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

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Status and Habitat Use of Snake River White SturgeonIdaho Power Companyby a wide variety of anadromous and freshwater fish, such as alewives and blue back herring.Anadromous fish and sturgeon have successfully used orifice-weir fish ladders. However, fishladders are most suitable for attracting surface-oriented fish. Sturgeon do not usually use fishladders because they greatly prefer to remain at depth and avoid light.4.2.1.2. Biological EffectivenessThe lower Snake River and Columbia River dams have pool and weir-type ladders, both ofwhich have proven effective for passing adult salmon but are also used occasionally by sturgeon.A typical pool and orifice-weir ladder is shown in Figure 7. The submerged orifice is crucial forsturgeon passage, since it allows this benthic (or bottom-dwelling) fish to travel upstream whileremaining submerged, as shown in Figure 8. In fact, for sturgeon, the overflow weir could beeliminated entirely and the ladder could still maintain equivalent sturgeon passage. Anothermodification for enhancing sturgeon passage is to enlarge the orifices to allow these large fish totravel easily from pool to pool.Sturgeon have been documented to use fish ladders at lower and middle Columbia River damsthat have vertical ascents of 65 to 105 ft. But, for unknown reasons, sturgeon use of the ladders ishighly variable among dams, although the ladders are similarly designed. Experience at theBonneville Dam, where both fish ladders and fish locks were included, has also shown that thevast majority of sturgeon passing the dam (97%) used the fish locks when they were operatingbetween 1938 and 1969. We have inferred, based on our experience and the bottom-dwelling andlight-avoidance habits of sturgeon, that fish ladders are of questionable effectiveness forupstream passage. This marginal effectiveness will be further reduced as vertical ascentincreases. Consequently, fish ladders are not considered a viable option for passing sturgeon.4.1.2.3. CostsFor dams with lower head (less than about 100 ft), fish ladders frequently present the mosteconomical approach. They also generally have lower operational costs than fish locks andelevators. One disadvantage of using ladders at sites with high head is that ladders can becomequite long: fish ladders generally cannot have a rate of rise that is steeper than 1 ft of vertical risefor every 10 ft of horizontal run (a slope of 10 to 1), and even at this slope, periodic horizontalresting pools are needed. There is also concern that some fish species may be physicallyincapable of absorbing the stresses imposed during the ascent of such a lengthy ladder.In 1983, a 42-step, vertical-slot fish ladder was constructed at Brunswick Dam on theAndroscoggin River in Maine. This ladder was 500 ft long and constructed for $4.3 million(Francfort et al. 1994). A fish passage study for the Cowlitz River hydroelectric project hasproposed two high-head fish ladders. The first ladder, at Mayfield Dam, is a half Ice Harbor-styleladder that is 8 ft wide and has a 10 to 1 slope. There are a number of resting pools, and the exitstructure accommodates a 10-ft fluctuation in the forebay elevation. The ladder also has abridged river crossing. The capital cost estimated for this ladder is $9,900,000, with an estimatedannual operations and maintenance (O&M) cost of $297,000. The second ladder is located at theMossy Rock Dam. It, too, is a half Ice Harbor-style ladder. The vertical rise for this ladder is216 ft. The exit structure is designed for a forebay elevation variance of 48 ft but also towithstand a total head of 143 ft during peak maximum flow. During high flows, when thePage 16Hells Canyon Complex
Idaho Power CompanyChapter 4: Conceptual Design for White Sturgeon Passage Facilitiesforebay elevation rises 48 ft above the minimum elevation of the forebay, the ladder is shutdown. Capital costs for this ladder were estimated at $22,400,000, with an O&M cost of$672,000 (Harza Northwest, Inc. 1999).Typical fish ladders cost between $100,000 and $200,000 per foot of rise. For sturgeon passage,the typical design would have to be modified to account for fish size and characteristics.Accommodating sturgeon could require a larger fish ladder with additional resting pools and amore gradual incline. The costs for such a ladder would run in the upper part of the cost range, ifnot higher. To account for their larger size, we have assumed that the ladders would need to betwice as long for sturgeon as for anadromous fish. Therefore, ladder length would be based on a1-ft vertical rise for every 20-ft horizontal run.4.2.2. Fish Locks4.2.2.1. DescriptionAlthough experimental fish locks were tried as early as the 1920s, they were not developed into apractical method for passing fish until the late 1940s. The first of these modern locks wasdesigned by J. H. T. Borland and constructed in Ireland. Subsequent installations have beenreferred to as Borland Locks.A typical Borland lock (Figure 9) consists of a top and bottom chamber connected by a slopingchamber. A certain amount of flow is released through the top gate and flows down the slopingchamber into the bottom chamber. This flow empties into the tailrace and attracts fish that aremigrating upstream. At a predetermined time in a cycle or when sufficient fish have entered thebottom chamber, the downstream gate is closed, the upstream gate is opened, and the lock fillswith water. The fish then swim up the shaft and into the forebay. Then the gates are adjusted, thelock is drained, and the process is repeated. Borland locks have been designed for dams as highas 200 ft (such as Orrin Dam in Scotland). To date, most fish locks are in Europe, although a fewhave been built in the United States. The primary functional disadvantage of the Borland lockshas been the inability to clear all fish from the vertical shaft in a timely manner. Locks also havea much smaller capacity than ladders and lifts (Clay 1995).Most of the Borland-type locks are constructed for passing salmon on smaller rivers in Europe.The Bonneville Dam was constructed with three pair of fish locks that were operated from1938 to 1969 (Figure 10). These locks have the added refinement of a grated floor, which wasraised to force the captured fish into the forebay. The locks were observed by a Russian fisheriesscientist in 1946 and used as a prototype for several fish locks in Russia. Fish locks were alsoused at McNary Dam during construction and at The Dalles Dam. Neither of these locks iscurrently in use.In Russia, fish locks are designed to pass sturgeon and other species and have features that werenot included in the earlier Borland and Bonneville locks. The Tzymlyanskij fish lock on theDon River was designed with a vertical shaft. It provides auxiliary water attraction, a fishcrowder to direct the fish into the lock, and a vertical crowder or lifting basket to ensure that thefish ascend the lock into the forebay (Figure 11). The Volzhskaya Dam on the Volkhov Riverand the Volgogradskiy Dam on the Volga River are similarly designed, except that both haveHells Canyon Complex Page 17
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