Upstream Salmon and Society in the Pacific Northwest (1996) / Chapter Skim
Currently Skimming:
9 Dams and Mitigation of Their Effects
9 Dams and Mitigation of Their Effects
Pages 226-253
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From page 226... ...
dams, 14 mainstem Columbia River and 13 mainstem Snake River dams were completed. By the late 1970s, potential sites and public support for major new dams had been virtually exhausted, and the growth phase ended.
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227 ~- V ~ Ct o ~ o ~ Ct ~ _ 5 U: el~''P"i o .
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From page 228... ...
Source: Columbia River Water Report for 1993. discharge at four points in the Columbia River system: the Columbia River at the international border reflects the effect of Canadian storage, the sum of the Okanogan and Methow rivers reflects regulation by the Lake Okanogan and upstream reservoirs in Canada, the Snake River at its mouth reflects the effects of all Snake River reservoirs, and the Columbia River at The Dalles reflects the effects of all major storage facilities on the Columbia River system except those on the Willamette, Cowlitz, and Lewis rivers.
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From page 229... ...
However, water below Bonneville Dam has shown longer and warmer summer conditions over the last 40-50 years (Quinn and Adams, in prep.~. Figure 9-3 shows the trend in the date when the spring water temperature on the Columbia mainstem exceeded 15.5° since 1938.
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In the Columbia River, however, reservoir rearing might substitute for lost flowing-river habitat and make up for lost quality and quantity of estuarine habitat (Rondorf et al. 1990, Chapman and Witty 1993~.
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From page 231... ...
Such dams block about one-third of the Columbia River watershed to access by anadromous fishes; owing to natural passage barriers, one-third was never accessible. One-third lost to anadromous fish is upstream from Grand Coulee Dam on the Columbia River and the Hell's Canyon complex of dams on the Snake River (Chief Joseph Dam, the reregulating dam for Grand Coulee, also is impassable)
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From page 232... ...
Interdam losses have been estimated at up to 25% for the reach from Bonneville Dam to John Day Dam, but current loss estimates are about 4-5% per project there and elsewhere in the Columbia River system (Chapman et al.
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From page 233... ...
prey for predators. At the Bonneville second powerhouse, extensive studies of fall chinook passing through turbines and the bypass revealed that the survivals through the two routes were not very different and that predators were keying on the stream of prey from the bypass outfall (Ledgerwood et al.
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From page 234... ...
However, there is dispute over the validity and interpretation of these data, as discussed in the next section. There is some evidence that predators, such as northern squawfish, have increased in abundance in the lower Columbia River.
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The implications such as have taken place in the Columbia River estuary and watershed need to be incorporated into contemporary estuarine and shorelands management strategies. In particular, proposals for comprehensive hydroelectric and water withdrawal developments, shoreline modifications, and navigation projects should all be evaluated in terms of potential consequences to the estuarine ecosystem and resulting effects on other resources, including fisheries, which depend on a highly convolved and biologically diverse estuanne environment.
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From page 236... ...
Growth rates of subyearlings in mainstem Columbia River reservoirs are very high (Chapman et al.
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From page 237... ...
dam (data tabulated in Fish Passage Center 19941. Those preliminary results, if confirmed by additional analysis and studies and augmented by reachspecific survival estimates at downriver dams on the Snake and Columbia rivers, would suggest high priority for mitigation efforts directed at increasing survival at the dam rather than speeding fish through pools.
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From page 238... ...
The four mainstem Snake River dams-Ice Harbor, Lower Monumental, Little Goose, and Lower Granite also have adult fishways. Juvenile passage facilities on most mainstem dams in the Columbia River system use deflection screens that project downward into the intakes of turbines and deflect fish upward from the turbine intake into the gatewell (Figure 9-41.
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From page 239... ...
