Development of a transient ground-water model for the Twin Falls area, Idaho. Research technical completion report

The City of Twin Falls, Idaho, located in south central Idaho along the south side of the Snake River, is rapidly outgrowing its current municipal water supply. The city is experiencing the greatest growth of any city in Idaho, with an estimated annual growth rate of 2.5 percent. Water supply and water quality are of great concern to the city water department and city planners. To plan for future needs, the City of Twin Falls contracted with the Idaho Water Resources Research Institute of the University of Idaho to design and implement a numerical ground-water flow model. The model is intended to represent the current hydrological conditions of the city and to be used as a planning tool to assist in predicting the impact of projected growth and changes in local water use. The study was done in two phases. Phase 1 was the design, implementation, calibration and verification of a steady state numerical ground-water flow model for the Twin Falls area (Cosgrove et al., 1997). Phase 2 included conversion of the numerical model to a transient model to be used for growth projections and future planning. This report covers the work done in Phase 2