Evaluation of Urbanization and Changes in Land Use on the Water Resources of Mountain Valleys

The impact of projected changes in land use on the aquifer and stream systems of the Big Wood River-Silver Creek area in southern Idaho was evaluated using a finite difference model of the groundwater system. Water budget components were measured for the 1975-76 irrigation season on the 30,000 acre area for calibration of the model. Both water table and confined aquifers were simulated. Simulated groundwater levels and spring flows were determined for several projected changes in land use including canal lining programs, subdivision development, conversion to sprinkler irrigation, groundwater development and for irrigation and artificial recharge. Severe decreases of up to 38 percent in the discharge of Silver Creek, a productive spring fed trout stream, were projected. Groundwater levels in the water table and artesian aquifers could decline up to 16 feet. The most severe impacts will result from conversion of present flood end furrow irrigated land to sprinkler irrigation with attendant decrease in aquifer recharge. The 1977 drought, during which irrigation diversions were only 28% of the 1975 diversions, was simulated and compared with measured data. Reasonable comparisons of simulated and measured groundwater levels and spring flows supports the validity of the model as a planning tool