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The Effect of Lower Snake Reservoir Drawdown 

 on Barge Transportation: Some Observations 



Joel R. Hamilton, tJniversity of Idaho 



Michael Martin, Oregon State University 



Ken Casavant, Washington State University 



Among the key problems faced by Columbia and Snake River salmon 

 stocks are the difficulties juveniles face in migrating to the ocean through 

 slackwater pools behind the series of dams on the lower river. Because the fish 

 depend at least in part on water flow for direction, they may become disoriented 

 and spend too long in the slackwater pools. This exposes them to predation and 

 throws off the critical timing of their biological adjustment to saltwater. 



Two possible ways to address this problem are to augment river flow or drop 

 reservoir levels during the critical migration period. Either approach aims to 

 boost the velocity of water moving down the river. Augmentation would do it by 

 identifying an increased "budget" of water to sluice through the slackwater pools. 

 Drawdown would do it by dropping the river profdc, reducing the cross sectional 

 area of the pools so that a given water flow produces more velocity. 



Biological data on the relationship of velocity to juvenile salmon survival 

 is limited, but it suggests that survival is bener in years when flows approached 

 140 kefs at the Lower Granite Dam. AXliile this a reasonable target flow from 

 a biological perspective, this target is rarely met, and it would be physically, 

 economically and politically very difficult to obtain the water needed to augment 

 flows ro this level in dry years. For this reason, most proposals that rely on 

 flow augmentation with a water budget use a more modest but biologically 

 less satisfactory 85 kefs target flow. Unfortunately, current proposals for flow 

 augmentation, such as those contained in the "Draft Flow EIS" by the US Army 

 Corps of Engineers (reference 4), have not shown where enough water could be 

 found to meet even the 85 kefs flow target in all years. 



Vv ith the reservoirs drawn down below minimum operating pool level, 

 river velocities equivalent to full pool velocities at 85 kefs or even 140 kefs can be 

 attained within the present water budget (see the Corps Draft EIS, reference 4). 

 However such a drawdown would affect barge transportation on the Lower 

 Snake. In recent years, the river has become a major avenue for shipping 

 agricultural and forest products downstream, and shipping fertilizer, fuel and 

 manufactured goods upstream. (See reference 3, the "Henry repon" to the 

 Idaho Governor's Office, which describes the scope and nature of the existing 

 barge transportation system.) 



