Complementary water quality modelling to support natural resource management decision making in Australia

Identifying sources and pathways of pollutants moving through catchments is a prerequisite for effectively targeting on-ground works to improve water quality. Simulation models are an important tool in this regard to: (i) Understand current catchment conditions including locating critical pollutant source areas, quantifying nutrient and sediment loads, determining delivery mechanism and elucidating cause-effect relationships. (ii) Summarise current knowledge into conceptual models of catchment function and system responses. (iii) Identify priority areas for intervention and assessing their likely impacts and cost-effectiveness. A large number of hydrologic, nutrient and sediment models exist for research and natural resource management support. In terms of complexity, the choice of the model determines the demand for input data and calibration parameters and the spatio-temporal resolution of the simulation. All these factors influence the extent to which models provide useful information to support decision makers. Model comparisons often lead to debates about which model is better, rather than the more constructive approach of applying different models for different purposes to improve understanding or predictive capacity. In this paper we investigate how three different water quality models, WaterCAST, CatchMODS and JAMS, could potentially complement one another to inform water quality management. The strengths, weaknesses and suitability of each model is discussed in the context of regional environmental investment planning within the Cradle Coast Natural Resource Management (NRM) region of north western Tasmania, a process typical of that being applied within Australia's 56 NRM regions. We suggest that the models potentially compliment one another in the following ways: (i) WaterCAST and CatchMODS are appropriate for carrying out rapid estimations of sediment and nutrient loads at subcatchment and catchment scales, (ii) JAMS is most appropriate for developing a conceptual understanding of hydrologic and solute processes and mapping critical pollutant source areas in space and time, (iii) JAMS is the most appropriate for developing and evaluating nutrient-based management interventions (iv) CatchMODS and JAMS together can be used to plan management interventions and evaluate the cost-effectiveness of different scenarios. Further work will demonstrate the practicability of this approach for a selected case study in North West Tasmania.