Shoreline Erosion in
Hells Canyon
Gary L. Holmstead
Terrestrial Ecologist
Technical Report
Appendix E.3.2-42
Hells Canyon Complex
FERC No. 1971
October 2001
Revised July 2003
Copyright © 2003 by Idaho Power Company
Idaho Power Company
Shoreline Erosion In Hells Canyon
TABLE OF CONTENTS
Table of Contents ............................................................................................................................. i
List of Tables.................................................................................................................................. iv
List of Figures ................................................................................................................................. v
List of Appendices .......................................................................................................................... v
Executive Summary ........................................................................................................................ 1
1. Introduction ................................................................................................................................ 4
2. Study Area.................................................................................................................................. 5
2.1. Location............................................................................................................................. 5
2.2. Political Boundaries .......................................................................................................... 7
2.3. Land Features .................................................................................................................... 7
2.4. Climate .............................................................................................................................. 8
2.5. Vegetation ......................................................................................................................... 9
3. Plant Operations ....................................................................................................................... 11
4. Methods.................................................................................................................................... 12
4.1. Issue Identification .......................................................................................................... 12
4.2. Inventory of Current Conditions ..................................................................................... 12
4.3. Current Condition Analysis and Assessment .................................................................. 13
5. Results ...................................................................................................................................... 14
5.1. Potential for Mass Soil Movements ................................................................................ 14
5.2. Factors Potentially Influencing Soil Erosion and Bank Stability.................................... 16
5.2.1. Climate ................................................................................................................... 17
5.2.2. Upland Ground Cover ............................................................................................ 17
5.2.3. Soil Type ................................................................................................................ 18
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5.2.4. Topography ............................................................................................................ 19
5.2.5. Riparian Vegetation Cover..................................................................................... 19
5.2.6. Groundwater Seepage ............................................................................................ 20
5.2.7. Floods ..................................................................................................................... 21
5.2.8. Wind-Driven Waves............................................................................................... 21
5.2.9. Boat-Driven Waves ................................................................................................ 22
5.2.10. Hydroelectric Operations (River and Reservoir Flows)....................................... 22
5.2.11. Livestock .............................................................................................................. 24
5.2.12. Roads.................................................................................................................... 25
5.2.13. Recreation............................................................................................................. 25
5.3. Current Conditions Inventory ......................................................................................... 25
5.3.1. Weiser Reach.......................................................................................................... 26
5.3.2. Brownlee Reservoir Reach..................................................................................... 27
5.3.3. Oxbow Reservoir Reach......................................................................................... 27
5.3.4. Hells Canyon Reservoir Reach .............................................................................. 28
5.3.5. Downriver Reach.................................................................................................... 29
6. Discussion ................................................................................................................................ 29
6.1. General Findings ....................................................................................................... 29
6.2. Weiser Reach............................................................................................................. 31
6.3. Brownlee Reservoir Reach........................................................................................ 31
6.4. Oxbow Reservoir Reach............................................................................................ 32
6.5. Hells Canyon Reservoir Reach ................................................................................. 33
6.6. Downriver Reach....................................................................................................... 34
6.7. Management Implications ......................................................................................... 35
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7. Acknowledgments.................................................................................................................... 36
8. Literature Cited ........................................................................................................................ 36
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LIST OF TABLES
Table 1.
Distribution of shoreline miles by reach and shoreline source in the
Hells Canyon Study Area...................................................................................... 43
Table 2.
Distribution of shoreline erosion sites by surface area class for each reach
in the Hells Canyon Study Area............................................................................ 43
Table 3.
Partial characteristics of the shoreline erosion sites in each reach of the
Hells Canyon Study Area...................................................................................... 44
Table 4.
Summary of cover types present on the 9 sites mapped in the Weiser
Reach of the Hells Canyon Study Area. Dominant refers to the cover type
covering a majority of the site margins. Associated refers to the cover type
covering only portions of the site margins. ........................................................... 45
Table 5.
Summary of cover types present on the 261 sites mapped in the
Brownlee Reservoir Reach of the Hells Canyon Study Area. Dominant
refers to the cover type covering a majority of the site margins. Associated
refers to the cover type covering only portions of the site margins. ..................... 46
Table 6.
Summary of cover types present on the 9 sites mapped in the
Oxbow Reservoir Reach of the Hells Canyon Study Area. Dominant refers
to the cover type covering a majority of the site margins. Associated refers
to the cover type covering only portions of the site margins. ............................... 47
Table 7.
Summary of cover types present on the 39 sites mapped in the
Hells Canyon Reservoir Reach of the Hells Canyon Study Area. Dominant
refers to the cover type covering a majority of the site margins. Associated
refers to the cover type covering only portions of the site margins. ..................... 48
Table 8.
Summary of cover types present on the 60 sites mapped in the reach below
Hells Canyon Dam in the Hells Canyon Study Area. Dominant refers to
the cover type covering a majority of the site margins. Associated refers to
the cover type covering only portions of the site margins. ................................... 49
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LIST OF FIGURES
Figure 1.
Location of the Hells Canyon Study Area. ........................................................... 51
Figure 2.
Köppen climate diagrams for the Weiser, Richland, Brownlee, and
Lewiston weather stations, in the Hells Canyon Study Area on the Idaho–
Oregon border. ...................................................................................................... 53
Figure 3.
Distribution by surface area class of soil types and shoreline erosion sites
within the Hells Canyon Study Area. (16 panels)................................................. 55
LIST OF APPENDICES
Appendix 1.
Summary of some soil characteristics using USDA Natural Resources
Conservation Service (1995) published information for the Hells Canyon
Study Area............................................................................................................. 87
Appendix 2.
Summary of shoreline soil inventory data for the Hells Canyon Study
Area. ...................................................................................................................... 94
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EXECUTIVE SUMMARY
From 1998 through 2001, Idaho Power Company ecologists investigated shoreline erosion along
the Snake River in Hells Canyon, from Weiser, Idaho, downstream to the confluence with the
Salmon River. The objectives were to 1) conduct a literature review to identify and summarize
information on the occurrence of erosion, the erodability of soils, and the potential for mass
movement of shoreline soils in the study area; 2) conduct a literature review to gather
information on the factors that cause shoreline soil erosion and the relative influence such factors
have on erosion in the study area; 3) inventory shoreline soil erosion in the study area; 4) assess
and summarize the factors that affect shoreline erosion in the study area; and 5) develop a
geographic information system (GIS) thematic coverage of shoreline erosion for the study area,
to be used in various other studies and analyses of natural resources in the Hells Canyon area.
The focus of this study was erosion of soils along and above the shoreline banks, not the
detachment and transport of sediments along the river’s bed.
Based on studies of environments similar to Hells Canyon, the principal factors affecting
shoreline erosion in the canyon were climate, upland ground cover, soil type, topography,
riparian vegetation, groundwater seepage, floods, wind-driven waves, boat-generated waves,
hydroelectric operations, livestock, roads, and recreation.
In this study, a field crew, using appropriate watercraft, searched for erosion sites in the study
area. The objective of this field survey was to inventory both thin, linear-shaped erosion sites and
larger, polygon-shaped erosion sites along the shoreline. The minimum mapping unit (MMU) for
thin, linear-shaped sites was at least 1 m high and 6 m long, for sites located above the normal
high-water level. The MMU for larger erosion sites was at least 3 m high and 6 m long. We
inventoried large slumps on the upland slopes, where the soil surface had fractured down to the
shoreline.
We inventoried approximately 432 mi of shoreline in the study area. By location, distribution of
miles was 185.5 mi in Idaho, 204.8 mi in Oregon, and 41.7 mi on islands. A total of 378
shoreline erosion sites were recorded, covering 57.4 mi, or 13.3%, of the shoreline inventoried.
The most common surface area for erosion sites (n = 104) ranged from 101 to 250 m2. Many
other sites (n = 82) occurred in the surface-area classes of 26 to 100 m2 and 251 to 500 m2
(n = 73). The smallest site mapped was 10 m long and 1 m high, and the largest site was 4,800 m
long and 7 m high. The total area of erosion sites in the study area was 100.7 acres. Excluding
sites in the upstream, unimpounded reach, 90.1 acres of erosion occurred along reaches
potentially influenced by HCC operations.
For analysis and discussion purposes, we divided the study area into 5 reaches. The upstream,
unimpounded Weiser Reach has relatively large amounts of bank erosion, 9 sites along about
7% of the available shoreline (3.4 mi of 45.8 mi). We estimated the total area of erosion at
10.58 acres. All sites were relatively large (3 to 20 m high and several hundred or several
thousand meters long) and occurred mostly where the river channel intercepted steep banks.
Although the banks in this reach are generally covered in relatively thick stands of riparian
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vegetation (40% cover of riparian vegetation within a 20-m shoreline corridor), water currents
are still capable of reworking the shorelines.
The Brownlee Reservoir Reach had the highest rate of bank erosion, 261 sites (69% of all sites)
along about 27% of the available shoreline (49.6 mi of 182.3 mi). Many sites (n = 43) were quite
large, belonging to the surface-area class of 1,001 to 5,000 m2. We estimated the total area of
erosion at 79.07 acres. Most erosion in this reach occurred below Farewell Bend, Oregon, where
the reservoir winds through mountains characterized by long, narrow ridges, V-shaped tributary
canyons, and steep, predominantly soil-covered slopes. The potential for mass soil movements is
extremely high because relatively deep, highly erodable soils are perched on steep slopes. Large
water-level fluctuations on Brownlee Reservoir undercut shoreline banks and accelerate bank
slumping and landslides of these erosion-prone soils, especially because they occur on steep
slopes. Because drawdowns are necessary for the reservoir to function for flood control,
anadromous fishery purposes, and hydroelectric generation, the effects of water-level
fluctuations on erosion cannot be attributed only to one operational purpose. Shorelines along
Brownlee Reservoir are susceptible to other natural and anthropogenic influences, including
wind-driven waves, boat-generated waves, groundwater seepage, grazing, roads, and recreation
(for example, bank fishing and camping in undeveloped sites).
The Oxbow Reservoir Reach had relatively little bank erosion, 9 sites along about 2% of the
available shoreline (0.51 mi of 25.0 mi). We estimated the total area of erosion at 1.34 acres. The
potential for mass soil movements is extremely high in this reach. Soils tend to be shallower than
those along Brownlee Reservoir, and more shoreline substrates are dominated by bedrock and
boulders of angular basalt. Shoreline slopes greater than 40 degrees are common. Because
Oxbow Reservoir is a reregulating reservoir, water levels fluctuate less dramatically than on
Brownlee Reservoir. These narrower fluctuations disturb the shoreline less than larger
fluctuations, and, therefore, riparian vegetation, which helps protect shoreline banks, is more
easily established. Shorelines along Oxbow Reservoir are susceptible to other natural and
anthropogenic influences, including wind-driven waves, boat-generated waves, grazing, and
recreation (for example, bank fishing and use of dispersed campsites).
The Hells Canyon Reservoir Reach had relatively little bank erosion, 39 sites occurring along
about 2.7% of the available shoreline (1.45 mi of 53.9 mi). We estimated the total area of erosion
at 3.45 acres. The potential for mass soil movements is extremely high in this reach. Slopes are
extremely steep (often greater than 60 degrees), and soils are usually shallow, when present. No
published soil survey information is available for most of the lower reaches in Hells Canyon, but
field observations indicate that soil becomes increasingly shallow along the reservoir to
Hells Canyon Dam. Like Oxbow Reservoir, Hells Canyon Reservoir reregulates flows from
upstream projects. Because Hells Canyon Reservoir is relatively stable, the shoreline is disturbed
less than at Brownlee Reservoir, and riparian vegetation, which helps protect the shoreline, is
able to become established. Shorelines along Hells Canyon Reservoir are susceptible to other
natural and anthropogenic influences, including wind-driven waves, recreation (for example,
bank fishing and use of dispersed campsites), channel flow, boat-driven waves, and roads.
The reach below Hells Canyon Dam had relatively little bank erosion, 60 sites along 2.1% of the
available shoreline (2.44 mi of 125 mi). We estimated the total area of erosion at 6.34 acres.
Below Hells Canyon Dam, the Snake River continues through the deep gorge of Hells Canyon.
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Slopes are extremely steep in the upper portions of the reach, often greater than 60 degrees, and
soils are usually shallow, when present. No published soil survey information is available for this
reach. Mass movements can be expected at any time along the main canyon and in side canyons.
Many of the canyon walls are precipitous, and rocks are crumbly and severely weathered.
Shoreline substrates are diverse, but are composed almost entirely of large basalt outcrops
(bedrock) and large boulders and cobbles, with few sands or gravels. The coarseness of shoreline
substrates reduces the potential for shoreline erosion. Most bank erosion occurred upslope of the
typical fluctuation zone and summer base flows, indicating that these areas were affected during
high flows. Boat-generated waves apparently can influence most shoreline erosion sites. Both
private and commercial jet boats are common in this reach, with some of the largest boats being
up to 42 ft long and carrying up to 55 passengers. Boat-driven waves erode riverbanks much
higher up the slope than current water levels. Shorelines below Hells Canyon Dam are also
susceptible to recreation disturbance (for example, camping and hiking trails), alluvial flooding,
and roads.
Given that the reservoirs in the HCC are relatively recent features, and assuming that they will
continue to function much as they currently do, some level of erosion is expected until the new
shorelines reach equilibrium with the existing ecological and imposed anthropogenic influences.
It may not be practical or feasible to stabilize and revegetate most of the shoreline erosion sites
in the study area. The steep topography and remoteness of the canyon makes reaching and
working on most sites logistically challenging. Unless control measures are designed and
installed properly to correct an erosion problem at its source, they will not work. Improper
design or implementation often causes problems more severe than the original problem.
Management actions would be best directed at controlling those human-caused activating factors
that trigger erosion on shoreline banks. These actions should focus on minimizing water-level
fluctuations, controlling recreation influences (for example, boat-driven waves, camping, trails,
and vehicle access), minimizing the effects of road and other construction and maintenance
activities, and reducing livestock grazing effects. Given that fluctuations are necessary if the
HCC continues to be used for flood control, anadromous fish spawning and protection,
downstream navigation, and hydroelectric generation, it may not be possible to eliminate all
negative anthropogenic impacts. Because streambank erosion is a natural geomorphic process,
the challenge is to minimize excessive rates of erosion in Hells Canyon.
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1. INTRODUCTION
Soil erosion is broadly defined as the detachment and transport of soil particles by abiotic and/or
biotic influences. The primary sources of erosion in upland ecosystems in the United States are
agriculture, silviculture, mining, and construction. Although agriculture produces the largest
percentage of the total sediment load, construction causes the most concentrated form of erosion
(Goldman et al. 1986). The four principal factors often considered in soil erosion are climate, soil
characteristics, topography, and ground cover. They form the basis of the universal soil loss
equation (USLE), which is a method for quantifying the interaction of the factors to estimate the
tonnage of soil loss per year (Wishmeier and Smith 1978, Goldman et al. 1986). A great portion
of the work of the Natural Resources Conservation Service in the United States concerns creating
detailed soil maps and recommending management systems, based on the USLE factors, for
different kinds of soils.
In addition to factors affecting soil erosion in upland settings, erosion along streambanks is
controlled by numerous natural properties of the river environment. These natural properties can
vary over time and space along the river. Such variable properties include the depth, velocity,
approach angle, and sediment content of the river; the type and density of vegetation; the height
and slope of the banks; the soil type; and the size of particles making up the potentially eroded
material. Leopold and Maddock (1953) and Osterkamp et al. (1983) describe in detail the roles
of some of these properties along riverine environments.
Streambank erosion is a natural geomorphic process that cannot and should not be completely
eliminated (Olson 1983, Dorava and Moore 1997). Natural erosion occurs as a result of many
factors acting alone or in concert. Streambank erosion is necessary to the health of fishproducing systems, providing the spawning gravels and stream morphology necessary to
maintain all life stages. Shoreline erosion can create or improve certain wildlife habitats. The
steep, bare banks offer excellent shallow denning areas, dead trees may provide nesting cavities,
and submerged fallen trees improve the fishery habitat. In many cases, shoreline erosion creates
beach and sandbar habitats that provide valuable resting and foraging areas, especially for
shorebirds (U.S. Army Corps of Engineers 1992a).
However, excessive erosion and sedimentation can cause both environmental and economic
impacts. Eroded soil contains nitrogen, phosphorus, and other nutrients, which, when carried into
water bodies, can trigger algal blooms that reduce water clarity, deplete oxygen, lead to fish kills,
and create odors. Excessive streambank erosion can increase turbidity, reduce in-channel depth,
and decrease streamside vegetation (Smith and Patrick 1979, Stern and Stern 1980, Yousef 1974,
U.S. Army Corps of Engineers 1992a). Excessive deposition of sediments in streams can blanket
the bottom fauna and destroy fish spawning areas. Additionally, erosion removes the smaller and
less dense constituents of topsoil. These constituents—clay, fine silt particles, and organic
material—hold nutrients that plants require. The remaining subsoil is often hard, rocky, infertile,
and droughty. Thus, reestablishment of vegetation is difficult and the eroded soil produces less
growth (Goldman et al. 1986).
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Economic impacts are difficult to quantify. It is difficult to set a value on loss of aquatic habitats
or diminished water clarity. As mentioned previously, erosion diminishes the ability of the soil to
support plant growth, and restoring this ability costs money. When streambank erosion
accelerates above normal rates, controversy often develops about the cause of the increased
erosion and how best to mitigate it. Each of these issues has an economic effect that, while
difficult to quantify, is significant.
The objectives of this study were to 1) conduct a literature review to identify and summarize
information on occurrence, erodability, and potential for mass movement of shoreline soils in the
study area; 2) conduct a literature review to gather information on the types of factors potentially
causing shoreline soil erosion and the relative influence of such factors on erosion in the study
area; 3) inventory shoreline soil erosion in the study area; 4) assess and summarize factors
affecting shoreline erosion in the study area; and 5) develop a geographic information system
(GIS) for thematic coverage of shoreline erosion for the study area, to be used in various other
studies and analyses regarding natural resources in the Hells Canyon area. The focus of this
study is on erosion of soils along and above the shoreline banks, not the detachment and
transport of sediments along the river’s bed. For information regarding sediment transport issues
in Hells Canyon, see Parkinson et al. (2001).
2. STUDY AREA
2.1. Location
Hells Canyon is situated in west-central Idaho and northeastern Oregon (Figure 1) and is over
160 mi long (from approximately RM 351-188). The Snake River, a major tributary to the
Columbia River, is the primary feature of Hells Canyon. The Snake River, generally flowing
northward, forms the boundary between Idaho and Oregon. Idaho Power Company’s (IPC)
Hells Canyon Complex (HCC) is located on the Snake River in the southern portion of
Hells Canyon and includes three hydroelectric dams and reservoirs: Brownlee, Oxbow, and
Hells Canyon. In the river reach below Hells Canyon Dam, the Snake River is unimpounded,
although the flows are controlled by the three-dam complex. The study area for this investigation
encompassed all lands along the Snake River and associated reservoirs along 163 river miles,
from the bridge (RM 351.2) near Weiser, Idaho, downriver to the confluence with the
Salmon River (RM 188.2), upriver of Lewiston, Idaho. It includes all associated river arms in
Brownlee Reservoir. The lateral extent of the study area included all lands within 0.25 mi of each
shoreline.
For analysis and discussion purposes, the study area was divided into five reaches (Table 1).
These reach boundaries were based on distinct geomorphic features, river characteristics, and
legal project boundaries.
The most upstream reach above Brownlee Reservoir, the Weiser Reach, is a 12.0-mi-long
unimpounded reach, running from the bridge near Weiser (RM 351.2) to Cobb Rapids
(RM 339.2). Flows in the Snake River are regulated by several hydroelectric facilities above
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RM 458 and by three major tributary rivers: the Boise River, which enters the Snake River at
RM 394 and is regulated by two flood control dams; the Payette River, which enters the
Snake River at RM 365.5 and is unregulated; and the Weiser River, which enters just upstream
of the Weiser Reach at RM 351.8 and is also unregulated. Although, compared with other study
reaches, the Weiser Reach is geomorphically distinct and surrounded by unique land uses,
including it in the study provides insight to some of the physical and biological factors
potentially influencing downstream reaches.
The Brownlee Reservoir Reach is 55.5 mi long, extending from Cobb Rapids (RM 339.2) to
Brownlee Dam (RM 283.7). Brownlee has a maximum depth approaching 300 ft near the dam
and has the potential for 101-ft drawdowns during late winter, as regulated by the U.S. Army
Corps of Engineers for flood control. In late summer and early fall, water in Brownlee Reservoir
is also used to aid the recovery and protection of anadromous fish, as directed by the National
Marine Fisheries Service. Since the early 1990s, the reservoir has been drawn down to provide
spawning flows and redd protecting flows downstream of Hells Canyon Dam. One of the most
dominant habitat features of Brownlee Reservoir is the transition zone between riverine habitat
and lacustrine habitat, typical of large mainstem reservoirs. The zone is especially pronounced
by reduced turbidity along a longitudinal gradient in Brownlee Reservoir. This reservoir serves
as a sedimentation basin, resulting in notably less turbid water leaving the Hells Canyon system.
A similar gradient is noticeable on a smaller scale in the Powder River arm of
Brownlee Reservoir. The Brownlee Dam hydroelectric facilities are capable of producing
585,400 kW of electricity.
The Oxbow Reservoir Reach is 14.2 mi long and extends below Brownlee Dam (RM 283.7) to
the Oxbow Dam (RM 269.5). Oxbow Dam is relatively narrow and shallow, with maximum
depths approaching 100 ft. The Snake River from the tailrace of Brownlee Dam to the mouth of
Wildhorse Creek (1 mi downstream) is a high-velocity narrow channel. Oxbow Dam is a
190,000-kW facility.
The Hells Canyon Reservoir Reach extends 22.0 mi below Oxbow Dam (RM 269.5) to
Hells Canyon Dam (RM 247.5). Hells Canyon Reservoir is also relatively narrow, with
maximum depth approaching 200 ft. The unique design of the Oxbow powerhouse and dam
results in a 2-mi stretch of the original river channel (from Oxbow Dam to the outflow of the
powerhouse) that flows at a minimum of 100 cfs, creating a backwater area that is relatively
shallow and slow. Indian Creek enters the Snake River in the Hells Canyon Reservoir Reach.
Reservoir shorelines are generally very steep, with substrates primarily of basalt outcrops and
talus slopes. The Hells Canyon powerhouse is a 391,500-kW facility.
The downstream reach runs for 59.3 mi, from Hells Canyon Dam to the confluence of the Snake
and Salmon rivers (RM 188.2). This unimpounded reach of Hells Canyon is considered the
deepest gorge in North America and is surrounded at the upstream end by nearly vertical cliff
faces. At the mouth of Granite Creek, approximately 7 mi below Hells Canyon Dam, the river
elevation is 1,480 ft and the canyon depth is 7,913 ft. The canyon becomes somewhat wider near
Johnson Bar (RM 230), with moderate to steep topography continuing to the Salmon River.
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2.2. Political Boundaries
Population centers within a 100-mi radius of some portion of Hells Canyon include Boise,
Cambridge, Council, Fruitland, Lewiston, Nampa, Payette, Riggins, and Weiser on the Idaho
side, and Baker City, Enterprise, Huntington, La Grande, Ontario, and Richland on the Oregon
side. Many of the people who use and benefit from the natural resources of Hells Canyon live in
these cities and towns.
The HCC is located within and across the political boundaries of Idaho, Adams, and Washington
counties in Idaho, and Wallowa, Baker, and Malheur counties in Oregon. State agencies with
direct responsibility for wildlife population and habitat management are the Idaho Department of
Fish and Game (IDFG) and the Oregon Department of Fish and Wildlife (ODFW). These
agencies also administer several areas within Hells Canyon specifically for wildlife habitat,
including the Cecil D. Andrus Wildlife Management Area in Idaho. Federal agencies, such as the
U.S. Department of the Interior (USDI) Bureau of Land Management (BLM) and the
U.S. Department of Agriculture (USDA) Forest Service (USFS), are responsible for managing
the majority of public lands in Hells Canyon. These areas fall within the jurisdictional
boundaries of the Wallowa-Whitman National Forest in Oregon; Payette National Forest in
Idaho; Nez Perce National Forest in Idaho; the Four Rivers Field Office (FO) of the Lower
Snake River District of the BLM in Idaho; Cottonwood FO of the Upper Columbia-Salmon
Clearwater District of the BLM in Idaho; and Baker FO and Malheur FO of the Vale District of
the BLM in Oregon. Other government agencies with natural resource jurisdiction in the greater
project area include the Idaho Department of Lands, the USDI National Marine Fisheries
Service, the USDI Bureau of Indian Affairs, and the USDI Fish and Wildlife Service.
Several special management areas also occur in Hells Canyon and are directly administered by
the USFS. These include the Eagle Cap Wilderness in Oregon, the Hells Canyon Wilderness in
Idaho and Oregon, the Hells Canyon National Recreation Area (HCNRA) in Idaho and Oregon,
the Wild and Scenic Imnaha River in Oregon, the Seven Devils Scenic Area in Idaho, and the
Wild and Scenic Snake River.
2.3. Land Features
Hells Canyon, the deepest and one of the most rugged river gorges in the continental United
States, ranges from 2,000 to 3,000 ft deep between Weiser and Oxbow Dam. Below
Oxbow Dam, the canyon enters a narrow, steep-sided chasm that is up to 5,500 ft deep. From the
confluence with the Grande Ronde River, the Snake River flows onto a lava-filled basin and
through a much shallower canyon to Lewiston, Idaho (U.S. Department of Energy 1985). The
elevation of the Snake River near Weiser is about 2,090 ft msl, descending to about 910 ft msl at
the confluence with the Salmon River, about 59 mi below Hells Canyon Dam.
