Stochastic reservoir management and system design for irrigation

An integrated intraseasonal and interseasonal stochastic dynamic programing model is developed to determine an optimal decision rule with respect to the following three classes of crop irrigation decisions: (1) intertemporal water application rates, (2) whether or not some acreage should be ‘abandoned’ from further irrigations for the remainder of the season, and (3) the optimal acreage to plant for potential irrigation at the beginning of the season. Solutions of the problem are shown to be a basis for optimizing the levels of three design variables, namely, developed irrigation acreage, reservoir capacity, and distribution system capacity. A method is presented for incorporating variance, as well as expected value, of net benefits into the decision criterion for optimal developed acreage. An application is made to a simplified real situation in which optimal acreage to develop is the only design variable. State variable transition probabilities are calculated by a simulation model. A significant trade off was found between expected net benefits and their variability in determination of the optimal developed acreage for irrigation.