A model is developed for the optimal operation of the releases from a reservoir which are used to irrigate an area in an arid environment. The operation is based on a forecast technique. The forecast consists of expected values based on the application of Dynamic Programming Technique as well as on the use of generated inflows. The generation model for rivers in arid areas consists of three components. The first determines if the following year will be dry or wet. The second generates a sequence of days in which a flow may occur, and the third calculates the magnitude of such a flow. The third component depends directly on the first. The optimization problem has two state variables and one decision variable, and is solved by Dynamic Programming. The state variables are the reservoir content and the soil moisture of the irrigation area. The decision variable is that quantity of water which should be applied to irrigation. Because of the rapidly changing inflow process the model has to provide "adequate" representation of the evaporation losses which are calculated on a daily basis. The optimal scheduling process is non-stationary because of the continuing reservoir sedimentation which gradually decreases the reservoir volume.