407 



Flow augmentation is a controlled release from upstream storage 

 reservoirs in order to speed up water in the lower pools through which the 

 salmon migrate. Flow augmentation in the Snake can only sustain a lower 

 target of 85,000 cubic feet per second in only half of recorded water years. 



In contrast, the proposed drawdowns in the four Lower Snake 

 reservoirs can attain a higher target for water speed (the equivalent flow of 

 140,000 cubic feet per second at full pool) reliably in 96 percent of 

 recorded water years. This target simply exceeds the physical capacity of 

 any flow augmentation regime. In 1990, federal, state, and Tribal biologists 

 stated that salmon require a minimum flow of 140,000 cubic feet per 

 second in the Lower Snake during the peak spring juvenile migration. 



Although untested in full-scale operation, reservoir drawdowns show 

 substantially stronger salmon recoveries in computer projections run by the 

 Northwest Power Planning Council and the Idaho Department of Fish and 

 Game — perhaps as many as 60,000 spring chinook by early in the next 

 century according to the former. TTie drawdowns "work" because, as 

 reservoir elevations drop, the same amount of water volume down the river 

 moves much faster through the manmade pool. 



Impacts from Drawdowns Are Capable of Successful Mitigation 



Drawdowns of the four Lower Snake reservoirs below minimum 

 operating pool during the peak juvenile salmon migration would curtail or 

 completely interrupt operation of fish passage equipment, hydropower 

 generators, irrigation pumps, and navigation locks. However, if the 

 drawdowns are limited to the 10- week peak of the juvenile migration 

 (beginning April 1 with re-fill on or before June 15), these impacts can be 

 successfully and economically mitigated. 



The U.S. Army Corps of Engineers has advanced several designs for 

 dam modifications, principally to adult and juvenile fish by-pass equipment, 

 which would then continue to operate safely during the drawdowns. The 

 two leading design options are a constant pool drawdown at 33-40 feet 

 below normal elevation, and a natural river drawdown with full evacuation of 

 the reservoir. Provided that re-fill begins on or before June 15, all four 

 reservoirs would return to normal elevations within hours in all water years 

 under all drawdown design options. 



Compared to flow augmentation regimes, drawdowns take a much 

 smaller "hit" on firm hydropower generation. Because hydropower 

 generators can continue to run at reduced outputs, because the fuel for 

 hydroelectric generation can remaiin in upstream storage reservoirs, firm 

 energy losses due to drawdowns would not exceed 150 megawatts. Starting 

 in 1991, BPA has signed contracts with California utilities for seasonal 

 electricity exchanges which deliver several times more power than this 



Drawdowns Offer Greatest Promise — Page 3 



