Optimization of multiple freshwater diversions in well-mixed estuaries

A method is presented to optimize diversions of freshwater from multiple points in a well-mixed estuary. The objective is to prevent salinity concentrations at a point in the brackish water zone from exceeding levels that are stipulated for environmental defense. Optimization is achieved using an efficient gradient-based search algorithm (quasi-Newton with Broyden–Fletcher–Goldfarb–Shanno update). Time-invariant and time-variant diversion rates are considered as control parameters, and time-variant diversion rates are shown to permit larger diversions overall. The latter requires the identification of a vastly larger number of parameters in a more complex parameter space. Computations are carried out using a ID model formulation applied to a series of hypothetical systems and the St. Jones estuary in Delaware.