Snake River White Sturgeon Conservation Plan ... - Idaho Power

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Status and Habitat Use of Snake River White SturgeonIdaho Power Companylikely to find and use the alternative. However, this tendency to swim at shallow depths variesamong species and sometimes within a species in response to various environmental conditions.During the 1970s and 1980s, the U.S. Army Corps of Engineers studied the effectiveness ofsurface collection by using existing ice and trash sluiceways at hydroelectric facilities on theColumbia and Snake rivers. Studies at Ice Harbor and The Dalles dams revealed that up to 50%of the juvenile salmon approaching the powerhouse could be attracted into the sluiceways byusing as little as 3.7% of the powerhouse flow (Johnson et al. 1984, Steig and Johnson 1986).A study at Bonneville Dam's second powerhouse indicated that, during daylight hours, as manyas 80% of the fish approaching the powerhouse could be attracted into the ice and trashsluiceway (Magne 1987). All three of the powerhouses have sluiceway entrances, which areshallow, adjustable overflow weirs located directly above the deeply submerged entrances to theturbines. The species being diverted at these projects included chinook, sockeye, and steelheadsmolts.Sturgeon, as bottom dwellers, are not as well suited to collection systems located at the surface.Nonetheless, using existing ice and trash sluiceways to facilitate downstream migration isappealing as an inexpensive alternative at dams where sluiceways are already installed. A moreexpensive option would be to design a new surface collection system. Using either alternativewould require research into designing a system that would ensure that sturgeon survive passageto the tailrace, especially since, as large fish, sturgeon would tend to strike objects rather thanflow around them. The efficiency of a surface system could be increased by creating a ramp at adepth that leads to the entrance into the forebay. Section 4.3.4. provides more information aboutusing a ramp as part of a behavioral guidance structure for sturgeon.4.3.1.2. Biological EffectivenessDespite a history of experience and research, predicting the biological effectiveness of surfacecollection systems, even for salmonids, can be difficult. Some installations, such as those atWells Dam on the mainstem Columbia River, have been very successful, while the effectivenessof others is disappointing. Use of surface collection for sturgeon is even more problematicbecause there is little research or experience to demonstrate how effective or safe these systemsare.4.3.1.3. CostsWe found no cost information for a surface-bypass system designed specifically for sturgeon.The prototype for salmon at Wanapum Dam costs approximately $10 million, and the surfacecollection system at Lower Granite Dam costs about $8.4 million.4.3.2. Spillway Release4.3.2.1. DescriptionAs an option for passing juvenile salmon downstream, spillway release has received muchattention in the past few years as a safe and effective method. The most basic process is topartially open a spill gate to pass flow and fish that are migrating downstream. If bottom spillPage 26Hells Canyon Complex
Idaho Power CompanyChapter 4: Conceptual Design for White Sturgeon Passage Facilitiesgates are installed at a dam, the fish are subjected to the deleterious effects of a rapid drop inpressure and acceleration as they pass under the gate. Another complication is that baffle blocks,which are placed in the stilling basin at some projects, present a significant hazard to fishreleased over the spillway.Spill studies at Rock Island Dam on the middle Columbia River confirmed previous studies thatshallow or surface spill is more effective than deep spill in passing juvenile salmon throughspillways (Odeh 1999). Various arrangements to create surface-flow patterns have includedmodifications to gates, additions of bulkheads in front of a gate to act as overflow weirs, and theinstallation of flow deflectors on the spillways to decrease the total dissolved gas.Wanapum Dam, on the mainstem Columbia River, uses a weir/bulkhead system installed in aspillbay to modify spillway flow. The weir was positioned upstream of the Tainter gate to blockthe lower 40 ft of the spillbay and produce a surface flow effect (Figure 17 and Figure 18).Another example of an overflow system is currently being constructed for the U. S. Army Corpsof Engineers for installation at Lower Granite Dam on the lower Snake River. This installationwill create a forebay flow pattern similar to the one at Wanapum Dam system, but it will add therefinement of a curved downstream section to eliminate the shock to the fish of a free fall over aweir (Figure 19). Again, research and experience have focused on salmon passage rather thansturgeon passage, so thorough studies are needed to determine the effectiveness, safety, andpracticality of using spill releases to pass sturgeon.4.3.2.2. Biological EffectivenessA few (n = 6) sturgeon between 76 and 211 cm total length (TL) have passed downstream atC.J. Strike Dam, presumably over the spillway. However, biological data on the use of spillwaypassage for sturgeon are essentially nonexistent. The safety of passing sturgeon over a spillwayis questionable because of the large size of sturgeon and the high velocities of spillway flows,especially at high-head dams. As mentioned previously, baffle blocks in the stilling basin poseanother possible hazard.4.3.2.3. CostsThe spillway bulkhead at Wanapum Dam was constructed and installed for around $2 million.The Removable Spillway Weir overflow system being built for Lower Granite Dam costs about$12 million and will pass a flow of about 6,000 cubic feet per second (cfs).4.3.3. Pressurized Passage Systems4.3.3.1. DescriptionJudging by known sturgeon behavior, a submerged fish passage system could improve attractionefficiency because the entrance could be located at the depths to which sturgeon are accustomed.This type of system would then transfer the fish to the tailrace side of the dam and lower them tothe tailrace using either a fish lock, a fish lift, or a chute.A pressurized fish lock (Figure 20) could be used to pass fish downstream. To construct thissystem, a shaft is mined in the body of the dam, a vertical shaft is installed on the downstreamHells Canyon Complex Page 27
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