Modeling hydrology and nitrogen export for the Thomas Brook Watershed with SWAT

Water resources planning and improvement can be potentially aided with the use of simulation models. However, prior to the model application, the model performance and reliability must be tested with measured data. The Soil and Water Assessment Tool (SWAT) is a widely used watershed simulation model tJ1at can simulate the impact of land use changes on flow and water quality. SWAT-2005 was used to model stream flow, sediment and nitrogen loads from the Thomas Brook Watershed, which drains a 7.84 km2 rural landscape in the Annapolis Valley of Nova Scotia, Canada. The developed SWAT model was comprised of 28 subbasins and 264 hydrologic response units, most of them containing agricultural land uses, which is the main non-point nitrogen source in the watershed. Crop rotation schedules were incorporated into the model using field data collected within Agriculture and Agri-food Canada's WEBs program. Model sensitivity analysis was conducted and parameters sensitive to model hydrology, sediment and nitrogen were identified. SWAT calibration (May-2004 - Dec-2006) and validation (2007-2008) was performed by using continuous stream flow, sediment and nitrogen export measurements at Station-4 within the watershed and meteorological data from Environment Canada's Greenwood weather station, located in close proximity to the watershed. Model performance was evaluated using the coefficient of determination (R 2) and Nash-Sutcliff efficiency (NSE). Study results show that the model performance was satisfactory (R2 > 0.5 and NSE > 0.4) for stream flow, sediment, nitrate-nitrogen (NO3-N), and total nitrogen (TN) simulations, with very good stream flow calibration statistics. This evaluation of SWAT demonstrated that the model has potential to be used as a decision support tool for agricultural watershed management in Nova Scotia.