Estimating the Residence Time and Lateral
Distribution of Juvenile Chinook Salmon Passing
Through the Spillway and Stilling Basin
of The Dalles Dam

The Problem

The National Marine Fisheries Services Biological Opinion on the Columbia River salmon listed under the Endangered Species Act sets guidelines for salmon recovery. Many of the guidelines address salmon passage issues at hydroelectric dams operated by the U.S Army Corps of Engineers (COE). To meet

Stilling basin of The Dalles Dam.

these guidelines, the COE has undertaken a series of studies to improve downstream passage conditions for juvenile salmonids. Studies include investigations of optimal spill patterns and volumes and improved fish collection systems designed to route fish away from turbine passage, as well as studies to estimate fish survival as they pass dams under various conditions. In general, the estimated mortality associated with turbine passage is about 10% per dam, whereas estimated spill passage mortality is typically less than 5% per dam.

However, results of studies in 1999 and 2000 indicate the mortality associated with spill passage at The Dalles Dam is about twice that of other dams. One possible cause of the relatively low spillway survival at The Dalles Dam is the pattern in which the water is spilled over the dam. To avoid passing fish through the spillway and into shallow areas downstream known to harbor piscivores, a juvenile spill pattern is used. This pattern, designed to pass fish through the northernmost spill bays and away from the shallow areas downstream, creates an unplanned lateral flow movement in the tailrace very near the spillway (i.e., the stilling basin) that could extend the amount of time passing fish spend in this extremely turbulent area. Several studies were initiated in 2001 to determine if entrainment in this lateral flow affects survival of juvenile salmonids.

Objectives

The objective of this subtask is to determine the extent of lateral transport in the stilling basin (the area of the spillway tailrace within about 200 m of the dam) and the length of time fish spend in that area. This study is coordinated with other USGS and non-USGS studies designed to determine the survival of fish passing the dam via these routes.

Methodology

Installing underwater antennas at The Dalles Dam.

This study is based on detections of radio-tagged juvenile salmon. Juvenile chinook salmon (Oncorhynchus tshawytscha) are implanted with a small radio tag and released into one of three spill bays through a hose. They are then detected during passage using aerial antennas mounted on the dam, which are connected to an automated fixed-site telemetry receiving system. An underwater detection array was tested in 2001 and 2002, but was ineffective due to structural damage in each year. In FY2002 approximately 320 tagged fish were released through each of the three spill bays during the spring and again in the summer.

Highlights and Key Findings

Data from the aerial system indicated that fish released near the southern end of the spill pattern had longer stilling basin residence times that those released near the north end, prompting funding for continued research in FY2002. The COE is planning a $5,000,000 structural modification for FY03-FY04 based on 2001 results of this and concurrent studies.

Where Are We Headed In 2003

The COE is investigating designs for a structural modification of the stilling basin for implementation in 2004, so no field studies will be conducted during 2003. Studies similar to this one will likely be used in 2004 to evaluate the effects of the structural modification.

Project Contact

John Beeman
U.S. Geological Survey
Western Fisheries Research Center
Columbia River Research Laboratory
5501-A Cook-Underwood Rd.
Cook, WA 98605-9717

Email: john_beeman@usgs.gov
Phone: 509-538-2299, ext. 257
Fax: 509-538-2843

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