A Model for the Conjunctive Management of Groundwater and Mains Supply in the Botany Area, Sydney

Urban water users within the Botany Area of Sydney have access to groundwater, mains and surface supplies. Strategies are developed in this study for the conjunctive management of water demand and these supply sources. The modelling system GAMS is used to create an optimisation model that incorporates water demand equations, cost functions and a simulation of the aquifer response. The objective is to minimise costs to the consumers while fulfilling environmental, capacity and demand constraints of the system. Water demand is forecasted for the next 20 years for various scenarios of demand management. Physical constraints are used to internalize the externalities of groundwater use involving wetland degradation, groundwater pollution and water logging. The model demonstrates that the current pattern of groundwater use differs from the optimal distribution. Other results indicate the control of both wetland depletion and flooding are critical constraints in the management of the groundwater system and that demand management influences the costs of these and other constraints. Conjunctive management of the system is shown to be more efficient than the current practice of separate management of the water resources of the area.