Dynamic catchment modelling to estimate nitrogen losses in the Toenepi catchment
Dynamic, processed-based integrated catchment models have the ability to simulate the changeable behaviour of complex processes in catchments. Since direct field measurements are rarely available at large-scales, these models help us to better understand hydrological and water quality processes.
NIWA Catchment Modeller Linh Hoang says, “For this study, we applied the Soil and Water Assessment Tool (SWAT), to simulate streamflow and nitrogen exports in the Toenepi River catchment in the Waikato Region.
“The Toenepi catchment is a typical New Zealand dairy farming-dominated catchment and has been used in previous NIWA research projects, including being one of the focus catchments of the Dairy Best Practice Catchment project.”
Model performance evaluation
The modelled results indicated that SWAT can simulate streamflow very well, with both flow magnitude and flow variation accurately predicted at monthly time steps (Figure 1). Modelled estimates of nitrate load and concentration also fit the available monthly observations closely (Figure 2). These results indicate that SWAT adequately represents hydrological and nitrogen processes in the Toenepi catchment.