Shoreline Erosion in Hells Canyon

Gary L. Holmstead Terrestrial Ecologist

Technical Report Appendix E.3.2-42 October 2001 Revised July 2003 Hells Canyon Complex FERC No. 1971 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

Hells Canyon Complex Page i Shoreline Erosion in Hells Canyon Idaho Power Company

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

Hells Canyon Complex Page 1 Shoreline Erosion in Hells Canyon Idaho Power Company 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 fish- producing 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

Hells Canyon Complex Page 7 Shoreline Erosion in Hells Canyon Idaho Power Company 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).

Page 8 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon

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

Hells Canyon Complex Page 9 Shoreline Erosion in Hells Canyon Idaho Power Company 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

Page 10 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon 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 polygon- shaped 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 soil- covered 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

Page 14 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon 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 • reservoir operation (drawdown, etc.) • ice scour • boat wakes • freezing and thawing • land use (forest, agriculture, urban development) • soil conditions • construction • shore geometry • beach use • rain/runoff • recreational vehicles • groundwater hydrology • trails (trampling) • wind • livestock • water currents • negligence/vandalism • topography • “property value enhancement” • floating debris (trees) fires • 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 site- specific 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

Hells Canyon Complex Page 19 Shoreline Erosion in Hells Canyon Idaho Power Company 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.

Page 20 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon

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), wind- generated 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.

Hells Canyon Complex Page 21 Shoreline Erosion in Hells Canyon Idaho Power Company

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 boat- driven 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

Page 22 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon 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

Hells Canyon Complex Page 23 Shoreline Erosion in Hells Canyon Idaho Power Company 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,

Page 24 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon 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.

Percentage of Acres of Length (mi) of Shoreline Miles Reach Erosion Sites Erosion Sites 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 Total 100.70 57.43 13.3

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).

Page 26 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon

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 Mean Cover (SD) Minimum Cover Maximum Cover Tree 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

Hells Canyon Complex Page 27 Shoreline Erosion in Hells Canyon Idaho Power Company 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), wind- generated 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 Mean Cover (SD) Minimum Cover Maximum Cover Tree 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

Page 28 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 surface- area 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

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• 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 full- pool 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.

Page 30 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 soil- covered 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 Page 31 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). Boat- generated 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 high- water 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, wind- generated 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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U.S. Forest Service. 1990. Final environmental impact statement and land resource management plan: Wallowa-Whitman National Forest. U.S. Dept. of Agric., Forest Serv., Pac. Northwest Reg., Baker, OR. 367 p.

U.S. Forest Service. 1994. Final environmental impact statement: Wild and Scenic Snake River recreation management plan. U.S. Dept. of Agric., Forest Serv., Hells Canyon Nat. Recr. Area, Wallowa-Whitman Nat. Forest, Pac. Northwest Reg., Baker, OR. 243 p.

Vallier, T. L. 1998. Islands and rapids—a geologic story of Hells Canyon. Confluence Press, Lewiston, ID. 151 p.

Von Krusenstierna, A. 1990. River bank erosion by boat-generated waves on the lower Gordon River, Tasmania. Austr. M.Sc. Thesis, Univ. of Wollongong. 136 p.

Walker, J. 1988. The amateur scientist—the feathery wake of moving boat is a complex 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 conservation planning. USDA Agriculture Handbook 537. Washington, D.C. U.S. Gov. Print. Off. 58 p.

Yousef, Y. A. 1974. Assessing effects on water quality by boating activity. U.S. Environ. Prot. Agency Rep. EPA-670/2-74-072. 58 p.

Page 42 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon

Table 1. 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 Total 125.0 53.9 25.0 182.3 45.8 432.0

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 Class (m2) 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.

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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.

Dominant Associated Total Cover Type Sites % Sites % 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 Upland 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 Land Use Industrial − − − − − − Cliff/Talus Slope − − − − − − Agriculture − − − − − − Parks/Recreation − − − − − −

Hells Canyon Complex Page 45 Shoreline Erosion in Hells Canyon Idaho Power Company

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.

Dominant Associated Total Cover Type Sites % Sites % Sites % Wetland Emergent Herbaceous 2 0.8 31 11.9 33 12.6 Scrub-Shrub 10 3.8 40 15.3 50 19.2 Forested 1 0.4 1 0.4 2 0.8 Upland Shrub Savanna 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 Land Use Industrial − − − − − − Cliff/Talus Slope − − − − − − Agriculture 1 0.4 − − 1 0.4 Parks/Recreation − − − − − −

Page 46 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon

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.

Dominant Associated Total Cover Type Sites % Sites % 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 Upland 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 − − − − − − Land Use Industrial − − 1 11.1 1 11.1 Cliff/Talus Slope 1 11.1 − − 1 11.1 Agriculture − − − − − − Parks/Recreation − − − − − −

Hells Canyon Complex Page 47 Shoreline Erosion in Hells Canyon Idaho Power Company

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.

Dominant Associated Total Cover Type Sites % Sites % Sites % Wetland Emergent Herbaceous − − 1 2.6 1 2.6 Scrub-Shrub 2 5.1 22 56.4 24 61.5 Forested 1 2.6 5 12.8 6 15.4 Upland Shrub Savanna 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 − − − − − − Land Use Industrial − − − − − − Cliff/Talus Slope 2 5.1 2 5.1 4 10.2 Agriculture − − − − − − Parks/Recreation 2 5.1 − − 2 5.1

Page 48 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon

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.

Dominant Associated Total Cover Type Sites % Sites % Sites % Wetland Emergent Herbaceous − − 6 10.0 6 10.0 Scrub-Shrub 18 30.0 14 23.3 32 53.3 Forested 4 6.7 3 5.0 7 11.7 Upland 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 Land Use Industrial − − − − − − Cliff/Talus Slope − − − − − − Agriculture − − − − − − Parks/Recreation − − − − − −

Hells Canyon Complex Page 49 Shoreline Erosion in Hells Canyon Idaho Power Company

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Page 54 Hells Canyon Complex Plotfile: soil_ero_p1.gra Plotting Scale: 15841 Theme: i:\relic\hellscan\baseinv\erosion_soils.aml Created: December 20, 2001

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Page 56 Hells Canyon Complex Plotfile: soil_ero_p2.gra Plotting Scale: 15841 Theme: i:\relic\hellscan\baseinv\erosion_soils.aml Created: December 20, 2001

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Page 58 Hells Canyon Complex Plotfile: soil_ero_p3.gra Plotting Scale: 15841 Theme: i:\relic\hellscan\baseinv\erosion_soils.aml Created: December 20, 2001

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Page 60 Hells Canyon Complex Plotfile: soil_ero_p4.gra Plotting Scale: 15841 Theme: i:\relic\hellscan\baseinv\erosion_soils.aml Created: December 20, 2001

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BR148 604143F 604143E 604103D 604145E 604143E 604145E 604143F 604136F 604143E 604153E BR151 604103D BR152 604169D 604136F 604103E 604103E 604103D 604153E BR153 604103E 604103E BR154 604143D 6045C 604143D 604103E604153E BR155 604143E 604143D k 604153E604103F BR156 e llow e 604153E 604143E 6 Ho 604145E 604145D r 604103E

604145E Holcomb Park C Hewitt/ ong 604143D604143F7 L 604152

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 5 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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DITCH F o s t e r