Throughout the canyon, topography is generally steep and broken, with slopes often dominated
by rock outcrops and talus slopes. At the deepest points of the canyon, the walls rise almost
vertically. Canyon walls are deeply dissected by numerous side canyons, which often support
tributaries to the Snake River. The upper reaches of the canyon walls are formed by the
Seven Devils Mountains to the east and the Wallowa Mountains to the west, both of which are
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comprised of jagged peaks reaching to almost 10,000 ft and having subalpine and alpine
conditions (U.S. Forest Service 1990).
Hells Canyon consists of a series of complexly folded and faulted, metamorphosed sediments
and volcanics overlain uncomformably by nearly horizontal flows of Columbia River basalt.
This basalt group covered much of eastern Washington, northern Oregon, and adjacent parts of
Idaho (Bush and Seward 1992). The older rocks in the series are Permian to Jurassic in age and
represent at least two episodes of island arc volcanism and adjacent marine sedimentation similar
to that found in the Aleutian Islands west of Alaska. These rock units represent old island arc
chains that were sequentially “welded” to the west coast of North America during the late
Paleozoic and early to mid-Mesozoic eras by subduction of a tectonic plate beneath the North
American Continental tectonic plate (Asherin and Claar 1976, U.S. Forest Service 1994).
In more recent geologic time, Hells Canyon was formed by the Snake River’s erosion of the
Blue Mountains in Oregon and the Seven Devils Mountains in Idaho (U.S. Department of
Energy 1985). The Snake River has existed from the Pliocene and probably cut to its present
level during the Pleistocene. During the Pleistocene, glacial meltwater provided abundant runoff
for down-cutting, while regional uplifting provided weak points in the 2,000- to 3,000-ft-thick
basalt plateau that overlaid the Blue and Seven Devils Mountains. Resulting erosion formed the
currently observed drainage pattern that established the Snake River (U.S. Department Energy
1985). Northeast-trending, high-angle fault patterns characterize the extensive Snake River fault
system running throughout the study area (Fitzgerald 1982).
Besides basalt, other rock types are also present within the study area. Extensive limestone
outcrops are found in some tributary drains, and local granitic outcrops also occur.
The soils throughout Hells Canyon are composed primarily of Columbian River basalt, covered
in most areas with a thin mantle of residual soils from weathered native rock. Isolated areas
contain deposits of windblown silt. Unconsolidated materials include river sands and gravel
deposited during the Bonneville floods 15,000 years ago, ash-loess from the Mount Mazama
eruption 6,900 years ago, and more recent colluvium and talus. Soil cover amounts decline
northward through Hells Canyon to a point near Hells Canyon Dam (RM 247.5), where most
rock faces are nearly vertical and have little soil cover (U.S. Forest Service 1994).
Most soil complexes are well drained and vary from very shallow to moderately deep. Loams are
the dominant textural class and vary from very stony to silty, often with a clay subsoil
component (Natural Resources Conservation Service 1995).
2.4. Climate
From late fall to early spring, the climate of west-central Idaho and eastern Oregon is typically
influenced by cool and moist Pacific maritime air. Periodically, this westerly flow is interrupted
by outbreaks of cold, dry, continental air from the north, normally blocked by mountain ranges to
the east. During summer months, a Pacific high-pressure system dominates weather patterns,
resulting in minimal precipitation and more continental climatic conditions overall (Ross and
Savage 1967).
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Hells Canyon, located in the High Desert region, is significantly influenced by the rain shadow
of the Cascade Mountain Range. The area is considered arid to semiarid with warm to hot, dry
summers and relatively cold winters (Harker et al. 1993). During winter, lower elevations in
Hells Canyon are generally milder (warmer temperatures and less snow accumulation) than
surrounding areas. Higher-elevation areas have greater precipitation and cooler temperatures
than the immediate canyon area.
Climatological information is summarized for Weiser, Richland, Brownlee Dam, and Lewiston
(Figure 2). Average annual precipitation is lowest at the southern end of the study area (Weiser,
286 mm), increases northward (Richland, 298 mm), peaks around Brownlee Dam (445 mm), and
declines toward Lewiston (326 mm). The average annual precipitation ranges from about 380 to
500 mm (15 to 20 inches), depending on elevation. Nearly 45% of the average annual
precipitation at Brownlee Dam (445 mm [17.8 inches]) falls from November through January;
this amount strongly contrasts with the 9% average recorded for July through September. Thus,
most precipitation occurs in spring and winter (Tisdale et al. 1969, Tisdale 1986, Johnson and
Simon 1987), and little or no precipitation falls during the hottest months of summer. Average
annual evapotranspiration is estimated to be about 1,300 mm (52 inches).
Mean annual temperatures are similar among the 4 weather stations. Generally, the climate tends
to become drier and warmer downstream of Brownlee Dam. Climatological information from
Brownlee Dam (RM 284.6) is probably characteristic of the central section of the study area. The
canyon bottom area is dry, with seasonal temperatures ranging from lows of about –5 °C in
January to highs of about 35 °C in July (Figure 2). Temperatures below freezing are normally
experienced from mid November through mid April. As a rule, winters higher in the canyons are
mild, while summers on the canyon floor may be hot. Mean temperatures at elevations above
2,000 m (6,562 ft msl) range from –9 °C in January to 13 °C in July. In contrast, mean
temperatures at elevations below 1,000 m (3,281 ft msl) range from 0 °C in January to between
28 °C and 33 °C in July (Johnson and Simon 1987).
2.5. Vegetation
The types of vegetation growing along the canyon slopes of the middle Snake River are the result
of three primary ecological factors: climate, topography, and soils. Climate exerts the strongest
influence on the development of plant life. The relatively mild winters below the canyon rim
have allowed the development of disjunct species. For example, hackberry (Celtis reticulata),
which is most often found in the southwestern states, commonly occurs in the middle and lower
Snake River area (Tisdale 1979, DeBolt 1992). Within the context of regional climate,
topography is a major influence on the development and distribution of vegetation (Tisdale et al.
1969; Tisdale 1979, 1986). The topographical complexity of Hells Canyon has produced a
mosaic of vegetation types (Tisdale 1979, Bonneville Power Administration 1984). Grassland,
shrubland, riparian (or wetland), and coniferous forest communities exist in close proximity.
Interfingering of grassland and forest, for example, occurs at a number of sites throughout the
canyon due to variations in aspect (Tisdale 1979).
Wetland and Riparian Communities
A narrow band of diverse riparian communities
intermittently follows the course of the Snake River and its many tributaries. Although limited in
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geographic area, this riparian zone is vital because of its biological diversity. Emergent wetland
communities are composed mostly of broad-leaved pepperweed (Lepidium latifolium), marsh
grass (Heleochloa alopecuroides), purple loosestrife (Lythrum salicaria), common cocklebur
(Xanthium strumarium), hemp dogbane (Apocynum cannabinum), alkali saltgrass (Distichlis
stricta), and purslane (Portulaca oleracea). Predominant shrub species in riparian areas include
netleaf hackberry (Celtis reticulata), false indigo (Amorpha fruticosa), coyote willow (Salix
exigua), common chokecherry (Prunus virginiana), poison ivy (Toxicodendron radicans),
syringa (or mock orange, Philadelphus lewisii), Himalayan blackberry (Rubus discolor), and
tamarisk (Tamarix parviflora). Predominant tree species include water birch (Betula
occidentalis), white alder (Alnus rhombifolia), black cottonwood (Populus trichocarpa), silver
maple (Acer saccharinum), and peachleaf willow (Salix amygdaloides). Most weedy exotic
species occur at and above the headwaters of Brownlee Reservoir (Holmstead 2001).
Many shoreline sections have no riparian vegetation. Rather, upland vegetation on steep canyon
slopes simply meets the rocky shoreline. Grassland and shrubland communities are common
along the Snake River and its tributaries.
Herbaceous-Dominated Vegetation Types
The dry climate and typically stony, shallow soils
of the canyon have favored the development of grassland steppe communities at the lower and
middle elevations (Tisdale 1979, 1986). Commonly occurring grass species in the study area
include bunchgrasses, such as bluebunch wheatgrass (Agropyron spicatum) and Idaho fescue
(Festuca idahoensis), and annual grasses, such as cheatgrass (Bromus tectorum) and medusahead
wildrye (Taeniatherum caput-medusae) (Holmstead 2001). Other grasses, such as sand dropseed
(Sporobolus cryptandrus) and red threeawn (Aristida longiseta), are locally common (Bonneville
Power Administration 1984, Tisdale 1986).
Shrub-Dominated Vegetation Types
Shrub species comprise a large segment of the canyon’s
overall vegetation composition. Shrub-steppe vegetation types occur at mid-elevations in the
Hells Canyon Study Area, especially in its southern region (Bonneville Power Administration
1984). Commonly occurring shrubs include big sagebrush (Artemisia tridentata), bitterbrush
(Purshia tridentata), gray rabbitbrush (Chrysothamnus nauseousus), hackberry, and serviceberry
(Amelanchier alnifolia) (Bonneville Power Administration 1984, Tisdale 1986, Holmstead
2001). For the most part, sagebrush stands are limited to the area around Brownlee Reservoir. In
these stands, the herbaceous layer is dominated by cheatgrass, with a variety of forbs also
occurring.
Tree-Dominated Vegetation Types
Although coniferous forest communities are generally
restricted to the higher elevations of steep canyon slopes, they do reach down as far as the river
at certain locations. For example, stands of ponderosa pine (Pinus ponderosa) or Douglas-fir
(Psuedotsuga menziesii), typically with a common snowberry (Symphoricarpos albus)
understory, extend to the river on north-facing slopes at sites around the main bodies of Oxbow
and Hells Canyon reservoirs, and downstream of Hells Canyon Dam (Holmstead 2001).
Fourteen cover types—for natural features, land use, and vegetation—were identified along the
Snake River in the Hells Canyon Study Area (Holmstead 2001). The area that was classified
covered up to approximately 0.5 mi on both sides of the Snake River or associated reservoirs and
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extended from above Brownlee Reservoir at the town of Weiser, Idaho (RM 351.2), downstream
to the confluence with the Salmon River (RM 188.2). The dominant cover types were Grassland
(35.5%), Shrub Savanna (21.0%), Lotic (16.1%), Shrubland (6.6%), and Cliff/Talus (5.6%) All
remaining cover types covered less than 5% of the area classified.
3. PLANT OPERATIONS
Hells Canyon, on the Oregon–Idaho border, is the deepest canyon in North America and home to
IPC’s largest hydroelectric generating complex, the HCC. The HCC includes the Brownlee,
Oxbow, and Hells Canyon dams, reservoirs, and power plants. Operations of the three projects of
the complex are closely coordinated to generate electricity and to serve many other public
purposes.
IPC operates the complex to comply with the FERC license, as well as to accommodate other
concerns, such as recreational use, environmental conditions and voluntary arrangements.
Among these arrangements are the 1980 Hells Canyon Settlement Agreement, the Fall Chinook
Recovery Plan adopted in 1991, and, between 1995 and 2001, the cooperative arrangement that
IPC had with federal interests in implementing portions of the Federal Columbia River Power
System (FCRPS) biological opinion flow augmentation, which is intended to avoid jeopardy of
the FCRPS operations below the HCC.
Brownlee Reservoir is the only one of the three HCC facilities—and IPC’s only project—with
significant storage. It has 101 vertical feet of active storage capacity, which equals
approximately 1 million acre-feet of water. On the other hand, Oxbow and Hells Canyon
reservoirs have significantly smaller active storage capacities—approximately 0.5 and 1.0% of
Brownlee Reservoir’s volume, respectively.
Brownlee Dam’s hydraulic capacity is also the largest of the three projects. Its powerhouse
capacity is approximately 35,000 cubic feet per second (cfs), while the Oxbow and Hells Canyon
powerhouses have hydraulic capacities of 28,000 and 30,500 cfs, respectively.
Target elevations for Brownlee Reservoir define the flow through the HCC. However, when
flows exceed powerhouse capacity for any of the projects, water is released over the spillways at
those projects. When flows through the HCC are below hydraulic capacity, all three projects
operate closely together to re-regulate flows through the Oxbow and Hells Canyon projects so
that they remain within the 1-foot per hour ramp rate requirement (measured at Johnson Bar
below Hells Canyon Dam) and meet daily peak load demands.
In addition to maintaining the ramp rate, IPC maintains minimum flow rates in the Snake River
downstream of Hells Canyon Dam. These minimum flow rates are for navigation purposes and
IPC’s compliance with article 43 of the existing license. Neither the Brownlee Project nor the
Oxbow Project has a minimum flow requirement below its powerhouse. However, because of the
Oxbow Project’s unique configuration, a flow of 100 cfs is maintained through the bypassed
reach of the Snake River below the dam (a segment called the Oxbow Bypass).
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4. METHODS
4.1. Issue Identification
IPC conducted a hierarchical literature review to identify and summarize information on
occurrence, erodability, and potential for mass movements of shoreline soils in the study area.
We also reviewed the literature to identify the types of factors potentially influencing shoreline
soil erosion in environments similar to the Hells Canyon area to assess the relative magnitude of
such factors on soil erosion.
4.2. Inventory of Current Conditions
A field crew used appropriate watercraft to cruise the shoreline in search of active erosion sites.
We defined active erosion sites as sites having exposed bare soil above the normal high water
mark because of obvious alterations of the topography caused by disturbance, compared with
surrounding areas. These sites exhibited signs of recent erosion, such as fresh breaks in the soil
profile, exposed roots of vegetation, and chunks of sloughed-off soil at the base of the slope
(often with intact vegetation in the topsoil). Generally, we did not inventory historic erosion
sites. We defined historic erosion sites as those sites where the soil had slumped or otherwise
eroded in the past, compared with surrounding topography, and where vegetation had
recolonized (revegetated) the majority of the site. Some sites we inventoried contained segments
of historic erosion intermixed with active erosion. These were mapped as continuous sites and
noted as containing both active and historic components.
The objective of the field survey was to inventory both thin, linear-shaped and larger polygonshaped erosion sites along the shoreline. Thin, linear-shaped sites are typical of natural erosion
along shorelines at sites equilibrating with the recent (in geologic time) reservoir and river
fluctuations. The minimum mapping unit (MMU) for thin, linear-shaped sites was at least 1 m
high and 6 m long, located above the normal high-water level. The MMU for larger erosion sites
was at least 3 m high and 6 m long. We also inventoried large slumps on the upland slopes where
the soil surface had fractured down to the shoreline. Slumps that had broken free more than 5 m
upslope and run down the slope, even to the shoreline, were not inventoried.
We used a separate data sheet to inventory each site, and we gave each site a unique number.
Each site was photographed with a 35-mm camera using color slide film. Key components of the
inventory included 1) differential global positioning system (DGPS) coordinates; 2) an estimate
of the length and average height of the erosional area; 3) slope and aspect categories referring to
the topography in the vicinity of the site; 4) dominant vegetation cover types present;
5) associated vegetation cover types present; 6) an ocular estimate of total plant cover and total
cover by life-form (tree, shrub, herbaceous) in surrounding undisturbed areas; 7) potential
disturbance factors; and 8) evidence of beneficial uses of erosion sites by riparian vegetation and
wildlife. All sites were mapped in the field on USGS 7.5-minute topographic quadrangles.
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When an erosion site was located, we decided whether to document it as a point feature or as a
linear feature. Point features were usually from 6 to 50 m long. For point features, we collected
location coordinates from the boat while using a hand-held global positioning system (GPS) unit
(the Trimble GeoExplorer®). The boat was held as steady as possible, usually about 10 m
offshore, at the approximate midpoint of the site. We photographed the site from this position,
while focusing on a representative view. For linear features, we collected two GPS coordinate
files from the boat, one at each end of the site. These sites were usually greater than 50 m long.
One (or more) representative color slide photograph was taken of the site. Because it was
difficult to map individual sites when they occurred continuously and in close proximity to each
other along the shoreline, the observer indicated whether or not the site was a composite. A
composite site consisted of several adjacent sites mapped as one site. Such a site was always
recorded as a linear feature. For composite sites, we recorded the percentage of the site area that
was actually eroded (in 10% intervals).
4.3. Current Condition Analysis and Assessment
We differentially corrected the GPS data points and linear features and determined Universal
Transverse Mercator (UTMs) coordinates for each site. These coordinates were used to build a
GIS for thematic coverage of erosion sites. The corrected coordinates were used in conjunction
with an existing GIS for shoreline coverage to plot erosion site locations. The coordinates were
snapped to a location on the shore that was perpendicular from the shoreline to the boat position.
If the site was inventoried as a point feature, the length of the site was entered into the GIS from
field observation data. For example, if a site was estimated to be 30 m long in the field, a
distance of 15 m was assigned to each side of the GIS shoreline location. If the site was
inventoried as a linear feature, the length of the site was calculated from the GIS data by
calculating the distance between the two points along the GIS shoreline location. This length,
rather than the estimated length value recorded on the field data sheet, was used in the database
and in area calculations.
All field data were entered into a spreadsheet database (in Microsoft Excel 2000®) and saved as
an ASCII comma-delimited file. This file was used to link the GIS spatial locations to field
attributes using ARC/INFO® software. A GIS thematic coverage was built for shoreline soil
erosion sites. The GIS software was used to calculate total shoreline miles covered during the
surveys and total length of shoreline with erosion sites. We plotted shoreline erosion sites by
surface-area classes. Sites were plotted with colors ranging from green to yellow, and then from
yellow to red as the estimated surface areas of erosion sites increased. This thematic coverage is
used as ancillary information regarding other terrestrial, aquatic, and recreation resources for
developing potential protection, mitigation, and enhancement measures for the HCC.
We did a qualitative assessment of the effects of current hydroelectric operations on shoreline
erosion by summarizing data about site characteristics and relevant information obtained from
the literature reviews. Of significant importance to this assessment were the location and size of
erosion sites, the most common disturbance factors recorded for the sites, and the relative
severity of disturbances.
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5. RESULTS
5.1. Potential for Mass Soil Movements
Upstream, the Snake River leaves the relatively flat lava- and sediment-filled Snake River Plain
of Idaho at Farewell Bend (Figure 1). Soils in the Weiser Reach and upper reaches of
Brownlee Reservoir are relatively deep and occur on flat to gentle topography. The Snake River
in this reach is a low-gradient (0.2–0.4 m/km) river, with several island complexes. The
influence of agriculture is apparent, with the many irrigation returns in the Weiser Reach and
upriver causing higher turbidities and increased nutrient loading. River substrates are small, with
fines and sand to medium-sized cobbles prevalent throughout (Johnson et al. 1992). The general
topography and characteristics of this region are not conducive to large mass movements.
However, shoreline banks in this reach can be undercut and eroded when influenced by the
tractive force of flowing water.
Between Farewell Bend and Oxbow Dam, the Snake River winds through a mountainous area
characterized by long narrow ridges; V-shaped tributary canyons; and steep, predominantly soilcovered slopes (Vallier 1998). This reach includes Brownlee and Oxbow reservoirs. For most of
this distance, the canyon is about 2,000 to 3,000 ft deep. The potential for mass soil movements
is extremely high, as evidenced by the many historic and recent slides in the area. Deep soils
perched on steep slopes are susceptible to movements ranging from small slumps a few meters
square to large failures several hectares in size. Following heavy rain or rapid snowmelt, new
slumps and erosion scarps on hillsides along Brownlee and Oxbow reservoirs can be readily
viewed by canyon visitors.
Shoreline substrates along Brownlee Reservoir are often complex and quite variable, ranging
from areas dominated by sand to areas dominated by bedrock, small- to medium-sized cobbles,
and boulders of angular basalt. Shoreline slopes in the range of 30 to 40 degrees are common.
Brownlee Reservoir has the potential for 101-ft drawdowns during late winter, as regulated by
the U.S. Army Corps of Engineers for flood control. In late summer and early fall, water in
Brownlee Reservoir is also used to aid the recovery and protection of anadromous fish, as
directed by the National Marine Fisheries Service. Large water-level fluctuations on
Brownlee Reservoir could cause undercutting of shoreline banks and accelerate bank slumping
and landslides on steep slopes, especially those that have soils prone to erosion. Bank slumping
may occur above or below the water line as gravity pulls materials downward. Slumping may
occur gradually as creep or catastrophically as a sudden slump.
Oxbow Reservoir is a relatively small, reregulating reservoir. Ninety percent of the time, its
water levels fluctuate daily within 5.6 ft of the normal, full-pool elevation. From the tailrace of
Brownlee Dam to the mouth of Wildhorse Creek (1 mi downstream of the tailrace), the
Snake River is a high-velocity, narrow channel. This reach tends to be susceptible to erosion of
shoreline soils on steep slopes that are subject to river flows. The Oxbow Reservoir Reach is
relatively narrow (maximum width is about 150 m) and shallow, with maximum depths
approaching 100 ft. Shorelines are primarily basalt outcrops and talus, except for alluvial fans
created by small tributaries. Shoreline soils tend to be stable along this reservoir because water
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levels fluctuate less here than at Brownlee Reservoir. Because water levels fluctuate less, there is
less shoreline disturbance (such as from the physical impact of waves and wetting/drying cycles)
and less interference to the soil-binding capabilities of vegetation roots. However, bank slumping
might still occur on this reservoir.
Below Oxbow Dam, the Snake River enters the deep gorge of Hells Canyon, which includes the
Hells Canyon Reservoir Reach and the unimpounded reach below Hells Canyon Dam. For more
than 60 mi, the river is 4,000 to 5,600 ft below the canyon’s western rim. Slopes are extremely
steep (often greater than 60 degrees), and soils are usually shallow, when present. No published
soil survey information is available for most of the lower reaches of Hells Canyon. Mass
movements should be expected at any time along the main canyon and in side canyons. Many of
the canyon walls are precipitous, and rocks are crumbly and severely weathered. Relatively large
earthquakes, as strong as magnitude 5 on the Richter scale and possibly as strong as magnitude 6,
have apparently occurred in the past and should be expected in the future (Vallier 1998). In
certain places, the rock strata dip steeply toward the river, particularly on the Idaho side in the
deeper parts of the canyon above and below Hells Canyon Dam. Large landslide and slump
deposits can be observed near the confluence with Copper Creek, near Bernard Creek, at
Rush Creek, between Marks and Waterspout creeks, and at Johnson Bar (Vallier 1998). Portions
of the hillside above Johnson Bar are gashed by small slump scarps that forecast future
landslides. Sections of that hillside may begin to move again after heavy rainfall saturates the
strata, particularly if an earthquake were to simultaneously shake the canyon slopes (Vallier
1998).
The Hells Canyon Reservoir is a reregulating reservoir and, 90% of the time, is operated within
3.8 ft of the normal, full-pool elevation. The reservoir shorelines are generally very steep, with
substrates primarily of basalt outcrops and talus slopes. Soil stability tends to be high along
Hells Canyon Reservoir shorelines because of its narrow fluctuations in water level and
coarseness of erodable substrates. Because the water level fluctuates narrowly, there is relatively
less shoreline disturbance (such as from the physical impact of waves and wetting/drying cycles)
than on Brownlee Reservoir, and shoreline vegetation is more easily established. However, bank
slumping might still occur.
Compared with the sediment transport capacity of the Weiser Reach, the steep gradient
(1.8 m/km) of the reach extending below Hells Canyon Dam to the confluence with the
Salmon River is capable of transporting approximately 16 times the amount of sediment (Blair et
al. 2001). Shoreline substrates are diverse; however, they are comprised almost entirely of large
basalt outcrops (bedrock), large boulders and cobbles, and very few sands or gravels (Miller et
al. 2001). Because the basic form and character of the river in this reach were established under
vastly higher flow conditions, the bed and bank materials provide extremely limited opportunity
for river movement (Parkinson et al. 2001). The coarseness of shoreline substrates reduces the
potential for shoreline erosion. Most of the erodable substrates have probably already been
removed in this steep canyon environment, except for areas of finer-sized substrate in recent
alluvial deposits in areas strongly affected by currents. Overall, the canyon bottom in this reach
is considered very stable and unchanged, or not significantly adjusted in modern times (Miller et
al. 2001).
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5.2. Factors Potentially Influencing Soil Erosion and Bank
Stability
The following list (provided by U.S. Army Corps of Engineers [1992b]) summarizes most of the
causes and related factors influencing shoreline erosion. The items fall into two main categories:
Natural causes and factors
Human causes and factors
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
waves
ice scour
freezing and thawing
soil conditions
shore geometry
rain/runoff
groundwater hydrology
wind
water currents
topography
floating debris (trees) fires
reservoir operation (drawdown, etc.)
boat wakes
land use (forest, agriculture, urban development)
construction
beach use
recreational vehicles
trails (trampling)
livestock
negligence/vandalism
“property value enhancement”
insufficient enforcement
politics
The relative significance of causes of erosion cannot be ranked easily because the significance of
causes varies considerably among individual reservoirs, depending on a broad variety of sitespecific factors. Based on the environments of Hells Canyon and the nature and type of
anthropogenic influences in the canyon, we identified the following factors as potentially
influencing shoreline erosion in the study area:
•
•
•
•
•
•
•
•
•
•
•
•
•
climate
upland ground cover
soil type
topography
riparian vegetation
groundwater seepage
floods
wind-driven waves
boat waves
hydroelectric operations (river and reservoir flows)
livestock
roads
recreation
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The following paragraphs describe the nature of these influences and their potential effects and
magnitude of influence on shoreline erosion in the canyon. Many of these factors are interrelated,
making it difficult to attribute the potential cause of erosion to any single influence.
