Economic Impacts of Irrigation Technologies in the Sevier River Basin

Abstract

The economic well-being of the semiarid inte.rmountain area requires efficient use of available water supplies. Agriculture, the major water-consuming industry, depends on i rr igat ion water. The adoption of sprinkler systems that increase on-farm irrigation eff iciencies and the area which can be irrigated from upstream divers ions 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 farmers 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 spr inkIer 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 consumpt ive use and return flows for downstream users within the Sevier River Basin. Cropping choices were made from information 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 and 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. Wi th relaxat ion of these restr ict ions, 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 empirical linear programming model developed to represent the agricultural economy of the Sevier River Basin was able to provide reasonable replication of cropping patterns, water use, and instream flows in the basin. This success generates some confidence in the model's ability to estimate the effects of adaptations of new irrigat ion technology and various basin water management policies on the cropping decisions made by basin farmers. The estimates 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.