Abstract
An optimization model is presented in order to allocate irrigation water, which is withdrawn from a river, to paddy field blocks in an irrigation system. A fuzzy linear programming is employed in the model formulation for dealing with uncertainties due to randomness of hydrologic and hydraulic parameters and fuzziness in management goals. In addition to the two objectives on minimization of irrigation water withdrawal from the river and maximization of total rice yield, considered in our last study, minimization of risk of water shortage in each block of paddy fields is taken into account to derive local benefit. Fuzzy sets with appropriate membership functions are defined to mathematically describe vagueness in achievement level of those competing management goals. The minimum-operator is adopted as a fuzzy decision, so that a solution which is adequately balanced among the three goals can be obtained. The model is applied to a hypothetical irrigation district, resulting in clarifying the effectiveness of consideration of water shortage risk in the irrigation water allocation.