EFFECTS OF POOL FLUCTUATIONS ON NATURAL RESOURCES IN THE ROCKY REACH PROJECT AREA Prepared by: A. E. Giorgi BioAnalysts, Inc. 7981 168th Avenue NE Redmond, WA 9805 and M. D. Miller BioAnalysts, Inc. 3653Rickenbacker Ste 200 Boise, ID 83705 Prepared for: Chelan County Public Utility District P.O. Box 1231 327 North Wenatchee Ave. Wenatchee, WA 98807 November 2000 2 TABLE OF CONTENTS INTRODUCTION............................................................................................................. 3 FACTORS AFFECTING POOL ELEVATION............................................................3 EFFECTS ON FISHERIES RESOURCES....................................................................4 Stranding ........................................................................................................................ 4 Spawning......................................................................................................................... 6 Wells Tailrace ............................................................................................................. 6 Chelan Falls.................................................................................................................7 Fish Migration................................................................................................................ 7 RIPARIAN HABITAT ..................................................................................................... 9 REFERENCES................................................................................................................ 13 Rocky Reach Project No. 2145 BioAnalysts, Inc. DRAFT REPORT 3 INTRODUCTION According to the directives provided in the Chelan PUD work statement, the purpose of this section is to investigate the potential effects of Rocky Reach Pool fluctuations on fisheries resources. The scope will include an assessment of effects on ESA-listed anadromous fish populations, as well as the riparian habitat bordering the pool. The operation of Rocky Reach Dam, and the Wells Project (Douglas County PUD), causes fluctuations in both surface water elevation and water velocity in Rock Reach Pool. Both of these responses may have an effect on salmonid stocks and their habitat. Potentially, reservoir dynamics can affect migration, spawning, rearing, and stranding of fish within the reservoir, as well as riparian zone structure and reservoir habitat. These issues are addressed herein. FACTORS AFFECTING POOL ELEVATION Changes in water level at the Rock Reach project can result from either drafting water at the dam or from fluctuating inflow to the reservoir, particularly as associated with Wells Project discharge. The forebay elevation is sensitive to drafting, but not Wells inflow. However, changes in discharge from Wells Dam does affect the water level in the upper reservoir. For example, between 25,000 cfs and 200,000 cfs a 25,000 cfs change in discharge can move the water elevation from 1.0 to 1.7 ft in the Wells tailrace (Chelan PUD 1991). As a consequence, discharge between 30,000-220,000 cfs can dramatically change pool elevation at Wells Dam tailrace (Figure 1). Forebay operating levels at the Rocky Reach Project generally fluctuate over a narrow range of about two feet. In the 1991 Pool Raise Application, Chelan PUD noted that since 1972, the Rocky Reach forebay level was stable within the top two feet (elevation 705 - 707 feet) for 98% of the hours, and within the upper one foot 90% of the time Rocky Reach Project No. 2145 BioAnalysts, Inc. DRAFT REPORT 4 (Chelan PUD 1991). Furthermore, forebay level changes slowly, because the surface area of the forebay is large in comparison to the hydraulic capacity of the powerhouse. Changes in surface water elevation are more pronounced at the upstream portion of the reservoir (near Wells Dam tailrace) than near Rocky Reach Dam. The backwater profile developed by Stone and Webster Engineering can best depict this (Figure 1). With Rocky Reach forebay elevation 707’, as flow increases from 30,000 cfs to 220,000 cfs the surface water elevation at Azwell in the Wells tailrace increase from 707.5’ to 719’. At river mile 497, approximately half way down the reservoir the fluctuation is only 707’ to 708.5 over the same change in flow. The frequency with which pool elevation changes are dictated by the frequency flow fluctuates. Daily load-following is the typical operating mode for the Wells and Rocky Reach projects. Changes in flow can be pronounced over a 24-h period. As an example we refer to Figure 2 (taken from Chapman et al. 1994). During the month of July over several years, daily fluctuations often exceeded 100,000 cfs. Lows typically were near 50,000 cfs at night and could exceed 150,000 cfs during the day. Clearly, water