Maximizing Reliable Crop Production in a Dynamic Stream/Aquifer System

Aprocedure for planning the optimal spatial distri-bution of crops to be reliably irrigated by conjunctive use of water resources is presented. The implicitly stochastic procedure utilizes a simulation/optimization model of a stream/aquifer system. The model utilizes linear optimization, hydrologic influence coefficients and time-varying crop water production functions. It appropriately simulates the time variant, interdependent responses of groundwater levels, stream stages and stream/aquifer interflow to groundwater pumping and diversion of river water to nonriparian lands. It determines the temporally and spatially varying distribution of groundwater and diverted river water that should be utilized in order to maximize annual crop yield in a water management district. The diversion of river water to nonriparian land and stream/aquifer interflow are constrained such that effluent from the district through the river satisfies downstream requirements. The model can be used to develop optimal seasonal water use strategies that are in harmony with long-term water use and agricultural development strategies. In that case it represents a suboptimization model applicable for either a period of regional potentiometric surface evolution or a steady-state era. If applied during an era in which the potentiometric surface is maintained at relatively constant elevations, groundwater pumping and recharge are managed such that groundwater levels return to their initial elevations by the end of a one-year simulation period. Thus, if the initial elevations are satisfactory, the optimal strategy is a safe sustained yield conjunctive water management strategy