Irrigation planning: 4. Optimal interseasonal water allocation

A series of models has been developed in previous papers to estimate the best sized area to develop for irrigation from a given reservoir under conditions of variable supply and demand for irrigation water. The best operating policies for such a system were also derived. The approach of this paper extends the previous approach by recognizing the value of water carried over from one season to the next. A modified version of the previous approach is used to generate reservoir level transition probabilities and expected benefits. A dynamic programing model is then used to estimate the expected benefits from allocating water optimally between seasons. These expected benefits are a function of acreage developed for irrigation and beginning-season reservoir levels. Such a function allows a decision maker at any decision point within an irrigation season to equate the expected net benefits from allocating water to the rest of the current season with the expected net benefits from saving such water for the following season. This decision-making process is simulated for a number of seasons. The results of an application of the models indicate that such interseasonal transfer can considerably increase the present value of expected benefits from the project.