5.2.1. Climate
Climate potentially affects erosion both directly and indirectly. Directly, rain is the driving force
of erosion. Raindrops dislodge soil particles, and runoff carries the particles away. The erosive
power of rain is determined by rainfall intensity (inches or millimeters of rain per hour) and
droplet size. A highly intense rainfall of relatively short duration can produce far more erosion
than a storm of long duration and low intensity. Also, storms with large raindrops are much more
erosive than misty rains with small droplets. Rainfall intensity, duration, and droplet size are
determined by geographic location (Goldman et al. 1986). The Hells Canyon area is located in a
region that has some of the lowest rainfall intensities in the contiguous states.
The indirect relation between climate and erosion is subtler. The yearly pattern of rainfall and
temperature largely determine both the extent and the growth rate of vegetation. Climates with
relatively mild year-round temperatures and frequent, regular rainfall are highly favorable to
plant growth. Vegetation grows rapidly and provides a complete ground cover, which protects
the soil from erosion. Cold climates, such as the higher elevations in the Rocky Mountains, and
dry climates, such as those in Hells Canyon and other semi-arid lands, are less favorable to plant
growth and thus are much more susceptible to erosion (Goldman et al. 1986).
5.2.2. Upland Ground Cover
The term ground cover refers primarily to vegetation but also includes bare ground surfaces
covered by litter (dead plant material) and rock fragments. Vegetation is, without question, the
most effective form of erosion control on upland soils; typically, very little erosion occurs on soil
covered with vegetation (Goldman et al. 1986). Studies by Rogers and Schumm (1991) showed
that vegetation disrupts overland water flow by both concentrating and deflecting flow around
individual vegetation obstructions. The presence of upland vegetation on a shoreline bank
surface may indicate that it has effectively prevented erosion, or more likely, that vegetation
exists because no erosion has occurred there (Reid 1992). Upland vegetation is often no match
for the energy of waves and currents in fluvial environments.
In the semi-arid canyon environment of Hells Canyon, most upland vegetation consists of
Grassland or Shrub Savanna cover types (Holmstead 2001). The Grassland cover type includes
a variety of plant assemblages dominated by native perennials and/or introduced annual grasses.
Some Shrub Savanna plant assemblages appear healthy and are codominated by native
bluebunch wheatgrass (Pseudoroegneria spicatum) and Sandberg bluegrass (Poa secunda). More
often, the assemblages are deteriorated in health, and introduced annual grasses, such as
cheatgrass (Bromus tectorum), bulbous bluegrass (Poa bulbosa), and medusahead wildrye
(Taeniatherum caput-medusae), dominate the herbaceous layer (Holmstead 2001).
Degraded native plant assemblages have typically been burned or overgrazed too frequently and
are more susceptible to erosion than healthy stands of native perennial grasses, forbs, and shrubs.
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Fires and overgrazing in the steep, dry canyon environment can expose the soil to erosive forces
and prohibit development of deep-rooted species that hold the soil. As one travels upstream of
Hells Canyon Dam, there is a general increase in degraded plant assemblages (Holmstead 2001).
Upland assemblages in many cover types that are dominated by nonnative or invasive species
(such as rabbitbrush [Chrysothamnus nauseosus], cheatgrass, bulbous bluegrass, medusahead
wildrye, and/or other annual grasses) are more prevalent in the Brownlee Reservoir Reach than
downstream, especially near the upper portions of Brownlee Reservoir.
In the steep and often rocky canyon slopes of Hells Canyon, upland habitat often reaches down
to the canyon bottom. Frequently, there is no riparian vegetation along the shoreline to protect
the banks, and the shorelines become more susceptible to erosion. Erosion may undercut the
bank and lead to increases in slumping of the overlying materials as the bank becomes
oversteepened. This process continues until the slope comes into equilibrium with erosional
forces.
5.2.3. Soil Type
Soils data for the southern portion of the study area, including the upper portion of the
Hells Canyon Reservoir Reach, were available from the Natural Resources Conservation Service
(1995) (Figure 3 and Appendix 1). Published data for areas north of about RM 265 on the Idaho
side and RM 261 on the Oregon side were not available. Nearly all soil types on the Oregon side
meet USDA requirements for “highly erodable lands.” Exceptions included areas of unweathered
bedrock and some extremely stony or very cobbly soil types that are resistant to erosion
(Appendix 1). Data on highly erodable lands were not available for the Idaho side, but we expect
that most of these soil types are also highly erodable. Nearly all soils consisted of fine loamy
particle sizes, as assigned at the family taxonomic class. The surface texture of most soil types
varied, but usually consisted of silty loam, silty clay, clay loam, or loam soils. Soil depth was
generally shallow for all soil types, with the depth to bedrock often just 10 to 20 inches
(Appendix 1).
Many of the soil types contained rock components that varied in classification from solid
bedrock through various classes of stones, cobbles, and gravels. When the soil type contained
rock, the erodability of the soil type usually decreased. Soil erodability, expressed as Kfactor, is
classified in relative values ranging from 0.05 to 0.60, with values increasing as soils become
more erodable. Soils are rated by susceptibility to either wind or water (both precipitation and
runoff) erosion. All soils in the study area were rated with a Kfactor of 0.24 to 0.49 in
susceptibility to sheet and rill erosion by water, when rocks were not a component of the soil
type. When the soil type contained rock, the Kfactor ranged from 0.05 to 0.49, with most types
classified in the 0.15 to 0.43 range (Appendix 1).
In essence, using available information, nearly all soils types in the canyon are highly erodable
when subjected to the erosional forces of water in the form of precipitation. River currents and
shoreline erosional influences increase the magnitude of erosion.
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5.2.4. Topography
Slope length, steepness, shape, and aspect are critical factors in erosion potential because they
determine, in large part, the velocity of runoff. The erosive potential of flowing water increases
as the square of the velocity (Goldman et al. 1986). Long, continuous slopes allow runoff to
build up momentum. The high-velocity runoff tends to concentrate in narrow channels and
produce rills and gullies. The shape of a slope also has a major bearing on erosion potential. The
base of a slope is more susceptible to erosion than the top because runoff has more momentum
and is more concentrated as it approaches the base. Slope aspect can also be a factor in
determining erosion potential. In northern latitudes, such as Hells Canyon, south-facing slopes
are hotter and drier than other slope orientations. In drier climates, vegetation is sparser on such
slopes, and reestablishing vegetation on these slopes can be relatively difficult. Conversely,
northern exposures tend to be cooler and moister, but they also receive less sun and, therefore,
have slower plant growth.
The topographic characteristics of the canyon have been described to some extent in Section 5.1.
Other factors being equal, the steeper the slopes of the bank, the less stable the bank. Extremely
steep slopes are common and exhibit an enormous additive influence to the potential for
shoreline erosion in the canyon. In the canyon, most bank failures occur through mass
movements, rather than from surface erosion processes. Given the steep topography, shoreline
margins with relatively stable water levels tend to be less erosive than shorelines that are subject
to large fluctuations in water level or forces of high-velocity flows.
5.2.5. Riparian Vegetation Cover
Shoreline erosion processes can lead either to degradation of existing wetlands through soil
removal or burial, or these same processes can lead to the creation of new wetlands (U.S. Army
Corps of Engineers 1992a). Riparian vegetation stabilizes sediments along streambanks and
helps prevent excessive soil erosion. Riparian zones trap sediments from upland sources before
they reach riverine environments (Osborne and Kovacic 1993, Daniels and Gilliam 1996,
Hairsine 1996). Dense stands of riparian vegetation in the floodplain can reduce downstream
flooding by causing the river to spread as it slows. This spread, in turn, enhances groundwater
recharge (Patten 1998). In Hells Canyon, such an influence would only be significant in the
upper reaches of Brownlee Reservoir and in the Weiser Reach, where a large floodplain allows
extensive riparian vegetation to become established and persist (Holmstead 2001). Based on the
map of cover types developed by Holmstead (2001) for Hells Canyon, approximately 40% of the
shoreline along the Weiser Reach within a 20-m planimetric corridor on each bank consists of
riparian vegetation. This reach has the highest abundance of riparian vegetation in the study area
and, therefore, receives the greatest protection by riparian vegetation from shoreline erosion.
Geomorphic features, such as canyons and valleys, control the size of the riparian zone. Below
the upper reaches of Brownlee Reservoir, the Snake River enters a steep canyon. It is also
converted to a reservoir by the HCC, until it leaves Hells Canyon Dam. Although soils tend to be
relatively deep on the slopes of Brownlee Reservoir, this reservoir is subject to large fluctuations
in water level and is not conducive to establishing persistent riparian vegetation. Persistent
riparian vegetation is found primarily near the mouths of tributary streams or in areas influenced
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by groundwater (for example, springs and seeps) (Holmstead 2001). The lack of riparian
vegetation along most of Brownlee Reservoir leaves these shorelines more vulnerable to erosive
forces. Based on the cover type map developed by Holmstead (2001) for Hells Canyon,
approximately 10% of the shoreline along the entire reach (within a 20-m band) consists of
riparian vegetation. Most of this riparian vegetation occurs near the headwaters of the reservoir
and along the Powder River arm of the reservoir. Aside from these two areas, most riparian
vegetation is found near the mouths of tributaries and at groundwater seeps, as previously stated.
Below Brownlee Dam, the river (reservoir) flows through a resistant canyon that often does not
have erodable margins (Vallier 1998). However, the relatively stable pool levels of Oxbow and
Hells Canyon reservoirs, combined with daily fluctuations that irrigate riparian vegetation,
promote a relatively wide band of riparian vegetation (Holmstead 2001). Approximately 21.5%
and 20.0% of the shoreline (within a 20-m band) along Oxbow and Hells Canyon reservoirs,
respectively, consist of riparian vegetation. Riparian vegetation is known to increase in coverage
and persistence along reservoirs with narrow water fluctuations (Kryzanek et al. 1986, Wilcox
and Meeker 1991). The increased abundance of riparian vegetation along Oxbow and
Hells Canyon reservoirs probably provides an increased measure of protection from shoreline
erosion, compared with Brownlee Reservoir.
Below Hells Canyon Dam, the river has little room to accumulate channel-margin sediment,
which is necessary to establish extensive riparian vegetation (Scott et al. 1996). However, as a
result of HCC operations, more stable and higher base flows (Parkinson 2001) have enabled
riparian vegetation to expand downslope. Today, in some locations in this reach, the margins of
the river are entirely bordered by netleaf hackberry (Celtis reticulata), while only scattered
individual plants were found there 60 to 80 years ago (Blair et al. 2001). Based on the map of
cover types developed by Holmstead (2001) for Hells Canyon, approximately 17.7% of the
shoreline in this reach (within a 20-m band) consists of riparian vegetation.
The width and density of riparian vegetation can directly influence the amount of soil and
sediment lost to the river from eroding, poorly managed upland areas (Patten 1998). The general
condition of upland habitats is discussed previously and is described in more detail by Holmstead
(2001). The relatively narrow linear bands of riparian vegetation along the steep shorelines in
Hells Canyon probably trap some sediments eroded from upland habitats. These trapped
sediments probably help increase the extent of the riparian zone, but a large portion of the eroded
sediments undoubtedly enters the river system because of the narrowness of the riparian corridor
and steep slopes.
5.2.6. Groundwater Seepage
The presence of groundwater in the banks, particularly if the groundwater is moving toward the
face of the bank, decreases the stability of the bank and increases the rate of erosion. A large
amount of moisture in the soil can make the bank weak, so that earthquakes, waves, foot traffic,
livestock, or other forces of even small magnitude might trigger failure (Reid 1992). In the
northern hemisphere, orientation to the sun causes northerly facing banks to retain more
moisture, thereby reducing their strength.
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Where groundwater seepage emerges near the shorelines, it improves the potential for
establishing persistent riparian vegetation. Along Brownlee Reservoir, such seepage sustains
riparian vegetation in areas where the vegetation would not otherwise persist, thereby providing
some measure of resistance to bank erosion.
5.2.7. Floods
Periodic floods, such as spring runoff, scour portions of the floodplain and redeposit sediments.
Floods can cause direct shoreline erosion and landslides, but floods also directly facilitate the
establishment and survival of riparian vegetation, which can stabilize sediments along streams
and reduce erosion. Frequency and duration of flooding, timing of inundation, and aggradation
and degradation shape fluvial landforms (Hupp 1988), and thereby determine which plant
communities are capable of becoming established and surviving on these alluvial surfaces
(Dominick and O’Neill 1998). Fluvial processes that form floodplains, point bars, and lateral
accretion bars create fresh surfaces for the establishment of new plant communities (Swanson
1980, McBride and Strahan 1981). Once established, vegetation becomes an integral part of the
fluvial system (Hupp and Osterkamp 1985) and may regulate the movement and temporary
storage of sediment from upstream sources.
In Hells Canyon, average high inflows to Brownlee Reservoir are about 47,000 cfs. Based on
USGS data from 1911 to 1990 at Weiser, flows of approximately 63,000 cfs about every 5 years,
86,000 cfs about every 25 years, and 102,000 cfs every 100 years can be expected. The effects of
hydroelectric operations on river flows are addressed in Parkinson (2001). Essentially, the
magnitude and frequency of peak discharges downstream of Hells Canyon Dam are unaffected
by flow regulation. Accordingly, high-water floods probably have little influence on shoreline
erosion along the reservoir reaches because elevated water levels do not affect lands that are
above full-pool levels. High flows can have a definite influence on shorelines in the unregulated
Weiser Reach and the reach downstream of the Hells Canyon Dam when shoreline banks that are
not normally scoured by flows are subjected to fluvial actions.
5.2.8. Wind-Driven Waves
Wind-generated waves are the predominant cause of erosion in large reservoirs (U.S. Army
Corps of Engineers 1992b). The magnitude of erosion and the most vulnerable sections of
shoreline are determined in part by factors such as the prevailing wind direction, fetch, duration,
and speed; soil conditions; and shoreline geometry. Banks that face into the strongest winds are
exposed to the largest waves. In the steep and sinuous sections of the canyon below
Brownlee Dam, where the reservoirs are relatively narrow (less than 100 m wide), windgenerated waves are relatively limited in their ability to generate substantial bank erosion. The
sections of curving canyon reduce the amount of bank that is exposed to any specific wind
direction. Where the canyon is wide or generally follows a course in one direction, as is common
on Brownlee Reservoir when pool levels are high, wind waves have much greater potential to
erode shorelines.
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5.2.9. Boat-Driven Waves
Many investigators recognize wakes generated by boats as a contributing cause of streambank
erosion (Klingeman et al. 1990, Johnson 1994, Nanson et al. 1994, Bradbury et al. 1995).
Relative to large reservoirs, boat wakes are a more significant cause of erosion in smaller
reservoirs and on rivers where shorter fetches limit the effect of wind-driven waves (U.S. Army
Corps of Engineers 1992b) and wakes do not have time to attenuate. Boats moving through the
water generate a system of wakes at the bow, stern, and wherever an abrupt change in the boat
hull geometry causes a pressure change in the flow field around the hull (Herbich and Schiller
1984, Walker 1988). The generation of wakes by boats is a complex interference pattern, where
the amplitude of wakes can increase when wakes are in phase (crests coincide with crests and
troughs coincide with troughs) or decrease when wakes are out of phase. Boat wakes travel
essentially perpendicular to the bank and move sediment by dislodging it on impact, by splashing
up and down the bank, and by causing a rapid inflow and outflow of water from permeable banks
(Simons and Li 1982). The maximum height of wakes in a wake train significantly affects the
ability of waves to erode material from a riverbank (Von Krusenstierna 1990, Nanson et al.
1994).
In Hells Canyon, maximum wake heights ranging from 0.01 to 1.50 ft might be expected, based
on results reported for the Kenai River, Alaska (Dorava and Moore 1997), a river similar in size
to the Snake. The study area reach most subject to boat-wake erosion extends downstream from
Hells Canyon Dam to the confluence with the Salmon River, where jet boats, including small
private boats and large commercial boats up to 42 ft long and carrying up to about 55 passengers,
are frequent. High boat traffic can also concentrate around large, developed recreation parks on
the reservoir reaches. Such areas include (upstream to downstream) Steck Park, Spring
Recreation Site, Hewitt Park, and Woodhead Park, on Brownlee Reservoir; McCormick Park,
Swedes Landing, and Oxbow Boat Launch, on Oxbow Reservoir; and Copperfield Park,
Copperfield Boat Launch, and Hells Canyon Park, on Hells Canyon Reservoir.
On large, open stretches along the reservoir reaches, we expect that the negative effects of boatdriven waves on shorelines are probably overshadowed by the larger, more frequent, and more
damaging effects that are typical of wind-driven waves (Reid 1992). Conversely, on the river
reaches, wind-driven waves are lessened by flows, and their effects on shoreline erosion are
probably overshadowed by the effects of larger, boat-driven waves.
5.2.10. Hydroelectric Operations (River and Reservoir Flows)
Every river is unique in terms of its flow patterns, the landscapes through which it flows, and the
species it supports. Such uniqueness implies that the design and operating pattern of every dam is
also unique, as are the effects of the dam on the river and its associated ecosystems (Johnson
1998, Jansson et al. 2000). The effects of dams on stream flow are dependent upon the
characteristics of the dam and the drainage basin. Following dam construction, rivers may
become wider, narrower, shallower, or deeper. The time necessary for a response ranges from
months to millennia, and the direction of the response may change over time (Petts 1984). The
response of rivers and riparian vegetation to upstream dams shows a regional pattern related to
physiographic and climatic factors that influence channel geometry (Friedman et al. 1998). The
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diversity of channel responses to dams occurs because fluvial processes that mediated each
response vary in relative importance from site to site.
The effects of erosion on shoreline habitat downstream of hydroelectric facilities are generally
caused by unpredictable flow regimes. Changes in shoreline erosion patterns tend to increase as
deviations from the natural flow regime increase. These changes, however, can be either negative
or positive for soils and the resulting vegetation communities and riparian-dependent wildlife.
For example, damming for hydroelectric production on steep-walled canyon rivers can reduce
the frequency of catastrophic floods that erode soil and eliminate riparian vegetation. At the
same time, large dams typically decrease downstream peak flows and sediment load.
The effects of the HCC on peak flows and sediment loads are discussed in Parkinson (2001) and
Parkinson et al. (2001), respectively. Post-impoundment floods in Hells Canyon are similar in
magnitude and frequency to those prior to regulation. Therefore, in the unregulated
Weiser Reach and the regulated downstream reach, these large floods continue to affect
streambank stability and erosion patterns much as they did prior to HCC construction and
operation. However, more stable and higher summer base flows have allowed riparian vegetation
to expand along the shoreline (Blair et al. 2001), and water level fluctuations generally occur in a
zone that would otherwise be scoured by spring flows.
Large dams can effectively trap sediments, which can cause a reduction of riverine deposits and
a loss of protective riparian vegetation along downstream shorelines. However, sediment loads
below Hells Canyon Dam largely depend on the sediment concentration of inflows from side
canyon tributaries that are not affected by the HCC (Parkinson et al. 2001). There is no evidence
that the HCC reservoirs have trapped significant quantities of sediment of sizes that could affect
riverine deposits below Hells Canyon Dam. Most of the material trapped in Brownlee Reservoir
is smaller than the smallest size fraction that could replenish the sand bars in this reach. These
small reservoir sediments are silts and clays that would be transported through Hells Canyon as
wash load in the absence of the HCC (Parkinson et al. 2001). Because of the coarseness of
shoreline substrates in the reach below Hells Canyon Dam, the potential for shoreline erosion is
relatively minor. Most of the erodable substrates have already been removed in this steep canyon
environment, with the exception of the continuing supplies of finer-sized substrate usually near
alluvial deposits or protected by geomorphic features in the relatively stable sand bars (Parkinson
et al. 2001). Sand bars have been and continue to be dynamic features of the river system.
Overall, the shoreline zone in this reach is considered very stable and unchanged, or not
significantly adjusted in modern times (Miller et al. 2001).
Reservoir-related fluctuations in water level resulting from hydroelectric operations can
negatively and positively influence shoreline soil resources. Large fluctuations in water level can
undercut shoreline banks and accelerate sloughing and landslides of soils prone to erosion,
especially when the soils are on steep slopes (O’Neal and McDonnell 1995). Reservoir
shorelines are young, compared with those of natural lakes, and are still moving toward a stable
equilibrium. Accordingly, many reservoirs are beset by shoreline erosion problems (Allen and
Wade 1991). Soil stability is greater along reservoirs with narrower water level fluctuations
because such reservoirs have less shoreline disturbance (such as from physical impacts of waves
and wetting/drying cycles) and because the roots of vegetation bind the soil. Vegetation can
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increase in coverage and persistence along reservoirs with narrower water fluctuations
(Kryzanek et al. 1986, Wilcox and Meeker 1991).
Shoreline erosion commonly occurs during drawdown. While the degree of drawdown varies
depending on physical parameters, such as soil condition and reservoir bathymetry, the speed
with which reservoirs are drained can affect the erosion rate. Rapid drops in water levels that do
not permit banks to drain can cause overburdened banks to calve off or slump downslope.
However, it is recognized that a reservoir built for flood control must be drawn down to fulfill its
flood-control function (U.S. Army Corps of Engineers 1992b).
River currents in the unregulated Weiser Reach, in short segments at the headwaters of Oxbow
and Hells Canyon dams, and along the reach below Hells Canyon Dam, produce tractive
erosional forces that are distributed along the river’s bed and banks. A greater force is exerted on
the riverbed than on the banks because the water is shallower against the banks. The energy
exerted by the tractive forces of the river current is determined by the velocity and depth of the
river and the amount of streambank exposed to the currents. This tractive erosion is commonly
evident along the outside edge of meander bends, where water depths and velocities are greater
than along the inside of the bend, where deposition of sediment is more prevalent.
How streambanks respond to river currents depends on their configuration, geometry, and
orientation (Dorava and Moore 1997). The type and size of material composing a bank affects its
resistance to erosion. For example, if a bank is vertical and oriented perpendicular to the river
flow and is composed of material that is loose, unconsolidated, fine grained, and unvegetated, the
bank will erode more readily than a gently sloping bank that is oriented parallel to the river flow
and composed of consolidated, coarse-grained materials that are covered with thick vegetation.
Because study reaches along Hells Canyon depict a variety of these characteristics, natural
erosion rates probably vary among sites.
5.2.11. Livestock
The effects of livestock grazing on infiltration, runoff, and sediment production in uplands have
been well studied (Packer 1953, Lusby 1970, Bohn and Buckhouse 1985, Thurow et al. 1986).
The grazing system, intensity, and timing; level of defoliation; and amount of trampling have all
been shown to affect infiltration, runoff, and sediment yield (Packer 1953, Bohn and Buckhouse
1985, Thurow et al. 1986). Livestock grazing typically reduces the protection afforded by
vegetation, reduces or scatters litter, and compacts the soil (Busby and Gifford 1981). Generally,
livestock grazing increases the amount of upland erosion in environments such as Hells Canyon,
where steep slopes and erodable soils amplify ground disturbance caused by the hooves of
livestock, especially large animals such as horses and cattle. Additionally, the weight of large
livestock near shorelines can cause banks to collapse and slump into the reservoir or river.
Where livestock grazing is allowed in riparian areas along shorelines—a practice typical for
Hells Canyon—degradation of riparian vegetation (which provides a measure of protection to
shoreline banks) is common. Livestock grazing in riparian communities typically compacts and
defoliates the soil (Kauffman et al. 1983, Bohn and Buckhouse 1985), or otherwise physically
damages the vegetation (Roath and Krueger 1982, Schulz and Leininger 1990). In Hells Canyon,
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large livestock have access to shorelines in most sections of all reaches above Hells Canyon
Dam. Below the dam, only a few sites on private land are used by livestock.
5.2.12. Roads
Erosion problems associated with road construction are generally related to poor construction
practices. Properly contoured and drained roadways reduce the effects. In Hells Canyon, portions
of each reach have several roads, which, at site-specific areas, might contribute to slope
instability, concentration of runoff, and reduced vegetation cover on cut-and-fill slopes.
5.2.13. Recreation
In addition to watershed and river characteristics, human factors, such as the effects of recreation
on vegetation and soils, can affect shoreline erosion rates. Research has documented the more
obvious effects of trampling and has improved our understanding of how independent variables,
such as type, amount, and location of use, influence the extent of the impact (Kuss and Graefe
1985; Cole 1987, 1988). It is not uncommon for river users and hikers to leave the marked paths
and to trample the vegetation that protects the shoreline as they walk to the river and along the
shoreline. The impacts of recreation on soil and vegetation are generally intense and persistent.
Recreational use of Hells Canyon is growing (Brown 2001). Much of this growth is directly
related to the riparian environment. People are drawn to these cool, shady areas along the river
and reservoirs, and these are prime camping and picnicking sites. Additionally, birds, wildlife,
and fish that use riparian ecosystems attract birders, naturalists, hunters, and anglers.
Recreational use and development—including foot and vehicle traffic, trampling, and
construction of trails, campsites, and other facilities that alter physical sites—can promote bank
erosion by disturbing the soil and vegetation. This erosion makes soils more likely to slump
under the weight of people and vehicles.
In the canyon, there are numerous undeveloped (also known as dispersed or impromptu)
camping sites and many developed recreation sites (parks and boat ramps) along the reservoirs.
People commonly park their vehicles as close as possible to the reservoirs and, on
Brownlee Reservoir, even drive down to the water during drawdown. Hiking and pack trails
sometimes follow the shoreline, especially along Hells Canyon Reservoir and in the downstream
reach. A description of existing developed recreation sites within the canyon is provided in
Moore and Brown (2001) and, for existing dispersed sites, in Hall and Bird (2001).
