PNNL

Abstract

The Hanford Reach is the only remaining unimpounded reach of the Columbia River in the United States above Bonneville Dam. Discharge in the Hanford Reach is regulated by several dams and is often subject to rapid changes. Sharp flow reductions have led to the stranding or entrapment, and subsequent mortality, of juvenile chinook salmon (Oncorynchus tshawytscha) and other important fish species within the Hanford Reach. A multi-block two-dimensional depth-averaged hydrodynamic model was used to simulate time-varying river velocity and stage in a 37~km portion of the Hanford Reach. Simulation results were used to estimate time-varying juvenile chinook salmon habitat area, and the part of that habitat affected by discharge fluctuations. Affected habitat area estimates were made for the chinook salmon rearing period of four years. These estimates were used, along with other important factors, to establish a statistical relationship between discharge fluctuation and juvenile chinook salmon mortality.