Modelling for Optimal Conjunctive Water Management: Irrigated Crop Production Versus NPS Pollution Prevention

Conjunctive water managernent{CWM)involves coordinating use of ground and surface water sources. Agricultural (A) and nonagricultural {NA)users compete for available water of adequate quality. A Simulation/Optimization (S/0) conjunctive water management model was developed to aid estimating the effects of water and environmental management decisions on crop yield and water quality. Included subsystems are groundwater, surface water, reservoir, delivery system, drainage, and A and NA water users. The nonlinear model addresses flows described by nonsrnooth piecewise-linear functions which have discontinuous derivatives. Embedded constraints describe all significant subsystem flows. For example 1 deep percolation and runoff from surface irrigation are explicitly described as functions of furrow inflow rate. Solution involves quasilinearization and cycling. We apply the model to a study area representative of part of Salt Lake Valley 1 Utah. We use the Econstraint method to maximize irrigated crop production subject to constraint on leaching to groundwater. Tested scenarios demonstrate model capabilities for transient management. INTRODUCTION Government agencies seek to assure the long-term availability of sufficient water of adequate quality. They commonly use simulation models (termed S models here) to predict the consequences of implementing different water management strategies. To compute management strategies they are also using more models that couple simulation with optimization algorithms (S/0 models) . Most models presented in the literature are somewhat specialized in applicability. There is a need for models that incorporate all significant flow processes and are broadly applicable. Water for irrigated agriculture (A) and nonagricultural (NA or municipal and industrial) use is obtained from groundwater and/or surface water sources. In return, water quality is frequently degraded by use. For example 1 fertilizers and pesticides are common nonpoint source (NPS) pollutants. NPS pollution often results in response to rainfall and irrigation when chemicals 1 Ingenio Providencia S.A., P.O. Box 224, Palmira, Valle, Colombia 2 Biological and Irrigation Engineering Department, Utah State University, Logan, Utah 843224105 30DRCP162.PAP, 29 November 94