5.3. Current Conditions Inventory
From late summer 1998 through spring 2001, IPC biologists inventoried approximately 432.0 mi
of shoreline in the study area. By location, distribution of miles was 185.5 mi in Idaho, 204.8 mi
in Oregon, and 41.7 m on islands (Table 1). Two biologists were the principal observers, while
several others helped collect data. The principal observers standardized the evaluation criteria by
working together on several sites at the beginning of the surveys and throughout the data
collection process. A total of 378 shoreline erosion sites were recorded (Figure 3), covering
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57.4 mi, or 13.3% of the shoreline that was inventoried. The most common surface area for
erosion sites (n = 104) ranged from 101 to 250 m2 (Table 2). Many other sites (n = 82 and
n = 73) were in surface-area classes of 26 to 100 m2 and 251 to 500 m2, respectively (Table 2).
The smallest site mapped was 10 m long and 1 m high, and the largest site was 4,800 m long and
7 m high. Nearly all of the sites were considered active erosion sites (n = 329) (Table 3).
Twenty-nine sites were considered historic sites, and 20 sites exhibited signs of both active and
historic erosion (Table 3). However, this survey did not focus on historic erosion and probably
under-represents the amount of historic erosion in the study area. Most erosion sites occurred on
slopes greater than 30 degrees (n = 247) or between 6 and 30 degrees (n = 105), and on Oregon
shorelines (n = 225) (Table 3).
The total area of erosion sites in the study area was 100.7 acres. This information is summarized
below by reach. Excluding sites in the Weiser Reach, 90.1 acres occurred along reaches
potentially influenced by HCC operations.
Reach
Acres of
Erosion Sites
Length (mi) of
Erosion Sites
Percentage of
Shoreline Miles
with Erosion
Weiser
10.58
3.45
7.5
Brownlee Reservoir
79.07
49.58
27.2
Oxbow Reservoir
1.34
0.51
2.0
Hells Canyon Reservoir
3.45
1.45
2.7
Downriver
6.24
2.44
2.0
100.70
57.43
13.3
Total
The most common factors potentially influencing erosion were excessive slope (n = 336), highly
erosive soil (n = 263), fluctuating water levels (n = 309), and large, wind-driven waves (n = 270)
(Table 3). Many sites occurred in areas frequented by motorboats, which probably subjected
these sites to erosion caused by boat-driven waves (n = 245). Evidence of the effects of
recreation was found at 63 sites, and roads seem to have affected 51 sites. Only a few sites
(n = 22) were used beneficially by burrowing wildlife; however, many sites provided
geomorphic characteristics that promote the growth of riparian habitats.
5.3.1. Weiser Reach
The unimpounded reach above Brownlee Reservoir had 9 erosion sites (Table 2 and Figure 3),
and erosion occurred along about 7.5% of the available shoreline (3.45 mi of 45.8 mi). All these
sites were relatively large (3–20 m high and several hundred or several thousand meters long)
and, therefore, were classified into the largest surface-area classes (Table 2). These sites tended
to occur where the river channel intercepted steep banks (Appendix 2). Most sites occurred at
locations dominated by Forested Wetland (n = 5, 56%) or Scrub-Shrub Wetland cover types
(n = 2, 22%) (Table 4).
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Average cover characteristics for each major physiognomic plant group and for total cover
surrounding erosion sites in the Weiser Reach are summarized as follows:
Group
Mean Cover (SD)
Minimum Cover
Maximum Cover
Tree
0.3
(0.7)
0.0
2.0
Shrub
8.9
(10.8)
0.0
3.0
Forb
29.4
(24.0)
0.0
60.0
Grass
26.7
(18.2)
5.0
60.0
Total Cover
65.0
(24.2)
20.0
90.0
5.3.2. Brownlee Reservoir Reach
The Brownlee Reservoir Reach had the most erosion sites in the study area (n = 261, 69%)
(Table 2 and Figure 3), and erosion occurred along about 27.2% of the available shoreline
(49.6 mi of 182.3 mi). Sites along Brownlee Reservoir occurred most in the surface-area classes
of 101 to 250 m2 (n = 69) and 251 to 500 m2 (n = 56); however, we also observed many sites
(n = 43) in the surface-area class of 1,001 to 5,000 m2. We mapped most of the sites of
1,001 to 5,000 m2 as composite sites because these sites on Brownlee Reservoir were very
numerous and nearly continuous. To save time and effort, we grouped many sites into such
composite sites and recorded the percentage of the area within the composite site that was
actually eroded (Appendix 2). Common factors that probably increased erosion on
Brownlee Reservoir included water-level fluctuation (n = 254), wind-generated waves (n = 245),
excessively steep slopes (n = 245), highly erosive soils (n = 178), and boat-generated waves
(n = 172) (Table 3 and Appendix 2). Most sites occurred at locations dominated by Shrub
Savanna (n = 114, 44%) or Grassland cover types (n = 102, 39%) (Table 5). However, we
thought that shoreline erosion at 85 sites (33%) explained the presence of wetlands in areas that
otherwise would have been void of wetland habitat. Shoreline slumping often resulted in the
formation of low-gradient, shallow-water habitats in this otherwise steep topography.
Average cover characteristics for each major physiognomic plant group and for total cover
surrounding erosion sites along Brownlee Reservoir are summarized as follows:
Group
Tree
Mean Cover (SD)
Minimum Cover
Maximum Cover
0.1
(1.6)
0.0
25.0
Shrub
10.8
(11.5)
0.0
80.0
Forb
11.4
(10.7)
0.0
50.0
Grass
31.8
(19.5)
0.0
80.0
Total Cover
53.9
(26.1)
0.0
120.0
5.3.3. Oxbow Reservoir Reach
The Oxbow Reservoir Reach had 9 erosion sites (Table 2 and Figure 3), and erosion occurred
along 2.0% of the available shoreline (0.51 mi of 25.0 mi). Most sites were in the smaller
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surface-area classes, although two sites extended more than 150 m along the shoreline and,
therefore, were categorized into some of the larger classes (Table 2). The larger sites occurred
along the headwaters of the reservoir, on shorelines subject to the erosive effects of channel
flow. Evidence of livestock disturbance was found at 4 sites, and evidence of recreation
disturbance was found at 4 sites (Table 3 and Appendix 2). Most sites occurred in areas
dominated by Forbland (n = 4, 44%) or Grassland cover types (n = 2, 22%), while nearly all
sites (n = 8) were associated with presence of riparian vegetation (Table 6).
Average cover characteristics for each major physiognomic plant group and for total cover
surrounding erosion sites along Oxbow Reservoir are summarized as follows:
Group
Mean Cover (SD)
Minimum Cover
Maximum Cover
Tree
0.0
(0.0)
0.0
0.0
Shrub
4.2
(6.3)
0.0
15.0
Forb
25.7
(17.3)
4.0
55.0
Grass
20.7
(20.7)
1.0
60.0
Total Cover
50.6
(33.5)
10.0
95.0
5.3.4. Hells Canyon Reservoir Reach
The Hells Canyon Reservoir reach had 39 erosion sites (Table 2 and Figure 3), and erosion
occurred along about 2.7% of the available shoreline (1.45 mi of 53.9 mi). Most sites (n = 16)
were in the surface-area class of 26 to 100 m2 (Table 2). Common factors that probably increased
erosion on this reservoir included water-level fluctuation (n = 39), steep slopes (n = 22), windgenerated waves (n = 22), and highly erosive soil (n = 20). Recreation effects were observed at
14 sites, and boat-generated waves affected 11 sites (Table 3 and Appendix 2). Most sites
occurred at locations dominated by Shrub Savanna (n = 12, 31%) or Shrubland cover types
(n = 9, 23%), while nearly all sites (n = 31) were associated with presence of riparian vegetation
(Table 7).
Average cover characteristics for each major physiognomic plant group and for total cover
surrounding erosion sites in the Hells Canyon Reservoir Reach are summarized as follows:
Group
Tree
Page 28
Mean Cover (SD)
Minimum Cover
Maximum Cover
2.4
(11.6)
0.0
70.0
Shrub
17.7
(19.7)
0.0
70.0
Forb
17.5
(12.3)
0.0
50.0
Grass
38.5
(23.2)
1.0
100.0
Total Cover
76.2
(34.2)
2.0
180.0
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
5.3.5. Downriver Reach
The reach below Hells Canyon Dam had 60 erosion sites (Table 2 and Figure 3), and erosion
occurred along 2.0% of the available shoreline (2.44 mi of 125 mi). Most sites were in surfacearea classes of 101 to 250 m2 (n = 21) or 26 to 100 m2 (n = 18) (Table 2). Common factors that
probably increased erosion in this reach included highly erosive soils (n = 60), boat-generated
waves (n = 58), and excessive slope (n = 59). Most sites were upslope of the typical fluctuation
zone, and only 8 sites showed possible negative effects associated with the fluctuation zone.
Evidence of recreation disturbance was found at 12 sites (Table 3 and Appendix 2). Most sites
occurred at locations dominated by Grassland (n = 24, 40%) or Scrub-Shrub Wetland cover
types (n = 18, 30%), while most of the sites (n = 45) were associated with the presence of
riparian vegetation (Table 8).
Average cover characteristics for each major physiognomic plant group and for total cover
surrounding erosion sites in the reach below Hells Canyon Dam are summarized as follows:
Group
Mean Cover (SD)
Minimum Cover
Maximum Cover
Tree
2.0
(5.8)
0.0
25.0
Shrub
9.5
(11.0)
0.0
60.0
Forb
3.5
(5.2)
0.0
20.0
Grass
15.1
(7.6)
0.0
30.0
Total Cover
30.1
(14.1)
0.0
75.0
6. DISCUSSION
6.1. General Findings
Many factors can contribute to streambank soil erosion, and each site’s combination of factors is
unique. Reid (1992) categorizes the factors that determine the presence and magnitude of
shoreline erosion as activating or passive. This distinction is useful because it helps explain why
sites vary in their inherent susceptibilities to erosion. Activating factors are those factors that
trigger erosion, such as earthquakes, waves, rain and runoff, groundwater discharge, frost thaw,
ice-shove, wind, and human-caused events (for example, excavation, explosions, vehicle
vibrations, and livestock impacts). Passive factors are less obvious. They are properties inherent
in the streambank material or in the geometry of the banks that make the bank relatively
susceptible to the effects of activating factors. Passive factors promoting failures include the
following:
•
•
•
a composition rich in clay
alternating layers of weak and strong beds
dense jointing, especially vertical
Hells Canyon Complex
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Shoreline Erosion in Hells Canyon
•
•
•
•
•
Idaho Power Company
protection from the sun and a high moisture content
steep slopes
lack or sparseness of vegetation
lack of protection from wind-driven waves
lack of natural or artificial riprap along shores
In this study, we identified climate, upland ground cover, soil type, topography, riparian
vegetation, groundwater seepage, floods, wind-driven waves, boat waves, hydroelectric
operations, livestock, roads, and recreation as the principal factors potentially influencing
shoreline erosion in the Hells Canyon area. At any given site, any one of these factors might or
might not contribute to shoreline erosion in the canyon. However, because many of these factors
are interrelated, it is difficult to attribute the cause of erosion to any single source.
For example, although an area might have extremely steep slopes, the soil might still be resistant
to erosion. However, steep slopes in semi-arid climates typically have sparse upland vegetation
cover on south-facing aspects and minimal riparian vegetation along shorelines. The shallow root
system of sparse upland vegetation provides little soil-binding capabilities, and the thin corridor
of riparian vegetation provides minimal protection to shoreline banks. Under these conditions, if
unusual weather, such as a heavy thunderstorm or rain on snow, were to occur, such slopes
would be prone to landslides and slumping. If a highly erodable soil were also added to the site
characteristics, the slope would be at high risk for failure. This interdependence of factors leads
to the conclusion that no single factor can completely account for the erosion of shoreline banks
(Lawson 1985).
Based on the available published information on soil types in the canyon, nearly all soils are
considered highly susceptible to erosion. Because the HCC reservoirs are relatively recent
features (in geologic time), the new shorelines have not yet reached equilibrium with soils at fullpool levels and within the fluctuation zones. Additionally, when these inherently erosive soils
along the shoreline are subject to water-level fluctuations, wind- and boat-generated waves, and
other erosive factors, the potential for erosion becomes great. Most bank failures in the canyon
occur through mass movements rather than from surface erosion processes.
Comparing reservoir and lake ecology provides a reference point for understanding the
environmental impacts associated with reservoir operations. Lakes are relatively stable
ecological systems. The equilibrium that lakes have achieved with their shorelines is generally
the result of decades, if not centuries, of interaction. Easily erodable shoreline substrates have
been leveled, creating shallow, low-gradient landscapes, while more durable substrates, such as
rock outcrops, remain as cliffs or steep-gradient shorelines. The degree to which reservoirs
function as natural lakes is, in large measure, tied to the water-level fluctuations in the reservoir.
Reservoirs that most closely mimic the water-level fluctuations of natural lakes tend to have
richer shoreline plant communities than reservoirs that fluctuate more. However, these
communities are not as rich as at natural lakes, because reservoir shorelines are not as stable or
complex as lake shorelines (Ganda 1996). In the following sections, we make some comparisons
among the HCC reservoirs using this understanding of reservoir versus lake ecology. The
following sections also discuss principal findings for each study reach.
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Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
6.2. Weiser Reach
The Weiser Reach has relatively high levels of shoreline erosion. Over 7% of this reach (3.4 mi
of 45.8 mi) exhibited active erosion. We estimated the total area of erosion at 10.58 acres. All
erosion sites were relatively large (3 to 20 m high and several hundred or several thousand
meters long) and occurred mostly where the river channel intercepted steep banks. Although the
banks in this reach are generally covered in relatively thick stands of riparian vegetation (40%
cover of riparian vegetation within a 20-m shoreline corridor), water currents are still capable of
reworking the shorelines. Average total vegetation cover surrounding erosion sites was 65%.
The amount of shoreline erosion from riverine processes is directly related to the erodability of
the soil and the occurrence of mass soil movement. In the Weiser Reach, the Snake River flows
through the relatively flat lava- and sediment-filled Snake River Plain of Idaho. Soils in this
region are relatively deep and occur on level to gently sloping topography. Although the general
topography of this region is not conducive to large mass soil movements, soils in this reach are
considered highly erodable, and localized areas along the riverbanks are highly susceptible to the
erosive forces of water currents and flow fluctuations. Several erosion sites were subject to
anthropogenic disturbances related to agriculture (for example, irrigation pump sites, buildings,
and roadways) (Appendix 2).
6.3. Brownlee Reservoir Reach
The Brownlee Reservoir Reach had the highest rate of shoreline erosion in the study area. We
inventoried 261 sites, which constituted 69% of all sites located in the study area (Table 2 and
Figure 3). Erosion occurred along about 27.2% of the available shoreline (49.6 mi of 182.3 mi).
Many of these sites (n = 43) were quite large, in the 1,001 to 5,000 m2 surface-area class. We
estimated the total area of erosion at 79.07 acres.
Most erosion occurred below Farewell Bend, where the reservoir winds through mountains
characterized by long narrow ridges, V-shaped tributary canyons, and steep, predominantly soilcovered slopes (Vallier 1998). The potential for mass soil movements in this reach is extremely
high, since relatively deep soils are perched on steep slopes. Shoreline substrates along
Brownlee Reservoir are often complex and quite variable, ranging from areas dominated by sand
to areas dominated by bedrock, small- to medium-sized cobbles, and boulders of angular basalt.
Shoreline slopes commonly range from 30 to 40 degrees.
Large water-level fluctuations on Brownlee Reservoir cause undercutting of shoreline banks and
accelerate bank slumping and landslides of these erosion prone soils, especially because they
occur on steep slopes. Bank slumping occurs both above and below the high-water line as gravity
pulls materials downward. Turbidity levels on Brownlee Reservoir are probably greatest during
low pool. This turbidity is typical in reservoirs when there are wide expanses of bare soil that are
easily eroded (U.S. Army Corps of Engineers 1992a). Because drawdowns are necessary for the
reservoir to function for flood control, anadromous fishery purposes, and hydroelectric
generation, the effects of water-level fluctuations on erosion cannot be attributed only to one
operational purpose. Rather, because water-level fluctuations are interrelated among operational
Hells Canyon Complex
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Shoreline Erosion in Hells Canyon
Idaho Power Company
purposes, determining responsibility for specific instances of erosion would be speculative at
best.
Shorelines along Brownlee Reservoir are susceptible to natural and anthropogenic influences.
The large, open nature of the reservoir makes it highly susceptible to erosion from wind-driven
waves. Although no data were collected on wind or wave characteristics, wind-driven waves
were identified as a potential erosion factor at nearly 94% of all sites (245 of 261 sites). Boatgenerated waves were identified as a potential erosion factor at 172 sites. Brownlee Reservoir is
one of the region’s top warmwater fisheries. It also has several boat ramps and high-volume boat
traffic. Groundwater was noted as potentially increasing bank failure at 43 sites. Roads were a
factor at 35 sites, and recreation (for example, bank fishing and use of dispersed campsites) was
a factor at 33 sites (Table 3 and Appendix 2).
Most shoreline erosion occurred at locations dominated by Shrub Savanna (n = 114, 44%) or
Grassland cover types (n = 102, 39%), the most common cover types along the reservoir
(Holmstead 2001). Average total vegetation cover surrounding the sites was about 54%. The
upland habitat along Brownlee Reservoir is often dominated by degraded plant assemblages that
do not provide as much protection from erosion as healthy, native stands of shrubs and
bunchgrasses (Holmstead 2001). Only about 10% of the area along a 20-m shoreline corridor is
covered by protective riparian vegetation.
Shoreline erosion at 85 sites (33% of the total sites on Brownlee Reservoir) probably explains
the presence of riparian vegetation in areas that otherwise would be void of riparian habitat;
shoreline slumping often formed low-gradient, shallow-water habitats (in this otherwise steep
topography) that could support riparian vegetation.
6.4. Oxbow Reservoir Reach
The Oxbow Reservoir Reach experiences relatively little shoreline erosion. A total of 9 sites
were found (Table 2 and Figure 3), and erosion occurred along 2.0% of the available shoreline
(0.51 mi of 25.0 mi). Most erosion sites were in the smaller surface-area classes, although two
sites extended for more than 150 m along the shoreline and were categorized into some of the
larger classes (Table 2). Total area of erosion was estimated at 1.34 acres.
The potential for mass soil movements is extremely high in this reach. Soils tend to be shallower
than those on Brownlee Reservoir, and more shoreline substrates are dominated by bedrock and
boulders of angular basalt. Shoreline slopes greater than 40 degrees are common.
Because Oxbow Reservoir is a reregulating reservoir, water levels fluctuate more frequently but
less dramatically than those on Brownlee Reservoir. Ninety percent of the time, water levels
fluctuate daily within 5.6 ft of the normal, full-pool elevation and are rarely drawn down the full
10 ft allowed in the license. As a result of relatively stable flows, Oxbow Reservoir’s shoreline is
relatively undisturbed (compared with Brownlee Reservoir). Where substrate and topography
permit, stable flows throughout the year and daily fluctuations that irrigate vegetation allow
riparian and wetland vegetation to grow in a relatively wide band (Holmstead 2001, Blair et al.
2001), which protects the shoreline. Approximately 21.5% of the area within a 20-m corridor
Page 32
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
along each shoreline is covered by riparian vegetation, compared with just 10% along
Brownlee Reservoir.
Most shoreline erosion along Oxbow Reservoir occurred at locations dominated by Forbland
(n = 4, 44%) or Grassland (n = 2, 22%) cover types. Average total vegetation cover surrounding
the sites was about 51%. Along this reservoir, most Forbland plant assemblages are dominated
by native species, such as arrowleaf balsamroot (Balsamorhiza sagittata), heart-leaved
buckwheat (Eriogonum compositum), or Gray’s lomatium (Lomatium grayi), while the
associated grasses are mostly introduced annuals (Holmstead 2001). The Grassland plant
assemblages are typically dominated by introduced annuals. Such degraded plant assemblages
are more susceptible to erosion than healthy, native stands of perennial grasses and forbs.
Shorelines along Oxbow Reservoir are susceptible to other natural and anthropogenic influences.
Although this reservoir is not nearly as large and open as Brownlee, it does have some long
expanses that are vulnerable to erosion from wind-driven waves. Although no data were
collected on the wind or wave characteristics, we identified wind-driven waves as a potential
erosion factor at 3 of the 9 sites. Additionally, boat-generated waves were an erosive factor at
4 sites, grazing was a factor at 4 sites, and recreation (for example, bank fishing and use of
impromptu campsites) was a factor at 4 sites (Table 3 and Appendix 2).
6.5. Hells Canyon Reservoir Reach
The Hells Canyon Reservoir reach had relatively little shoreline erosion. A total of 39 erosion
sites were found (Table 2 and Figure 3), and erosion occurred along about 2.7% of the available
shoreline (1.45 mi of 53.9 mi). Most sites (n = 16) were in the surface-area class of 26 to 100 m2
(Table 2). We estimated the total area of erosion at 3.45 acres.
Below Oxbow Dam, the Snake River enters the deep gorge of Hells Canyon. Slopes are
extremely steep (often greater than 60 degrees), and soils are usually shallow, when present. No
published soil survey information is available for most of the lower reaches in Hells Canyon, but
field observations indicate that soil becomes increasingly shallow along the reservoir and
downriver of Oxbow Dam. Mass movements should be expected at any time along the main
canyon and in side canyons. Many of the canyon walls are precipitous, and rocks are crumbly
and severely weathered.
Like Oxbow Reservoir, Hells Canyon Reservoir reregulates flows from upstream projects.
Ninety percent of the time, water levels fluctuate daily within 3.8 ft of the full, normal pool
elevation, and this reservoir is rarely drawn down the 10 ft allowed in the license. Because of this
relative stability, the shoreline is disturbed less than at Brownlee Reservoir. Where substrate and
topography permit, stable flows throughout the year and daily fluctuations that irrigate
vegetation allow a relatively wide band of riparian and wetland vegetation to grow (Holmstead
2001, Blair et al. 2001), protecting the shoreline. Although slopes are extremely steep along this
reach, approximately 20% of the area within a 20-m corridor along each shoreline is covered by
riparian vegetation.
Most shoreline erosion sites occurred at locations dominated by Shrub Savanna (n = 12, 31%) or
Shrubland cover types (n = 9, 23%). Average total vegetation cover surrounding the sites was
Hells Canyon Complex
Page 33
Shoreline Erosion in Hells Canyon
Idaho Power Company
about 76%. The plant assemblages are generally healthier along Hells Canyon Reservoir than
along upstream reaches (Holmstead 2001), and, therefore, they protect against erosion better than
assemblages dominated by introduced annual species.
Shorelines along Hells Canyon Reservoir are susceptible to other natural and anthropogenic
influences. Although this reservoir is not nearly as large and open as Brownlee, it does have
some long expanses that are vulnerable to erosion from wind-driven waves. Although no data
were collected on wind or wave characteristics, we identified wind-driven waves as a potential
erosion factor at 22 of the 39 sites. Recreation (for example, bank fishing and use of dispersed
campsites) was a potential erosion factor at 14 sites, channel flow was a factor at 13 sites (at the
upper reaches of the reservoir), boat-driven waves were a factor at 11 sites, and roads were a
factor at 7 sites (Table 3 and Appendix 2).
6.6. Downriver Reach
The reach below Hells Canyon Dam has relatively little shoreline erosion, compared with
Brownlee Reservoir or the unimpounded reach above the HCC. A total of 60 erosion sites were
inventoried (Table 2 and Figure 3), and erosion occurred along 2.0% of the available shoreline
(2.44 mi of 125 mi). Most sites (n = 21) were in the surface area class of 101 to 250 m2 or
26 to 100 m2 (n = 18). We estimated the total area of erosion at 6.34 acres.
Below Hells Canyon Dam, the Snake River continues through the deep gorge of Hells Canyon.
Slopes are extremely steep in the upper portions of the reach, often greater than 60 degrees, and
soils are usually shallow, when present. No published soil survey information is available for
most of the lower reaches in Hells Canyon. Field observations suggest that soils are very shallow
for the first 17 to 18 mi downstream, to about Sheep Creek, but then might increase in depth in
the lower reaches, down to the confluence with the Salmon River. Mass movements should be
expected at any time along the main canyon and in side canyons. Many of the canyon walls are
precipitous, and rocks are crumbly and severely weathered. Shoreline substrates are diverse, but
are almost entirely composed of large, basalt outcrops (bedrock), large boulders and cobbles,
with few sands or gravels. However, fine sediments occur in the interstitial spaces between
coarser materials and in subsurface substrates. The coarseness of shoreline substrates reduces the
potential for shoreline erosion. Most shoreline erosion sites were upslope of the average highwater levels. Eight sites were identified in the zone below high-water levels.
Boat-generated waves apparently affect most shoreline erosion sites (58 of 60) (Table 3). In this
reach, both private and commercial jet boats are common, with some of the largest boats being
up to 42 ft long and carrying up to 55 passengers. Although no wake-gauge data are available for
wake heights or frequencies along the Snake River in this reach, large, fast-moving boats in the
canyon could generate waves greater than 1.5 ft high. Dorava and Moore (1997), studying the
Kenai River in Alaska, found that boats from 10 to 26 ft long generated waves in the range of
0.10 to 1.50 ft high. Wakes greater than 0.45 ft high removed exponentially more material from
the riverbanks than wakes less than 0.45 ft high. Boat-driven waves, therefore, can generate
erosional forces on riverbanks much higher up the slope than current water levels.
Page 34
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
Shorelines below Hells Canyon Dam are susceptible to other natural and anthropogenic
influences. We identified recreation as a factor of erosion (for example, camping and hiking
trails) at 12 sites, alluvial flooding at 5 sites, and roads at 2 sites.
