WaterCAST: whole of catchment hydrology model. An overview

Abstract

Sharing of water resources between traditional water users and the environment is becoming increasingly complex due to competion by different sectors of the economy and environment for what is often a diminishing resource and has resulted in the need for a whole-of-catchment modeling approach that can be used to improve the strategic management of water resources. WaterCAST (Water and Contaminant Analysis and Simulation Tool) is a whole of catchment model which has been developed by the eWater CRC in response to this demand. Catchment models are by necessity a compromise between detailed description of processes local scale which are then summed up and description of emergent processes that are manifest at large scales. WaterCAST provides a flexible modelling framework in which the level of detail is dependent upon data availability and the questions that are being asked of the model. Developments to WaterCAST are aimed at improving its capabilities. In particular major developments are occurring to improve the capability of WaterCAST so that is can reliably estimate water, solute and sediment transport in regulated and unregulated catchments. An overview of the structure of WaterCAST and future developments is presented. WaterCAST presently uses a spatial structure consisting of functional units (FUs), sub-catchments, nodes and links. FUs are the smallest spatial unit and are areas of consistent hydrologic response. The sub-catchments are defined usually from a digital elevation models but allow users to refined these subcatchments. Sub-catchments have at least one FU and a node at the bottom through which outputs of water and constituents (solute and sediments). They may also contain a link if other sub-catchments discharge into them. Both surface generated and groundwater are transported to the nodes and filter models can be used to change the delivered volume or time of delivery. The nodes are linked to form a network that ends at the final node at the end of the catchment. The spatial structure is being modified to include a gridded structure within the sub-catchment and future developments will include the concept of area bands within sub-catchments. The hydrology is generated from one of a range of water balance models available and applied at the FU scale. Generation of constituents is modeled using either; event mean concentration and dry weather concentration concepts, corelation between water flow and constituents or observed data. The water, solutes and sediments are transported from the FU's to a node in a sub-catchment via filter functions. Current developments include a new water balance model, stochastic rainfall generation, and more process based sediment generation and nutrient transport models. The model structure is developed on a plug and play basis which allows users to implement their own component models if they wish. The eWater CRC WaterCAST model represents state of the art, software designed for practitioners and researchers to solve real world problems..