OPTIMAL USE OF GROUND AND SURFACE WATER IN THE

Intraseasonal interaction of the ground and surface water system figures prominently in this irrigation-planning study of a river basin. A model for optimizing use of variable streamflows and supplemental groundwater reserves is developed that simultaneously evaluates economic interaction occurring within the ground and surface water system during four discrete periods of the irrigation season. Development of the model encompasses three stages. First, the hydrologic system is analyzed and groundwater discharge is functionally related to water table height in eight hydrologic subareas over four time periods. Second, a nonstochastic model is developed to allocate intraseasonal surface supply and utilize supplemental groundwater subject to interspatial-intertemporal groundwater interactions determined by water table balances in each period. This model is used to compute well investment levels associated with assumed fixed surface supplies and different distribution efficiencies. Third, the probability distribution of annual streamflow is evaluated and the optimal level of well investment (within the class of well developments computed above) is determined for each field efficiency condition with stochastic surface input. Post-optimal analysis, including sensitivity analysis of variable pumping costs, well investment costs