Most sites occurred in areas dominated by Grassland (n = 24, 40%) or Scrub-Shrub Wetland
cover types (n = 18, 30%), while most of the sites (n = 45) were associated with wetland habitats
(Table 8). Average total vegetation cover surrounding the sites was about 30%. As indicated by
the number of erosion sites located in areas dominated or associated with Scrub-Shrub Wetland,
water currents are still capable of reworking the shorelines, despite the protection afforded these
sites by riparian vegetation. About 17.7% of the shoreline within a 20-m corridor is dominated
by riparian vegetation cover.
6.7. Management Implications
Given that the reservoirs in the HCC are relatively recent features, and assuming that they will
continue to function as they currently do, we can expect erosion to continue to some degree until
the new shorelines reach equilibrium with the existing ecological and imposed anthropogenic
influences. Those areas in the canyon that have highly erodable soils on steep slopes are
inherently susceptible to shoreline erosion. Water-level fluctuations and wave erosion are
probably the most significant activating factors that can trigger shoreline erosion in the canyon.
On a site-specific basis, other factors can negatively trigger bank erosion, including recreation,
construction (roads and industrial projects), and poor livestock grazing practices.
It might not be practical or feasible to stabilize and revegetate most of the shoreline erosion sites
in the study area. The subsoil remaining at these sites is probably often hard, rocky, infertile, and
droughty, making it difficult to reestablish vegetation cover. Without soil amendments, the
remaining soil probably could not support adequate growth and, therefore, would not adequately
stabilize the banks. The steep topography and remoteness of the canyon makes it logistically
challenging to access and work on most sites. However, proper stabilization and revegetation
techniques possibly could be employed at specific sites if analysis indicated that such techniques
were appropriate. The challenge is to apply the technology correctly and thereby control the
problem at its source. Unless control measures were designed and installed properly, according
to the specific site, they would not work. Often, improper design or implementation causes
problems more severe than the original problem.
Rather than attempting to stabilize and restore most erosion sites, the best management plan
would address those human-caused activating factors that trigger erosion on shoreline banks. The
plan should focus on minimizing water-level fluctuations, controlling recreation influences (for
example, boat-driven waves, camping, trails, and vehicle access), minimizing the effects of road
and other construction and maintenance activities, and reducing the negative effects of livestock
grazing. Given that water-level fluctuations are necessary if the HCC is used for flood control,
anadromous fish spawning and protection, or downstream navigation purposes, it may not be
possible to eliminate all negative anthropogenic impacts. Because streambank erosion is a
natural geomorphic process, the challenge is to minimize excessive rates of erosion in
Hells Canyon. The only reach currently experiencing what might be considered excessive rates
of bank erosion is the Brownlee Reservoir Reach. However, the amount of shoreline erosion is
Hells Canyon Complex
Page 35
Shoreline Erosion in Hells Canyon
Idaho Power Company
not surprising, considering the inherent site characteristics, large water-level fluctuations, windgenerated waves, and other activating forces influencing this reach.
Because many factors can contribute to shoreline bank erosion, an objective pattern of erosion in
a particular reach may not emerge without many years of observations and documentation
(Dorava and Moore 1997). This report documents existing levels and the extent of shoreline
erosion in the study area and could be used as a tool in future research and monitoring. Valuable
observations by researchers (or regular river users) could be lost to those working on shoreline
erosion issues, unless these observations are properly and consistently recorded.
7. ACKNOWLEDGMENTS
Thanks go to Kelly Wilde, Pat Aldrich, Heather Swartz, Carl Pedersen, Von Pope, Casey Pevey,
Lisa Hahn, Marie Kerr, and Ann Rocklage for assisting with field work for this study. Thanks
also go to Gary Wilbert and Chris Huck for GIS support. Theri King and Pam Peterson edited the
draft manuscript. Corporate Publishing, IPC, formatted the manuscript.
8. LITERATURE CITED
Allen, H. H., and F. J. Wade. 1991. The scope and nature of shoreline erosion problems at Corps
of Engineers reservoir projects: a preliminary assessment. Springfield, VA: Nat. Tech.
Info. Serv. Misc. Pap. W-91-3. 22 p.
Asherin, D. A., and J. J. Claar. 1976. Inventory of riparian habitats and associated wildlife along
the Columbia and Snake rivers. Volume IIIA. Coll. of For., Wildl. and Range Sci., Univ.
of ID, Moscow. 556 p.
Blair, C., J. Braatne, R. Simons, S. Rood, and B. Wilson. 2001. Effects of constructing and
operating the Hells Canyon Complex on wildlife habitat. In: Technical appendices for
Hells Canyon Complex Hydroelectric Project. Tech. Rep. E.3.2-44. Idaho Power Co.,
Boise, ID. 200 p.
Bohn, C. C., and J. C. Buckhouse. 1985. Some response of riparian soils to grazing management
in northeastern Oregon. J. Range Manage. 38:378-381.
Bonneville Power Administration. 1984. Hells Canyon environmental investigation. Prepared by
CH2M-Hill, Boise, ID. 300 p.
Bradbury, J., P. Cullen, G. Dixon, and M. Pemberton. 1995. Monitoring and management of
streambank erosion and natural revegetation on the lower Gordon River, Tasmanian
Wilderness World Heritage Area, Australia. Environ. Manage. 19:259-272.
Brown, M. 2001. Reservoir-related recreational use at the Hells Canyon Complex. Idaho. In:
Technical appendices for Hells Canyon Complex Hydroelectric Project. Tech.
Rep. E.5-2. Idaho Power Co., Boise, ID.
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Hells Canyon Complex
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Idaho Power Company
Shoreline Erosion In Hells Canyon
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Hells Canyon Complex
Page 39
Shoreline Erosion in Hells Canyon
Idaho Power Company
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morphology relations: U.S. Geol Surv. Prof. Pap. 1288. 21 p.
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ID.
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Page 40
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
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42 p.
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interference pattern. Sci. Amer. 258:80-83.
Hells Canyon Complex
Page 41
Shoreline Erosion in Hells Canyon
Idaho Power Company
Wilcox, A. W., and J. E. Meeker. 1991. Disturbance effects on aquatic vegetation in regulated
and unregulated lakes in Northern MN. Canadian J. of Bot. 69:1542-51.
Wishmeier, W. H., and D. D. Smith. 1978. Predicting rainfall erosion losses-A guide to
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Agency Rep. EPA-670/2-74-072. 58 p.
Page 42
Hells Canyon Complex
Idaho Power Company
Table 1.
Shoreline Erosion In Hells Canyon
Distribution of shoreline miles by reach and shoreline source in the
Hells Canyon Study Area.
No. Miles by Reach1
Shoreline Source
HB
HC
OX
BR
BA
Total
Idaho
62.5
26.0
13.0
72.2
11.8
185.5
Oregon
62.5
27.5
12.0
91.0
11.8
204.8
Islands
0.0
0.4
0.0
19.1
22.2
41.7
125.0
53.9
25.0
182.3
45.8
432.0
Total
1 Where HB = Below Hells Canyon Dam, HC = Hells Canyon Reservoir, OX = Oxbow Reservoir, BR = Brownlee Reservoir, and
BA = Weiser.
Table 2.
Distribution of shoreline erosion sites by surface area class for each reach
in the Hells Canyon Study Area.
No. Sites by Reach1
Surface Area
2
Class (m )
HB
HC
OX
BR
BA
Total
1-10
1
0
0
0
0
1
11-25
1
2
1
2
0
6
26-100
18
16
2
46
0
82
101-250
21
12
2
69
0
104
251-500
9
4
1
56
3
73
501-1000
5
3
1
31
1
41
1001-5000
4
1
2
43
2
52
>5000
1
1
0
14
3
19
Total
60
39
9
261
9
378
1 Where HB = Below Hells Canyon Dam, HC = Hells Canyon Reservoir, OX = Oxbow Reservoir, BR = Brownlee Reservoir, and
BA = Weiser.
Hells Canyon Complex
Page 43
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Idaho Power Company
Table 4.
Shoreline Erosion In Hells Canyon
Summary of cover types present on the 9 sites mapped in the Weiser
Reach of the Hells Canyon Study Area. Dominant refers to the cover type
covering a majority of the site margins. Associated refers to the cover type
covering only portions of the site margins.
Dominant
Cover Type
Sites
%
Associated
Sites
%
Total
Sites
%
Wetland (riparian)
Emergent Herbaceous
1
11.1
1
11.1
2
22.2
Scrub-Shrub
2
22.2
4
44.4
6
66.6
Forested
5
55.5
−
−
5
55.5
Shrub Savanna
1
11.1
1
11.1
2
22.2
Shrubland
−
−
−
−
−
−
Grassland
−
−
1
11.1
1
11.1
Desertic Shrubland
−
−
−
−
−
−
Desertic Herbland
−
−
−
−
−
−
Forbland
−
−
4
44.4
4
44.4
Barrenland
−
−
2
22.2
2
22.2
Industrial
−
−
−
−
−
−
Cliff/Talus Slope
−
−
−
−
−
−
Agriculture
−
−
−
−
−
−
Parks/Recreation
−
−
−
−
−
−
Upland
Land Use
Hells Canyon Complex
Page 45
Shoreline Erosion in Hells Canyon
Table 5.
Idaho Power Company
Summary of cover types present on the 261 sites mapped in the
Brownlee Reservoir Reach of the Hells Canyon Study Area. Dominant
refers to the cover type covering a majority of the site margins. Associated
refers to the cover type covering only portions of the site margins.
Dominant
Cover Type
Associated
Sites
%
Total
Sites
%
Sites
%
2
0.8
31
11.9
33
12.6
10
3.8
40
15.3
50
19.2
1
0.4
1
0.4
2
0.8
114
43.7
1
0.4
115
44.1
Shrubland
19
7.3
7
2.7
26
10.0
Grassland
102
39.1
14
5.4
116
44.4
Desertic Shrubland
1
0.4
−
−
1
0.4
Desertic Herbland
3
1.2
2
0.8
5
1.9
Forbland
6
2.3
8
3.1
14
5.4
Barrenland
2
0.8
71
27.2
73
28.0
Industrial
−
−
−
−
−
−
Cliff/Talus Slope
−
−
−
−
−
−
Agriculture
1
0.4
−
−
1
0.4
Parks/Recreation
−
−
−
−
−
−
Wetland
Emergent Herbaceous
Scrub-Shrub
Forested
Upland
Shrub Savanna
Land Use
Page 46
Hells Canyon Complex
Idaho Power Company
Table 6.
Shoreline Erosion In Hells Canyon
Summary of cover types present on the 9 sites mapped in the
Oxbow Reservoir Reach of the Hells Canyon Study Area. Dominant refers
to the cover type covering a majority of the site margins. Associated refers
to the cover type covering only portions of the site margins.
Dominant
Cover Type
Sites
%
Associated
Sites
%
Total
Sites
%
Wetland
Emergent Herbaceous
−
−
2
22.2
2
22.2
Scrub-Shrub
1
11.1
4
44.4
5
55.5
Forested
−
−
1
11.1
1
11.1
Shrub Savanna
−
−
−
−
−
−
Shrubland
1
11.1
−
−
1
11.1
Grassland
2
22.2
−
−
2
22.2
Desertic Shrubland
−
−
−
−
−
−
Desertic Herbland
−
−
−
−
−
−
Forbland
4
44.4
−
−
4
44.4
Barrenland
−
−
−
−
−
−
Industrial
−
−
1
11.1
1
11.1
Cliff/Talus Slope
1
11.1
−
−
1
11.1
Agriculture
−
−
−
−
−
−
Parks/Recreation
−
−
−
−
−
−
Upland
Land Use
Hells Canyon Complex
Page 47
Shoreline Erosion in Hells Canyon
Table 7.
Idaho Power Company
Summary of cover types present on the 39 sites mapped in the
Hells Canyon Reservoir Reach of the Hells Canyon Study Area. Dominant
refers to the cover type covering a majority of the site margins. Associated
refers to the cover type covering only portions of the site margins.
Dominant
Cover Type
Sites
%
Associated
Total
Sites
%
Sites
%
1
2.6
1
2.6
Wetland
Emergent Herbaceous
−
−
Scrub-Shrub
2
5.1
22
56.4
24
61.5
Forested
1
2.6
5
12.8
6
15.4
12
30.8
1
2.6
13
33.3
Shrubland
9
23.1
−
−
9
23.1
Grassland
6
15.4
−
−
6
15.4
Desertic Shrubland
−
−
−
−
−
−
Desertic Herbland
−
−
−
−
−
−
Forbland
5
12.8
−
−
5
12.8
Barrenland
−
−
−
−
−
−
Industrial
−
−
−
−
−
−
Cliff/Talus Slope
2
5.1
2
5.1
4
10.2
Agriculture
−
−
−
−
−
−
Parks/Recreation
2
5.1
−
−
2
5.1
Upland
Shrub Savanna
Land Use
Page 48
Hells Canyon Complex
Idaho Power Company
Table 8.
Shoreline Erosion In Hells Canyon
Summary of cover types present on the 60 sites mapped in the reach
below Hells Canyon Dam in the Hells Canyon Study Area. Dominant refers
to the cover type covering a majority of the site margins. Associated refers
to the cover type covering only portions of the site margins.
Dominant
Cover Type
Sites
%
Associated
Sites
%
Total
Sites
%
Wetland
Emergent Herbaceous
−
−
6
10.0
6
10.0
18
30.0
14
23.3
32
53.3
4
6.7
3
5.0
7
11.7
Shrub Savanna
8
13.3
7
11.7
15
25.0
Shrubland
5
8.3
3
5.0
8
13.3
Grassland
24
40.0
15
25.0
39
65.0
Desertic Shrubland
−
−
−
−
−
−
Desertic Herbland
−
−
1
1.7
1
1.7
Forbland
−
−
−
−
−
−
Barrenland
1
1.7
11
18.3
12
20.0
Industrial
−
−
−
−
−
−
Cliff/Talus Slope
−
−
−
−
−
−
Agriculture
−
−
−
−
−
−
Parks/Recreation
−
−
−
−
−
−
Scrub-Shrub
Forested
Upland
Land Use
Hells Canyon Complex
Page 49
Shoreline Erosion in Hells Canyon
Idaho Power Company
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Page 50
Hells Canyon Complex
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Legend
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Hells Canyon Study
Area Map
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UTM GRID AND 1987
MAGNETIC NORTH
DECLINATION AT CENTER
OF OXBOW QUADRANGLE
2.5
5
10
15
Miles
Scale = 1:582,285
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 52
Hells Canyon Complex
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Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 54
Hells Canyon Complex
Plotfile: soil_ero_p1.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
656066
656002
656002
656066
656003
656003
656003
656052
656002
BA
2
342
341
Por
Isla ter
nd
656160
656017
656179
656082
656179
656035
656179
656017
656153
343
56003
BA3
Snake River
R.V. Park
656173
656082
656016
656035
656180
340
Oasis
656153
656129
BR303
656001
BA4
656190
656083
656095
656093
656082
1
BA
339
Darrows
Island
656102
656102
BR3 0 2
344
656017
656175
656092
656034
656017
656169
BA8
656174
ke
tla
es
W
BR308
656173
656173
656034
656034
656173
345
656179
656179
McRea
Island
BA6
BA7
349 656179
656082
656017
656034
656015
Weiser
656173
350
656179
656034
351
656034
656173
nd
la
Is
656174
348
656015
656067
656016
656174
0
346
656016
352
656015
BA9656067
347
353
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 1 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
*
GN
0O 08’
2 MILS
Tech. Report E.3.2 - 42, Figure 3
MN
Soil Types and Shoreline
Erosion Sites, Hells Canyon
17 O 30’
311 MILS
101- 250
251- 500
501- 1000
1001- 5000
UTM GRID AND 1987
MAGNETIC NORTH DECLINATION
AT CENTER OF OXBOW QUADRANGLE
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
1
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 56
Hells Canyon Complex
Plotfile: soil_ero_p2.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
656003
BR3 0 4
C
r
eek
5
RI
VE
R
7
5
BR
29
BR2194
BR
29
2
BR2 9
1
BR2
90
604143E 604145E
656179
656089
335
656177
656064
97
BR2
604145E
604143F
604143E
333
28
BR
30
BR
BR2
89
BR2 88
7
28
BR
6
28
BR
5
28
BR
SN
AK
4
E
8
656088
656089
656089
604145E
BR
29
656111
9
336
656180
604143F
656095
BR
29
604136F
604145E
332
9
604143E
604130E
BR29 3
BR
29
6
Steck
Park
656095
BR
30
656088
60496F
604130F
60496E
604145E
BR
28
3
328
338
Hu
ff m
an
Isl
an
d
Grouse
6
331
604130F
604130E
656111
BR
30
330
656180
BR
30
656111
329
656093
337
656153
656180
BR30 0
BR3 01
656002
334
604124D
604171B
Farewell
Bend
BR281
1
20
BR
0
20
BR
9
19
BR
604130E
604130F
60496F
327
4
19
BR
95
BR1
604130F
604130E
60496F
60496E
60440A
60496E
60496E
Riv e r
604130E
60496E
604130F
60496E
60496F
60496F
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 2 of 16
604127A
Huntington
604130E
60496F
BR1
Spring
Rec. Site 9 6
20
BR
B
R
19
8
93
BR1
2
326
BR
28
2
604122C
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 58
Hells Canyon Complex
Plotfile: soil_ero_p3.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
656162
Plotting Scale: 15841
Created: December 20, 2001
C
656088
314
re
il
Tra
656093
Rock
656162
656073
BR21
9
315
BR2
20
656074
656180
04152F
656162
656180
316
656073
BR
21
8
4
17
604102C
BR
60496E
604178F
BR2 0 7
BR208
BR2 0 9
6
BR
20
324
60496E
60496E
604130E
60496E
604130F60496F
604103E
60496F
604153E
656129
656129
604130F
20
BR
60496E
325
5
e
604130E
rs
Ho
BR
19
0
3
604130F
60496F
60496F
y
Ba
604130F
604130F
604130F
60496F
Morgan
60496E
BR19 2
Creek
656088
BR2 0 4
BR203
604169C
656129
60496F
60496F604130F
604152F
604103E
BR
21
0
BR211
BR212
60496F
604130F
604130F
60496F
604130F
60496F
604130F
BR191
604152F
656180
323
BR
18
BR
7
BR 18 8
18
9
ba
604130E
60496F
322
BR18 6
604103D
604103F
604130F
RIVER
BR
18
5
k
ee
r
C
BR
17
9
rd
b
Hi
604152F
0
18
BR
KE
A
N
S
319
604153E
656180
BR18
4
320
604103E
604103F
656129
656111
321
BR1
83
656093
BR216
Cr
e
318
604153E
17
BR2
ek
656094
604103D
656162
BR18 2
656162
BR181
604102C
60494C
604103F
BR213
604103F
656088
656162
BR214
604153E
656088
BR215
604152F
317
BR
17
8
604103E
BR
17
6
BR
17
7
BR175
604102C
604153E
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 3 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
6
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 60
Hells Canyon Complex
Plotfile: soil_ero_p4.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
BR2
30
656087
656162
656087
ft
Ra
304
9
656087
22
BR
308
604152F
8
16
R
B
604103D
604103F
604152F
604153E
604103E
604103E
4
22
656094
BR
656093
22
BR
604152F
3
656087
656088
656162
2
309
6045C
656087
22
BR
604152F
604103F
604103F
604152F604103F
5
KE
A
SN
604103F
22
BR
656094
604153E
BR
16
3
604103F
6
656088
656088
BR2
21
307
604153E
604103E
Dennett
BR22 7
656180
BR162
604152F
656087
656087
Mountain
Man Resort
BR2 2 8
306
604103F
Quicks
604152F
BR
1
BR 5 8
15
9
BR1
60
BR
15
7
604103E
BR161
a n d Cre
ek
604103F
656087
B
R
O
W
N
LEE
6045C
604153E
656162 656087
656087
.
604103E
604153E
604103E
604153E
656162
BR16 5
BR166
BR16 7
604169D
604103D
4103E
604153E
BR1
64
BR
22
BR
15
BR1 3
54
BR1
55
BR1
56
305
RE
S
BR15
1
BR15
2
604169D
04103D
604103F
311
310
604152F
604153E
BR
16
9
312
604103F
604103F
656088
313
604103E
604153E
604152F
604103E
604152F
604103E
604153E
Wo
lf
604152F
656087
EE
L
N
W
O
.
BR RES
604153E
604103E
BR170
Little Deacon
Creek
604103F
21
BR2
656162
656088
604103F
604103E
604153E
314
604103E
1
17
BR 604153E
il
Tra
656093
604103F
656162
604152F
3
17
BR
604103F
604153E
ly
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 4 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Soil Types *
--------------------
1- 10
656017 -
26- 100
604153E
604102C
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
-------------------------------------11- 25
315
604152F
4
17
604102C
BR
eek
r
C
Thematic Features Legend
BR2
20
2
17
BR
Base Features Legend
656074
604102C
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 62
Hells Canyon Complex
Plotting Scale: 15841
Created: December 20, 2001
95
BR
604143F
604136F
OW
R
B
N
Plotfile: soil_ero_p5.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
1
BR2 5
656074
294
96
BR 7
9
BR 8
9
BR
656180
656014
656095 656088
656087
656014
656180
R
VE BR2
I
R
34
BR14
0
BR141
BR142
604143F
604136F
604136F
3
14
BR
604142C
604145E
604136F
302
604143F
604143E
604145D
604143E
604145E
604136F
604143F
604136F
604143E
BR
14
4
BR
10
8
604143F
604145E
604145D
604143F
604103E
604143E
604143E
6
Hollow
604145D
604145E
g
L on
7
604143F
604143D
e
ive
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 5 of 16
604169D
604103D
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
6045C
604153E
6 04103F
604153E
604103E
604152
Base Features Legend
Study Area
604145E 604143F
656
604169D
604103D
604153E
604103E
604103E
604153E
604103E
604143D
604145E
604153E
604153E
604103D
604136F 604103E 604103E
Hewitt/
Holcomb
Park
604143D
604143E
604153E
604103D
604103D
304
k
604145E
604143E
656087
Cree
604136F
656087
303
604143E
Sna k
3
BR147
604145E
604136F
Boise
23
BR
BR146
604143E
604155E
5
604143E
656087
604143E
604145E
604143D
ep
S he
656087
ek
656162
BR1
45
BR
1
BR 12
11
3
604143F
604145E
5
BR2
30
BR
11
4
BR
13
9
301
Cr
e
300
604143E
604136F
604143E
604143E
23
BR
604143E
604143E
BR
15
BR1 3
54
BR1
55
BR1
56
BR
11
5
604136F
BR15
1
BR15
2
604143F
656162
BR2 31
604169D
604143E
604143F
604136F
BR148
BR149
BR150
604143F
604136F
656088
656166
2
604143F
604136F
656014
BR
23
604143D
299
ill
BR238
656180
604136F
604143F
604145D
604143F
656087
298
604143D
rg
St u
656087
656070
BR239
BR237
BR236
604143D
604145D
656014
BR240
297
656014
BR24 3
BR242
BR
24
5
656074
604143D
604143E
3
656087
BR
24
1
BR
12
4
604143E
604145E
604145D
5
13
BR
n
BR13 8
604143D
BR13 6
604143D
604145E
6
11
BR
604143D
604145D
604169C
604145D
BR
13
4
604145D
3
13
BR
604145D
BR131
32
BR1
604143D
ks o
656072
BR
24
8
656087
296
BR12 9
BR130
2
25
BR1
BR12 6
BR12 7
BR128
1
604143E
604143D
656180
604143D
4
10
BR
604143F
656074
BR137
604143F
604145E
BR2 4 9
BR103
BR102
604136F
Gulc h
656070
BR2 4 4
295
604133C
604133C
Jac
0
BR247
BR2
46
BR
B
1
BR R10 0 0
BR 12 1
BR
12
0
BR 12 2 1
12
3
25
BR
SNAK
E
BR
99
656095
Thematic Features Legend
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 64
Hells Canyon Complex
Plotfile: soil_ero_p6.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
DIT
CH
F
er
ost
Gulch
ek
Cre
604133C
604145E
604143E
604145E
604143F
604145E
4
604136F
604143D
604143E
9
BR
11
0
BR
11
1
BR
10
6
7 0
1
10
BR BR
604136F
5
10
R
B
604143D
604143E
BR
1
BR 12
11
3
6
60417C
604142C
6
11 604145E
BR
604136F
604145E
604143D
604143F
60440A
604143E
7
60412A
60440A
604145D
604143E
604143E
604127A
604143F
604145E
604145D
25
BR1
BR12 6
BR12 7
28
BR1
604169C
604143D
604143D
60412A
604127A
604145D
60412A
604145D
60440A
60415A
604145E
60440A
60423A 60413A
60415A
604145D
604143D
BR131
32
BR1
60416B
9
604176A
604143D
60416D
60413A
604145E
25
BR
BR
BR 12 2
12
3
604145D
604145E
604143E604143D
604143D
BR
B
1
BR R10 0 0
12 1295
0
1
12
BR
River
1
BR12 9
BR130
604143E
604143D
60412B
60416B
3
13
BR
604145D
604143D
L on
604143F
g
BR13 6
e
ive
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
BR
24
656087
8
Jac
656072
604136F
656074
BR247
k
Sna k
656074
297
604136F
Base Features Legend
Panel 6 of 16
d
604143F
604169D
r
656180
BR
13
4
604143D
5
13
BR
604143E
Boise
656088
656087
656070
Thematic Features Legend
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
w oo
604145D
604143D
656014
656072
296BR2 4 9
604143D
60416D
656088
656014
656074
604145D
604145D
604142C
656095
656095
604143D
60416D
656180
293
Cott o n
604145D
60416B
Study Area
0
60416B
NLEE
W
O
BR 294
BR103
BR102
604136F
BR25 2
8
604143E
BR
99
604143E
1
BR2 5
Hewitt/
Holcomb
Park
604133C
96
BR
97
BR 8
9
BR
604143E
604127A
604133C
4
10
BR 604143F
2
BR
12
4
604145D
BR
11
5
604127A
604176A
604143D
604136F
92
BR
3
BR9
4
BR9
604145E
604143F
BR
11
4
604136F
604169D
604143D
BR
BRB 8 8
9
604145E
604145E
604145E
91
BR
60417C
60412B
604143F
3
95
BR
Richland
60412B
60412A
604176A
5
BR
10
8
604143E
604143E
604143D
604143E
604143E
604143F
604145E
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
*
GN
0O 08’
2 MILS
Tech. Report E.3.2 - 42, Figure 3
MN
Soil Types and Shoreline
Erosion Sites, Hells Canyon
17 O 30’
311 MILS
101- 250
251- 500
501- 1000
1001- 5000
UTM GRID AND 1987
MAGNETIC NORTH DECLINATION
AT CENTER OF OXBOW QUADRANGLE
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
1
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 66
Hells Canyon Complex
Duk
656087
656087
Woodhead
Park
3
656087
656088
BR
26
287
18
BR 19
BR 2 0
R
60459D B
BR
26
2
656180
B
BR R21
BR 2 2
BR 2 3
24
288
289
VE
RI
BR31
BR32
BR
B 33
BR R3 4
B 35
BR R3 6
37
604146D
BR30
604144F
656180
604144E
BR28
BR29
BR
2
BR2 6 5
BR27
604144E
656088
BR264
3
27
BR
656071
604143F
656014
BR265
BR2
74
BR
BR 16
17
60459D
656074
286
BR
15
BR
BR 11
1
BR 2
13
9
BR R10
B
604144F
BR26 8
BR266
656014
656087
656074
BR271
BR2 7 0
BR269
656068
BR267
BR
27
285
656087
656068
BR272
19
OX1
OX
7
656014
5
656013
604144E
BROWNLEE DAM
60438F
284
604133C
OX Ranch
60459F
OX8
283
604144E
656060
B
BR R2 7 8
27
7
BR2
76
6045C
656087
656180
656087
BR
14
656131
656087
656014
BR
BR 2 8 0
27
9
656013 656132
OX6
Canyon
Black
656184
604143F
R
60459F
Creek
60459E
McCor
Park
Plotting Scale: 15841
Created: December 20, 2001
nlee
Plotfile: soil_ero_p7.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
656088
1
26
BR
656069
604144F
604143F
656014
26
BR
604138F
38
BR 9
3
BR
0
656088
290
604143E
656180
59
BR2
BR BR2
25
7 58
BR
25
6
0
BR4
BR4 2
656014
656014
656069
54
83
BR
BR
84
604143F
S.
