Development and testing of watershed-scale models for poorly drained soils
Watershed-scale hydrology and water quality models were used to evaluate the crrmulative impacts of land use and management practices on dowrzstream hydrology and nitrogen loading of poorly drained watersheds. Field-scale hydrology and nutrient dyyrutmics are predicted by DRAINMOD in both models. In the first model (DRAINMOD-DUFLOW), field-scale predictions are coupled to the canavstream routing and in-stream water quality model DUFLOW; which handles Jow routing and nutrient transport and transfornation in the drainage canaustream network. In the second model (DRAINMOD-W), DRAINMOD was integrated with a new one-dimensional canal and water quality model. The hydrology and hydraulic routing components ofthe models were tested using data from a 2950 ha drained managedforest watershed in the coastal plain of eastern North Carolina. Both models simulated the hydrology and nitrate-nitrogen (NO3-N) loading ofthe watershed acceptably. Simulated outflows and N03-N loads at the outlet ofthe watershed were in good agreement with the temporal trend for five years of observed data. Over a five-year period, total outfow was within 1% of the measured value. Similarly, NO3-N load predictions were within 1% of the measured load. Predictions of the two models were not statistically difierent at the 5% level of significance.