DEVELOPMENT AND TESTING OF A MODEL FOR DETERMINING OPTIMAL PUMPING AND RECHARGE OF LARGE-SCALE AQUIFERS.

A methodology is developed for determining optimal pumping and recharge of large scale artesian and/or nonartesian aquifers. This methodology couples optimization techniques with existing groundwater simulation models. It can be applied to both groundwater policy evaluation (allocation) such as large-scale aquifers and to hydraulic management problems such as the dewatering of mining or excavation sites. The state variables which represent the heads, and the control variables which represent the pumpages, are implicitly related through the groundwater simulator. The simulator equations are used to express the states in terms of the controls, yielding a much smaller reduced problem. Techniques for computing gradients of reduced problem functions are described. The reduced problem is solved by combining augmented Lagrangian and reduced gradient procedures. The two models coupled are the University of Texas generalized reduced gradient code GRG2 and the Texas Department of Water Resources groundwater simulation model GWSIM. The overall model is referred to as GWMAN.