G Creek

u

l

c h

604133C

604145E

604143E 604145E 604143F 604145E 604143E

604136F BR111 BR107 BR109BR1104 BR106

604136F BR105 604143D 604143D 604143E 604143E

604145E 604143F 604143E 604143F

604143E BR112 3 604145E 604143D 604143E BR113 BR88 604145E 604143F B 5 604145E 60412B BR9 604133C 604136F BR91 60412A 604169D 604136F 60417C 604176A 604143D BR108 604145E 604136F BR95 BR94 604145E 604143D 604145D Richland BR116 2 604133C BR93 BR92 60412B BR114 604142C BR104 604143F 604143E 604176A604127A 60417C 6 BR115 604143D 604145E 604143E BR96 604127A 604143E 604145D 604143E BR97 604127A 604143F 604143E BR124 60440A BR98 604143F 60440A60412A 7 604143D 604145D 604145E BR125 60412A BR99 604127A BR126 60412A 604145D BR127 EE 293 604143E NL 604169C BR128 604136F Hewitt/ 604143D BR103 W 604145D 1 O BR252 8 604143E BR102 R 294 Holcomb BR129 656088 604143D B 604145DBR130 604143D BR100 Park BR101 BR251 60440A 60415A 604145E 604143D BR120 BR121 295 656180 60440A 60416B BR131 BR122 656014 River 60423A 604145D 60413A 9 604145E 656095 60415A 604176A 604143E604143D BR123 604143D BR132 BR250 60416D 604145E60413A 60412B 60416B 656014 60416B C 604145D 60416B 656074 o 656072 604145D 604143D BR133 656095 t 60416D 604143D t BR249 o 604145D 604145D 296 604142C 656088 n 656087 60416D 604143D 656070 w 656180 604145D o BR134 o 604143D 604143D BR135 d 604143E 604143F 656074

L 604136F 297 o BR248 656087 n g 604143F BR136 656072Ja 656074 c 604169D 604136F BR247 k

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 * MN Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * GN Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 17 O 30’ O 11- 2 5 numeric codes 0 08’ 311 MILS r Panel 6 of 16 Unimproved Road IPC Project Facility 2 MILS Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream UTM GRID AND 1987 10MILES.5 IDAH O > 5000 MAGNETIC NORTH DECLINATION Ditch or Canal AT CENTER OF OXBOW QUADRANGLE POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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Page 66 Hells Canyon Complex Plotfile: soil_ero_p7.gra Plotting Scale: 15841 Theme: i:\relic\hellscan\baseinv\erosion_soils.aml Created: December 20, 2001

604143F 656184

60459E 60459F 656087 Duk 656132 656014 656013 656087 n 656060 yo 656087 656180 Can McCor Park Black 656131 6045C 283 OX6 284 656013 604144E 604133C BR280 656014 BR279 BR278 656087 656087 OX8 BR277 60459F OX7 656068 656087 656087

60438F 604144E OX119 BR276 656074

285 656068

656014 Creek

BR275 656014 e e l

OX Ranch n

BR269 Woodhead

Park 656088 656074 BR270

BR9 286 BR271 BR10 604144F 60459D BR11 BR274 BR12

BR13 BR272 BR14

656087

BR268

BR15 656071 BR273

BR267 BR266 604143F

BR16 BR265 656088 BR264

BROWNLEE DAM BR17 287 BR263 BR18 656180 BR19 60459D BR20

288 656180

604144E BR21

R 289 BR262

BR22 656014

BR23 604144E E

604144FBR24

V

I 656088 BR25 BR33 R

BR26 BR34

BR27 BR31 BR29

BR32 BR30

BR28 BR35 604146D 604144F BR261656069 604143F BR36 BR37

604138F BR260

656088 BR38 290 604143E BR39 656180

BR259 BR40 656014

BR258

BR42 BR257 656014 656069 604158E BR256 656087 BR41 291 656180 604143E BR255

656014 BR43 BR254 BR44

604158E 604143F

604146D BR45 BR83 RES. 292 BR253 BR84 BR85 656087 BR86 604143EBR87 BR88 BR89 BR90 656088 BR91

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 7 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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Page 68 Hells Canyon Complex

Plotfile: soil_ero_p8.gra Plotting Scale: 15841

Theme: i:\relic\hellscan\baseinv\erosion_soils.aml Created: December 20, 2001

Creek

e

s r

o

h

d

l

i

W Salt

656185

656132 656185 656132 656132 656130 656132

7 656185 656132 656185OX3

656185

656090 656132 656132 656131

656185 .

276 S 656130

E 656132 604DAM R 656185 656132 59D 656185 277 656185 273 656132 60438F 60459F

656131 OX4 656184 OX5 656130 656184 656132 275 656185

60438F 278 656130

656185 Ramp 60459F OXBOW OX2 60438F 60459F 60459F 60438E 60438F 60438F 60438E 60438F 279 656090 270 60449D 274 60459E

60438F Boat Oxbow 60438F 60459F 60438F 60438E 60449E

60459F

OX1

280SNAKE

60459F 656130 HC 60459E 60438F 60438F

60459F60440A 0438F 60459F 60440A 60438E 656026

281 River 60459F

k Carters 60459E e Landing

e 60438E

r 604133C 656090 C 60459E 60438F

60459F 656131

282 656184

60459E Wildhorse

604143F 60459E 656132 656087 n 656013 656014 yo 656087 Black Can McCormick Park 6045C 283 OX6 604144E 604133C 656013

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 8 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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Page 70 Hells Canyon Complex

Plotfile: soil_ero_p9.gra Plotting Scale: 15841

Theme: i:\relic\hellscan\baseinv\erosion_soils.aml Created: December 20, 2001

n

a

i

258 d n

I

I

R

k

e

e r

259 C HC77

260 261

6045C HC49

60459D

60459D 262

60459F n a

i

HC48 d n I

60438F

60459F

60459E 263

Park Hells Canyon Creek 60459E SNAKE HC47 HC76 656132

60438F HC46 60459F 60438E60459E 656131 264 656184

60438F Blue 656049 6045C 656191 272 Oxbow Dam 60438E 656131 HC117

ek 60459F

e HC75 w

r o

b 604DA

C HC118

60438F 656090 656191 x 60459D

265 6045C O

656181 e

656131

60459F 656090 271 h HC72 656090 T n HC74 HC70 a HC73 HC71 rm HC69 60459E 6045C 267 6045C e HC68

H 6045C 266 60459D 268 656131

RIVER 656090 27 HC65 60438F 60459F 60438F HC67

60459F 60459F 60438E HC66 60438F 60459F 60438F 60438F 60459E 60459F 60438F 60438F 269

60459F HC64 604167D 6045C

60459E 60459D HC63

60

Park 60438F

60438F 60438E 60459F 60459E 60459E 60438F Copperfield

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 9 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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k e re C

it p

aw

S h

t N

O r

Y

o

N L L S HC59 E H

249 A

N C 250

251 HC57 252

HC60

k e 253 e r 254 C 255

HC56 HC55

t

HC61 BigBar n HC81 i

o HC80 HC82 P HC62 o HC79 tw ty 256 ir HC78 h T k HC54 e HC52 HC53 e HC51 257 r

C

h HC50

c

n y R

L E 258 V

I R

259

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 10 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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e re Th

238 Granite

239 HB5

240

HB4

241

HB2

HB3

R 244 Deep I V E R 243

242

E 245 K

A

N S Creek

246

k

ee 247

r Deep Cr. Trail

.

C S Barton Heights

E

R

HB1 248 N Battle Rec. Site

Hells

Dam

HC58

d Canyon tu

S Hells Canyon Cr.

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 11 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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229 228 27

HB 230

HB19 HB18

HB17 HB16 231

ek HB15

re 232 C RIVER

233 k

e 234

e HB14 r

HB13 C

Rush

HB12 235 SNAKE

236

e HB11 HB10 HB9 r 237 Th

Sluice HB6 HB8 HB7 238

H RIDGE

k k

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 12 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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Page 78 Hells Canyon Complex Plotfile: soil_ero_p13.gra Plotting Scale: 15841 Theme: i:\relic\hellscan\baseinv\erosion_soils.aml Created: December 20, 2001

C

n y

o e t ll

p a o

l V

K d t

Mtn o s R 217E V

I Creek o

Triangle o R w L k

HB35 r 216 HB34 i K HB33 218HB32 Pittsburg Admin. Site Admin. Kirby

215 HB36

HB31 219

220 k Ranch Historic

Kirkwood e SNAKE e r C

221

Creek HB30 u o b i r a Cougar C

HB29222

t

n 223

a

s

a

HB27

e HB28

l P 224

Creek 225 HB26

HB24 226

HB25 HB23 Salt

Creek

227 Creek HB20 HB22

HB21

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 13 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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r

C

n

o

t

Creek p

o

l

K

Kurry n Pittsburg Admin. Site Admin.

