A canal irrigation water allocation model.

Abstract

A water allocation model was developed to assist with allocation of canal water to competing crop irrigation demands. Multi-period linear programming was utilized to optimally allocate water in both time and space to maximize benefits for an irrigated farm. Irrigation scheduling, crop response and canal water delivery models were used to support the water allocation decisions. The irrigation scheduling model supplied information on crop evapotranspiration and soil water storage. The crop response model predicted crop yield in response to the irrigation water applications. The canal delivery model checked the feasibility of supplying the allocation quantities through the control structures and turnouts. The allocation model was evaluated by tests of water allocation for the University of Arizona, Maricopa Agricultural Center demonstration farm. In crop scenarios which emphasized cotton production, the model recommended deficit irrigation for the barley, cotton, grapes and wheat fields during periods when the quantity of irrigation water demanded was greater than that supplied. Analysis of the effects of changes in water cost and crop returns showed the basis of the solution remained unchanged for a wide range of data. The basis was, however, found to be unstable with very limited water supplies. In addition to serving as a planning tool, the allocation model could be used as a real time management tool. It is believed to have broad applicability to other irrigation projects in other areas with characteristics similar to Arizona test conditions.