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SNAKE RIVER RESERVOIR DRAWDOWNS 

 ENVIRONMENTAL AND ECONOMIC IMPACTS 



Proposals to drawdown the Snake River Reservoirs to near 

 spillway crest operations are currently being reviewed. If 

 enacted, the Snake River Reservoir drawdowns would lead to 

 significant environmental and economic impacts, with great 

 uncertainty for gaining any weak stock salmon benefits. 



Estimated biological benefits of drawdowns: 



— Under low flow conditions, researchers with the University 

 of Washington, the Northwest Power Planning Coimcil, and 

 the Northwest Irrigation Utilities all concluded that any 

 conceivable benefits from a drawdown would be less than the 

 fish benefits derived from the exsiting smolt transportation 

 program. 



- Researchers caution that a drawdown would likely incur several 

 critical problems: 



• High rates of predator concentrations affecting 

 reservoir passage. 



• Decreased fish guindance efficiency for turbine passage. 

 " High levels of gas super-saturation. 



• Latent smolt mortality below Bonneville Dam due to the 

 the effects of cumulative project passage. 



• Additional stress for adult return migrations and project 

 passage. 



-- These critical problems make drawdowns a high-risk, low- 

 biological benefit option. 



Estimated Enviroimiental Impacts: 



~ A drawdown would have significant impacts to existing wetlands 

 and natural habitat, and to resident fish and wildlife. 



Estimated Economic Costs: 



— Economic costs would be borne by: hydropower, irrigated 

 agriculture, river commerce and navigation, recreation, and 

 local communides. 



- The capital costs for project modificatioiis would likely be in 

 the $2-5 billion range. 



~ A lower range estimate of the annual direct net costs to the 

 region would about $175 million. 



Implementing a Drawdown Action: 



~ It would take several years to implement a Snake River 



Reservoir drawdown. Army Corps of Engineer estimates range 

 from seven to fourteen years for project modifications. 



Dau Soorces: Army Corps of Engineen 

 NMFS EeonoaiGi Comminee. NIU, PNUCC 



