SECTAR for Economically Optimal, Sustained Ground‐Water Yield Planning

Abstract

This paper presents an approach for computing economically optimal sustained yield ground‐water extraction strategies and supportable irrigated crop acreages. Computed regional strategies maximize the present value of net economic return. They are useful for long‐term agricultural planning because they are sustainable even beyond the planning period considered within the economic optimization. The hybrid approach uses only steady‐state flow equations and iterative simulation/optimization to reduce optimization memory requirement below that required by conventional models using both steady and unsteady equations. SECTAR, a quadratic optimization planning model, assumes heads will evolve toward the optimal steady state but initially does not know the nonlinear rates of evolution in each cell. Rates of change in head are assumed, and optimization is performed. Subsequently, a simulation model computes actual time‐varying rates of head change that would result from implementing the optimal strategy. Rates of change assumed in the optimization model are then corrected to correspond to simulated values. The process of assuming, optimizing, and then simulating is repeated. Assumed and simulated heads are very similar within three or four cycles. Convergence occurs because of the common tendency to evolve to steady state. The procedure is applied using data from an unconfined aquifer. Optimal water‐use strategies are fairly stable regardless of initial potentiometric surface and tested aquifer and economic parameters.