Creek o HB36

y 215 n a

Island C Pleasant Valley

214 HB37

213

k

e

e

r

HB38 C HB39

e

g Creek n Big a 212

r

h g Valley i

H

211

Jones

t

n

a

s

a

e l

210 P

HB41 209 Creek 207

RIVER 208 HB40

206

HB42 HB43 Somers

205

HB44 45

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 11- 2 5 numeric codes r Panel 14 of 16 Unimproved Road IPC Project Facility Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream 10MILES.5 IDAH O > 5000 Ditch or Canal POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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195

Doug Creek

196 Dug Bar

C a 197 m p

C

r

e

e

k

k

e e 198 r C

HB49 ek 200 HB48 e 201 r HB50 C HB51 g 199 u 202 D HB47 Wolf

Deep 203 SNAKE

204 SUMMIT

Creek Roland Cr

HB46 HB44 205 HB45 HB43 HB42

Cat Creek

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 * MN Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * GN Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 17 O 30’ O 11- 2 5 numeric codes 0 08’ 311 MILS r Panel 15 of 16 Unimproved Road IPC Project Facility 2 MILS Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream UTM GRID AND 1987 10MILES.5 IDAH O > 5000 MAGNETIC NORTH DECLINATION Ditch or Canal AT CENTER OF OXBOW QUADRANGLE POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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185 ER

186 River Divide

187

Cherry 2

Salmon 1 188

0

HB60

HB58 HB59

189 HB57 HB56

Wiley Creek

Creek

190

HB52 194 193 HB53 191 195 HB55 HB54 192 Doug Creek

Base Features Legend Thematic Features Legend Tech. Report E.3.2 - 42, Figure 3 * MN Primary Route Study Area Erosion Site Surface Area (square m) + Soil Types * GN Study Area ------Soil Types and Shoreline Secondary Route Water Body 1- 10 656017 - and all other colored Erosion Sites, Hells Canyon Light Duty Road River Mile polygons with 6-digit 17 O 30’ O 11- 2 5 numeric codes 0 08’ 311 MILS r Panel 16 of 16 Unimproved Road IPC Project Facility 2 MILS Boise e (not shown in this legend) v i 26- 100 Snak R Trail Pump Station e 101- 250 Railroad Spring 251- 500 Transmission Line Well Vicinity Map 501- 1000 Perennial River or Stream 1001- 5000 Intermittent River or Stream UTM GRID AND 1987 10MILES.5 IDAH O > 5000 MAGNETIC NORTH DECLINATION Ditch or Canal AT CENTER OF OXBOW QUADRANGLE POWER + See Appendix 2 for erosion sites and *See Appendix 1 for map codes Geographic Information Services Political Boundary alpha-numeric codes Shoreline Erosion in Hells Canyon Idaho Power Company

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Page 86 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon

Appendix 1. Summary of some soil characteristics using USDA Natural Resources Conservation Service (1995) published information for the Hells Canyon Study Area.

STATE MUID MUNAME PARTSIZE SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH PHL PHH MUWATHEL OR 604102C LOVLINE CHANNERY LOAM, 2 096 CN-L 20 40 0.20 0.32 0 0 6.6 7.3 1 TO 12 % SLOPES OR 604103D LOVLINE CHANNERY LOAM, 12 096 CN-L 20 40 0.20 0.32 0 0 6.6 7.3 1 TO 30 % NORTH SLOPES OR 604103E LOVLINE CHANNERY LOAM, 30 096 CN-L 20 40 0.20 0.32 0 0 6.6 7.3 1 TO 50 % NORTH SLOPES OR 604103F LOVLINE CHANNERY LOAM, 50 096 CN-L 20 40 0.20 0.32 0 0 6.6 7.3 1 TO 70 % NORTH SLOPES OR 604122C POALL VERY FINE SANDY 096 VFSL 0 0 0.43 0.43 0 0 7.4 8.4 1 LOAM, 2 TO 12 % SLOPES OR 604124D POALL VERY FINE SANDY 096 VFSL 0 0 0.43 0.43 0 0 7.4 8.4 1 LOAM, 12 TO 40 % SOUTH SLOPES OR 604127A POWVAL SILT LOAM, 0 TO 3 % 096 SIL 0 0 0.37 0.37 0 0 7.4 8.4 1 SLOPES, WARM OR 60412A BAKER SILT LOAM, 0 TO 2 % 096 SIL 0 0 0.37 0.37 0 0 6.6 7.8 1 SLOPES, WARM OR 60412B BAKER SILT LOAM, 2 TO 7 % 096 SIL 0 0 0.37 0.37 0 0 6.6 7.8 1 SLOPES, WARM OR 604130E REDCLIFF GRAVELLY LOAM, 30 096 GR-L 20 40 0.24 0.32 0 0 7.4 7.8 1 TO 50 % NORTH SLOPES OR 604130F REDCLIFF GRAVELLY LOAM, 50 096 GR-L 20 40 0.24 0.32 0 0 7.4 7.8 1 TO 75 % NORTH SLOPES OR 604133C ROBINETTE-GWINLY COMPLEX, 096 SIL 40 60 0.43 0.43 0 0 6.6 7.3 1 2 TO 12 % SLOPES OR 604136F ROCK OUTCROP-RUCLICK 096 UWB 0 0 0.00 0.00 0 0 0.0 0.0 3 COMPLEX, 50 TO 70 % NORTH SLOPES OR 60413A BALDOCK SILT LOAM, 0 TO 2 % 096 SIL 0 0 0.32 0.32 0 2 7.9 8.4 1 SLOPES OR 604142C RUCKLES-RUCLICK COMPLEX, 096 STV-CL 10 20 0.17 0.43 0 0 6.6 7.8 1 2 TO 12 % SLOPES OR 604143D RUCKLES-RUCLICK COMPLEX, 096 STV-CL 10 20 0.17 0.43 0 0 6.6 7.8 1 12 TO 35 % SOUTH SLOPES

Hells Canyon Complex Page 87 Shoreline Erosion in Hells Canyon Idaho Power Company

Appendix 1. (Cont.)

STATE MUID MUNAME PARTSIZE SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH PHL PHH MUWATHEL OR 604143E RUCKLES-RUCLICK COMPLEX, 096 STV-CL 10 20 0.17 0.43 0 0 6.6 7.8 1 35 TO 50 % SOUTH SLOPES OR 604143F RUCKLES-RUCLICK COMPLEX, 096 STV-CL 10 20 0.17 0.43 0 0 6.6 7.8 1 50 TO 70 % SOUTH SLOPES OR 604144E RUCKLES-RUCLICK-SNELLBY 096 STV-CL 10 20 0.17 0.43 0 0 6.6 7.8 1 COMPLEX, 35 TO 50 % SLOPES OR 604144F RUCKLES-RUCLICK-SNELLBY 096 STV-CL 10 20 0.17 0.43 0 0 6.6 7.8 1 COMPLEX, 50 TO 70 % SLOPES OR 604145D RUCLICK VERY COBBLY SILT 096 CBV-SIL 20 40 0.24 0.37 0 0 6.6 7.3 1 LOAM, 12 TO 35 % NORTH SLOPES OR 604145E RUCLICK VERY COBBLY SILT 096 CBV-SIL 20 40 0.24 0.37 0 0 6.6 7.3 1 LOAM, 35 TO 50 % NORTH SLOPES OR 604146D SAG-SNELL COMPLEX, 12 TO 35 096 SIL 40 60 0.43 0.43 0 0 6.1 7.3 1 % NORTH SLOPES OR 604152F SNAKER CHANNERY LOAM, 50 096 CN-L 10 20 0.20 0.32 0 0 6.6 7.3 1 TO 80 % SOUTH SLOPES OR 604153E SNAKER-DARKCANYON 096 CN-L 10 20 0.20 0.32 0 0 6.6 7.3 1 COMPLEX, 30 TO 50 % SOUTH SLOPES OR 60415A BALM LOAM, 0 TO 3 % SLOPES 096 L 0 0 0.28 0.28 0 2 7.9 8.4 1 OR 604167D TOP-MCGARR COMPLEX, 12 TO 096 SIL 40 60 0.32 0.32 0 0 6.1 7.3 1 35 % NORTH SLOPES OR 604169C UKIAH SILTY CLAY LOAM, 2 TO 096 SICL 20 40 0.32 0.32 0 0 6.1 7.3 1 12 % SLOPES OR 604169D UKIAH SILTY CLAY LOAM, 12 TO 096 SICL 20 40 0.32 0.32 0 0 6.1 7.3 1 20 % SLOPES OR 60416B BARNARD SILT LOAM, 2 TO 7 % 096 SIL 0 0 0.37 0.37 0 0 6.1 7.3 1 SLOPES OR 60416D BARNARD SILT LOAM, 12 TO 20 096 SIL 0 0 0.37 0.37 0 0 6.1 7.3 1 % SLOPES OR 604171B VIRTUE SILT LOAM, 2 TO 7 % 096 SIL 0 0 0.32 0.32 0 0 6.6 7.3 1 SLOPES

Page 88 Hells Canyon Complex Idaho Power Company Shoreline Erosion In Hells Canyon

Appendix 1. (Cont.)

