Evaluation of a Prototype Surface Flow Bypass for Juvenile Salmon and Steelhead at the Powerhouse of Lower Granite Dam, Snake River, Washington, 1996–2000

Abstract

A surface flow bypass takes advantage of the natural surface orientation of most juvenile salmon Oncorhynchus spp. and steelhead O. mykiss by providing a route in the upper water column that downstream migrant fishes can use to pass a hydroelectric dam safely. A prototype structure, called the surface bypass and collector (SBC), was retrofitted on the powerhouse of Lower Granite Dam and was evaluated annually with biotelemetry and hydroacoustic techniques during the 5‐year life span of the structure (1996–2000) to determine the entrance configuration that maximized passage efficiency and minimized forebay residence time. The best tested entrance configuration had maximum inflow (99 m3/s) concentrated in a single surface entrance (5 m wide, 8.5 m deep). We identified five important considerations for future surface flow bypass development in the lower Snake River and elsewhere: (1) an extensive flow net should be formed in the forebay by use of relatively high surface flow bypass discharge (>7% of total project discharge); (2) a gradual increase in water velocity with increasing proximity to the surface flow bypass (ideally, acceleration <1 m/s per meter) should be created; (3) water velocities at an entrance should be high enough (>3 m/s) to entrain the subject juvenile fishes; (4) the shape and orientation of the surface entrance(s) should be adapted to fit site‐specific features; and (5) construction of a forebay wall to increase fish availability to the surface flow bypass should be considered. The efficiency of the SBC was not high enough (maximum of 62% relative to passage at turbine units 4–5) for the SBC to operate as a stand‐alone bypass. Anywhere that surface‐oriented anadromous fish must negotiate hydroelectric dams, surface flow bypass systems can provide cost‐effective use of typically limited water supplies to increase the nonturbine passage, and presumably survival, of downstream migrants.

Hydroacoustic Evaluation of Juvenile Salmonid Passage and Distribution at Detroit Dam, 2011

“…Split-beam data were used to estimate the average backscattering cross section of fish for detectability modeling and to determine the direction of fish travel through sampling volumes to allow for meeting the assumptions of the acoustic screen model. The methods used in this study were similar to those used in other hydroacoustic fish passage distribution studies for the USACE (e.g., Johnson et al 2005;Khan et al 2009Ploskey et al 2003Ploskey et al , 2005, including those at Lookout Point Dam on the Middle Fork Willamette River during 2010 ). …”

“…Johnson et al (2005) describe methods to estimate variances for the passage rate estimates. The variances associated with each passage rate estimate were likely underestimated because between-intake variability in passage within a given turbine unit could not be accounted for because of sampling limitations.…”

“…In general, hydroacoustics-based fish passage research conducted at Columbia River basin dams has informed USACE and fisheries managers. Research topics over the last 25 years have included spill efficiency, horizontal and vertical distributions, seasonal and diel distributions, surface flow outlet efficiency, and dam operations effects (e.g., Johnson et al 1992Johnson et al , 2005Khan et al 2009Khan et al , 2012Ploskey and Weiland 2006;Ploskey et al 2007). Use of hydroacoustic techniques is appropriate to advance understanding of juvenile salmonid passage and distribution at DET.…”

Evaluation of a Behavioral Guidance Structure at Bonneville Dam Second Powerhouse including Passage Survival of Juvenile Salmon and Steelhead using Acoustic Telemetry, 2008

“…Regardless, we were able to determine that the BGS did increase B2CC efficiency for fish that navigated to the south gap. However, the overall efficiency of the B2CC only increased for yearling Chinook when comparing 2008 results to those from 2004and 2005(Counihan et. al 2006, suggesting forebay distribution of juvenile steelhead or subyearling Chinook may not have been significantly altered from prior years without a BGS present.…”

“…The purpose of the BGS was to alter the forebay distribution of smolts migrating downstream by guiding them away from turbines on the south side of the dam and toward a surface bypass collector to the north. Using radio telemetry and hydroacoustics, U.S. Geological Survey (USGS) and PNNL studies showed that about 80% of the fish moving toward the south turbines were successfully diverted north (Johnson et al 2005). Further investigations showed how forebay distribution was affected by the presence of the BGS at Lower Granite.…”