411 



TABLE 1. Reservoir Drawdowns vs. Flow Augmentatioii in the Lower Snake 

 River 



In tabular form, reservoir drawdowns and flow augmentation stack up 

 against each other as follows: 



Drawdown Augmentation Augmentation 



Casel Case2 



now Target 140.000 85.000 140.000 



(cubic feet per second) 

 (Drawdown is equivalent flow at full pool.) 



Firm Hydropower Losses 75 - 1 50 412 2800-4500 



(megawatts) 

 (Sources: Ek;onoinics Technical Team. 



NaUonal Marine Fisheries Service; 



BonneviUe Power Administration) 



Operating Costs 50-112 67-120 153-1169 



(AnnuaJUzed 1990 $ miUion) 

 (Source: Economics Technical Team, 



National Marine Fisheries Service) 



Capital Costs 122.5 



(Annualized 1990 $ miUion) 

 (Sources: Ek;onomics Technical Team. 



National Marine Fisheries Service: 



U.S. Army Corps of Engineers) 



Combined Program Costs 172.5-234.5 67-120 153-1169 



(Annualized 1990 $ million) 

 (Sources: Ek;onomics Technical Team, 



National Marine Fisheries Service: 



U.S. Army Corps of Engineers) 



Probability of Achievement 96 50 



(percent of water years) 

 (Source: U.S. Army Corps of Engineers) 



Compared to flow augmentation at 85,000 cubic feet per second, the 

 reservoir drawdowns achieve the equivalent of 150 percent greater river 

 flows, offer nearly perfect 96 percent reliability, and control costs by 

 emphasizing one-time capital expenditures. Federal, state, and Tribal 

 biologists have concluded that 140,000 cubic feet per second is a minimiun 

 flow target for salmon survival. Due to its relative unreliability, a flow 

 augmentation regime with a target of only 85,000 cubic feet per second 

 would probably serve best as an interim measure until completion of dam 

 modifications. 



Drawdowns Oflfer Greatest Promise — Page 7 