STATE MUID MUNAME PARTSIZE SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH PHL PHH MUWATHEL OR 604176A WINGVILLE SILT LOAM, 0 TO 2 096 SIL 0 0 0.28 0.28 0 0 7.4 8.4 1 % SLOPES OR 604178F XERIC TORRIORTHENTS-ROCK 096 STX-L 10 60 0.20 0.37 0 0 6.6 7.8 3 OUTCROP COMPLEX, 50 TO 80 % SLOPES OR 60417C BARNARD COBBLY SILT LOAM, 096 CB-SIL 0 0 0.32 0.43 0 0 6.6 7.3 1 7 TO 20 % SLOPES OR 60423A BOYCE SILT LOAM, 0 TO 2 % 096 SIL 0 0 0.37 0.37 0 2 7.4 8.4 1 SLOPES OR 60438E COPPERFIELD-ROCK 050 CBV-SIL 0 0 0.24 0.37 0 0 6.6 7.3 3 OUTCROP COMPLEX, 30 TO 50 % NORTH SLOPES OR 60438F COPPERFIELD-ROCK 050 CBV-SIL 0 0 0.24 0.37 0 0 6.6 7.3 3 OUTCROP COMPLEX, 50 TO 80 % NORTH SLOPES OR 60440A CUMULIC HAPLOXEROLLS, 0 096 L 0 0 0.32 0.37 0 0 6.6 7.8 1 TO 2 % SLOPES OR 60449D EMILY SILT LOAM, 12 TO 35 % 096 SIL 0 0 0.32 0.32 0 0 6.1 7.3 1 NORTH SLOPES OR 60449E EMILY SILT LOAM, 35 TO 60 % 096 SIL 0 0 0.32 0.32 0 0 6.1 7.3 1 NORTH SLOPES OR 60459D GWINLY-IMMIG VERY COBBLY 056 CBV-SIL 10 20 0.17 0.37 0 0 6.6 7.8 1 SILT LOAMS, 12 TO 35 % SOUTH SLOPES OR 60459E GWINLY-IMMIG VERY COBBLY 056 CBV-SIL 10 20 0.17 0.37 0 0 6.6 7.8 1 SILT LOAMS, 35 TO 50 % SOUTH SLOPES OR 60459F GWINLY-IMMIG VERY COBBLY 056 CBV-SIL 10 20 0.17 0.37 0 0 6.6 7.8 1 SILT LOAMS, 50 TO 70 % SOUTH SLOPES OR 6045C ARIDIC HAPLOXEROLLS, 2 TO 002 STV-L 0 0 0.24 0.37 0 0 6.6 7.3 1 12 % SLOPES OR 60494C LEGLER SILT LOAM, 2 TO 8 % 096 SIL 0 0 0.43 0.43 0 2 6.6 7.3 1 SLOPES

Hells Canyon Complex Page 89 Shoreline Erosion in Hells Canyon Idaho Power Company

Appendix 1. (Cont.)

STATE MUID MUNAME PARTSIZE SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH PHL PHH MUWATHEL OR 60496E LICKSKILLET VERY GRAVELLY 096 GRV-SL 10 20 0.15 0.28 0 0 6.6 8.4 1 SANDY LOAM, 30 TO 50 % SOUTH SLOPES OR 60496F LICKSKILLET VERY GRAVELLY 096 GRV-SL 10 20 0.15 0.28 0 0 6.6 8.4 1 SANDY LOAM, 50 TO 70 % SOUTH SLOPES OR 604DAM DAM 096 0 0 0.00 0.00 0 0 0.0 0.0 0 OR 604W WATER 0 0 0.00 0.00 0 0 0.0 0.0 0 ID 656001 ABO SILT LOAM, 0 TO 2 % 096 SIL 60 60 0.49 0.49 0 2 7.4 8.4 0 SLOPES ID 656002 AGERDELLY CLAY, 4 TO 30 % 096 C 60 60 0.24 0.24 0 2 6.6 8.4 0 SLOPES ID 656003 AGERDELLY CLAY, 30 TO 60 % 096 C 60 60 0.24 0.24 0 2 6.6 8.4 0 SLOPES ID 656013 BAKEOVEN-REYWAT 096 STX-L 4 10 0.05 0.37 0 0 6.1 7.8 0 COMPLEX, 2 TO 30 % SLOPES ID 656014 BAKEOVEN-REYWAT-ROCK 096 STX-L 4 10 0.05 0.37 0 0 6.1 7.8 0 OUTCROP COMPLEX, 30 TO 60 % SLOPES ID 656015 BALDOCK SILT LOAM, 0 TO 2 % 096 SIL 60 60 0.32 0.32 2 4 7.9 8.4 0 SLOPES ID 656016 BALDOCK CLAY LOAM, O TO 2 096 CL 60 60 0.37 0.37 2 4 7.9 8.4 0 % SLOPES ID 656017 BISSELL LOAM, 0 TO 2 % 096 L 60 60 0.32 0.32 0 0 6.1 7.3 0 SLOPES ID 656026 BROWNLEE SANDY LOAM, 20 096 SL 60 60 0.37 0.37 0 0 6.1 6.5 0 TO 35 % SLOPES ID 656034 CLEMS FINE SANDY LOAM, 0 096 FSL 60 60 0.32 0.32 0 2 6.6 8.4 0 TO 2 % SLOPES ID 656035 CLEMS FINE SANDY LOAM, 2 096 FSL 60 60 0.32 0.32 0 2 6.6 8.4 0 TO 4 % SLOPES ID 656049 DESHLER EXTREMELY STONY 096 STX-CL 20 40 0.10 0.37 0 0 6.6 7.3 0 CLAY LOAM, 2 TO 30 % SLOP ES

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Appendix 1. (Cont.)

