. The rationale for action was that unique field conditions made for non-reproducible
results with high data uncertainty. The second was that the number of subsurface sampling sites
and sample size and sieve methods was modified to fit actual field conditions. The sediment
particle size was too great to remove the prescribed sample size and to have it processed by a lab.
FINAL REPORT WATER RESOURCES – GEOMORPHOLOGY
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The number of sample sites was decreased based on relative homogeneity of conditions observed
and an unanticipated low quantity of gravel bars exposed at low flow.
8 REFERENCES
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Bovee, K.D. 1982. A guide to stream habitat analysis using the instream flow incremental
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Analysis.” Sediment Transport in Gravel-Bed Rivers. Ed. C. R. Thorne, J. C. Bathurst,
and R. D. Hey. John Wiley and Sons, pp. 43-88.
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Wohl, E. 2000. Mountain Rivers. American Geophysical Union. Washington, D.C.
Yager, E. M., W. E. Dietrich, J. W. Kirchner, and B. W. McArdell. 2012), Prediction of
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Appendix 1: Grant Lake Shoreline Geomorphology Site
Photos
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Note: Locations of photos are shown on Figure 4.1-1.
Geomorphic Unit “Type Sections” and Field Notes
Photo 1 (by P.Pittman, 8/24/2013): Grant Lake typical “Beach Deposit” Geomorphic Unit.
Field Note - WSE at visit is was approximately 2 feet over the Grant Creek outlet invert.at this
location of the lake is approximately 3 -feet higher than the WSE at the time of the field visit and
likely represents an apparent OHWM increased because of wave run up. The OHWM in
protected areas of the lake was approximately 1 to 2 feet above the WSE at the time of the field
visit. An increase in WSE of 2 feet will cause a shoreward retreat of the shoreline and vegetation
loss below the OHWM.
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Photo 2 (by P.Pittman, 8/24/2013): Grant Lake typical “Landslide” Geomorphic Unit and field
interpretation.
Photo 3 (by P.Pittman, 8/24/2013): Grant Lake typical “Alluvial Fan Deposit” Geomorphic
Unit.
Headscarp
Landslide Debris
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Photo 4 (by P.Pittman, 8/24/2013): Grant Lake typical “Bedrock” Geomorphic Unit.
Photo 5 (by P.Pittman, 8/24/2013): Grant Lake typical “Bedrock” Geomorphic Unit at the Grant
Field Note: Lake narrows between the upper basin and lower basin. At low WSE conditions,
the gap will narrow and water depths will be 2-feet or less, and it is anticipated that the
submerged topographic saddle is bedrock.
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Photo 6 (by P.Pittman, 8/24/2013) Field Note: Grant Lake pocket beach along a bedrock
shoreline.
Photo 7 (by P.Pittman, 8/24/2013): Grant Lake typical “Alluvial Fan Deposit” Geomorphic Unit
showing contribution from both alluvial transport and avalanche activity.
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Photo 8 (by P.Pittman, 8/24/2013): Grant Lake typical “Colluvium” Geomorphic Unit.
Photo 9 (by P.Pittman, 8/24/2013): Field Note - Evidence of shoreline erosion occurring on an
“Alluvial Fan Deposit” Geomorphic Unit.
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Grant Lake Hydroelectric Project Kenai Hydro, LLC
FERC No. 13212 Appendix 1 Page 6 June 2014
Photo 10 (by P.Pittman, 8/24/2013): “Alluvial Fan” Geomorphic Unit.
Field Note - Streams along the Grant Lake shoreline are susceptible to WSE and incision,
armoring, channel straightening, and loss of floodplain connectivity is anticipated with decreases
in WSE, particularly if WSE remains low during high flow conditions.
Photo 11 (by P.Pittman, 8/24/2013): Grant Lake typical “Alluvial Deltaic” Geomorphic Unit at
Inlet Creek.
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Photo 12 (by P.Pittman, 8/24/2013): Field Note - Interspersed alluvial fan and colluvium
deposits dominate the shoreline of the Grant Lake upper basin.
Photo 13 (by P.Pittman, 8/24/2013): Field Note - Accumulation of organic debris and forest
encroachment at a shallow gap in the Grant Lake narrows between the upper and lower basin.
This accumulated debris will likely be inundated and dislodged when the lake WSE is increased.
During low WSE conditions, an isthmus will be exposed.
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Photo 14 (by P.Pittman, 8/24/2013): Field Note - WSE increase cause a retreat of shoreline
vegetation and temporary shoreward erosion will occur as a result of the loss of root strength and
winnowing of finer sediments and soils. The erosion should self-mitigate once root strength and
vegetation can reestablish in the disturbed areas.
Photo 15 (by P.Pittman, 8/24/2013): Field Note - Steep bedrock shorelines dominate the
shoreline areas of the Grant Lake lower basin.
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Photo 16 (by HDR, circa spring 2009): Field Note - Low WSE under natural conditions at the
“Beach Deposit” Geomorphic Unit.
Photo 17A (by HDR, 6/10/2009)
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Photos 17B (by HDR, 6/10/2009)
Photos 17A and 17B: Field Note - Grant Lake outlet at Grant Creek. Bedrock sill grade control
visible beneath water (approximately 2 feet deep estimated at time of field visit.
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Photo 17C (by HDR, circa spring 2009): Field Note - Grant Lake outlet at Grant Creek where
the proposed gravity diversion structure will be constructed.
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