Digital model simulation of the hydrologic flow system, with emphasis on ground water in Spokane Valley, Washington and Idaho

A digital-computer model of the hydrologic flow system, with emphasis on ground water, was developed for Spokane Valley, Washington and Idaho. The current rate of ground-water pumping in Spokane Valley has little effect on water levels in the Spokane aquifer, although short-term water-level declines occur locally. The model was used to show the effects of increased ground-water pumpage on aquifer heads and streamflow. A simulated pumping rate twice that of actual 1977 pumping rates of 227 cubic feet per second lowered water levels in the Spokane aquifer less than 3 feet during a 1-year simulation period. This doubling of the ground water pumpage caused a decrease in discharge of the Spokane River, as measured at Spokane, of about 150 cubic feet per second during the summer months and about 50 cubic feet per second during the rest of the year. Leakage from the aquifer to the Little Spokane River was decreased by less than 10 cubic feet per second.