STATE MUID MUNAME PARTSIZE SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH PHL PHH MUWATHEL ID 656052 DESHLER-AGERDELLY 096 SICL 20 40 0.24 0.24 0 0 6.1 7.3 0 COMPLEX, 30 TO 60 % SLOPES ID 656060 DETERSON SILT LOAM, 30 TO 096 SIL 60 60 0.32 0.32 0 0 6.1 7.3 0 60 % SLOPES 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 % 096 SIL 60 60 0.43 0.43 0 0 6.6 7.8 0 SLOPES ID 656067 FALK FINE SANDY LOAM, 0 TO 096 FSL 60 60 0.20 0.20 0 0 6.1 7.3 0 2 % SLOPES ID 656068 GEM STONY CLAY LOAM, 2 TO 096 ST-CL 20 40 0.32 0.37 0 0 6.1 7.8 0 30 % SLOPES ID 656069 GEM STONY CLAY LOAM, 30 096 ST-CL 20 40 0.32 0.37 0 0 6.1 7.8 0 TO 60 % SLOPES ID 656070 GEM EXTREMELY STONY CLAY 096 STX-CL 20 40 0.15 0.37 0 0 6.1 7.8 0 LOAM, 2 TO 30 % SLOPES ID 656071 GEM-BAKEOVEN COMPLEX, 2 096 STV-CL 20 40 0.15 0.37 0 0 6.1 7.8 0 TO 30 % SLOPES ID 656072 GEM-BAKEOVEN COMPLEX, 30 096 STV-CL 20 40 0.15 0.37 0 0 6.1 7.8 0 TO 60 % SLOPES ID 656073 GEM-REYWAT COMPLEX, 2 TO 096 STV-CL 20 40 0.15 0.37 0 0 6.1 7.8 0 30 % SLOPES ID 656074 GEM-REYWAT COMPLEX, 30 096 STV-CL 20 40 0.15 0.37 0 0 6.1 7.8 0 TO 65 % SLOPES ID 656082 GREENLEAF SILT LOAM, 0 TO 2 096 SIL 60 60 0.49 0.49 0 0 6.6 8.4 0 % SLOPES ID 656083 GREENLEAF SILT LOAM, 2 TO 4 096 SIL 60 60 0.49 0.49 0 0 6.6 8.4 0 % SLOPES ID 656087 GROSS SILT LOAM, 30 TO 65 % 096 SIL 20 40 0.28 0.32 0 0 6.6 7.3 0 SLOPES ID 656088 GROSS-BAKEOVEN COMPLEX, 096 SIL 20 40 0.28 0.32 0 0 6.6 7.3 0 30 TO 65 % SLOPES ID 656089 GROSS-BAKEOVEN COMPLEX, 096 ST-L 20 40 0.28 0.37 0 0 6.6 7.3 0 30 TO 65 % SLOPES, STONY ID 656090 GWIN-ROCK OUTCROP 096 STV-L 10 20 0.20 0.43 0 0 6.6 7.3 0 COMPLEX, 40 TO 65 % SLOPES

Hells Canyon Complex Page 91 Shoreline Erosion in Hells Canyon Idaho Power Company

Appendix 1. (Cont.)

STATE MUID MUNAME PARTSIZE SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH PHL PHH MUWATHEL ID 656092 HARPT LOAM, 4 TO 8 % 096 L 60 60 0.32 0.32 0 2 6.1 7.3 0 SLOPES ID 656093 HAW SILT LOAM, 4 TO 8 % 096 SIL 60 60 0.43 0.43 0 0 6.1 7.8 0 SLOPES ID 656094 HAW SILT LOAM, 8 TO 12 % 096 SIL 60 60 0.43 0.43 0 0 6.1 7.8 0 SLOPES ID 656095 HAW SILT LOAM, 12 TO 30 % 096 SIL 60 60 0.43 0.43 0 0 6.1 7.8 0 SLOPES 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, 0 096 GR-L 60 60 0.17 0.24 0 0 6.6 7.3 0 TO 3 % SLOPES ID 656129 LORELLA-ROCK OUTCROP 096 STV-CL 10 20 0.15 0.28 0 0 6.6 7.3 0 COMPLEX, 50 TO 65 % SLOPES ID 656130 MCDANIEL STONY LOAM, 10 096 ST-L 60 60 0.28 0.32 0 0 6.6 7.3 0 TO 60 % SLOPES ID 656131 MCDANIEL-ROCKLY COMPLEX, 096 STV-L 60 60 0.20 0.37 0 0 6.6 7.3 0 10 TO 70 % SLOPES ID 656132 MCDANIEL-STARVEOUT 096 STV-L 60 60 0.20 0.37 0 0 6.6 7.3 0 COMPLEX, 10 TO 60 % SLOPES ID 656153 MULETT-MACKEY COMPLEX, 096 STV-L 10 20 0.17 0.37 0 0 7.4 8.4 0 30 TO 60 % SLOPES ID 656160 NYSSATON SILT LOAM, 0 TO 2 096 SIL 60 60 0.49 0.49 0 2 7.9 8.4 0 % SLOPES ID 656162 OLDSFERRY SHALY LOAM, 25 096 SH-L 20 40 0.20 0.37 0 0 6.6 7.3 0 TO 65 % SLOPES ID 656166 OWYHEE SILT LOAM, 4 TO 8 % 096 SIL 60 60 0.49 0.49 0 0 6.6 8.4 0 SLOPES ID 656169 PANIOGUE LOAM, 0 TO 2 % 096 L 60 60 0.32 0.32 0 2 7.4 8.4 0 SLOPES ID 656173 POWER-PURDAM SILT LOAMS, 096 SIL 60 60 0.43 0.43 0 0 6.6 7.8 0 0 TO 2 % SLOPES ID 656174 POWER-PURDAM SILT LOAMS, 096 SIL 60 60 0.43 0.43 0 0 6.6 7.8 0 2 TO 4 % SLOPES ID 656175 POWER-PURDAM SILT LOAMS, 096 SIL 60 60 0.43 0.43 0 0 6.6 7.8 0 4 TO 8 % SLOPES

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Appendix 1. (Cont.)

STATE MUID MUNAME PARTSIZE SURFTEX ROCKDEPL ROCKDEPH KFACT KFFACT SALINL SALINH PHL PHH MUWATHEL ID 656177 RIGGINS EXTREMELY STONY 096 STX-L 10 20 0.10 0.43 0 0 6.1 7.3 0 LOAM, 30 TO 50 % SLOPES ID 656179 RIVERWASH 096 0 0 0.00 0.00 0 0 0.0 0.0 0 ID 656180 ROCK OUTCROP-BAKEOVEN 096 0 0 0.05 0.37 0 0 6.1 7.8 0 COMPLEX, 60 TO 80 % SLOPES ID 656181 ROCKLY VERY STONY LOAM, 096 STV-L 5 12 0.15 0.37 0 0 6.1 7.3 0 12 TO 60 % SLOPES ID 656184 ROCKLY-ROCK OUTCROP 096 STV-L 5 12 0.15 0.37 0 0 6.1 7.3 0 COMPLEX, 10 TO 50 % SLOPES ID 656185 ROCKLY-STARVEOUT- 096 STV-L 5 12 0.15 0.37 0 0 6.1 7.3 0 MCDANIEL ASSOCIATION, 3 TO 70 % SLOPES ID 656190 SHOEPEG SILTY CLAY LOAM, 0 096 SICL 60 60 0.32 0.32 0 0 6.6 7.8 0 TO 3 % SLOPES ID 656191 STARVEOUT-GWIN-MCDANIEL 096 L 60 60 0.28 0.28 0 0 6.1 7.3 0 ASSOCIATION, 3 TO 45 % SL OPES ID 656204 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 Idaho Power Company

Appendix 2. Summary of shoreline soil inventory data for the Hells Canyon Study Area.

SITE STA LEN HT COMP PRCT BANK SL 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

OX1 A 30 2.5 N G S 3 3 3 SSW 0 15 1 4 20 OX2 AH 100 5 N I S 2 2 4 2 G EHW SSW FW 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 3 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 4 4 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 BR17 AH 100 3.5 N G S 2 2 4 G 0 0 50 40 90 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

