Development of a Mathematical Ground Water Model

The development of a mathematical model for study of water management and budget of the irrigated area of the Snake River Fan in eastern Idaho was initiated in May, 1970. The study was initiated to develop alternate management solutions for correcting the problem of increasing high water table problems which has been causing inconvenience and financial hardships to local residents. A more fundamental reason for the study was to develop methods of solving regional groundwater problems. Water levels in wells raise a s much a s 40 feet during the irrigation season to within one - three feet of the surface in some areas. The study area has a dense network of canals with seepage rates averaging 3.5 cubic feet per square foot per day, irrigated soils with high infiltration rates and in some cases inefficient irrigation practices have contributed to t h e f a c t that diversions for irrigation are significant in excess of the state average. In 1970 the net diversion from the Snake River was 16.5 acre feet per irrigated acre and the net irrigation application was 9.6 acre feet per acre for the entire irrigation season. The mathematical model is a digital model and utilizes alternating direction implicit procedures for finite difference solutions to the basic flow equations. A special treatment of a flow boundary is incorporated in the model. Data on water table fluctuation, soils, crop distribution, irrigation diversions, distribution system losses and wastes, evapotranspiration, and irrigation practices were obtained for input to the model. The input data to the model is evaluated in two separate input programs in order to keep the actual program of the model a s general a s possible. An attempt is made to apply the model to the study area