E
R BR2
B
BR R4 3
44
BR
45
604158E
604146D
656180
292
B
B R
BR R8 8 6
7
BRBR8 8 8
90 9
85
BR
656014
3
291
604143E
BR
25
1
BR4
656087
BR2
55
604158E
656087
604143E
91
BR
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 7 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
656088
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 68
Hells Canyon Complex
Plotfile: soil_ero_p8.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
Cre
ek
Wi
Salt
ld
h
o
rse
656185
656132
656185
OX3
656132
656132
7
656185
656132
656131
60459F
60459F
60438E
270
274
60438F
HC
OX
1
60438F
60459F
656184
656130
278
60438F
60438F
656185
60438F 60459F
60459F
60438F
60438E
656184
279
60449D
60459E
656090
60438F
60459F
280
60459F
60459E
60438F
60440A
60459F
0438F
656130
656185
60438F
60438E
60449E
656132
656185
60438F
60459F 60440A
60438E
656130
656026
281
60459F
60459E
re
e
60438E
k
C
604133C
656090
60459E
60438F
60459F
282
656131
656184
60459E
604143F
60459E
Black
656132
Canyon
656013
6045C
283
604133C
604144E
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 8 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Soil Types *
--------------------
1- 10
656017 -
26- 100
656087
656013
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
-------------------------------------11- 25
656087
656014
OX6
OX2
275
60438F
Park
656131
Oxbow Boat
Ramp
656132
656132
River
277
Wil
dho
rse
McCormick
273
656185
Carters
Landing
656185
656130
656132
OX4
OX5
604DAM
59D
S
N
AK
E
276
O
X
BO
W
656132
656185
R
E
S.
656090
656130
656132
656132
656185
656185
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 70
Hells Canyon Complex
Plotfile: soil_ero_p9.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
In
d
ian
HC7 7
RI
258
C
r
ee k
259
260
HC49
261
6045C
263
7
6
HC
7
HC
4
60459E
Oxbow Dam
60459F
60459E
HC
4
6
656132
60438F
60459F
264
656131
656184
268
60459F
60459F
60459F
60459F
60438F
60438F
60438F
60438F
60459E
656131
656090
60438E
HC6 6
60459D
269
60459F
604167D
60438F
60438E
60459F
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 9 of 16
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Soil Types *
--------------------
1- 10
656017 -
26- 100
60438F
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
-------------------------------------11- 25
60
60438F
60459E
60459E
Primary Route
60438F
6045C
60459D
60459E
Thematic Features Legend
27
60459F
60438F
Base Features Legend
HC65
6045C
271
HC6
7
267
6045C
266
6045C
656181
604DA
60459D
HC6
8
60459E
656090
HC7 0
656131
HC
71
656090
HC6 9
r
n
ma
He
656191
6045C
60459F
60438F
60459F
Copperfield
63
Park
HC
656090
HC7 4
HC
73
265
HC72
60438F
HC
117
HC118
5
HC
7
656131
R
I
V
ER
eek
Cr
272
e
60438E
656049
656191
Th
6045C
ow
B
l
ue
60438F
Ox
b
60459E
60438E
64
HC
KE
A
SN
HC48
60438F
Creek
60459F
In
d
ia
n
262
60459D
Hells Canyon
Park
60459D
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 72
Hells Canyon Complex
Plotting Scale: 15841
Created: December 20, 2001
ek
Plotfile: soil_ero_p10.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
HC
5
9
N o r th
Sa
w
pit
e
Cr
HEL LS
C
250
Cre
ek
252
9
8
0
HC
8
P
wo
HC
7
51
HC
257
HC5 0
HC5 2
HC5 3
C r ee
k
HC
5
4
256
ER
RIV
Ly n c h
Th
t
ri ty
HC
7
255
HC6
2
Big Bar
HC5 5
254
o i nt
HC5
6
253
HC
61
HC
81
HC
82
ON
HC5 7
251
HC60
AN
Y
249
258
259
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 10 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 74
Hells Canyon Complex
Plotting Scale: 15841
Created: December 20, 2001
re
e
Plotfile: soil_ero_p11.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Th
ite
n
a
Gr
HB
5
238
239
HB
4
240
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 11 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Soil Types *
--------------------
1- 10
656017 -
26- 100
248
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
-------------------------------------11- 25
Deep Cr. Trail
Cr
Thematic Features Legend
247
HellsHB1
Canyon
Dam
B
a
ttle
Stu
d
k
HC5
8
Barton Heights
ee
Hells Canyon Cr.
Rec. Site
HB3
HB2
246
RE S
.
E
Creek
245
N
243
S
N
AK
242
ep
De
244
RIVER
241
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 76
Hells Canyon Complex
Plotfile: soil_ero_p12.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
229
228
18
HB
HB19
HB
27
230
17
HB
16
HB
HB
15
ek
232
234
HB
12
sh
Ru
KE
A
SN
HB13
233
HB1
4
C r e ek
RIVER
Cr
e
231
235
re
HB
9
Th
R
I
D
G
E
HB
8
HB
7
Slu
ice
237
HB
6
HB
11
HB
10
236
H
238
k
k
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 12 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 78
Hells Canyon Complex
Plotfile: soil_ero_p13.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
st
Vall
ey
Lo
o od
kw
HB
31
215
r
Ki
Kir
by
HB
32
HB3
3
218
36
HB
HB34
R IV E R
216
HB35
217
Cre
ek
Triangle
Mtn
Pittsburg
Admin. Site
Klop
ton
C
Cr
eek
e ek
Cr
220
Kirkwood
Historic
Ranch
KE
A
SN
219
221
ar
Co
ug
ar
ibou
30
HB
C
sant
a
e
l
P
9
B2
H
222
27
HB
223
28
HB
ek
Cre
227
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 13 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
HB
21
22
Base Features Legend
20
HB
HB
23
226
Cr
eek
HB
lt
Sa
HB
25
Creek
HB2
4
225
HB2 6
224
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 80
Hells Canyon Complex
Plotting Scale: 15841
Created: December 20, 2001
on
Klopt
36
HB
Pittsburg
Admin. Site
Pleasant Valley
Island
215
37
HB
on
Cany
Cree
k
ry
Kur
Creek
Cr
Plotfile: soil_ero_p14.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
es
Jon
sant
a
e
l
P
211
40
HB
Cre
ek
HB41
210
209
207
re
38
HB
39
HB
Big
k
ee
r
C
H ig h
range
212
V
a
lle
y
ER
RIV
C
213
ek
214
208
3
HB4 2
4
HB
206
Some
rs
205
45
HB4
4
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 14 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Tech. Report E.3.2 - 42, Figure 3
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
Soil Types and Shoreline
Erosion Sites, Hells Canyon
101- 250
251- 500
501- 1000
1001- 5000
1
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 82
Hells Canyon Complex
Plotfile: soil_ero_p15.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
Plotting Scale: 15841
Created: December 20, 2001
195
k
Cree
g
Dou
196
Dug Bar
Cr
e ek
Creek
mp
Ca
197
ee k
r
C
200
HB51
HB4
9
HB48
201
HB50
199
202
HB47
f
Wol
p
Dee
203
SN
AK
E
Sna k
e
ive
Boise
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 15 of 16
46
HB
Cr
ee
k
ek
Cre
IT
MM
SU
45
HB
205
3
HB4 2
HB4
Ca
t
Base Features Legend
Study Area
204
Cr
d
lan
o
R
HB4
4
Du
g
198
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
*
GN
0O 08’
2 MILS
Tech. Report E.3.2 - 42, Figure 3
MN
Soil Types and Shoreline
Erosion Sites, Hells Canyon
17 O 30’
311 MILS
101- 250
251- 500
501- 1000
1001- 5000
UTM GRID AND 1987
MAGNETIC NORTH DECLINATION
AT CENTER OF OXBOW QUADRANGLE
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
1
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 84
Hells Canyon Complex
Plotting Scale: 15841
Created: December 20, 2001
185
ER
Riv
er
Plotfile: soil_ero_p16.gra
Theme: i:\relic\hellscan\baseinv\erosion_soils.aml
186
ide
v
i
D
187
2
Ch
er
ry
Salm1on
188
0
0
HB6
HB5 9
8
HB5
189
HB57
HB56
eek
y Cr
Wile
Creek
190
HB5 2
194
193
HB53
191
195
HB55
reek
C
g
Dou
HB54
192
Base Features Legend
Boise
Sna k
e
ive
Study Area
r
R
Vicinity Map
IDAHO
POWER
Geographic Information Services
Panel 16 of 16
Primary Route
Study Area
Secondary Route
Water Body
Light Duty Road
River Mile
Unimproved Road
IPC Project Facility
Trail
Pump Station
Railroad
Spring
Transmission Line
Well
Perennial River or Stream
Intermittent River or Stream
Ditch or Canal
Political Boundary
Thematic Features Legend
Erosion Site Surface Area (square m) +
--------------------------------------
Soil Types *
--------------------
1- 10
656017 -
11- 25
26- 100
and all other colored
polygons with 6-digit
numeric codes
(not shown in this legend)
*
GN
0O 08’
2 MILS
Tech. Report E.3.2 - 42, Figure 3
MN
Soil Types and Shoreline
Erosion Sites, Hells Canyon
17 O 30’
311 MILS
101- 250
251- 500
501- 1000
1001- 5000
UTM GRID AND 1987
MAGNETIC NORTH DECLINATION
AT CENTER OF OXBOW QUADRANGLE
> 5000
+ See Appendix 2 for erosion sites and
alpha-numeric codes
*See Appendix 1 for map codes
1
.5
0 MILES
Shoreline Erosion in Hells Canyon
Idaho Power Company
This page left blank intentionally.
Page 86
Hells Canyon Complex
Idaho Power Company
Appendix 1.
STATE
MUID
Shoreline Erosion In Hells Canyon
Summary of some soil characteristics using USDA Natural Resources Conservation Service (1995)
published information for the Hells Canyon Study Area.
MUNAME
PARTSIZE SURFTEX ROCKDEPL ROCKDEPH
KFACT KFFACT SALINL SALINH
PHL
PHH
MUWATHEL
OR
604102C LOVLINE CHANNERY LOAM, 2
TO 12 % SLOPES
096
CN-L
20
40
0.20
0.32
0
0
6.6
7.3
1
OR
604103D LOVLINE CHANNERY LOAM, 12
TO 30 % NORTH SLOPES
096
CN-L
20
40
0.20
0.32
0
0
6.6
7.3
1
OR
604103E LOVLINE CHANNERY LOAM, 30
TO 50 % NORTH SLOPES
096
CN-L
20
40
0.20
0.32
0
0
6.6
7.3
1
OR
604103F LOVLINE CHANNERY LOAM, 50
TO 70 % NORTH SLOPES
096
CN-L
20
40
0.20
0.32
0
0
6.6
7.3
1
OR
604122C POALL VERY FINE SANDY
LOAM, 2 TO 12 % SLOPES
096
VFSL
0
0
0.43
0.43
0
0
7.4
8.4
1
OR
604124D POALL VERY FINE SANDY
LOAM, 12 TO 40 % SOUTH
SLOPES
096
VFSL
0
0
0.43
0.43
0
0
7.4
8.4
1
OR
604127A POWVAL SILT LOAM, 0 TO 3 %
SLOPES, WARM
096
SIL
0
0
0.37
0.37
0
0
7.4
8.4
1
OR
60412A
BAKER SILT LOAM, 0 TO 2 %
SLOPES, WARM
096
SIL
0
0
0.37
0.37
0
0
6.6
7.8
1
OR
60412B
BAKER SILT LOAM, 2 TO 7 %
SLOPES, WARM
096
SIL
0
0
0.37
0.37
0
0
6.6
7.8
1
OR
604130E REDCLIFF GRAVELLY LOAM, 30
TO 50 % NORTH SLOPES
096
GR-L
20
40
0.24
0.32
0
0
7.4
7.8
1
OR
604130F REDCLIFF GRAVELLY LOAM, 50
TO 75 % NORTH SLOPES
096
GR-L
20
40
0.24
0.32
0
0
7.4
7.8
1
OR
604133C ROBINETTE-GWINLY COMPLEX,
2 TO 12 % SLOPES
096
SIL
40
60
0.43
0.43
0
0
6.6
7.3
1
OR
604136F ROCK OUTCROP-RUCLICK
COMPLEX, 50 TO 70 % NORTH
SLOPES
096
UWB
0
0
0.00
0.00
0
0
0.0
0.0
3
OR
60413A
BALDOCK SILT LOAM, 0 TO 2 %
SLOPES
096
SIL
0
0
0.32
0.32
0
2
7.9
8.4
1
OR
604142C RUCKLES-RUCLICK COMPLEX,
2 TO 12 % SLOPES
096
STV-CL
10
20
0.17
0.43
0
0
6.6
7.8
1
OR
604143D RUCKLES-RUCLICK COMPLEX,
12 TO 35 % SOUTH SLOPES
096
STV-CL
10
20
0.17
0.43
0
0
6.6
7.8
1
Hells Canyon Complex
Page 87
Shoreline Erosion in Hells Canyon
Appendix 1.
STATE
MUID
Idaho Power Company
(Cont.)
MUNAME
PARTSIZE SURFTEX ROCKDEPL ROCKDEPH
KFACT KFFACT SALINL SALINH
PHL
PHH
MUWATHEL
OR
604143E RUCKLES-RUCLICK COMPLEX,
35 TO 50 % SOUTH SLOPES
096
STV-CL
10
20
0.17
0.43
0
0
6.6
7.8
1
OR
604143F RUCKLES-RUCLICK COMPLEX,
50 TO 70 % SOUTH SLOPES
096
STV-CL
10
20
0.17
0.43
0
0
6.6
7.8
1
OR
604144E RUCKLES-RUCLICK-SNELLBY
COMPLEX, 35 TO 50 % SLOPES
096
STV-CL
10
20
0.17
0.43
0
0
6.6
7.8
1
OR
604144F RUCKLES-RUCLICK-SNELLBY
COMPLEX, 50 TO 70 % SLOPES
096
STV-CL
10
20
0.17
0.43
0
0
6.6
7.8
1
OR
604145D RUCLICK VERY COBBLY SILT
LOAM, 12 TO 35 % NORTH
SLOPES
096
CBV-SIL
20
40
0.24
0.37
0
0
6.6
7.3
1
OR
604145E RUCLICK VERY COBBLY SILT
LOAM, 35 TO 50 % NORTH
SLOPES
096
CBV-SIL
20
40
0.24
0.37
0
0
6.6
7.3
1
OR
604146D SAG-SNELL COMPLEX, 12 TO 35
% NORTH SLOPES
096
SIL
40
60
0.43
0.43
0
0
6.1
7.3
1
OR
604152F SNAKER CHANNERY LOAM, 50
TO 80 % SOUTH SLOPES
096
CN-L
10
20
0.20
0.32
0
0
6.6
7.3
1
OR
604153E SNAKER-DARKCANYON
COMPLEX, 30 TO 50 % SOUTH
SLOPES
096
CN-L
10
20
0.20
0.32
0
0
6.6
7.3
1
OR
60415A
096
L
0
0
0.28
0.28
0
2
7.9
8.4
1
OR
604167D TOP-MCGARR COMPLEX, 12 TO
35 % NORTH SLOPES
096
SIL
40
60
0.32
0.32
0
0
6.1
7.3
1
OR
604169C UKIAH SILTY CLAY LOAM, 2 TO
12 % SLOPES
096
SICL
20
40
0.32
0.32
0
0
6.1
7.3
1
OR
604169D UKIAH SILTY CLAY LOAM, 12 TO
20 % SLOPES
096
SICL
20
40
0.32
0.32
0
0
6.1
7.3
1
OR
60416B
BARNARD SILT LOAM, 2 TO 7 %
SLOPES
096
SIL
0
0
0.37
0.37
0
0
6.1
7.3
1
OR
60416D
BARNARD SILT LOAM, 12 TO 20
% SLOPES
096
SIL
0
0
0.37
0.37
0
0
6.1
7.3
1
OR
604171B VIRTUE SILT LOAM, 2 TO 7 %
SLOPES
096
SIL
0
0
0.32
0.32
0
0
6.6
7.3
1
Page 88
BALM LOAM, 0 TO 3 % SLOPES
Hells Canyon Complex
Idaho Power Company
Appendix 1.
STATE
MUID
Shoreline Erosion In Hells Canyon
(Cont.)
MUNAME
PARTSIZE
SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH
PHL
PHH
MUWATHEL
OR
604176A WINGVILLE SILT LOAM, 0 TO 2
% SLOPES
096
SIL
0
0
0.28
0.28
0
0
7.4
8.4
1
OR
604178F XERIC TORRIORTHENTS-ROCK
OUTCROP COMPLEX, 50 TO 80
% SLOPES
096
STX-L
10
60
0.20
0.37
0
0
6.6
7.8
3
OR
60417C
BARNARD COBBLY SILT LOAM,
7 TO 20 % SLOPES
096
CB-SIL
0
0
0.32
0.43
0
0
6.6
7.3
1
OR
60423A
BOYCE SILT LOAM, 0 TO 2 %
SLOPES
096
SIL
0
0
0.37
0.37
0
2
7.4
8.4
1
OR
60438E
COPPERFIELD-ROCK
OUTCROP COMPLEX, 30 TO 50
% NORTH SLOPES
050
CBV-SIL
0
0
0.24
0.37
0
0
6.6
7.3
3
OR
60438F
COPPERFIELD-ROCK
OUTCROP COMPLEX, 50 TO 80
% NORTH SLOPES
050
CBV-SIL
0
0
0.24
0.37
0
0
6.6
7.3
3
OR
60440A
CUMULIC HAPLOXEROLLS, 0
TO 2 % SLOPES
096
L
0
0
0.32
0.37
0
0
6.6
7.8
1
OR
60449D
EMILY SILT LOAM, 12 TO 35 %
NORTH SLOPES
096
SIL
0
0
0.32
0.32
0
0
6.1
7.3
1
OR
60449E
EMILY SILT LOAM, 35 TO 60 %
NORTH SLOPES
096
SIL
0
0
0.32
0.32
0
0
6.1
7.3
1
OR
60459D
GWINLY-IMMIG VERY COBBLY
SILT LOAMS, 12 TO 35 %
SOUTH SLOPES
056
CBV-SIL
10
20
0.17
0.37
0
0
6.6
7.8
1
OR
60459E
GWINLY-IMMIG VERY COBBLY
SILT LOAMS, 35 TO 50 %
SOUTH SLOPES
056
CBV-SIL
10
20
0.17
0.37
0
0
6.6
7.8
1
OR
60459F
GWINLY-IMMIG VERY COBBLY
SILT LOAMS, 50 TO 70 %
SOUTH SLOPES
056
CBV-SIL
10
20
0.17
0.37
0
0
6.6
7.8
1
OR
6045C
ARIDIC HAPLOXEROLLS, 2 TO
12 % SLOPES
002
STV-L
0
0
0.24
0.37
0
0
6.6
7.3
1
OR
60494C
LEGLER SILT LOAM, 2 TO 8 %
SLOPES
096
SIL
0
0
0.43
0.43
0
2
6.6
7.3
1
Hells Canyon Complex
Page 89
Shoreline Erosion in Hells Canyon
Appendix 1.
STATE
MUID
Idaho Power Company
(Cont.)
MUNAME
PARTSIZE
SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH
PHL
PHH MUWATHEL
OR
60496E
LICKSKILLET VERY GRAVELLY
SANDY LOAM, 30 TO 50 %
SOUTH SLOPES
096
GRV-SL
10
20
0.15
0.28
0
0
6.6
8.4
1
OR
60496F
LICKSKILLET VERY GRAVELLY
SANDY LOAM, 50 TO 70 %
SOUTH SLOPES
096
GRV-SL
10
20
0.15
0.28
0
0
6.6
8.4
1
OR
604DAM DAM
0
0
0.00
0.00
0
0
0.0
0.0
0
096
OR
604W
WATER
0
0
0.00
0.00
0
0
0.0
0.0
0
ID
656001
ABO SILT LOAM, 0 TO 2 %
SLOPES
096
SIL
60
60
0.49
0.49
0
2
7.4
8.4
0
ID
656002
AGERDELLY CLAY, 4 TO 30 %
SLOPES
096
C
60
60
0.24
0.24
0
2
6.6
8.4
0
ID
656003
AGERDELLY CLAY, 30 TO 60 %
SLOPES
096
C
60
60
0.24
0.24
0
2
6.6
8.4
0
ID
656013
BAKEOVEN-REYWAT
COMPLEX, 2 TO 30 % SLOPES
096
STX-L
4
10
0.05
0.37
0
0
6.1
7.8
0
ID
656014
BAKEOVEN-REYWAT-ROCK
OUTCROP COMPLEX, 30 TO 60
% SLOPES
096
STX-L
4
10
0.05
0.37
0
0
6.1
7.8
0
ID
656015
BALDOCK SILT LOAM, 0 TO 2 %
SLOPES
096
SIL
60
60
0.32
0.32
2
4
7.9
8.4
0
ID
656016
BALDOCK CLAY LOAM, O TO 2
% SLOPES
096
CL
60
60
0.37
0.37
2
4
7.9
8.4
0
ID
656017
BISSELL LOAM, 0 TO 2 %
SLOPES
096
L
60
60
0.32
0.32
0
0
6.1
7.3
0
ID
656026
BROWNLEE SANDY LOAM, 20
TO 35 % SLOPES
096
SL
60
60
0.37
0.37
0
0
6.1
6.5
0
ID
656034
CLEMS FINE SANDY LOAM, 0
TO 2 % SLOPES
096
FSL
60
60
0.32
0.32
0
2
6.6
8.4
0
ID
656035
CLEMS FINE SANDY LOAM, 2
TO 4 % SLOPES
096
FSL
60
60
0.32
0.32
0
2
6.6
8.4
0
ID
656049
DESHLER EXTREMELY STONY
CLAY LOAM, 2 TO 30 % SLOP
ES
096
STX-CL
20
40
0.10
0.37
0
0
6.6
7.3
0
Page 90
Hells Canyon Complex
Idaho Power Company
Appendix 1.
STATE
MUID
Shoreline Erosion In Hells Canyon
(Cont.)