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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 D2 D3 A1 A2 A3 T S G F TT BR28 A 210 3.5 N G S 2 2 4 G S 0 10 55 5 70 BR29 A 5 10 N G S 2 2 4 G S 0 5 70 20 95 BR30 AH 700 2.5 N G M 2 2 4 G SSW 0 10 45 40 95 BR31 H 150 1.5 N G M 2 2 4 SSW G 0 80 5 5 90 BR32 A 200 10 N G S 2 2 4 G F 0 5 80 5 90 BR33 A 230 4 N S S 2 2 4 G F 0 5 80 10 95 BR34 H 30 8 N G S 2 2 4 G F 0 3 80 7 90 BR35 A 50 2 N G M 2 2 4 G S F 0 15 50 15 80 BR36 A 150 1.5 N G S 2 2 4 G S F 0 5 70 15 90 BR37 A 100 3 N G S 2 2 2 4 3 F S G 0 10 30 50 90 BR38 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 A 20 6 N G S 2 2 4 2 G F 0 0 60 30 90 BR41 A 50 4 N G M 2 2 4 G S G 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 2 G S 0 10 70 10 90 BR44 AH 45 6 N G S 2 2 4 SS SSW 0 40 30 10 80 BR45 A 20 10 N G S 2 2 4 G SSW 0 10 75 5 90 HC46 A 25 2 N G M 2 2 2 3 4 F SSW FW 0 0 40 40 80 HC47 A 60 3.5 N G S 2 2 2 5 4 F SSW 0 0 20 10 30 HC48 A 50 4 N G S 2 2 2 4 4 4 F SSW 0 0 20 15 35 HC49 AH 50 4 N G L 2 2 2 2 3 3 S SSW 0 40 30 20 90 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 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 HC55 A 20 4 N G S 2 2 4 4 2 SS 0 5 40 15 60 HC56 A 40 3 N G S 2 2 4 4 SS SSW 0 5 35 20 60 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 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 2 4 3 2 G SSW 0 20 50 10 80 HC63 A 50 3 N G L 2 4 4 2 PR 0 0 20 40 60 HC64 A 80 3.5 N G L 2 2 4 3 SS 0 5 10 20 35 HC65 H 50 4 N I M 2 2 3 2 S SSW SS 0 10 40 20 70 HC66 A 15 3 N I M 2 4 S SSW 0 60 5 5 70 HC67 A 30 3 N I S 2 4 4 SS 0 20 30 10 60 HC68 A 15 4 N I S 4 2 3 3 S FW 0 40 40 5 85 HC69 A 35 4 N I S 4 2 2 S SSW 0 70 40 10 120 HC70 A 35 4 N I M 4 2 2 S CTS 5 70 40 10 125 HC71 AH 40 4 N I M 2 3 2 S SSW FW 0 30 90 10 130 HC72 A 80 2.5 N I S 2 4 3 2 G SSW 0 0 55 10 65 HC73 A 85 6 N I S 2 4 2 S SSW 0 40 30 30 100 HC74 A 30 15 N I S 2 4 2 SS SSW 0 10 70 0 80 HC75 A 25 3 N I M 3 2 SSW SS CTS 0 30 40 15 85 HC76 A 100 1 N I M 3 2 3 PR SSW 20 0 100 0 120 HC77 A 20 1.5 N I S 2 4 5 F SSW 0 0 5 20 25 HC78 A 20 1.5 N I M 3 2 3 FU SSW 70 20 80 10 180 HC79 A 100 4 N I L 2 2 2 3 2 F SSW 0 0 20 40 60 HC80 A 30 1 N G M 2 2 2 2 SS SSW 0 20 40 30 90 HC81 A 25 1 N I L 2 2 2 2 3 3 SS 0 20 60 30 110

Page 96 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 D2 D3 A1 A2 A3 T S G F TT HC82 A 20 1 N I L 2 2 2 2 3 3 S SSW 0 25 60 20 105 BR83 A 40 4 N G S 2 2 4 SS 0 5 30 25 60 BR84 A 75 6 N G S 2 2 4 3 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 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 0 5 15 10 30 BR105 H 35 10 N G S 2 2 2 5 3 SS SSW 0 10 45 20 75 BR106 AH 40 6 N G S 2 2 2 5 3 SS 0 5 45 15 65 BR107 A 35 6 N G S 2 2 4 2 G 0 0 60 15 75 BR108 A 45 4 N G S 2 2 4 2 G 0 0 75 20 95

Hells Canyon Complex Page 97 Shoreline Erosion in Hells Canyon Idaho Power Company

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 D2 D3 A1 A2 A3 T S G F TT BR109 A 40 30 N G S 2 2 5 G 0 0 80 15 95 BR110 A 60 4 N G S 2 2 5 2 G 0 0 80 15 95 BR111 A 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 BR116 A 50 4 N G S 2 2 4 2 SS 0 10 75 20 105 HC117 A 150 3.5 N I S 2 3 2 5 4 SS SSW FW 0 30 30 40 100 HC118 A 50 1.5 N G M 2 3 3 3 3 G EHW 0 0 40 20 60 OX119 A 50 3 N G M 2 3 4 F I 0 0 5 10 15 BR120 A 70 4 N G S 2 2 4 SS F 0 5 45 15 65 BR121 A 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 A 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 2 5 3 SS 0 10 15 15 40

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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 D2 D3 A1 A2 A3 T S G F TT BR136 AH 70 5 N G S 2 2 4 SS F 0 5 25 30 60 BR137 A 80 5 N G S 2 2 5 G 0 0 40 10 50 BR138 A 8 3 N G S 2 2 4 S 0 35 60 20 115 BR139 A 45 3 N G S 2 2 4 G 0 0 30 15 45 BR140 A 8 5 N G S 2 2 4 G 0 0 35 10 45 BR141 A 40 4 N G S 2 2 4 S 0 35 50 15 100 BR142 AH 140 2 N G S 2 2 4 SS 0 10 35 20 65 BR143 A 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 4 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 SS SSW 0 10 25 5 40 BR161 A 600 3 Y 95 G S 2 2 2 2 2 2 SS EHW SSW 0 10 25 5 40 BR162 A 100 3 N G S 2 2 2 4 2 4 2 2 2 SS EHW 0 15 5 5 25

Hells Canyon Complex Page 99 Shoreline Erosion in Hells Canyon Idaho Power Company

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 D2 D3 A1 A2 A3 T S G F TT BR163 A 150 3 Y 95 G S 2 2 2 4 4 SS B 0 10 10 0 20 BR164 A 180 2 N G S 2 2 2 4 4 SS B 0 10 20 10 40 BR165 A 15 2 N G M 2 2 2 2 4 SS EHW 0 10 5 5 20 BR166 A 15 2 N G M 2 2 2 2 2 4 B B 0 0 5 20 25 BR167 A 40 2 N G L 2 2 2 2 4 F DH 0 10 10 20 40 BR168 A 500 2 N G M 2 2 2 3 4 SS B 0 0 5 5 10 BR169 A 1000 5 N G S 2 2 2 4 4 G B 0 0 20 0 20 BR170 A 800 6 N G M 2 2 2 3 4 SS SSW 0 10 10 5 25 BR171 A 1000 2 N G M 2 2 2 3 4 SS SSW 0 10 5 5 20 BR172 A 150 2 N G M 2 2 2 4 4 SS SSW 0 10 10 0 20 BR173 A 800 3 Y 95 G S 2 2 2 4 4 2 SS SSW 0 20 10 0 30 BR174 A 450 2 N G M 2 2 2 3 4 SS SSW 0 10 20 10 40 BR175 A 1500 1 N G M 2 2 2 2 4 2 2 SS SSW 0 5 25 5 35 BR176 A 20 2 N G M 2 2 2 3 4 2 SS EHW 0 25 10 5 40 BR177 A 20 3 N G M 2 2 2 3 4 2 SS SSW 0 25 10 0 35 BR178 A 15 3 N G S 2 2 2 4 4 S FW 0 40 5 5 50 BR179 A,H 2000 2 N G S 2 2 2 4 4 2 2 SS EHW 0 20 15 5 40 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 2 4 4 SS SSW 0 10 20 10 40 BR185 A 600 5 N G S 2 2 2 3 4 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 2 SS B 0 10 20 5 35 BR189 A 30 2 N G S 2 2 2 4 4 3 2 SS EHW 0 5 30 5 40

