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

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Status and Habitat Use of Snake River White SturgeonIdaho Power Company4.2.4. Pressurized Passage Systems4.2.4.1. DescriptionA pressurized passage system uses a pressure lock to allow sturgeon to pass into the forebaybelow the reservoir surface. This system might be considered a good option for upstream passagefor several reasons. First, it would be able to operate over a wide range of forebay elevations,such as those at Brownlee Dam. Second, this system would reduce the vertical lift required andtherefore reduce the cycle time and possibly lower construction costs. Third, a pressurizedpassage system can be operated in reverse for downstream passage because its entrance islocated at the accustomed depth of sturgeon. Section 4.3.3. discusses in more detail how apressurized passage system could be used for passing sturgeon downstream.To construct a pressurized fish lock, a horizontal shaft is mined into the body of the dam and avertical shaft is installed on the downstream face. Two pressurized gates, a collection facility,and three mechanical crowders are installed (Figure 14). Fish are attracted to the collectionfacility by a discernable downstream flow that is created by water passing through a screenedand regulated outlet to the tailrace.When fish are to be moved to the forebay, the lower horizontal crowder forces the fish to thevertical shaft, where they are crowded vertically to the top of the shaft. Then the attraction flowis stopped and the tailrace gate is closed. After the gate is closed, the pressure is slowly increaseduntil it equals the water pressure in the forebay. Finally, the forebay gate is opened and ahorizontal crowder moves the fish into the forebay.In a pressurized fish lock (Figure 15), fish are transferred to the forebay by a series of operations.A structure for collecting fish using an attraction-water supply is built at the base of the dam, inthe tailrace. Once fish are attracted into the collection chamber, they are crowded into the lifthopper and, using the horizontal shaft that is mined through the body of the dam, raised to thetransfer chamber. The transfer chamber is constructed on the downstream face of the dam.This chamber has two valved outlets, one to pressurize the chamber and one to accept fish fromthe fish lift. The fish are then transferred into the transfer chamber and the lift valve is closed.The transfer chamber is then filled with water, and the pressure is slowly increased until itmatches the forebay pressure. Finally the forebay gate is opened and the fish are forced into theforebay by the mechanical crowder.Pressurized passage is an unusual and largely unproven passage concept. The only example wefound of a pressurized passage system being used is a system with a 6-m lift (19.5 ft) that wasconstructed in 1992 at the Rygene Dam in Norway. Consequently, pressurized passage isconsidered an experimental concept that will need research and development before it becomes aviable alternative. To allow captured sturgeon to safely acclimate to higher pressures, allpressurized fish locks must be carefully designed to ensure a gradual pressurization. Such asystem might use the highly compressible properties of air (as applied in air bladder tanks usedto pressurize domestic well systems) to reliably control water pressure in the lock. Anotherpossibility is to use an open standpipe system, so that the rate of drawdown can be closelymonitored. We anticipate that additional engineering challenges and biological constraints willbe discovered as this technology is developed.Page 20Hells Canyon Complex
Idaho Power CompanyChapter 4: Conceptual Design for White Sturgeon Passage Facilities4.2.4.2. Biological EffectivenessWe found no biological data for sturgeon using pressurized fish locks. Similarly, we found noinformation that helped us evaluate the design of a chute (for the biological effectiveness of fishlocks or fish lifts used as part of a pressurized passage system, see Sections 4.2.2.2. and 4.2.3.2.,respectively). Research is needed to prove the biological safety of this system. Of particularinterest is the reaction of sturgeon to changes in pressure, particularly when the surroundingwater is supersaturated with dissolved oxygen. The conclusions from such research woulddetermine the safe cycle time of a pressurized system. As with a fish lift or fish lock, theefficiency of the attraction system of a pressurized passage system would largely be determinedby the conditions at entrance to the facility.4.2.4.3. CostsBecause it is an untried system, we found no model of costs for a pressurized passage system.Additionally, because this system is experimental, there is significantly greater risk of costoverruns than for conventional methods of passing fish.4.2.5. Trap and Transport4.2.5.1. DescriptionA trap and transport facility collects migrating juvenile and adult fish above or below a dam,places them in transport vehicles, and releases them in the forebay or at another predeterminedlocation upstream of the dam.Trap and transport is a proven method that has been used for fisheries research and for gatheringbroodstock for sturgeon culture. A trap and transport facility can be designed as a separatefacility or adapted as part of a fish lift (described in Section 4.2.3.1.) (Figure 16). For example, ata lift facility (either before or after sorting), fish can be passed directly into the forebay, intoholding tanks for future movement, or directly into trucks for immediate transportation.Trap and transport systems have been used extensively to transport fish around both artificial andnatural obstructions. Sunset Falls Trap and Haul, located on the South Fork of theSkykomish River in western Washington and operated by the Washington Department of Fishand Wildlife, provides a successful example. That trap and transport facility began operating in1958 and passes migrating salmon past three natural falls. It was constructed to mitigate losthabitat in the lower Puget Sound system, and it opened up 90 mi of spawning and rearing areathat had previously been unavailable to salmon. It is currently used to transport up to 24,000 wildfish per year to the new, natural spawning areas. The Washington Department of Fish andWildlife had considered building fish ladders around the three falls, but has found that the trapand transport system is an effective and cost-efficient method of passing fish.For upstream passage, trapping needs to be based on the volitional drive of migrating sturgeon,including potential spawners or juvenile and nonreproductive fish that are sufficiently motivatedto move upstream and enter the trapping facility. Consequently, a holding structure with asuitably designed entrance and an attraction-flow system would need to be developed for thisHells Canyon Complex Page 21
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Snake River White Sturgeon Conservation Plan ... - Idaho Power

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