Condit Dam Removal Condit Dam Removal - Access Washington

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Condit Dam Hydroelectric Project Final Supplemental EIS 4.3.5 Significant Unavoidable Adverse Impacts All fish and aquatic macroinvertebrates within the White Salmon River channel downstream of the dam would likely be killed or displaced by the load of suspended solids released during dam breaching. While the actions having the effects will be short-term in duration and will diminish as the level of suspended sediments is reduced over time, the effect on populations of macroinvertebrates would likely take several years to fully reestablish. One potential year-class of chum salmon naturally spawned in the White Salmon River would be lost because of the high concentrations of suspended and deposited sediment and their inability to access stream habitat above the dam or cofferdam. Potential chum salmon spawners that enter the Bonneville pool during the fall and winter immediately following dam removal would spawn in other tributaries of the Columbia River or in the mainstem of the Columbia River. Potential chum salmon production is not expected to be lost, but chum salmon smolts that are imprinted to return to the White Salmon River would not be produced. This impact would be long term (at least several 3- to 5-year generation cycles for chum salmon), but slight because chum salmon are in the early stages of recolonizing tributaries of the Bonneville pool through the process of straying from natal spawning grounds below Bonneville Dam. Because of their poor jumping ability relative to other species of salmon in the White Salmon River, adult chum salmon may not be able to pass a fall located at RM 2.6 on the mainstem of the White Salmon River to utilize spawning habitat located upstream of Condit Dam. In addition, it is likely that the spawning substrate necessary for their reproduction will be impaired by fine sediment during the second year (and not fully recovered for 1 to 3 years after that). New gravel recruited from upstream may not reach the lower 2.6 miles during that time, and what gravel does reach the lower portion of the stream will likely be heavily embedded with fine sediments. The result would be essentially a potential loss of several naturally produced year-classes of chum salmon smolts that have been imprinted to return to the White Salmon River. The number of documented spawning adult chum salmon in the White Salmon River is very low and likely represents strays from a population below Bonneville Dam that have the potential of eventually recolonizing the White Salmon River basin and reestablishing a viable population. The loss of these stray chum salmon during the removal of Condit Dam and recovery of spawning gravels in the lower White Salmon River would not be expected to have a measurable effect on the number of potential chum salmon colonists entering the White Salmon River and other Columbia River tributaries above Bonneville Dam. The increase in available spawning habitat in the White Salmon River after natural channel building processes remove deposited fine sediments should increase the potential for a successful recolonization of the White River basin by chum salmon. The removal of Condit Dam may also open available chum salmon spawning habitat above the dam, but chum salmon characteristically spawn in the lower reaches of high-gradient rivers and may not migrate past the fall at RM 2.6 or upstream above the Condit Dam site. Large returns of chum salmon can cause competition for spawning gravel and cause chum salmon to migrate farther upstream than normal. However, even if none of the falls present in the river below Condit dam or under reservoir sediments is a barrier to chum salmon migration, this is unlikely to occur at the present levels of chum salmon occurrence in the White Salmon River. 4.3-29
Condit Dam Hydroelectric Project Final Supplemental EIS Natural spawning by the year-class of fall-run Chinook salmon returning to the White Salmon River during the year of dam removal would be lost due to the high concentrations of suspended and deposited sediment and their inability to access stream habitat above the dam or cofferdam. Although natural spawning of fall-run Chinook will not occur during the year of dam removal, PacifiCorp has proposed to capture and transport to a hatchery the fall Chinook returning to the White Salmon River before the dam is breached in October to mitigate for the loss of natural spawning for one year-class of Chinook salmon. After restoration of passage through the dam site and the removal of the cofferdam, fall-run Chinook salmon would be able to access upstream spawning and rearing habitat. Therefore, subsequent year-classes should have adequate spawning and rearing areas in the upstream reaches. Sediments flushed out of the reservoir would settle at the mouth of the White Salmon River and fill in the large pool between RM 0 and RM 0.5. These sediments also would likely fill in the pools and runs in the lower 2.8 miles of the White Salmon River between RM 0.5 and RM 3.3. High flow events subsequent to dam removal would transport the sediments deposited in pools above RM 0.5 and form a channel over 100 feet wide and up to 17 feet deep through the deposited sediments. This would likely occur within one year of dam removal. There would be an unavoidable short-term impact to available thermal refuge until sediment deposited in 1) pools between RM 0.5 and RM 3.3 and 2) the lake bed between RM 3.3 and RM 5.0, is transported to below RM 0.5 and a channel forms below RM 0.5. However, new thermal refuge habitat would be available above RM 5.0 as soon as passage is possible past the dam and cofferdam sites. When passage is restored past the cofferdam, there would be a net gain in available thermal refuge that would increase over time as sediments deposited in pools after dam breaching are removed by high flow events. The quality of thermal refuge below the dam site will also be slightly improved because of lower water temperatures after dam removal. During the period immediately following the breaching of the dam, suspended sediment concentrations entering the Bonneville pool would be relatively high and the discharge of the White Salmon River would make up approximately seven percent of the Columbia River flow. Columbia River fish may be displaced from the most sediment-laden portions of the plume until it has completely mixed with the Columbia River, approximately three miles downstream from the mouth of the White Salmon River (PacifiCorp 2005). Beyond this point, the plume may briefly interfere with foraging behavior and predator-prey relationships through the Bonneville pool and downstream of Bonneville Dam (PacifiCorp 2005, Korstrom and Birtwell 2006). Because there are listed fish that would be in the Bonneville pool at that time, this has been considered a take by NMFS (2006). After the initial six hours, the White Salmon River would return to a normal flow and make up only approximately 0.6 percent of the Columbia River flow, dramatically reducing suspended sediment concentrations as they mix with the Bonneville pool. After approximately the first week, sustained concentrations in the Columbia River would be at essentially background levels, with brief spikes in concentrations occurring over the first month. Fish may be displaced from an area on the north side of the river downstream of the mouth of the White Salmon River, but migration in the Columbia River should not be impacted (PacifiCorp 2005). Downstream of this area, interference with foraging behavior 4.3-30
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Condit Dam Removal Final SEPA Suppl
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March 23, 2007 Dear interested part
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Condit Dam Hydroelectric Project Fi
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Appendix A Memorandum of Agreement
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Appendix C Supplemental Aquatic Res
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Agency and Organization Letters and
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Contents Public Meetings Response P
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Contents Individuals Individuals A-
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