Groundwater component of the WaterCAST catchment modelling framework

Greater pressure on water resources and the environment as well as the need to better model stream flow constituent generation has led to more interest in low-flow conditions. Rainfall-runoff models have traditionally focused on estimating total stream flows with less emphasis on modelling the groundwater component. There is a need for approaches to be developed which more explicitly consider the impacts of surface water – groundwater interactions on the prediction of stream flow. The WaterCAST model (developed by the eWATER CRC) aims to link changes in catchment management and climatic variability to stream flow quantity and quality within upland catchments and to predict stream flows from unregulated tributaries for subsequent use as input to regulated river management models. This paper describes the development and application of a groundwater module to be used as part of WaterCAST. The groundwater module lumps the water-balance results from multiple 1-D modelling runs (which allows the ability to model land-use changes), explicitly includes variation in groundwater delays across the modelled area, stream losses, and can be calibrated to fit gauged flows. Preliminary work at a monthly time scale gave good results in the Tarcutta catchment (NSW, Australia), providing an excellent match for low flows.