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The Pacific Northwest National Laboratory conducted this study for the Bonneville Power Administration (BPA) with funding provided through the Northwest Power and Conservation Council(a) and the BPA Fish and Wildlife Program. The study was conducted in the Hanford Reach of the Columbia River. The goal of study was to determine the physical habitat factors necessary to define the redd capacity of fall Chinook salmon that spawn in large mainstem rivers like the Hanford Reach and Snake River. The study was originally commissioned in FY 1994 and then recommissioned in FY 2000 through the Fish and Wildlife Program rolling review of the Columbia River Basin projects. The work described in this report covers the period from 1994 through 2004; however, the majority of the information comes from the last four years of the study (2000 through 2004). Results from the work conducted from 1994 to 2000 were covered in an earlier report. More than any other stock of Pacific salmon, fall Chinook salmon (Oncorhynchus tshawytscha) have suffered severe impacts from the hydroelectric development in the Columbia River Basin. Fall Chinook salmon rely heavily on mainstem habitats for all phases of their life cycle, and mainstem hydroelectric dams have inundated or blocked areas that were historically used for spawning and rearing. The natural flow pattern that existed in the historic period has been altered by the dams, which in turn have affected the physical and biological template upon which fall Chinook salmon depend upon for successful reproduction. Operation of the dams to produce power to meet short-term needs in electricity (termed power peaking) produces unnatural fluctuations in flow over a 24-hour cycle. These flow fluctuations alter the physical habitat and disrupt the cues that salmon use to select spawning sites, as well as strand fish in near-shore habitat that becomes dewatered. The quality of spawning gravels has been affected by dam construction, flood protection, and agricultural and industrial development. In some cases, the riverbed is armored such that it is more difficult for spawners to move, while in other cases the intrusion of fine sediment into spawning gravels has reduced water flow to sensitive eggs and young fry. Recovery of fall Chinook salmon populations may involve habitat restoration through such actions as dam removal and reservoir drawdown. In addition, habitat protection will be accomplished through set-asides of existing high-quality habitat. A key component to evaluating these actions is quantifying the salmon spawning habitat potential of a given river reach so that realistic recovery goals for salmon abundance can be developed. Quantifying salmon spawning habitat potential requires an understanding of the spawning behavior of Chinook salmon, as well as an understanding of the physical habitat where these fish spawn. Increasingly, fish biologists are recognizing that assessing the physical habitat of riverine systems where salmon spawn goes beyond measuring microhabitat like water depth, velocity, and substrate size. Geomorphic features of the river measured over a range of spatial scales set up the physical template upon which the microhabitat develops, and successful assessments of spawning habitat potential incorporate these geomorphic features. We had three primary objectives for this study. The first objective was to determine the relationship between physical habitats at different spatial scales and fall Chinook salmon spawning locations. The second objective was to estimate the fall Chinook salmon redd capacity for the Reach. The third objective was to suggest a protocol for determining preferable spawning reaches of fall Chinook salmon. To ensure that we collected physical data within habitat that was representative of the full range of potential spawning habitat, the study area was stratified based on geomorphic features of the river using a two-dimensional river channel index that classified the river cross section into one of four shapes based on channel symmetry, depth, and width. We found that this river channel classification system was a good predictor at the scale of a river reach ((almost equal to)1 km) of where fall Chinook salmon would spawn. Using this two-dimensional river channel index, we selected study areas that were representative of the geomorphic classes. A total of nine study sites distributed throughout the middle 27 km of the Reach (study area) were investigated. Four of the study sites were located between river kilometer 575 and 580 in a section of the river where fall Chinook salmon have not spawned since aerial surveys were initiated in the 1940s; four sites were located in the spawning reach (river kilometer [rkm] 590 to 603); and one site was located upstream of the spawning reach (rkm 605).