The downstream-migrant facilities described above have been installed or are being installed on Bonneville, The Dalles, John Day, McNary, and the four Snake River dams operated by the Corps of Engineers. On the Columbia River upstream from the mouth of the Snake River, where five dams are operated by public utility districts, the only dam with an operating fish bypass system is Wells
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From page 240... ...
They have been low at Bonneville Dam, whose bypass facilities were incorporated in the design rather than being retrofitted, and range from at least 70~o at John Day and McNary dams to 55% at Lower Granite Dam. Predator Control The dynamics of the interaction between squawfish and smelts has received relatively little attention except in the pool of John Day Dam (see Raymond 1979, Rieman et al.
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From page 241... ...
In the Columbia River system, transportation programs deliver juveniles to the Bonneville Dam tailrace, largely by barge. Barges control water quality, e.g., by preventing the occurrence of gas supersaturation.
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Even so, gas supersaturation is often greater than 115% and sometimes as high as 140~o (Fish Passage Center weekly reports) below major dams on the Columbia River and Snake River where spill occurs.
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The projects on the lower Snake and middle and lower Columbia rivers were to operate near "full pool" (the maximum reservoir water level authorized in the projects' design)
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Army Corps of Engineers, view the water budget as "a cooperative arrangement," not a mandate, so water-budget volumes are not guaranteed, especially in low-flow years, when they are most needed.
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DAMS AND MITIGATION OF THEIR EFFECTS 245 Third, other operating considerations have higher priority, e.g., for secondary power release and in some cases refill of downstream reservoirs. Fourth, BPA mitigates the cost of the water budget by selling the resulting excess spring power, then buying it back in the summer from other sources, thus causing
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From page 246... ...
It might well be important that the system operating policy treats the NPPC "targets" of 85 kcfs at Lower Granite Dam and 134 kcfs at Priest Rapids Dam as operating constraints, rather than operating targets; i.e., these targets are given precedence over power production. Flow augmentation should be implemented in such a way that targets are met in all years when storage is available, not just in average and above-average years.
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From page 247... ...
The System Operation Review found that the natural river options "decrease travel time (from the mouth of the Salmon River to Bonneville Dam) between 710 days, depending on the stock." However, effects are limited to Snake River populations since the action is restricted to the Snake River Basin.
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From page 248... ...
In addition, dams trap sediment, which significantly reduces their active storage capacity and economic value. Although sedimentation in most Columbia River reservoirs is minor compared to dams on rivers elsewhere, which carry higher sediment loads under natural conditions, the economic life of all reservoirs is ultimately affected by sedimentation.
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The Elwha River Proposal The Elwha River dams provide a useful case study that gives some idea of the magnitude of the dam removal problem. The Elwha River drains 831 km2 of the Olympic Mountains, WA, and discharges to the Strait of Juan de Fuca.
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From page 250... ...
The lowest-cost alternative is a combination of low-level diversion through the dam, or progressive notching of the dam and top-down removal at Glines Canyon, and construction of a surface diversion channel at Elwha Dam. If topdown removal were used at Glines Canyon, it would be accomplished by construction of multiple notches 15.2 m (50 It)
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Further, it was estimated that approximately 20 years would be required to remove all of the material from Lake Mills. An alternative of dredging the Lake Mills delta material and disposing of the dredged material over Glines Canyon Dam before removal was also investigated.
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From page 252... ...
At this point, the strongest candidates for dam removal in the Columbia system appear to be the run-of-the-river dams in the middle Columbia and lower Snake, which are the targets of current flow-augmentation studies. The most obvious differences between the Elwha River and middle Columbia and Snake dams are the size of the structures and the climate.
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From page 253... ...
On the other hand, the amount of sediment deposited behind the middle Columbia and lower Snake dams is likely to be less, because these dams were constructed after upstream dams had already trapped much of the sediment that would otherwise have been deposited. Nonetheless, the costs of removing a middle Columbia or lower Snake River dam would be much larger than those estimated for the Elwha River dams.
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