Document Type

Report

Publication Date

January 1981

Abstract

The economic well-being of the semiarid intermountain area requires efficent use of available water supplies. Agriculture, the major water-consuming industry, depends on irrigation water. The adoption of sprinkler systems that increase on-farm irrigation "efficiencies" and the area which can be irrigated from upstream diversions may interfere with the "tenure" of downstream water rights. These downstream effects need to be evaluated before allowing farmers to use the water "saved" to irrigate additional acreages or crops to obtain greater profits. The problem in letting farms expand their irrigated acreage is that the individual farmer increases his profits through increased consumptive use. The consequent reduction in return flows reduces the water available to the downstream irrigators and violates the downstream user's proper rights. Water rights administrators have a responsibility to both users. They need to protect downstream water rights. In doing so, the policies should not deny those who install new sprinkler systems the right to any water they really save from wasteful consumptive use (e.g., by weeds or evaporation). A linear programming model was developed to evaluate the effect of changes in irrigation technology on basinwide cropping patterns and hence consumptive use and return flows for downstream users within the Sevier River Basin. Cropping choices were made from inforamtion on field slopes and soil types as represented by land classifications, consumptive use for nine crops, and the characteristics of four on-farm irrigation systems (flood and sprinkler irrigation systems with lined and unlined ditches). In addition, water diversions any available irrigated acreages were constrained to the limits imposed by the State Engineer's Office as a means of protecting property rights. Modern irrigation systems were estimated to be profitable and hence would be adopted with the present acreage and diversion restrictions. Basin output would increase; however, downstream water rights would not be met. With relations of these restrictions, the farm economy would gain even more from the adoption of new irrigation systems. Again, present water rights would not be met. Federal and state cost sharing programs could also aggravate the water rights problem and possibly cause environmental problems by reducing instream flows. The empiracle linear programming model developed to represent the agricultural economy of the Sevier River Basin was able to provide reasonable replication of cropping patterns, wate ruse, and instream flows in the basin. This success generates some confidence in the model's ability to estimate the effects of adaptations of new irrigation technology and various basin water management policies on the bropping decisions made by basin farmers. The estiamtes made by the model provide a valuable tool for equitable water rights administration, but the results would be much improved if refined to incorporate hydrologic routing, hydrosalinity effects, optimal irrigation levels, and year-to-year variation in water availability.