GROUND-WATER TEMPERATURE FLUCTUATIONS AT LYONS FERRY FISH HATCHERY, WASHINGTON

The well field serving the Lyons Ferry Fish Hatchery has experienced reduced water temperatures following continued, periodic withdrawal of large volumes of water. In January 1985, the well field temperature was 49/sup 0/F, which is less than the optimal 52/sup 0/F for raising salmon and steelhead trout. The aquifer supplying the hatchery is in hydraulic and thermal connection with the Snake River and a flooded embayment of the Palouse River. Ground-water temperatures in the well field cycle on an annual basis in response to changes in surface water temperature and pumping rate. Numerical simulation of the well field, using a simplified mixing cell model, demonstrates the coupling of well field hydraulics and aquifer thermal response. Alternative pumping schedules indicate that it is feasible to adjust ground-water pumping to effectively store heat in the aquifer during the summer months when surface water temperatures are elevated. Sensitivity analysis of this model indicated that the primary controls of the system's thermal response are the volume of the aquifer assumed to contribute to the well field and temperature of the overlying surface water body.