Publication Summary

The Washington State Department of Ecology used the steady-state QUAL2E model to evaluate potential water quality changes from proposed operational changes by the U.S. Bureau of Reclamation at the Chandler Canal and Columbia Canal diversions. The study area for this modeling project encompassed the lower 47 miles of the Yakima River, downstream of Prosser. The proposed operational changes are part of the USBR Columbia River Pump Exchange Project. Two synoptic surveys were conducted by Ecology, in September 1999 and July 2000, to assess water quality characteristics during the summer low-flow season. The water quality data from these surveys were used to calibrate and confirm the QUAL2E model.

The Washington State Department of Ecology used the steady-state QUAL2E model to evaluate potential water quality changes from proposed operational changes by the U.S. Bureau of Reclamation (USBR) at the Chandler Canal and Columbia Canal diversions. The study area for this modeling project encompassed the lower 47 miles of the Yakima River, downstream of Prosser. The proposed operational changes are part of the USBR Columbia River Pump Exchange Project. Two synoptic surveys were conducted by Ecology, in September 1999 and July 2000, to assess water quality characteristics during the summer low-flow season. The water quality data from these surveys were used to calibrate and confirm the QUAL2E model.

Poor upstream water quality was concluded to be the foremost determinant of water quality conditions in the last 47 miles of the lower Yakima River evaluated in this study. Changes in operational flows at Chandler Canal cannot overcome the water quality degradation occurring upstream. The QUAL2E model mainly predicted some dilution effects on water quality parameters due to increased water volumes associated with the operational changes. Reduced settling of chlorophyll a and total suspended solids was also predicted due to increased velocities of flows. These effects were especially apparent in the Prosser Dam to Chandler Return reach. The proposed operational change at Columbia Canal diversion is predicted to have no noticeable impact on water quality conditions downstream of that diversion.

Compared to current conditions, the operational changes were predicted to decrease mean daily water temperatures by less than a 0.5 degrees F in any reach and dissolved oxygen (DO) concentrations by less than 0.1 mg/L within any reach. Chlorophyll a levels throughout the study area were predicted to increase slightly from current conditions with each operational-change scenario. The Washington State temperature and DO criteria would continue to be violated because of elevated water temperatures and algae/periphyton productivity. Upstream boundary conditions would determine both the temperature and productivity regimes within the whole study area.

Link to EIM data for User Study ID CARR0001