Downstream fish passage for large storage dams
Question 1: Can downstream fish passage be developed for large storage dams that minimize O&M costs by allowing fish to self guide into an intake structure that will provide for a smooth transition from the reservoir into the downstream river channel without injury to fish.
Question 2: Can a downstream passage design be developed that can provide self guided fish passage whether the dam is 50 ft high or over 100 ft high and has wide-spread application to large dams throughout Reclamation.
Question 3: Can a downstream fish passage design be developed that will allow for fish passage in a reservoir where water surface fluctuations typically range in the 10's to 100's of feet in elevation due to seasonal releases?
Background: Throughout the Pacific Northwest region there is renewed effort to provide upstream and downstream passage at main stem storage reservoirs to access high value resident and anadromous salmonid habitat previously accessible prior to dam construction. Storage reservoirs present many unique challenges to fish passage. The most obvious challenge is dam height, with many dams being from 100 ft to upwards of 500 ft high. Second, storage reservoirs are operated to store and release agriculture and M&I water seasonally, creating reservoir water surface fluctuations of 10's or 100's of feet in a year. Coupled with these challenges,are many other less obvious yet important challenges to the successful design and operation of fish passage on a storage reservoir.
We would like to pursue the development of a concept for downstream passage that would be applicable to a number of Reclamation's large storage reservoirs using new concepts that will allow fish to self-guide into a structure that carries them around the dam and into the downstream river channel; thus, significantly reducing associated O&M costs.
Need and Benefit
Providing access to high value spawning and rearing habit that has been cut off due to the construction of dams is a key component for the recovery of endangered fish species. Dams constructed without allowance for upstream and downstream fish passage, have resulted in the extirpation of anadromous salmon and steelhead populations in many areas. Historically, tens of thousands of sockeye, coho, and spring Chinook salmon and steelhead returned annually to spawn in Lakes and their upstream tributaries. The annual return of salmon was an important source of marine-derived nutrients that helped maintain ecosystem health. For example, fishing encampments were established by people of the Yakama Nation at both the inlet and outlet of Cle Elum Lake and it was here that the Yakama people harvested and dried primarily sockeye salmon to sustain them during the winter months and to trade with coastal tribes in the Puget Sound region.
Our understanding of fishery needs and advances in engineering that allow those needs to be met have advanced greatly in the last decade. While many fish passage projects on run of river dams continue to be constructed, recovery of anadromous species in many Pacific drainages now includes efforts to provide upstream and downstream passage at main stem storage reservoirs. To date most high dams where downstream fish passage has been established are for hydropower generation facilities with minimal fluctuation in pool elevation and generally these facilities consist of manned surface collectors, and trap and haul methods that require large operation and maintenance (O&M)costs.
Recently, NOAA Fisheries has included the requirement for investigating passage for a number of main stem dams on the Sacramento River and its tributaries, including Shasta Dam and Folsom Dam. These are large complex hydro power and water storage facilities holding back large reservoirs. They are also passage barriers to large areas of high quality fisheries habitat. Continued research in this area is needed to reduce the high cost of implementing passage on storage reservoirs.
A design concept now being considered for downstream fish passage at Cle Elum Dam, has the potential to be adapted for downstream fish passage at other locations. However designers need a basis for a general design (non site specific) from which to begin, and guidelines for adapting that design to meet the specific needs of a specific site. Physical modeling will be used to refine a Helix design concept (with vertical multi inlet structure) and determine design features that are most conducive and adaptable to a wide range of future dam sites.
An HL-series report will be provided at the end of the study describing the model study, results, analyses, and guidelines for the design of downstream fish passage for large storage dams.