MUNAME
PARTSIZE
SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH
PHL
PHH MUWATHEL
ID
656052
DESHLER-AGERDELLY
COMPLEX, 30 TO 60 % SLOPES
096
SICL
20
40
0.24
0.24
0
0
6.1
7.3
0
ID
656060
DETERSON SILT LOAM, 30 TO
60 % SLOPES
096
SIL
60
60
0.32
0.32
0
0
6.1
7.3
0
ID
656064
DUNELAND
096
0
0
0.00
0.00
0
0
0.0
0.0
0
ID
656066
ELIJAH SILT LOAM, 8 TO 12 %
SLOPES
096
SIL
60
60
0.43
0.43
0
0
6.6
7.8
0
ID
656067
FALK FINE SANDY LOAM, 0 TO
2 % SLOPES
096
FSL
60
60
0.20
0.20
0
0
6.1
7.3
0
ID
656068
GEM STONY CLAY LOAM, 2 TO
30 % SLOPES
096
ST-CL
20
40
0.32
0.37
0
0
6.1
7.8
0
ID
656069
GEM STONY CLAY LOAM, 30
TO 60 % SLOPES
096
ST-CL
20
40
0.32
0.37
0
0
6.1
7.8
0
ID
656070
GEM EXTREMELY STONY CLAY
LOAM, 2 TO 30 % SLOPES
096
STX-CL
20
40
0.15
0.37
0
0
6.1
7.8
0
ID
656071
GEM-BAKEOVEN COMPLEX, 2
TO 30 % SLOPES
096
STV-CL
20
40
0.15
0.37
0
0
6.1
7.8
0
ID
656072
GEM-BAKEOVEN COMPLEX, 30
TO 60 % SLOPES
096
STV-CL
20
40
0.15
0.37
0
0
6.1
7.8
0
ID
656073
GEM-REYWAT COMPLEX, 2 TO
30 % SLOPES
096
STV-CL
20
40
0.15
0.37
0
0
6.1
7.8
0
ID
656074
GEM-REYWAT COMPLEX, 30
TO 65 % SLOPES
096
STV-CL
20
40
0.15
0.37
0
0
6.1
7.8
0
ID
656082
GREENLEAF SILT LOAM, 0 TO 2
% SLOPES
096
SIL
60
60
0.49
0.49
0
0
6.6
8.4
0
ID
656083
GREENLEAF SILT LOAM, 2 TO 4
% SLOPES
096
SIL
60
60
0.49
0.49
0
0
6.6
8.4
0
ID
656087
GROSS SILT LOAM, 30 TO 65 %
SLOPES
096
SIL
20
40
0.28
0.32
0
0
6.6
7.3
0
ID
656088
GROSS-BAKEOVEN COMPLEX,
30 TO 65 % SLOPES
096
SIL
20
40
0.28
0.32
0
0
6.6
7.3
0
ID
656089
GROSS-BAKEOVEN COMPLEX,
30 TO 65 % SLOPES, STONY
096
ST-L
20
40
0.28
0.37
0
0
6.6
7.3
0
ID
656090
GWIN-ROCK OUTCROP
COMPLEX, 40 TO 65 % SLOPES
096
STV-L
10
20
0.20
0.43
0
0
6.6
7.3
0
Hells Canyon Complex
Page 91
Shoreline Erosion in Hells Canyon
Appendix 1.
STATE
MUID
Idaho Power Company
(Cont.)
MUNAME
PARTSIZE
SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH
PHL
PHH MUWATHEL
ID
656092
HARPT LOAM, 4 TO 8 %
SLOPES
096
L
60
60
0.32
0.32
0
2
6.1
7.3
0
ID
656093
HAW SILT LOAM, 4 TO 8 %
SLOPES
096
SIL
60
60
0.43
0.43
0
0
6.1
7.8
0
ID
656094
HAW SILT LOAM, 8 TO 12 %
SLOPES
096
SIL
60
60
0.43
0.43
0
0
6.1
7.8
0
ID
656095
HAW SILT LOAM, 12 TO 30 %
SLOPES
096
SIL
60
60
0.43
0.43
0
0
6.1
7.8
0
ID
656102
JENNY CLAY, 0 TO 2 % SLOPES
096
C
60
60
0.28
0.37
0
2
6.1
7.8
0
ID
656111
LANGRELL GRAVELLY LOAM, 0
TO 3 % SLOPES
096
GR-L
60
60
0.17
0.24
0
0
6.6
7.3
0
ID
656129
LORELLA-ROCK OUTCROP
COMPLEX, 50 TO 65 % SLOPES
096
STV-CL
10
20
0.15
0.28
0
0
6.6
7.3
0
ID
656130
MCDANIEL STONY LOAM, 10
TO 60 % SLOPES
096
ST-L
60
60
0.28
0.32
0
0
6.6
7.3
0
ID
656131
MCDANIEL-ROCKLY COMPLEX,
10 TO 70 % SLOPES
096
STV-L
60
60
0.20
0.37
0
0
6.6
7.3
0
ID
656132
MCDANIEL-STARVEOUT
COMPLEX, 10 TO 60 % SLOPES
096
STV-L
60
60
0.20
0.37
0
0
6.6
7.3
0
ID
656153
MULETT-MACKEY COMPLEX,
30 TO 60 % SLOPES
096
STV-L
10
20
0.17
0.37
0
0
7.4
8.4
0
ID
656160
NYSSATON SILT LOAM, 0 TO 2
% SLOPES
096
SIL
60
60
0.49
0.49
0
2
7.9
8.4
0
ID
656162
OLDSFERRY SHALY LOAM, 25
TO 65 % SLOPES
096
SH-L
20
40
0.20
0.37
0
0
6.6
7.3
0
ID
656166
OWYHEE SILT LOAM, 4 TO 8 %
SLOPES
096
SIL
60
60
0.49
0.49
0
0
6.6
8.4
0
ID
656169
PANIOGUE LOAM, 0 TO 2 %
SLOPES
096
L
60
60
0.32
0.32
0
2
7.4
8.4
0
ID
656173
POWER-PURDAM SILT LOAMS,
0 TO 2 % SLOPES
096
SIL
60
60
0.43
0.43
0
0
6.6
7.8
0
ID
656174
POWER-PURDAM SILT LOAMS,
2 TO 4 % SLOPES
096
SIL
60
60
0.43
0.43
0
0
6.6
7.8
0
ID
656175
POWER-PURDAM SILT LOAMS,
4 TO 8 % SLOPES
096
SIL
60
60
0.43
0.43
0
0
6.6
7.8
0
Page 92
Hells Canyon Complex
Idaho Power Company
Appendix 1.
STATE
MUID
Shoreline Erosion In Hells Canyon
(Cont.)
MUNAME
PARTSIZE
096
SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH
ID
656177
RIGGINS EXTREMELY STONY
LOAM, 30 TO 50 % SLOPES
STX-L
10
ID
656179
RIVERWASH
096
0
ID
656180
ROCK OUTCROP-BAKEOVEN
COMPLEX, 60 TO 80 % SLOPES
096
0
ID
656181
ROCKLY VERY STONY LOAM,
12 TO 60 % SLOPES
096
STV-L
5
ID
656184
ROCKLY-ROCK OUTCROP
COMPLEX, 10 TO 50 % SLOPES
096
STV-L
ID
656185
ROCKLY-STARVEOUTMCDANIEL ASSOCIATION, 3 TO
70 % SLOPES
096
ID
656190
SHOEPEG SILTY CLAY LOAM, 0
TO 3 % SLOPES
ID
656191
ID
656204
20
PHL
PHH MUWATHEL
0.10
0.43
0
0
6.1
7.3
0
0
0.00
0.00
0
0
0.0
0.0
0
0
0.05
0.37
0
0
6.1
7.8
0
12
0.15
0.37
0
0
6.1
7.3
0
5
12
0.15
0.37
0
0
6.1
7.3
0
STV-L
5
12
0.15
0.37
0
0
6.1
7.3
0
096
SICL
60
60
0.32
0.32
0
0
6.6
7.8
0
STARVEOUT-GWIN-MCDANIEL
ASSOCIATION, 3 TO 45 % SL
OPES
096
L
60
60
0.28
0.28
0
0
6.1
7.3
0
WATER
096
0
0
0.00
0.00
0
0
0.0
0.0
0
Where:
MUID = Map unit ID code (as referenced on Figure 3)
MUNAME = Map unit name
PARTSIZE = Soil type at family taxonomic class; 096 = fine loamy, 056=clayey skeletal, 050 =loamy skeletal, 002=not used.
SURFTEX = Surface soil texture; C = clay, CB = cobbly, CBV = very cobbly, CL = clay, CN = channery, FSL = fine sandy loam, GR = gravelly, GRV = very gravelly, L = loam,
SICL = silty clay, SIL = silt loam, SL = sandy loam, ST = stony, STV = very stony, STX = extremely stony, UWB = unweathered bedrock, VFSL = very fine sandy loam
ROCKDEPL = The minimum value for the range in depth to bedrock, expressed in inches.
ROCKDEPH = The maximum value for the range in depth to bedrock, expressed in inches.
KFACT = Soil erodability factor, adjusted for the effect of rock fragments.
KFFACT = Soil erodability factor, rock fragments free
SALINL = The minimum value for the range in soil salinity measures as electrical conductivity of the soil in a saturated paste. Values expressed in mmhos/cm.
SALINH = The maximum value for the rage in soil salinity in mmhos/cm.
PHL = The minimum value for the range in soil reaction (pH) for the soil layer.
PHH = The maximum value for the range in soil reaction (pH) for the soil layer.
MUWATHEL = The highly erodable lands rating for the soil map unit where: 1 = highly erodable, 2 = potential highly erodable, 3 = not highly erodable.
Hells Canyon Complex
Page 93
Shoreline Erosion in Hells Canyon
Appendix 2.
Idaho Power Company
Summary of shoreline soil inventory data for the Hells Canyon Study Area.
SITE
STA
LEN
HT
COMP PRCT BANK
SL
OX1
A
30
2.5
N
G
S
OX2
AH
100
5
N
I
S
1
2
3
2
4
2
5
4
6
7
8
9
3
3
10
11
12
13
3
2
14
D1
D2
D3
A1
A2
A3
SSW
G
EHW SSW FW
T
S
G
F
TT
0
15
1
4
20
0
2
60
33
95
OX3
A
60
1.5
N
I
M
2
2
2
2
4
F
SSW
0
5
10
55
70
OX4
A
70
3
N
I
S
2
2
2
3
3
S
EHW
0
15
40
40
95
OX5
A
10
2
N
I
M
2
2
2
4
G
SSW
0
1
40
29
70
OX6
A
150
12
N
I
M
2
2
3
2
4
CTS
0
0
5
5
10
OX7
A
250
8
N
G
L
2
3
3
3
4
F
0
0
15
35
50
OX8
A
100
6
N
G
L
2
2
2
2
F
SSW
0
0
10
20
30
BR9
A
15
8
N
G
S
2
2
4
SS
SSW
0
5
75
20
100
BR10
H
15
10
N
G
S
2
2
4
SS
0
15
35
10
60
BR11
A
65
2.5
N
G
S
2
2
4
SS
0
10
35
30
75
BR12
A
6
8
N
G
S
2
2
4
S
0
30
40
15
85
BR13
H
50
5
N
G
S
2
2
4
SS
0
10
50
30
90
BR14
H
10
6
N
G
S
2
2
4
G
0
0
60
30
90
BR15
A
115
2.5
N
G
S
2
2
4
SS
0
10
45
30
85
BR16
A
30
5
N
G
S
2
2
4
G
0
0
50
45
95
100
3.5
N
G
S
2
2
4
G
0
0
50
40
90
BR17 AH
4
4
3
BR18
H
12
8
N
G
S
2
2
4
SS
0
10
40
30
80
BR19
A
70
9
N
G
S
2
2
4
SS
0
5
55
30
90
BR20
A
30
20
N
G
S
2
2
4
SS
0
5
50
25
80
BR21
A
45
5
N
G
S
2
2
4
G
0
0
60
20
80
BR22
A
20
8
N
G
S
2
2
4
G
0
0
60
20
80
BR23
A
10
8
N
G
S
2
2
4
SS
0
10
50
25
85
BR24
A
200
3
N
G
S
2
2
4
SS
0
5
45
25
75
BR25
A
45
3
N
G
S
2
2
4
SS
0
10
45
35
90
BR26
A
60
4
N
G
S
2
2
4
S
0
30
30
25
85
BR27
A
250
4
N
G
S
2
2
4
SS
0
10
45
35
90
Page 94
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
SL
BR28
A
210
3.5
N
G
S
BR29
A
5
10
N
G
BR30 AH
700
2.5
N
BR31
H
150
1.5
N
BR32
A
200
10
BR33
A
230
BR34
H
30
BR35
A
BR36
A
BR37
A
BR38
1
4
5
T
S
G
F
TT
2
2
4
G
S
0
10
55
5
70
S
2
2
4
G
S
0
5
70
20
95
G
M
2
2
G
M
2
2
4
G
SSW
0
10
45
40
95
4
SSW
G
0
80
5
5
90
N
G
S
2
2
4
G
F
0
5
80
5
90
4
N
S
S
2
2
4
G
F
0
5
80
10
95
8
N
G
S
2
2
4
G
F
0
3
80
7
90
50
2
N
150
1.5
N
G
M
2
2
4
G
S
F
0
15
50
15
80
G
S
2
2
4
G
S
F
0
5
70
15
90
100
3
N
G
S
2
2
4
F
S
G
0
10
30
50
90
A
50
3
N
G
S
2
2
4
F
G
0
0
25
40
65
BR39
H
15
2.5
N
G
S
2
2
4
S
G
0
75
10
5
90
BR40
BR41
A
20
6
N
G
S
2
2
4
G
F
0
0
60
30
90
A
50
4
N
G
M
2
2
4
G
S
0
15
70
10
95
BR42
H
40
3
N
G
S
2
2
4
F
G
0
0
40
50
90
BR43
A
30
10
N
G
S
2
2
4
G
S
0
10
70
10
90
BR44 AH
45
6
N
G
S
2
2
4
SS
SSW
0
40
30
10
80
2
4
G
SSW
0
10
75
5
90
F
SSW
0
0
40
40
80
4
F
SSW
0
0
20
10
30
4
F
SSW
0
0
20
15
35
S
SSW
0
40
30
20
90
2
2
3
BR45
A
20
10
N
G
S
2
HC46
A
25
2
N
G
M
2
2
2
HC47
A
60
3.5
N
G
S
2
2
2
5
HC48
A
50
4
N
G
S
2
2
2
4
50
4
N
G
L
2
2
2
HC49 AH
6
7
8
9
10
3
2
2
3
4
2
3
4
3
11
12
13
14
D1
D2
D3
A1
A2
G
FW
A3
HC50
A
80
5
N
G
S
2
2
5
5
SS
0
20
35
10
65
HC51
A
350
15
N
G
S
2
2
5
5
CTS
0
0
2
2
4
HC52
A
25
3
N
G
S
2
2
5
5
SS
0
10
40
20
70
HC53
A
150
14
N
G
S
2
2
5
5
2
SS
0
10
40
20
70
HC54
A
120
8
N
G
S
2
2
5
5
2
CTS
0
0
1
1
2
Hells Canyon Complex
Page 95
Shoreline Erosion in Hells Canyon
Idaho Power Company
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
SL
HC55
A
20
4
N
G
S
HC56
A
40
3
N
G
S
1
2
3
4
5
6
7
2
2
4
4
2
2
4
4
8
9
10
11
12
13
2
14
D1
D2
D3
A1
A2
T
S
G
F
TT
0
5
40
15
60
SSW
0
5
35
20
60
SS
SS
A3
HC57
A
30
4
N
G
S
2
2
4
4
G
FW
0
0
70
10
80
HC58
A
20
4
N
G
S
2
2
4
4
G
SSW
0
0
50
25
75
HC59
A
140
1.5
N
I
M
2
2
2
2
G
SSW
0
10
50
10
70
HC60
A
20
2
N
I
M
2
2
2
SS
0
40
30
10
80
HC61
H
30
3
N
I
S
2
2
2
3
SSW
0
30
5
50
85
HC62
A
40
1.5
N
I
L
3
2
HC63
A
50
3
N
G
L
2
4
HC64
A
80
3.5
N
G
L
2
2
HC65
H
50
4
N
I
M
2
HC66
A
15
3
N
I
M
2
HC67
A
30
3
N
I
S
2
HC68
A
15
4
N
I
S
4
2
HC69
A
35
4
N
I
S
4
HC70
A
35
4
N
I
M
4
HC71 AH
40
4
N
I
M
2
HC72
A
80
2.5
N
I
S
2
4
HC73
A
85
6
N
I
S
2
4
HC74
A
30
15
N
I
S
2
4
HC75
A
25
3
N
I
M
HC76
A
100
1
N
I
M
3
2
2
4
2
3
3
3
A
20
1.5
N
I
S
HC78
A
20
1.5
N
I
M
3
HC79
A
100
4
N
I
L
2
HC80
A
30
1
N
G
M
2
HC81
A
25
1
N
I
L
2
4
3
0
20
50
10
80
PR
G
SSW
0
0
20
40
60
SS
0
5
10
20
35
0
10
40
20
70
SSW
4
S
SSW
0
60
5
5
70
4
4
SS
0
20
30
10
60
3
3
S
FW
0
40
40
5
85
2
2
S
SSW
0
70
40
10
120
2
2
S
CTS
5
70
40
10
125
3
2
S
SSW
0
30
90
10
130
3
2
G
SSW
0
0
55
10
65
2
S
SSW
0
40
30
30
100
2
SS
SSW
0
10
70
0
80
CTS
0
30
40
15
85
SSW
20
0
100
0
120
SSW
2
2
4
2
2
2
2
S
2
3
2
3
FW
PR
F
SSW
0
0
5
20
25
3
FU
SSW
70
20
80
10
180
2
F
SSW
0
0
20
40
60
SS
SSW
0
20
40
30
90
0
20
60
30
110
2
2
SS
SS
3
5
2
2
2
4
2
2
HC77
Page 96
2
3
SS
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
SL
1
2
3
4
L
2
2
2
S
2
HC82
A
20
1
N
I
BR83
A
40
4
N
G
BR84
A
75
6
N
G
S
2
2
4
SS
0
5
40
25
70
BR85
A
30
4
N
G
M
2
2
2
4
2
SS
0
15
40
30
85
BR86
A
45
4
N
G
M
2
2
2
3
2
SS
0
15
40
30
85
BR87
A
60
7
N
G
M
2
2
2
3
3
SS
0
20
40
30
90
BR88 AH
110
6
N
G
M
2
2
2
3
3
2
S
0
25
30
25
80
BR89
A
75
4
N
G
M
2
2
3
3
2
SS
0
10
40
30
80
BR90
A
60
5
N
G
M
2
2
3
3
SS
0
10
40
30
80
BR91
A
85
3
N
G
M
2
2
3
3
SS
0
10
40
20
70
BR92
A
50
3
N
G
M
2
2
2
2
SS
0
5
40
30
75
BR93
A
180
3
N
G
M
2
2
3
3
SS
0
10
40
20
70
BR94 AH
100
2
N
G
M
2
2
3
SS
0
10
40
20
70
BR95
A
50
3
N
G
S
2
2
4
3
SS
0
10
30
20
60
BR96
A
80
3
N
G
S
2
2
4
3
SS
0
5
20
15
40
BR97
A
35
5
N
G
S
2
2
4
3
SS
0
10
25
15
50
BR98
A
120
3
N
G
S
2
2
4
2
SS
0
5
40
15
60
2
5
6
7
8
9
2
3
3
4
10
11
12
13
14
D1
S
D2
D3
A1
SSW
SS
3
A2
A3
T
S
G
F
TT
0
25
60
20
105
0
5
30
25
60
BR99
A
85
3
N
G
S
2
2
4
SS
0
10
35
10
55
BR100
A
40
7
N
G
S
2
2
4
SS
0
5
40
15
60
BR101
A
150
3.5
N
G
S
2
2
4
SS
0
5
50
15
70
BR102
A
80
6
N
G
S
2
2
5
3
G
0
3
80
20
103
BR103
A
40
10
N
G
S
2
2
5
3
SS
0
20
30
30
80
BR104
H
20
12
N
G
S
2
2
5
3
SS
BR105
H
35
10
N
G
S
2
2
2
5
3
SS
BR106 AH
40
6
N
G
S
2
2
2
5
3
BR107
A
35
6
N
G
S
2
2
4
BR108
A
45
4
N
G
S
2
2
4
Hells Canyon Complex
0
5
15
10
30
0
10
45
20
75
SS
0
5
45
15
65
2
G
0
0
60
15
75
2
G
0
0
75
20
95
SSW
Page 97
Shoreline Erosion in Hells Canyon
Idaho Power Company
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
BR109
A
40
30
N
G
BR110
A
60
4
N
G
BR111
A
SL
1
2
3
4
5
S
2
2
5
S
2
2
5
6
7
8
9
10
11
12
13
2
14
D1
D2
D3
A1
A2
A3
T
S
G
F
TT
G
0
0
80
15
95
G
0
0
80
15
95
40
3
N
G
S
2
2
4
2
SS
0
15
80
15
110
BR112 AH
20
5
N
G
S
2
2
4
2
SS
0
10
80
15
105
BR113 AH
50
4
N
G
S
2
2
4
2
SS
0
10
75
20
105
BR114 AH
50
4
N
G
S
2
2
4
2
S
0
25
80
15
120
BR115
A
150
3
N
G
S
2
2
4
2
SS
0
10
75
20
105
2
2
4
2
0
10
75
20
105
0
30
30
40
100
BR116
A
50
4
N
G
S
HC117
A
150
3.5
N
I
S
HC118
A
50
1.5
N
G
OX119
A
50
3
N
BR120
A
70
4
N
BR121
A
2
SS
3
2
5
4
M
2
3
3
3
G
M
2
3
G
S
2
2
4
4
3
SS
SSW
FW
G
EHW
0
0
40
20
60
F
I
0
0
5
10
15
SS
F
0
5
45
15
65
80
5
N
G
S
2
2
4
G
0
0
70
15
85
BR122 AH
110
2
N
G
S
2
2
4
SS
0
5
45
10
60
BR123
60
3
N
G
S
2
2
4
SS
0
10
55
15
80
BR124 AH
500
35
N
G
S
2
2
2
4
2
SS
0
10
50
20
80
BR125
A
150
15
N
G
S
2
2
2
4
2
SS
0
5
50
20
75
BR126
A
130
2.5
N
G
M
2
2
2
4
2
SS
0
10
55
15
80
BR127
A
70
2
N
G
S
2
2
2
4
2
S
0
30
50
20
100
BR128
A
200
30
N
G
S
2
2
2
4
2
G
0
0
55
15
70
BR129
A
80
5
N
G
S
2
2
2
4
2
S
0
30
45
15
90
BR130
A
100
3
N
G
S
2
2
2
4
2
F
0
0
25
40
65
BR131
A
80
4
N
G
S
2
2
2
4
2
SS
0
10
45
15
70
BR132
A
80
3
N
G
S
2
2
2
4
2
SS
0
15
45
15
75
BR133
A
120
1.5
N
G
M
2
2
2
3
2
SS
0
15
40
25
80
BR134
A
8
4
N
G
S
2
4
SS
0
5
15
15
35
BR135
A
60
30
N
G
S
2
5
SS
0
10
15
15
40
A
Page 98
2
3
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
Appendix 2. (Cont.)
