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GOAL
The Kennewick Irrigation District (KID) and United States Bureau of Reclamation
(USBR) are considering a range of alternatives to reduce diversions of water at
Prosser Dam and thereby increase flows in the lower Yakima River. The key
motivation for this work is the assumption that higher flows will increase
survival of emigrating juvenile salmonids and ultimately increase returns of
adult salmon to the Yakima River.
PROCESS
Cramer Fish Sciences was retained to estimate the effects of flow on emigrating
salmonids and to quantify the potential benefits to salmon of the various flow
alternatives being considered. Using passive integrated transponder (PIT) tag
data from 1998-2004 for spring Chinook, fall Chinook and coho salmon juveniles
emigrating between Prosser Dam and McNary Dam, we developed relationships between
daily survival estimates and flow, temperature, travel time, etc. These
relationships were then combined with historic smolt passage estimates and
results of hydrological modeling to predict the potential increases in smolt
and adult abundances associated with each flow alternative.
RESULTS
Our results showed that flow had a strong effect on Prosser-to-McNary survival
rates for fall Chinook, an intermediate effect for coho, and a minimal effect
for spring Chinook. Commensurate with flow-survival relationships, estimated
increases in smolts surviving to McNary were relatively high for fall Chinook,
intermediate for coho, and minimal for spring Chinook. Although estimates were
uncertain, they provide valuable information for decision makers who must weigh
the costs and benefits of numerous flow alternatives.
KEY OUTCOMES
- Flow has a strong effect on salmonid survival rates
- Survival rates vary for different salmonid species
- Prediction of increases in fish abundances with each flow scenario
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