SEDIMENT DYNAMICS IN THE ROCKY REACH PROJECT AREA Final ROCKY REACH HYDROELECTRIC PROJECT FERC Project No. 2145 December 15, 2000 Prepared by: BioAnalysts, Inc. Boise, Idaho Prepared for: Public Utility District No. 1 of Chelan County Wenatchee, Washington Sediment Dynamics TABLE OF CONTENTS SECTION 1: INTRODUCTION ................................................................................................. 1 SECTION 2: SEDIMENT TRANSPORT PROCESSESS......................................................... 2 SECTION 3: SEDIMENTATION PATTERNS........................................................................... 4 3.1 Deltas............................................................................................................................................................. 4 3.2 Suspended Sediment Patterns........................................................................................................................ 5 3.3 Deposited Sediment Patterns ......................................................................................................................... 5 SECTION 4: DOWNSTREAM EFFECTS............................................................................... 16 SECTION 5: SUMMARY......................................................................................................... 17 SECTION 6: REFERENCES .................................................................................................. 18 APPENDIX A: ADDITIONAL AERIAL PHOTOS OF THE LOWER ENTIAT RIVER LIST OF FIGURES Figure 3-1: Timeline of major events in the Entiat River drainage. .............................................................................. 6 Figure 3-2: Aerial photograph of the lower Entiat River in 1910. ................................................................................ 7 Figure 3-3: Aerial photograph of the lower Entiat River in 1930. ................................................................................ 8 Figure 3-4: Aerial photograph of the lower Entiat River in July 1946.......................................................................... 9 Figure 3-5: Aerial photograph of the lower Entiat River in 1955. .............................................................................. 10 Figure 3-6: Aerial photograph of the lower Entiat River in September 1968.............................................................. 11 Figure 3-7: Aerial photograph of the lower Entiat River in August 1975. .................................................................. 12 Figure 3-8: Aerial photograph of the lower Entiat River in July 1985........................................................................ 13 Figure 3-9: Aerial photograph of the lower Entiat River in July 1992........................................................................ 14 Figure 3-10: Aerial photograph of the lower Entiat River in October 1998................................................................ 15 Figure A 1: Aerial photograph of the lower Entiat River in 1945............................................................................... 23 Figure A 2: Aerial photograph of the lower Entiat River in 1954............................................................................... 24 Figure A 3: Aerial photograph of the lower Entiat River in August 1989................................................................... 25 Final Study Report Rocky Reach Project No. 2145 December 15, 2000 Page i SS/2487 Sediment Dynamics SECTION 1: INTRODUCTION Hydroelectric facilities alter sediment transport and deposition within alluvial river channels (Baxter and Glaude 1980; Williams and Wolman 1984; Spence et al. 1996; Brookes 1996; Nilsson and Berggren 2000). This alteration can significantly influence the ecological response of the system. Considering the physical accumulation of sediment in reservoirs alone indicates its potential importance in ecosystem structure and function. For example, upstream from most dams fine sediment settles to the bottom, covering coarser substrate and depriving downstream reaches of sediment input. The reduction in sediment downstream of dams leads to changes in channel morphology (Williams and Wolman 1984; Marcus et al. 1990; Nilsson and Berggren 2000). In addition, sediments deposited upstream from dams may carry pesticides and herbicides, organic residues, nutrients, and pathogenic organisms, which can affect the biota within the river (Baxter and Glaude 1980; Sharpley et al. 1987; McCarthy and Gale 1999). Rocky Reach Dam is essentially a “run-of-the-river” project. Flows pass through as turbine discharge and/or spill, creating noticeable river currents. Nevertheless, Rocky Reach Dam has presumably affected the sediment dynamics within the project