SITE
STA
LEN
HT
BR136 AH
70
5
N
G
S
BR137
A
80
5
N
G
BR138
A
8
3
N
BR139
A
45
3
N
BR140
A
8
5
BR141
A
40
140
BR142 AH
BR143
A
COMP PRCT BANK
SL
1
2
3
4
5
2
2
S
2
G
S
G
S
N
G
4
N
2
N
6
7
8
9
10
11
12
13
14
D1
D2
4
SS
F
2
5
G
2
2
4
2
2
4
S
2
2
4
G
S
2
2
G
S
2
2
D3
A1
A2
A3
T
S
G
F
TT
0
5
25
30
60
0
0
40
10
50
S
0
35
60
20
115
G
0
0
30
15
45
G
0
0
35
10
45
4
S
0
35
50
15
100
4
SS
0
10
35
20
65
40
6
N
G
S
2
2
4
G
0
0
50
40
90
BR144 AH
25
5
N
G
S
2
2
5
SS
0
10
30
15
55
BR145
A
50
2
N
G
S
2
2
4
SS
0
10
40
15
65
BR146
A
180
1.5
N
G
S
2
2
4
SS
0
10
40
20
70
BR147
A
40
2
N
G
S
2
2
4
F
0
0
30
40
70
BR148
A
20
8
N
G
S
2
2
4
S
0
35
30
20
85
BR149
A
20
5
N
G
S
2
2
4
S
0
30
30
20
80
BR150
A
75
1
N
G
S
2
2
4
SS
0
10
30
20
60
BR151
A
60
2
N
G
M
2
2
2
3
2
SS
0
20
40
20
80
BR152
A
15
3
N
G
M
2
2
2
3
2
SS
0
20
40
20
80
BR153
A
150
2
N
G
M
2
2
2
3
SS
0
10
40
20
70
BR154
A
25
3
N
G
S
2
2
2
4
S
0
40
30
20
90
BR155
A
10
5
N
G
S
2
2
4
SS
0
30
50
20
100
BR156
A
200
2.5
N
G
S
2
2
4
SS
0
10
20
10
40
BR157
A
85
8
N
G
S
2
2
5
SS
0
10
25
15
50
BR158
A
75
17
N
G
S
2
2
4
SS
0
15
25
10
50
BR159
A
45
5
N
G
S
2
2
4
S
0
30
40
15
85
BR160
A
140
3
N
G
S
2
2
2
4
4
BR161
A
600
3
Y
G
S
2
2
2
2
2
2
BR162
A
100
3
N
G
S
2
2
2
4
4
2
Hells Canyon Complex
95
4
2
2
2
SS
SSW
0
10
25
5
40
SS
EHW SSW
0
10
25
5
40
SS
EHW
0
15
5
5
25
Page 99
Shoreline Erosion in Hells Canyon
Idaho Power Company
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
BR163
A
150
3
Y
BR164
A
180
2
BR165
A
15
BR166
A
15
BR167
A
BR168
1
2
3
4
5
6
7
8
9
10
11
12
13
14
D1
D2
D3
A1
A2
A3
T
S
G
F
TT
G
S
2
2
2
4
4
SS
B
0
10
10
0
20
N
G
S
2
2
2
4
4
SS
B
0
10
20
10
40
2
N
G
M
2
2
2
2
2
N
G
M
2
2
2
2
40
2
N
G
L
2
2
2
A
500
2
N
G
M
2
2
2
BR169
A
1000
5
N
G
S
2
2
BR170
A
800
6
N
G
M
2
BR171
A
1000
2
N
G
M
2
BR172
A
150
2
N
G
M
BR173
A
800
3
Y
G
BR174
A
450
2
N
BR175
A
1500
1
BR176
A
20
2
BR177
A
20
BR178
A
15
BR179 A,H 2000
95
SL
4
SS
EHW
0
10
5
5
20
2
4
B
B
0
0
5
20
25
2
4
F
DH
0
10
10
20
40
3
4
SS
B
0
0
5
5
10
2
4
4
G
B
0
0
20
0
20
2
2
3
4
SS
SSW
0
10
10
5
25
2
2
3
4
SS
SSW
0
10
5
5
20
2
2
2
4
4
SS
SSW
0
10
10
0
20
S
2
2
2
4
4
SS
SSW
0
20
10
0
30
G
M
2
2
2
3
4
SS
SSW
0
10
20
10
40
N
G
M
2
2
2
2
4
2
SS
SSW
0
5
25
5
35
N
G
M
2
2
2
3
4
2
SS
EHW
0
25
10
5
40
3
N
G
M
2
2
2
3
4
2
SS
SSW
0
25
10
0
35
3
N
G
S
2
2
2
4
4
S
FW
0
40
5
5
50
2
N
G
S
2
2
2
4
4
2
SS
EHW
0
20
15
5
40
95
2
2
2
BR180
A
1500
3
N
G
S
2
2
2
4
4
2
S
SSW
0
25
10
5
40
BR181
A
300
4
N
G
S
2
2
2
4
4
2
SS
SSW
0
20
10
5
35
BR182
A
120
3
N
G
S
2
2
2
3
4
2
G
SSW
0
5
40
0
45
BR183
A
100
2
N
G
S
2
2
2
4
4
G
SSW
0
5
35
0
40
BR184
A
300
2
N
G
S
2
2
2
4
4
SS
SSW
0
10
20
10
40
BR185
A
600
5
N
G
S
2
2
2
3
4
G
G
0
5
35
5
45
BR186
A
250
2
N
G
S
2
2
2
4
4
G
SSW
0
5
40
0
45
BR187
A
75
8
N
G
S
2
2
2
4
4
SS
EHW
0
10
30
0
40
BR188
A
40
5
N
G
S
2
2
2
4
4
SS
B
0
10
20
5
35
BR189
A
30
2
N
G
S
2
2
2
4
4
SS
EHW
0
5
30
5
40
Page 100
2
4
2
3
2
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
BR190
A
80
8
N
G
BR191
A
400
3
N
BR192
A
80
3
BR193
A
50
2
BR194
A
75
BR195
A
2
3
4
5
7
8
S
2
2
2
4
4
3
SS
G
S
2
2
2
3
4
2
G
N
G
S
2
N
G
S
2
2
2
3
3
2
2
3
3
2
N
G
S
2
2
2
3
4
90
3
N
G
S
2
2
2
4
4
G
BR196 A,H
800
5
Y
G
S
2
2
2
4
4
G
BR197
A
300
3
N
BR198
A
400
2
N
G
S
2
2
2
4
4
2
I
M
2
2
2
3
4
4
BR199
A
40
2
N
I
S
2
2
2
3
4
BR200
A
100
7
Y
I
S
2
2
2
4
BR201
A
30
3
N
I
S
2
2
2
4
BR202
A
30
BR203
A
30
2
N
I
S
3
N
I
S
BR204
A
40
3
N
I
BR205
A
130
6
Y
BR206
A
20
5
N
BR207
A
120
4
N
I
S
2
2
2
3
4
2
BR208
A
175
2
N
I
S
2
2
2
4
4
3
BR209
A
400
2
Y
I
S
2
2
2
4
4
2
BR210
A
15
7
N
I
S
2
2
2
4
BR211
A
20
5
N
I
S
2
2
2
4
BR212
A
300
2
N
I
S
2
2
2
4
4
BR213
A
75
4
Y
50
I
S
2
2
2
4
4
BR214
A
4000
3
Y
95
I
S
2
2
2
4
4
BR215
A
40
2
Y
90
I
M
2
2
2
2
2
BR216
A
250
2
Y
95
I
M
2
2
2
2
2
Hells Canyon Complex
95
40
75
95
SL
1
6
9
10
11
12
13
14
T
S
G
F
TT
B
0
5
10
5
20
B
0
0
15
10
25
SS
B
0
20
20
5
45
G
SSW
0
5
40
0
45
G
B
0
5
30
0
35
0
10
35
0
45
B
0
10
35
0
45
G
B
0
5
40
0
45
SS
B
0
5
15
0
20
G
SSW
0
5
25
0
30
4
G
B
0
5
25
5
35
4
G
G
0
5
25
5
35
3
D1
D2
D3
A1
A2
A3
2
2
2
4
4
G
SSW
0
5
30
0
35
2
2
2
4
4
G
EHW
0
5
25
0
30
S
2
2
2
4
4
G
B
0
5
25
0
30
I
S
2
2
2
4
4
G
B
0
5
40
0
45
I
S
2
2
2
3
4
G
B
0
5
35
0
40
G
B
0
5
25
0
30
G
DH
0
5
25
0
30
G
B
0
5
20
0
25
4
G
B
0
5
20
0
25
4
B
B
0
5
5
0
10
2
3
G
SSW
0
5
20
0
25
DH
B
0
0
5
5
10
G
EHW
0
5
25
0
30
4
SS
B
0
10
25
5
40
4
SS
SSW
0
10
25
5
40
2
2
Page 101
Shoreline Erosion in Hells Canyon
Idaho Power Company
Appendix 2. (Cont.)
SITE
STA
LEN
HT
BR217
A
250
2
Y
BR218
A
1500
5
N
BR219
A
250
8
Y
BR220
A
400
2
Y
BR221
A
4800
7
Y
BR222
A
1400
4
Y
BR223
A
200
1
N
BR224
A
40
1
N
I
L
2
2
2
2
BR225
A
30
2
N
I
M
2
2
2
2
BR226
A
20
1
N
I
L
2
2
2
2
BR227
A
2800
5
Y
I
S
2
2
2
5
BR228
A
600
3
N
I
S
2
2
2
4
BR229
A
3200
2
Y
98
I
S
2
2
2
4
4
BR230
A
200
2
Y
95
I
S
2
2
2
4
4
BR231
A
2000
5
Y
97
I
S
2
2
2
5
BR232
A
30
3
N
I
S
2
2
2
BR233
A
100
4
N
I
S
2
2
BR234
A
900
2
Y
90
I
S
2
BR235
A
200
5
Y
50
I
S
2
BR236
A
600
5
N
I
S
2
HB1
A
45
10
N
G
HB2
A
10
1
N
HB3
A
15
1
HB4
H
10
15
HB5
H
25
3
Y
HB6
H
200
15
HB7
H
40
3
Page 102
COMP PRCT BANK
90
SL
1
2
3
4
5
6
7
8
9
10
11
12
13
14
D1
2
2
2
3
2
4
G
2
3
D2
D3
A1
A2
A3
T
S
G
F
TT
EHW
0
5
30
5
40
G
B
0
5
30
5
40
I
M
I
M
2
2
2
2
3
95
I
S
2
2
2
2
4
4
G
B
0
5
35
5
45
95
I
S
2
2
2
4
4
G
B
0
5
20
0
25
99
I
M
2
2
2
3
4
SS
B
0
10
15
5
30
95
I
S
2
2
2
3
3
2
G
B
0
5
30
0
35
I
L
2
2
2
3
2
S
SSW
0
25
10
5
40
4
G
EHW
0
0
35
5
40
4
S
SSW
0
30
10
0
40
A
SSW
0
0
0
0
0
5
G
B
0
0
25
0
25
4
G
B
0
0
30
0
30
98
2
2
2
2
2
2
G
B
0
5
30
0
35
G
B
0
0
30
0
30
5
G
B
0
0
30
0
30
4
4
G
B
0
0
30
0
30
2
4
4
G
B
0
0
30
0
30
2
2
4
5
G
B
0
0
30
0
30
2
2
5
5
G
B
0
0
2
0
2
2
2
5
5
G
B
0
0
30
0
30
S
2
3
3
4
B
B
0
0
0
0
0
I
M
2
2
SSW
SSW
0
20
10
5
35
N
I
M
2
2
3
4
G
B
0
0
25
0
25
N
G
S
2
3
4
4
S
S
0
30
10
0
40
95
G
M
2
4
4
S
S
0
25
15
0
40
Y
90
I
S
2
4
4
SSW
SSW
0
20
20
0
40
Y
95
G
M
2
4
4
SSW
SSW
0
20
20
0
40
2
2
2
2
2
2
4
2
2
2
3
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
SL
1
2
3
4
5
6
7
8
9
10
11
12
13
14
D1
HB8
A
40
3
N
G
S
2
4
4
2
G
HB9
H
20
5
N
I
M
2
4
4
2
SSW
HB10
H
25
5
Y
80
G
M
2
4
4
2
HB11
A
30
5
Y
80
G
S
2
4
4
HB12
A
250
20
Y
65
G
S
2
4
HB13
A
100
6
Y
80
G
S
2
HB14
A
30
10
N
I
S
2
HB15
A
40
20
N
I
S
2
HB16
A
30
15
N
G
S
2
HB17
A
400
15
N
G
S
HB18
A
30
5
N
G
HB19
A
45
2
N
HB20
A
100
4
Y
HB21
A
50
3
N
HB22
A
40
30
HB23
A
35
HB24
A
15
D2
D3
A1
A2
A3
T
S
G
F
TT
SSW
0
10
30
0
40
SSW
0
25
15
0
40
SS
SS
0
20
20
0
40
SSW
SSW
10
20
15
0
45
4
G
G
0
0
30
0
30
4
5
SSW
SSW
10
25
10
0
45
4
4
SSW
SSW
0
20
10
0
30
2
4
4
S
S
5
10
20
0
35
2
4
4
SS
SS
0
15
15
0
30
2
4
4
SS
SS
0
10
20
0
30
M
2
3
4
SS
SS
5
10
10
0
25
G
S
2
3
4
G
G
0
0
20
0
20
I
M
2
3
4
G
G
0
5
25
5
35
I
M
2
3
4
G
B
0
0
30
0
30
N
I
S
2
4
4
G
B
0
0
25
0
25
3
N
I
S
2
4
4
SS
B
0
10
20
5
35
3
N
I
M
2
3
4
SS
SS
0
10
15
5
30
50
2
2
HB25
A
90
3
N
G
M
2
3
4
G
G
0
5
25
5
35
HB26
A
40
3
N
I
M
2
3
4
SS
SS
0
10
20
5
35
HB27
A
25
3
N
G
M
2
3
4
SSW
SSW
5
20
10
0
35
HB28
A
400
3
N
G
M
2
3
4
G
DH
0
0
15
10
25
HB29
A
50
4
N
I
M
2
3
4
S
G
0
5
20
0
25
HB30
A
125
6
N
I
M
2
3
4
HB31
A
60
2
N
I
L
2
2
4
HB32
A
15
2
N
I
M
2
3
4
HB33
A
30
2
N
G
S
2
4
HB34
A
60
3
N
G
M
2
3
Hells Canyon Complex
2
2
FW
SSW
5
10
10
0
25
SSW
EHW
0
60
5
0
65
SSW
EHW
0
10
10
5
25
4
SSW
SSW
0
15
10
0
25
4
SSW
SSW
5
10
10
0
25
2
Page 103
Shoreline Erosion in Hells Canyon
Idaho Power Company
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
SL
1
2
3
HB35
A
75
5
N
G
M
2
HB36
A
150
5
N
G
L
2
HB37
A
80
8
N
G
S
HB38
A
10
5
N
G
S
HB39
A
10
4
N
I
HB40
A
70
3
N
HB41
A
20
2
HB42
A
20
HB43
A
40
HB44
A
HB45
HB46
4
5
6
7
3
4
2
4
2
4
2
4
M
2
G
M
N
I
5
N
4
N
30
3
A
45
A
50
8
9
10
12
13
14
D1
D2
D3
A1
A2
A3
T
S
G
F
TT
G
B
0
5
20
5
30
FW
FW
25
15
10
0
50
4
G
SSW
0
15
0
0
15
4
G
G
0
0
20
10
30
3
4
SSW
B
0
0
5
0
5
2
3
4
FW
FW
25
25
20
0
70
M
2
3
4
G
G
0
0
20
10
30
I
M
2
3
4
SS
B
0
0
5
10
15
I
S
2
4
4
S
SS
0
15
5
5
25
N
I
M
2
3
5
SSW
EHW
0
0
5
10
15
1
N
G
M
2
3
4
SSW
EHW
0
5
10
20
35
2
N
G
L
2
2
4
SSW
EHW
0
5
10
20
35
3
HB47
A
120
2
N
G
M
2
3
HB48
A
100
3
N
I
M
2
3
HB49
A
20
4
N
G
M
2
HB50
A
15
3
N
I
M
HB51
A
60
8
N
G
M
HB52
A
40
3
N
I
M
2
3
HB53
A
35
5
N
G
S
2
4
HB54
A
30
2
N
G
M
2
3
4
HB55
A
125
2
N
I
M
2
3
HB56
A
30
4
N
I
M
2
3
2
11
2
2
3
2
4
FW
FW
25
20
20
10
75
4
G
B
0
0
5
5
10
3
4
G
G
0
0
20
10
30
2
3
4
SSW
SSW
0
10
10
0
20
2
3
4
G
G
0
0
20
15
35
4
G
EHW
0
0
10
15
25
4
SSW
G
0
0
20
10
30
G
G
0
0
25
5
30
4
G
G
0
5
25
5
35
4
G
G
0
0
20
0
20
2
2
HB57
A
20
3
N
G
M
2
3
4
G
B
0
0
5
0
5
HB58
A
100
3
Y
85
I
M
2
3
4
G
G
0
0
15
0
15
HB59
A
70
2
Y
95
G
M
2
3
4
G
G
0
0
10
0
10
HB60
A
35
5
N
G
M
2
3
4
G
B
0
0
5
0
5
BR237
A
100
3
y
I
S
5
5
G
B
0
5
30
5
40
Page 104
20
2
2
2
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
BR238
A
220
2
Y
BR239
A
30
6
BR240
A
275
BR241
A
1500
BR242
A
BR243
1
2
3
4
5
6
7
8
9
10
11
12
13
14
D1
D2
D3
A1
A2
A3
T
S
G
F
TT
I
S
2
2
2
4
4
G
G
0
5
15
5
25
N
I
S
2
2
2
4
4
DS
B
0
15
5
5
25
4
N
I
S
2
2
2
4
4
3
N
I
M
2
2
2
2
4
50
3
Y
80
I
S
2
2
2
4
A
145
10
Y
65
I
S
2
2
2
BR244
A
300
5
Y
80
I
S
2
2
2
BR245
A
20
4
N
I
S
2
2
2
4
BR246
A
120
5
Y
95
I
S
2
2
2
4
BR247
A
100
3
Y
95
I
S
2
2
2
BR248
A
1000
18
N
I
M
2
2
BR249
A
100
20
Y
I
S
2
2
BR250
A
1100
3
N
I
S
2
2
2
4
BR251
A
500
3
N
I
S
2
2
2
2
4
BR252
A
1600
3
Y
I
S
2
2
2
2
4
BR253
A
400
1
N
I
M
2
2
2
2
BR254
A
400
2
Y
50
I
S
2
2
2
BR255
A
70
2
Y
80
I
M
3
2
BR256
A
150
3
N
I
S
3
2
BR257
A
60
3
N
I
M
3
BR258
A
80
1
N
I
S
BR259
A
1000
1
Y
60
I
M
BR260
A
800
3
Y
90
I
BR261
A
200
8
Y
70
I
BR262
A
1000
1
Y
90
BR263
A
40
3
BR264
A
40
3
Hells Canyon Complex
20
SL
G
B
0
5
25
0
30
G
B
0
5
25
5
35
4
G
B
0
0
35
5
40
4
4
G
B
0
5
25
5
35
4
4
DH
B
0
5
5
5
15
2
3
4
G
B
0
0
25
5
30
4
G
B
0
5
20
5
30
4
3
G
EHW
0
5
25
5
35
2
3
4
G
B
0
5
20
5
30
2
5
4
G
B
0
5
20
5
30
4
G
B
0
10
20
5
35
4
SS
B
0
10
20
5
35
4
SS
B
0
20
20
5
45
3
4
G
B
0
5
35
0
40
2
4
4
G
B
0
5
35
0
40
2
2
3
3
SS
B
0
15
20
0
35
2
2
4
4
G
SSW
0
5
35
0
40
2
2
2
3
4
G
B
0
5
35
0
40
2
2
2
4
4
G
B
0
0
35
0
35
2
2
2
4
4
SS
EHW
0
10
30
0
40
S
2
2
2
3
3
SS
B
0
10
20
0
30
S
2
2
2
4
4
G
B
0
5
35
0
40
I
S
2
2
2
3
3
G
0
0
25
5
30
N
I
S
2
2
2
4
3
DH
B
0
0
10
10
20
N
I
S
2
2
2
3
3
G
G
0
0
25
5
30
50
90
3
2
2
Page 105
Shoreline Erosion in Hells Canyon
Idaho Power Company
Appendix 2. (Cont.)
SITE
STA
LEN
HT
2
3
4
5
6
7
T
S
G
F
TT
BR265 A, H
60
2
N
I
S
2
2
2
3
2
3
G
EHW
0
0
25
0
25
BR266
A
150
3
N
I
M
3
3
2
3
2
3
G
B
0
0
20
10
30
BR267
A
600
3
BR268
A
110
2
N
I
M
2
2
2
3
N
I
S
2
2
2
4
4
G
B
0
0
20
5
25
3
G
B
0
0
35
0
35
BR269
A
60
2
N
I
S
2
2
2
4
4
G
B
0
0
25
5
30
BR270
A
60
2
N
I
S
2
2
2
3
4
G
EHW
0
5
25
5
35
BR271
A
30
2
Y
95
I
S
2
2
2
3
4
SS
B
0
15
20
5
40
BR272
A
600
2
Y
90
I
S
BR273
A
400
2
N
I
M
3
3
2
4
3
3
SS
B
0
10
15
5
30
4
4
3
3
4
3
SS
B
0
0
35
5
40
BR274
A
2700
5
N
I
M
3
3
3
3
4
2
3
G
B
0
5
30
5
40
BR275
A
450
3
N
I
S
3
3
3
4
4
2
G
B
0
5
30
5
40
BR276
A
800
5
Y
I
S
2
2
3
4
4
2
SS
EHW
0
10
20
5
35
BR277
A
20
3
BR278
A
20
3
N
I
M
2
2
3
3
4
SS
EHW
0
5
10
15
30
N
I
S
2
2
3
4
4
SS
EHW
0
10
20
5
35
BR279
A
50
15
N
I
S
3
2
2
4
3
SS
B
0
10
20
5
35
BR280
A
30
30
N
I
S
3
2
2
4
3
G
B
0
5
20
5
30
BR281
A
120
2
N
O
S
2
2
2
3
3
3
SS
G
0
25
5
5
30
BR282
BR283
A
50
5
Y
80
O
S
2
2
2
2
4
4
SS
G
0
15
5
5
25
A
700
4
Y
95
O
S
2
2
2
4
4
SS
G
0
15
5
5
25
BR284
A
40
2
N
O
S
2
2
2
4
4
SS
0
15
5
5
25
BR285
A
50
5
Y
O
S
2
2
2
5
4
G
0
5
10
5
20
BR286
A
120
3
N
O
S
2
2
2
4
4
SSW
SS
0
30
5
5
40
BR287
A
170
2
N
BR288
A
350
5
Y
BR289
A
30
1
N
BR290
A
190
3
Y
BR291
A
150
3
Y
Page 106
COMP PRCT BANK
60
70
SL
1
2
8
3
9
10
11
12
13
4
14
D1
D2
D3
A1
A2
A3
O
S
2
2
2
2
4
4
SS
EHW
0
30
5
10
45
O
S
2
2
2
2
4
4
SS
SSW
0
25
10
5
40
O
S
2
3
2
2
3
3
SSW
EHW
0
15
5
10
30
95
O
S
2
3
2
2
3
3
SSW
EHW
0
25
5
10
40
90
O
S
2
3
2
2
3
3
EHW
SSW
0
10
5
20
35
98
2
Hells Canyon Complex
Idaho Power Company
Shoreline Erosion In Hells Canyon
Appendix 2. (Cont.)
SITE
STA
LEN
HT
COMP PRCT BANK
SL
1
2
3
4
BR292
A
50
2
N
BR293
A
600
5
Y
O
L
2
2
2
2
O
S
2
2
3
2
3
BR294
A
100
1
N
I
M
2
3
BR295
A
150
1
N
I
M
2
3
2
2
2
2
2
2
2
3
BR296
H
150
2
N
I
L
2
3
2
2
2
3
2
BR297
A
2000
10
Y
O
L
2
4
2
2
4
2
BR298
A
85
5
N
O
S
2
4
2
2
4
4
3
BR299
A
150
5
N
O
BR300
A
30
3
N
O
S
2
4
2
2
4
4
4
L
2
4
2
2
4
2
2
BR301
A
120
2
N
O
L
2
3
2
2
4
4
2
BR302
A
150
1
N
S
L
2
2
2
2
3
BR303
H
1000
3
Y
50
I
L
2
BR304
H
450
3
BR305
A
700
5
Y
70
I
L
2
Y
50
I
L
2
BR306
H
1100
3
Y
70
I
L
2
BR307
H
150
3
Y
50
I
M
2
BR308
H
1800
3
Y
65
O
S
2
BR309
H
2500
BA1
H
700
3
Y
50
O
S
2
5
N
O
S
BA2
H
2500
5
N
I
S
3
BA3
H
120
3
N
I
S
4
BA4
A
40
10
Y
O
S
BA5
BA6
H
20
20
N
I
M
A
150
5
N
I
S
BA7
A
225
10
Y
50
I
S
4
BA8
A
600
10
Y
80
I
S
4
Hells Canyon Complex
92
99
50
5
6
7
3
3
2
4
3
2
2
10
3
4
3
2
2
9
3
2
2
8
11
12
13
14
2
D2
D3
A1
A2
A3
T
S
G
F
TT
2
EHW
SSW
0
15
5
15
30
2
SSW
EHW
5
25
5
10
45
FW
SSW
25
30
0
5
60
SSW
EHW
0
25
5
20
50
SSW
EHW
0
25
10
15
50
SSW
EHW
0
30
5
15
50
SS
G
0
15
10
5
30
4
SS
EHW
0
15
5
10
30
4
SSW
EHW
0
50
5
10
60
2
SSW
EHW
0
50
5
10
60
3
SS
EHW
0
25
10
10
45
0
25
30
10
65
2
2
D1
3
2
3
3
2
2
2
2
4
SS
G
SSW EHW
2
2
G
SSW
2
4
SS
2
4
2
G
SSW
0
25
30
10
65
0
10
70
10
90
2
2
4
G
SSW
0
10
70
10
90
2
4
S
G
SSW EHW
0
35
50
10
80
G
SS
SSW
0
20
50
10
70
SS
F
2
4
2
2
4
2
S
G SSW
0
30
50
10
80
4
3
SSW
SSW
1
30
15
5
50
EHW SSW
EHW SSW
0
10
30
40
80
4
4
4
3
3
4
B
0
5
5
10
20
SS
SS
0
20
50
0
70
FW
G
0
0
60
30
90
4
FW
F
0
0
20
60
80
4
3
FW
F
0
0
30
50
80
4
4
FW
F
0
0
20
60
80
4
3
FW
4
F
Page 107
Shoreline Erosion in Hells Canyon
Idaho Power Company
Appendix 2. (Cont.)
SITE
STA
LEN
HT
BA9
A
1200
20
COMP PRCT BANK
Y
80
O
SL
S
1
2
3
4
5
4
6
7
8
4
2
9
10
11
12
13
14
D1
D2
SSW
SS
D3
A1
A2
SSW SSW
A3
T
S
G
F
TT
B
2
15
10
10
35
Where:
SITE = site number
STA = Status; active (A) or historic (H)
LEN = site length (m)
HT = site height (m)
COMP = mapped as a composite site; yes or no
PRCT = if mapped as a composite site the percentage of site actually eroded
BANK = on Oregon (G) or Idaho (I) bank
SL = slope; low (L)(0–5 degrees), moderate (M)(5–30 degrees), steep (S)(> 30 degrees)
Disturbance types: (ranked by disturbance level; 2 = slight, 3 = moderate, 4 = high, 5 = extreme)
1 = groundwater
2 = wind waves
3 = boat waves
4 = fluctuation zone
5 = excessive topography
6 = livestock
7 = highly erosive soil
8 = roads
9 = recreation
10 = alluvial (flood)
11 = channel flow
12 = fire
13 = industrial
14 = other
D1 = Dominant cover type (code)
D2 = Dominant cover type (code)
D3 = Dominant cover type (code)
A1 = Associated cover type (code)
A2 = Associated cover type (code)
A3 = Associated cover type (code)
T = % tree cover
S = % shrub cover
G = % grass cover
F = % forb cover
TT = % total cover
Page 108
Hells Canyon Complex