Multi-year optimal management of quantities and salinities in water supply systems

A seasonal multi-year model for management of water quantities and salinity in water supply systems has been developed; the Water Supply System (WSS) has sources (aquifers, reservoirs and desalination plants), a conveyance system (distribution network) and consumers (demand zones) who require certain quantities of water under specified salinity constraints. The objective is to operate the system with minimum multi-year total cost under technological, administrative and environmental constraints. The cost and the constraints of each year consist of seasonal desalination, pumping, delivery and an extraction levy from the aquifers. The objective function and some of the constraints in the model are nonlinear, leading to a nonlinear optimization problem which is solved efficiently by adapting a set of manipulations that reduce model size and a compact finite difference scheme for calculating the derivatives required by the optimization algorithm, termed Time-Chained-Method (TCM).