Simulation/Optimization Modeling for Water Resources Management

Many important advances have been made in the development of mathematical models for conjunctive water management and reservoir management. However, the conjunctive use models that have detailed stream/aquifer system interactions have not considered reservoir management rules. Conversely, reservoir management models have not simulated stream/aquifer interactions in detail. There is a need for enhanced linking of reservoir and stream/aquifer systems in conjunctive water management models. This paper presents a simulation/optimization model that integrates linear reservoir decision rules, detailed simulations of stream/aquifer system flows, conjunctive use of surface and ground water, and delivery via branching canals to water users. The linear decision rule is an example of a rule that has been widely discussed in reservoir operation literature and is simple to program. State variables, including aquifer hydraulic head, streamflow, and surface water/aquifer interflow, are represented through discretized convolution integrals and influence coefficients. Reservoir storage and branching canal flows and interflows are represented using embedded continuity equations. Results of model application to a hypothetical study area under several scenarios indicate that the more detail used to represent the physical system, the better the conjunctive management. The most detailed representation provides 13% more water than the least detailed system.