Combining 'Paddock models' and geographical information systems can be a powerful tool in catchment planning

A gap exists in catchment modelling approaches that can be filled by bio-physical models. We have run bio-physical models for a catchment to describe the water balance and erosion due to the interactions between the soil, vegetation, management and climate for each paddock. The paddock scale results were used in two ways. Firstly, the water balance components and erosion rates were presented as a map and used as a risk assessment tool. Secondly, the runoff, drainage and erosion from each paddock were added together to predict whole catchment stream flow, groundwater recharge and sediment export rate respectively. Stream flow and groundwater recharge were also used as inputs into the 2CSalt model to predict salt export from the sub-catchment. Monthly runoff for the catchment was well described by the models (R2= 0.9). Sediment export rates were not easily tested due to limited observations but bio-physical modelling has proved useful for catchment planners to prioritise erosion management. We see the advantage bio-physical models provide over other methods, is the ability to assess a proposed land use system at the paddock scale (a manageable land unit), while also being able to assess the impact of paddock scale action on the catchment. © HWRS 2006.