Page 100 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 D2 D3 A1 A2 A3 T S G F TT BR190 A 80 8 N G S 2 2 2 4 4 3 SS B 0 5 10 5 20 BR191 A 400 3 N G S 2 2 2 3 4 2 G B 0 0 15 10 25 BR192 A 80 3 N G S 2 2 2 3 3 SS B 0 20 20 5 45 BR193 A 50 2 N G S 2 2 2 3 3 G SSW 0 5 40 0 45 BR194 A 75 2 N G S 2 2 2 3 4 3 G B 0 5 30 0 35 BR195 A 90 3 N G S 2 2 2 4 4 G 0 10 35 0 45 BR196 A,H 800 5 Y 95 G S 2 2 2 4 4 G B 0 10 35 0 45 BR197 A 300 3 N G S 2 2 2 4 4 2 G B 0 5 40 0 45 BR198 A 400 2 N I M 2 2 2 3 4 4 SS B 0 5 15 0 20 BR199 A 40 2 N I S 2 2 2 3 4 G SSW 0 5 25 0 30 BR200 A 100 7 Y 40 I S 2 2 2 4 4 G B 0 5 25 5 35 BR201 A 30 3 N I S 2 2 2 4 4 G G 0 5 25 5 35 BR202 A 30 2 N I S 2 2 2 4 4 G SSW 0 5 30 0 35 BR203 A 30 3 N I S 2 2 2 2 4 4 G EHW 0 5 25 0 30 BR204 A 40 3 N I S 2 2 2 4 4 G B 0 5 25 0 30 BR205 A 130 6 Y 75 I S 2 2 2 4 4 G B 0 5 40 0 45 BR206 A 20 5 N I S 2 2 2 3 4 3 G B 0 5 35 0 40 BR207 A 120 4 N I S 2 2 2 3 4 2 G B 0 5 25 0 30 BR208 A 175 2 N I S 2 2 2 4 4 3 G DH 0 5 25 0 30 BR209 A 400 2 Y 95 I S 2 2 2 4 4 2 G B 0 5 20 0 25 BR210 A 15 7 N I S 2 2 2 4 4 G B 0 5 20 0 25 BR211 A 20 5 N I S 2 2 2 4 4 B B 0 5 5 0 10 BR212 A 300 2 N I S 2 2 2 4 4 G SSW 0 5 20 0 25 BR213 A 75 4 Y 50 I S 2 2 2 4 4 2 DH B 0 0 5 5 10 BR214 A 4000 3 Y 95 I S 2 2 2 4 4 2 G EHW 0 5 25 0 30 BR215 A 40 2 Y 90 I M 2 2 2 2 2 4 SS B 0 10 25 5 40 BR216 A 250 2 Y 95 I M 2 2 2 2 2 4 SS SSW 0 10 25 5 40

Hells Canyon Complex Page 101 Shoreline Erosion in Hells Canyon Idaho Power Company

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 D2 D3 A1 A2 A3 T S G F TT BR217 A 250 2 Y 90 I M 2 2 2 3 2 4 G EHW 0 5 30 5 40 BR218 A 1500 5 N I M 2 2 2 2 3 2 3 G B 0 5 30 5 40 BR219 A 250 8 Y 95 I S 2 2 2 2 4 4 G B 0 5 35 5 45 BR220 A 400 2 Y 95 I S 2 2 2 4 4 G B 0 5 20 0 25 BR221 A 4800 7 Y 99 I M 2 2 2 3 4 2 SS B 0 10 15 5 30 BR222 A 1400 4 Y 95 I S 2 2 2 3 3 2 G B 0 5 30 0 35 BR223 A 200 1 N I L 2 2 2 2 3 2 S SSW 0 25 10 5 40 BR224 A 40 1 N I L 2 2 2 2 4 G EHW 0 0 35 5 40 BR225 A 30 2 N I M 2 2 2 2 4 S SSW 0 30 10 0 40 BR226 A 20 1 N I L 2 2 2 2 2 2 2 A SSW 0 0 0 0 0 BR227 A 2800 5 Y 98 I S 2 2 2 5 2 5 G B 0 0 25 0 25 BR228 A 600 3 N I S 2 2 2 4 4 G B 0 0 30 0 30 BR229 A 3200 2 Y 98 I S 2 2 2 4 4 G B 0 5 30 0 35 BR230 A 200 2 Y 95 I S 2 2 2 4 4 2 G B 0 0 30 0 30 BR231 A 2000 5 Y 97 I S 2 2 2 5 5 G B 0 0 30 0 30 BR232 A 30 3 N I S 2 2 2 4 4 G B 0 0 30 0 30 BR233 A 100 4 N I S 2 2 2 4 4 G B 0 0 30 0 30 BR234 A 900 2 Y 90 I S 2 2 2 4 5 G B 0 0 30 0 30 BR235 A 200 5 Y 50 I S 2 2 2 2 5 5 G B 0 0 2 0 2 BR236 A 600 5 N I S 2 2 2 5 5 G B 0 0 30 0 30 HB1 A 45 10 N G S 2 3 3 4 2 2 3 B B 0 0 0 0 0 HB2 A 10 1 N I M 2 2 4 2 SSW SSW 0 20 10 5 35 HB3 A 15 1 N I M 2 2 3 4 G B 0 0 25 0 25 HB4 H 10 15 N G S 2 2 3 4 4 S S 0 30 10 0 40 HB5 H 25 3 Y 95 G M 2 4 4 S S 0 25 15 0 40 HB6 H 200 15 Y 90 I S 2 4 4 2 SSW SSW 0 20 20 0 40 HB7 H 40 3 Y 95 G M 2 2 4 4 2 SSW SSW 0 20 20 0 40

Page 102 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 D2 D3 A1 A2 A3 T S G F TT HB8 A 40 3 N G S 2 4 4 2 G SSW 0 10 30 0 40 HB9 H 20 5 N I M 2 4 4 2 SSW SSW 0 25 15 0 40 HB10 H 25 5 Y 80 G M 2 4 4 2 SS SS 0 20 20 0 40 HB11 A 30 5 Y 80 G S 2 4 4 2 SSW SSW 10 20 15 0 45 HB12 A 250 20 Y 65 G S 2 4 4 G G 0 0 30 0 30 HB13 A 100 6 Y 80 G S 2 4 5 SSW SSW 10 25 10 0 45 HB14 A 30 10 N I S 2 4 4 SSW SSW 0 20 10 0 30 HB15 A 40 20 N I S 2 2 4 4 S S 5 10 20 0 35 HB16 A 30 15 N G S 2 2 4 4 SS SS 0 15 15 0 30 HB17 A 400 15 N G S 2 4 4 SS SS 0 10 20 0 30 HB18 A 30 5 N G M 2 3 4 2 SS SS 5 10 10 0 25 HB19 A 45 2 N G S 2 3 4 G G 0 0 20 0 20 HB20 A 100 4 Y 50 I M 2 3 4 G G 0 5 25 5 35 HB21 A 50 3 N I M 2 3 4 G B 0 0 30 0 30 HB22 A 40 30 N I S 2 4 4 G B 0 0 25 0 25 HB23 A 35 3 N I S 2 4 4 SS B 0 10 20 5 35 HB24 A 15 3 N I M 2 3 4 SS SS 0 10 15 5 30 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 2 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 2 FW SSW 5 10 10 0 25 HB31 A 60 2 N I L 2 2 4 SSW EHW 0 60 5 0 65 HB32 A 15 2 N I M 2 3 4 2 SSW EHW 0 10 10 5 25 HB33 A 30 2 N G S 2 4 4 SSW SSW 0 15 10 0 25 HB34 A 60 3 N G M 2 3 4 SSW SSW 5 10 10 0 25

Hells Canyon Complex Page 103 Shoreline Erosion in Hells Canyon Idaho Power Company

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 D2 D3 A1 A2 A3 T S G F TT HB35 A 75 5 N G M 2 3 4 2 G B 0 5 20 5 30 HB36 A 150 5 N G L 2 3 2 4 2 FW FW 25 15 10 0 50 HB37 A 80 8 N G S 2 4 4 G SSW 0 15 0 0 15 HB38 A 10 5 N G S 2 4 4 G G 0 0 20 10 30 HB39 A 10 4 N I M 2 3 4 SSW B 0 0 5 0 5 HB40 A 70 3 N G M 2 3 4 2 FW FW 25 25 20 0 70 HB41 A 20 2 N I M 2 3 4 G G 0 0 20 10 30 HB42 A 20 5 N I M 2 3 4 SS B 0 0 5 10 15 HB43 A 40 4 N I S 2 4 4 S SS 0 15 5 5 25 HB44 A 30 3 N I M 2 3 5 3 SSW EHW 0 0 5 10 15 HB45 A 45 1 N G M 2 3 4 SSW EHW 0 5 10 20 35 HB46 A 50 2 N G L 2 2 4 2 SSW EHW 0 5 10 20 35 HB47 A 120 2 N G M 2 3 4 FW FW 25 20 20 10 75 HB48 A 100 3 N I M 2 3 2 4 G B 0 0 5 5 10 HB49 A 20 4 N G M 2 3 4 G G 0 0 20 10 30 HB50 A 15 3 N I M 2 3 4 SSW SSW 0 10 10 0 20 HB51 A 60 8 N G M 2 3 4 G G 0 0 20 15 35 HB52 A 40 3 N I M 2 3 4 G EHW 0 0 10 15 25 HB53 A 35 5 N G S 2 4 4 SSW G 0 0 20 10 30 HB54 A 30 2 N G M 2 3 4 2 G G 0 0 25 5 30 HB55 A 125 2 N I M 2 3 4 G G 0 5 25 5 35 HB56 A 30 4 N I M 2 3 4 G G 0 0 20 0 20 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 20 I S 2 2 2 5 5 G B 0 5 30 5 40