velocity throughout the reservoir is sensitive to flow. Figure 3 illustrates this point. The index reach in this example includes the reach spanning Wells tailrace to Rock Island Dam. Chapman et al (1994) estimated water velocity through this reach over a range of flow, using the water volume displacement method. At 80,000-cfs water velocity through this index reach averages near 1 fps, whereas at 180,000 cfs velocity is estimated near 2.5 fps. EFFECTS ON FISHERIES RESOURCES Stranding Changing water surface elevation can strand fish as water recedes. Smaller fish are particularly susceptible to this. Since smolt stages of ESA-listed salmonid stocks inhabit Rocky Reach Project No. 2145 BioAnalysts, Inc. DRAFT REPORT 5 this reservoir, the potential for stranding is a concern. However the fish that are most susceptible to stranding are the summer/fall chinook salmon fry that are not listed under the ESA. They typically inhabit shallow-water, near-shore areas and embayments. Chinook fry move into shallows at night and have been observed to select depths less than 60 cm in areas with sand substrate (Hillman et al. 1988). As water levels recede, depressions form pools where oxygen can be depleted, or fish desiccate if water percolates through the substrate. However, the upper part of the reservoir where elevation fluctuations are most pronounced, has little shallow-water habitat where fry would be expected to congregate. Large changes in inflow within short time periods result in water level fluctuations in the middle and upper reservoir that could strand fish. Changes in flow associated with load- following occur daily throughout the Columbia River system (Figure 2). However, according to information compiled for the pool raise application in 1991, only one incident of fish stranding and mortality had been observed. That occurred in May 1988, as a result of an unusual combination of events an extreme reduction of flow in combination with near maximum drawdown of the Rocky Reach reservoir. These conditions were a consequence of flow reductions for bank stability tests at the Chief Joseph Dam, and drafting of the Rocky Reach forebay to maintain spill scheduled for bypassing downstream-migrant salmon and steelhead smolts. The fish kill was exacerbated because this event occurred in May, when recently emerged fall chinook fry were rearing throughout the shallow, low-velocity areas of the Rocky Reach Reservoir. No mortality estimates were reported in the report accounting of the incident. To the best of our knowledge there have been no observed fish strandings in Rocky Reach pool since that date. We could not locate any reports describing stranding/mortality events. We also queried Chelan PUD biologists. They were not aware of any further incidents. Rocky Reach Project No. 2145 BioAnalysts, Inc. DRAFT REPORT 6 Spawning Changes in pool elevation can potentially affect spawning activity of salmonids in Rocky Reach Pool. Only summer/fall chinook have been documented as spawning in areas under the influence of Rocky Reach project operations. In 1990 and 1991, Giorgi (1992) investigated the effects of changes in Rocky Reach pool elevation on summer/fall chinook spawning in the reservoir and adjacent waters affected by pool operations. Spawning activity was observed in two areas. One site was downstream from the tailrace at Wells Dam, near river-miles 514-516. The second site was at the mouth of the Chelan River near where it enters the Columbia River. The mouth of the Entiat River was included in those surveys in 1990 and 1991, but no redds we observed in the area influenced by the pool. However, four fall chinook redds were observed in the braided stream area well upstream from the boundary defining the pool (Giorgi 1992). Wells Tailrace Over the range of river discharge levels and associated surface water elevations that occurred in the fall of 1990 and 1991, water velocity across the spawning beds was swift. Velocity in the vicinity of redds typically exceeded 2-3 fps (Giorgi 1992). These velocities are well above the minimum (1.0 fps) observed at summer/fall chinook spawning areas in the Columbia River and some of its tributaries (Giorgi 1992). As synthesized by Giorgi (1992), the close proximity of the spawning areas to the Wells Dam ensures the maintenance of fast currents in this river-like segment of the reservoir. Normal operations of Rocky Reach Project maintain water velocities well above the minimum of 1.0 fps. Potentially fluctuations in surface water elevation could affect redd distribution. If summer/fall chinook preferred shallow areas, there may be a risk of redd dewatering and desiccation or freezing, due to load-following. However, this does not appear to be an important concern at the Wells Dam spawning