The development of the Snake River hydroelectric system has affected fall Chinook salmon smolts by shifting their migration timing to a period (mid- to late-summer) when downstream reservoir conditions are unfavorable for survival. Subsequent to the Snake River Chinook salmon fall-run Evolutionary Significant Unit being listed as Threatened under the Endangered Species Act, recovery planning has included changes in hydrosystem operations (e.g., summer flow augmentation) to improve water temperature and flow conditions during the juvenile Chinook salmon summer migration period. In light of the limited water supplies from the Dworshak reservoir for summer flow augmentation, and the associated uncertainties regarding benefits to migrating fall Chinook salmon smolts, additional approaches for improved smolt survival need to be evaluated. This report describes research conducted by the Pacific Northwest National Laboratory (PNNL) that evaluated relationships among river discharge, hyporheic zone characteristics, and egg pocket water temperature in Snake River fall Chinook salmon spawning areas. This was a pilot-scale study to evaluate these relationships under existing operations of Hells Canyon Dam (i.e., without any prescribed manipulations of river discharge) during the 2002-2003 water year. The project was initiated in the context of examining the potential for improving juvenile Snake River fall Chinook salmon survival by modifying the discharge operations of Hells Canyon Dam. The potential for improved survival would be gained by increasing the rate at which early life history events proceed (i.e., incubation and emergence), thereby allowing smolts to migrate through downstream reservoirs during early- to mid-summer when river conditions are more favorable for survival. PNNL implemented this research project at index sites throughout 160 km of the Hells Canyon Reach (HCR) of the Snake River. The HCR extends from Hells Canyon Dam (river kilometer [rkm] 399) downstream to the upper end of Lower Granite Reservoir near rkm 240. We randomly selected 14 fall Chinook salmon spawning locations as study sites, which represents 25% of the most used spawning areas throughout the HCR. Interactions between river water and pore water within the riverbed (i.e., hyporheic zone) at each site were quantified through the use of self-contained temperature and water level data loggers suspended inside of piezometers. Surrounding the piezometer cluster at each site were 3 artificial egg pockets. In mid-November 2002, early-eyed stage fall Chinook salmon eggs were placed inside of perforated polyvinyl chloride (PVC) tubes, along with a temperature data logger, and buried within the egg pockets. Fall Chinook salmon eggs were also incubated in the laboratory for the purpose of developing growth curves that could be used as indicators of emergence timing. The effects of discharge on vertical hydrologic exchange between the river and riverbed were inferred from measured temperature gradients between the river and riverbed, and the application of a numerical model. The hydrologic regime during the 2002-2003 sampling period exhibited one of the lowest, most stable daily discharge patterns of any of the previous 12 water years. The vertical hydraulic gradients (VHG) between the river and the riverbed suggested the potential for predominantly small magnitude vertical exchange. The VHG also showed little relationship to changes in river discharge at most sites. Despite the relatively small vertical hydraulic gradients at most sites, results from the numerical modeling of riverbed pore water velocity and hyporheic zone temperatures suggested that there was significant vertical hydrologic exchange during all time periods. The combined results of temperature monitoring and numerical modeling indicate that only 2 of 14 sites were significantly affected by short-term (hourly to daily) large magnitude changes in discharge. Although the two sites exhibited acute flux reversals between river water and hyporheic water resulting from short-term large magnitude changes in discharge, these flux reversals had minimal effect on emergence timing estimates. Indeed, the emergence timing estimates at all sites were largely unaffected by the changes in river stage resulting from hydropower operations at Hells Canyon Dam. Our results indicate that the range of emergence timing estimates due to differences among the eggs from different females can be as large as or larger than the emergence timing estimates due to site differences (i.e., bed temperatures among sites). We conclude that during the 2002-2003 fall Chinook salmon incubation period, hydropower operations of Hells Canyon Dam had an insignificant effect on fry emergence timing at the study sites.

Hells Canyon Dam

United States. Congress. House. Committee on Interior and Insular Affairs. Subcommittee on Irrigation and Reclamation

Published: 1952

Total Pages: 918


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Committee Serial No. 20.