ESTUARY MANAGEMENT BY STOCHASTIC LINEAR-QUADRATIC OPTIMAL-CONTROL

A new type of estuary-management model based on discrete-time stochast ic linear quadratic optimal control is presented. It is a feedback-con trol model that enables decision makers to determine the upstream rese rvoir releases during a time interval after the salinity and nutrient levels are observed at specified locations in the estuary at the begin ning of the time interval. The optimal upstream reservoir releases are determined so that the salinity and nutrient levels at these location s are as dose as possible to the prescribed levels for the remaining t ime intervals in the sense of statistical expectation. The ungauged in flows, precipitation, and evaporation are incorporated into the model as random variables. The control vector for the estuarine system consi sts of the freshwater inflows into the estuary, and the state vector c ontains the salinity and nutrient levels at specified locations for me asurement in the estuary. The dynamic-programming principle is used to analytically derive the feedback-control law that expresses the contr ol vector as a linear function of the state vector. The parameter matr ix in the system equation is recursively updated by recursive least sq uares. Numerical examples are performed for the Lavaca-Tres Palacios E stuary in Texas for the purposes of illustrating the viability of this methodology.