The Catchment Analysis Tool: Demonstrating the Benefits of Interconnected Biophysical Models

Abstract

The Catchment Analysis Tool (CAT) is a hydrological model that helps to define the surface and subsurface movement of water and nutrients in a catchment, and evaluate the impact of different farming systems and land management strategies on vegetative growth and productivity, stream quality, streamflows and groundwater. It was created in response to a growing desire by decision makers to be able to examine modified landscapes and look at the trade-offs in biophysical responses such as, crop yield, soil erosion, salinity and water dynamics.

The CAT captures the hydrological dynamics of the whole landscape by combining a suite of mature models that individually describe a variety of landscape processes such as crop growth, forest growth, grazing systems, water balance and groundwater models. The basic spatial and temporal input data required to run the CAT are generally commensurate with available data. These include land use, elevation, soil characteristics and climate data. Detailed analysis of groundwater systems and watertable mapping requires a full geophysical conceptualisation of the underlying groundwater systems and an extensive calibration process based on statistical optimisation, expert consultation, and modification of underlying assumptions about the groundwater systems being modelled.

At the catchment scale there are very few points in the landscape where relevant data are measured and captured, and as such, validation of the CAT remains challenging. Where possible modelled results are validated against data captured from stream gauges, bore data and point studies. This chapter describes the CAT,discusses briefly the individual components and their linkages, and provides a case study example of how the CAT can be used to inform a policy decision. A discussion of the weaknesses and difficulties inherent in the creation of such integrative modelling frameworks is also presented.