Page 104 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 D2 D3 A1 A2 A3 T S G F TT BR238 A 220 2 Y 20 I S 2 2 2 4 4 G G 0 5 15 5 25 BR239 A 30 6 N I S 2 2 2 4 4 DS B 0 15 5 5 25 BR240 A 275 4 N I S 2 2 2 4 4 G B 0 5 25 0 30 BR241 A 1500 3 N I M 2 2 2 2 4 2 3 G B 0 5 25 5 35 BR242 A 50 3 Y 80 I S 2 2 2 4 4 G B 0 0 35 5 40 BR243 A 145 10 Y 65 I S 2 2 2 4 4 G B 0 5 25 5 35 BR244 A 300 5 Y 80 I S 2 2 2 4 4 DH B 0 5 5 5 15 BR245 A 20 4 N I S 2 2 2 4 4 G B 0 0 25 5 30 BR246 A 120 5 Y 95 I S 2 2 2 4 2 4 G B 0 5 20 5 30 BR247 A 100 3 Y 95 I S 2 2 2 4 3 G EHW 0 5 25 5 35 BR248 A 1000 18 N I M 2 2 2 3 4 G B 0 5 20 5 30 BR249 A 100 20 Y 50 I S 2 2 2 5 4 G B 0 5 20 5 30 BR250 A 1100 3 N I S 2 2 2 4 4 G B 0 10 20 5 35 BR251 A 500 3 N I S 2 2 2 2 4 4 SS B 0 10 20 5 35 BR252 A 1600 3 Y 90 I S 2 2 2 2 4 4 SS B 0 20 20 5 45 BR253 A 400 1 N I M 2 2 2 2 3 4 G B 0 5 35 0 40 BR254 A 400 2 Y 50 I S 2 2 2 2 4 4 G B 0 5 35 0 40 BR255 A 70 2 Y 80 I M 3 2 2 2 3 3 SS B 0 15 20 0 35 BR256 A 150 3 N I S 3 2 2 2 4 4 G SSW 0 5 35 0 40 BR257 A 60 3 N I M 3 2 2 2 3 4 G B 0 5 35 0 40 BR258 A 80 1 N I S 2 2 2 4 4 G B 0 0 35 0 35 BR259 A 1000 1 Y 60 I M 3 2 2 2 4 4 2 SS EHW 0 10 30 0 40 BR260 A 800 3 Y 90 I S 2 2 2 3 3 SS B 0 10 20 0 30 BR261 A 200 8 Y 70 I S 2 2 2 4 4 G B 0 5 35 0 40 BR262 A 1000 1 Y 90 I S 2 2 2 3 3 G 0 0 25 5 30 BR263 A 40 3 N I S 2 2 2 4 3 DH B 0 0 10 10 20 BR264 A 40 3 N I S 2 2 2 3 3 G G 0 0 25 5 30

Hells Canyon Complex Page 105 Shoreline Erosion in Hells Canyon Idaho Power Company

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 D2 D3 A1 A2 A3 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 N I M 2 2 2 3 4 G B 0 0 20 5 25 BR268 A 110 2 N I S 2 2 2 4 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 3 3 2 4 3 3 3 SS B 0 10 15 5 30 BR273 A 400 2 N I M 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 60 I S 2 2 3 4 4 2 SS EHW 0 10 20 5 35 BR277 A 20 3 N I M 2 2 3 3 4 SS EHW 0 5 10 15 30 BR278 A 20 3 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 4 SS G 0 25 5 5 30 BR282 A 50 5 Y 80 O S 2 2 2 2 4 4 SS G 0 15 5 5 25 BR283 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 70 O S 2 2 2 5 4 G 0 5 10 5 20 BR286 A 120 3 N O S 2 2 2 2 4 4 SSW SS 0 30 5 5 40 BR287 A 170 2 N O S 2 2 2 2 4 4 SS EHW 0 30 5 10 45 BR288 A 350 5 Y 98 O S 2 2 2 2 4 4 SS SSW 0 25 10 5 40 BR289 A 30 1 N O S 2 3 2 2 3 3 SSW EHW 0 15 5 10 30 BR290 A 190 3 Y 95 O S 2 3 2 2 3 3 SSW EHW 0 25 5 10 40 BR291 A 150 3 Y 90 O S 2 3 2 2 3 3 2 EHW SSW 0 10 5 20 35

Page 106 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 D2 D3 A1 A2 A3 T S G F TT BR292 A 50 2 N O L 2 2 2 2 3 2 EHW SSW 0 15 5 15 30 BR293 A 600 5 Y 92 O S 2 2 3 2 3 3 3 3 4 2 SSW EHW 5 25 5 10 45 BR294 A 100 1 N I M 2 3 2 2 2 3 2 FW SSW 25 30 0 5 60 BR295 A 150 1 N I M 2 3 2 2 2 2 3 SSW EHW 0 25 5 20 50 BR296 H 150 2 N I L 2 3 2 2 2 3 2 SSW EHW 0 25 10 15 50 BR297 A 2000 10 Y 99 O L 2 4 2 2 4 2 2 3 2 2 SSW EHW 0 30 5 15 50 BR298 A 85 5 N O S 2 4 2 2 4 4 3 3 3 SS G 0 15 10 5 30 BR299 A 150 5 N O S 2 4 2 2 4 4 4 4 SS EHW 0 15 5 10 30 BR300 A 30 3 N O L 2 4 2 2 4 2 2 4 SSW EHW 0 50 5 10 60 BR301 A 120 2 N O L 2 3 2 2 4 4 2 2 SSW EHW 0 50 5 10 60 BR302 A 150 1 N S L 2 2 2 2 3 2 3 SS EHW 0 25 10 10 45 BR303 H 1000 3 Y 50 I L 2 2 2 2 2 4 SS G SSW EHW 0 25 30 10 65 BR304 H 450 3 Y 70 I L 2 2 2 2 2 4 SS G SSW 0 25 30 10 65 BR305 A 700 5 Y 50 I L 2 2 2 4 3 2 4 2 G SSW F 0 10 70 10 90 BR306 H 1100 3 Y 70 I L 2 2 2 2 4 G SSW 0 10 70 10 90 BR307 H 150 3 Y 50 I M 2 2 4 S G SSW EHW 0 35 50 10 80 BR308 H 1800 3 Y 65 O S 2 2 4 2 G SS SSW 0 20 50 10 70 BR309 H 2500 3 Y 50 O S 2 2 2 2 4 2 S SS GSSW 0 30 50 10 80 BA1 H 700 5 N O S 4 3 SSW SSW 1 30 15 5 50 BA2 H 2500 5 N I S 3 4 EHW SSW EHW SSW 0 10 30 40 80 BA3 H 120 3 N I S 4 3 FW B 0 5 5 10 20 BA4 A 40 10 Y 50 O S 4 4 3 SS SS 0 20 50 0 70 BA5 H 20 20 N I M 4 FW G F 0 0 60 30 90 BA6 A 150 5 N I S 4 4 4 FW F 0 0 20 60 80 BA7 A 225 10 Y 50 I S 4 3 4 3 FW F 0 0 30 50 80 BA8 A 600 10 Y 80 I S 4 4 4 FW F 0 0 20 60 80

Hells Canyon Complex Page 107 Shoreline Erosion in Hells Canyon Idaho Power Company

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 D2 D3 A1 A2 A3 T S G F TT BA9 A 1200 20 Y 80 O S 4 4 2 SSW SS SSW SSW 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