area1 by reducing water velocities upstream from the project. This report reviews existing information on the effects of Rocky Reach Dam on the sediment dynamics within the project area. The report first briefly discusses sediment transport processes. It then describes sedimentation patterns and deposition zones. At that point in the report we examine aerial photos to describe sediment deposition near the mouth of the Entiat River, an important source of sediment to Rocky Reach Reservoir. Finally, the report discusses sediment processes downstream from Rocky Reach Dam. Because there is virtually no information on sediment dynamics within the project area, we extrapolate general information in the literature to the project area. This obviously assumes that general information on sediment dynamics applies to the Rocky Reach project area. We conducted no field studies to validate this assumption. The Rocky Reach Natural Sciences Working Group will use this report to formulate management decisions and plans. 1 The Rocky Reach project area extends from the upstream end of Rocky Reach Reservoir to Rock Island Reservoir. Final Study Report Rocky Reach Project No. 2145 December 15, 2000 Page 1 SS/2487 Sediment Dynamics SECTION 2: SEDIMENT TRANSPORT PROCESSESS The amount of sediment transported to a reservoir is directly related to the size of the drainage basin upstream from the reservoir (Baxter and Glaude 1980; Thornton et al. 1990). That is, larger drainage basins associated with reservoirs generally result in greater annual flows entering the reservoir and therefore potentially greater sediment and nutrient loads. Although the drainage area upstream from Rocky Reach Dam is huge (87,800 mi2 or 227,402 km2), sediment transport to the project area is low (CPUD 1991). This is because sediments from the upper Columbia River basin are deposited in Roosevelt Lake upstream from Grand Coulee Dam.2 Wells Reservoir traps most sediments that originate from the Okanogan and Methow basins and the Columbia River between Chief Joseph Dam and Wells Dam. Lake Chelan traps sediments from the Chelan Basin. Therefore, inputs of sediments to the Rocky Reach project area come from sediments passing through the Wells project, a relatively small area just downstream from Wells Dam, the Chelan River, the Entiat Basin, and several mostly ephemeral or intermittent streams that drain directly into the reservoir. The Columbia River and Entiat River basin (419 mi2 or 1,085 km2) are probably the largest contributors of sediment to the Rocky Reach Reservoir. Other factors such as geology, soil types, topography, climate, fires, and land uses within the basin upstream from the reservoir also affect sediment transport (Baxter and Glaude 1980; Dingman 1994). The Rocky Reach project area lies between two different physiographic areas (CPUD 1991). To the west, the Cascade Mountains are comprised of highly metamorphosed schists and gneisses, slightly metamorphosed marine sedimentary rock, volcanic rocks, and granitic batholiths. To the east, the Columbia River Plateau consists mostly of basalt. The last glaciation deposited till on top of the basalt. These rock types are fairly resistant to erosion. Topography in the mid-Columbia Basin is steep and dissected. Soils in the area consist of two basic types (CPUD 1991). Near the toe of rock slopes, soils are mainly colluvial and composed of angular rock fragments. Here, soils are well graded, and soil fragments range in size from clay to large boulders. In the lowlands the predominant soils are fluvial and lacustrine. These soils range from clay to gravel and cobbles. Mullan et al. (1992) described the soils as highly erodible and unstable. The climate consists of hot, dry summers and mild to severe winters. Precipitation varies widely depending on the elevation and proximity to the Cascade Mountains. Mean annual precipitation varies from 35 inches (89 cm) in the lower Cascades, to about 11 inches (28 cm) on the Columbia Plateau, to 8.5 inches (22 cm) in the project area (CPUD 1991). 2 Grand Coulee Dam was built in 1942. Therefore, it affected stream flows and sediment dynamics in the project area long before Rocky Reach Dam was constructed. In Canada, large storage facilities such as Hugh Keenleyside, Mica, and Revelstoke dams were built in 1968, 1973, and 1983, respectively. Sherwood et al. (1990) and Chapman et al. (1994) concluded that storage in the upper Columbia River has altered the hydrograph of the main Columbia River. Sherwood et al. (1990) analyzed monthly mean flows of the Columbia River, and found that large-scale regulation of the flow cycle began around 1969. They noted that river storage and flow regulation has greatly reduced the probability of large freshets having important sedimentological