Results of Simulated Temperature Control Device Operations on In-Reservoir and Discharge Water Temperatures Using CE-QUAL-W2

Abstract

ABSTRACT A computer model of the operation of the Shasta Lake temperature control device (TCD) confirms the device's ability to maximize power production and simultaneously reduce summer discharge water temperatures. The TCD's in-reservoir thermal effects were consistent for a wide range of hydrologic conditions. Changes in the thermal structure were most pronounced in the hypolimnion, where summer water temperatures were about 1°C cooler, but up to 5°C warmer in the late fall compared to without-TCD conditions. Epilimnetic effects of the TCD were negligible, with mean temperature differences between with- and without-TCD conditions in the top 20 meters of the reservoir of less than 0.5°C throughout die year. The zone of impact of the TCD was unexpectedly large; in-reservoir temperature changes were seen up to 20 km upstream of the dam in all three major branches. However, in-reservoir temperature changes did not carry over into subsequent years with continued TCD use. Discharge temperature targets were not met by simple, month-to-month changes in selective withdrawal elevations, but more complex TCD operational schemes did provide the required outlet temperatures throughout me year. This more complex operation involved mixing waters from multiple shutter outlets and varying the mix daily. The application of bioenergetics equations to the temperature output from CE-QUAL-W2 indicates that TCD operations may not have significant direct effects on water temperature-driven scope for growth of rainbow trout and smallmouth bass in the reservoir.