A feedback method of control has been used to develop a model for optimal determination of freshwater inflow to bays and estuaries. A modification of the feedback method of control was implemented which makes the technique applicable to certain constrained optimal control problems. The modified feedback model for estuary management consists of a hydrodynamic-transport salinity model, HYD-SAL, coupled to a dynamic programming optimization model. The constraints of the model are the monthly freshwater inflows and the salinities. A quadratic criterion representing a weighted sum of squared deviations from target salinity and freshwater level is chosen as the objective function. The constrained optimal control algorithm employs a penalty function that uses a similar quadratic criterion as the objective function. This algorithm has performed efficiently for computing the optimal freshwater inflows into the Lavaca-Tres Palacios Estuary in Texas while satisfying the freshwater requirements for other components in the system. Copyright Kluwer Academic Publishers 1999
