147 



Sntkt Rlv*r Spill 



Analysis of Snake River Spill 



Information based on the CRiSP' research project 



James Anderson 

 University of Washington 



The impacts of the 1995 Snake River Spill actions were analyzed with the CRiSP smolt 

 passage model. The CRiSP model considers mortality associated with dam passage and gas bub- 

 ble trauma produced from spill-generated gas supersaturation. In addition, the model considers 

 the effects of fish depth and exposure time on the gas bubble trauma. The model was calibrated 

 with a variety of data sets and model predictions were checked against independent data in a 

 model validation (page 2). 



A model sensitivity analysis indicated that spill can have a small benefit on in-river pas- 

 sage if the total dissolved gas level is below 120% supersaturation. Above this level the mortality 

 from gas bubble trauma is significant. Under the current assumptions on transportation of fish, 

 spill at collector dams has no benefit since the survival of transported fish is larger than the sur- 

 vival of fish passing in-river (page 3). 



The 1995 spill actions and monitoring studies were analyzed with CRiSP. The model pro- 

 duced levels of mortality similar to those observed in the cage studies below Ice Harbor dam. The 

 model indicated that survival between Ice Harbor Dam tailrace and Bonneville Dam trailrace was 

 between 31 and 34% depending on the depth of fish passing through the river. In comparison, 

 with no spUl the predicted in-river survival was 35% (page 4). 



Monitoring of fish passing in-river has revealed few signs of gas bubble trauma and the 

 CRiSP modeling has likewise predicted little impact. Furthermore, model analysis indicates that 

 the small increase in dam survival resulting from the spill program was negated by a small 

 increase in mortality from gas bubble trauma. Uncertainty exists as to the precise levels of the fac- 

 tors, but given the available information the result of the spring 1995 spill program was most 

 likely small and negative. 



1. The University of Washington has developed the Columbia River Salmon Passage model 

 under funding by Bonneville Power Administration, The project began in 1989. 



2. Dr. James J. Anderson is an Associate Professor in the School of Fisheries and Center for 

 Quantitative Science at the University of Washington. His work on salmon issues has been 

 funded by Bonneville Power Administration and the Army Corps of Engineers. The views 

 in this document are a result of that research. This paper was supponed by the Direct 

 Service Industries, Inc. 



Ja/^M Anderson 



Un»v*rvty 01 Wa&^u^glon 



A,"* 22. 199S 



