Dynamic agricultural non-point source assessment tool (DANSAT): Model application

The dynamic agricultural non-point source assessment tool (DANSAT) is a distributed-parameter, physically based, and continuous-simulation model for simulating spatial and temporal impacts of best management practices (BMPs) on hydrology and water quality in small agricultural watersheds. Information on the development of the model components was described in a companion paper. In this paper, the results on temporal and spatial evaluation, sensitivity analysis and application of the model are presented. DANSAT was applied to two agricultural watersheds in Virginia to evaluate the capability of model for considering impacts of temporal variations and spatial distribution of agricultural land management on hydrology and sediment. The hydrology component of DANSAT was in reasonable agreement with field results considering both the temporal and spatial variations in stream flow at a watershed scale, while the sediment component showed acceptable agreement only for the watershed where measured stream flow and sediment yield showed better relationships. Minimum adjustment was necessary to consider the internal consistency of sediment yield between sub watersheds. Sensitivity analysis showed that soil parameters such as field capacity and total porosity were sensitive for all selected output variables. Stream flow and sediment yield were commonly sensitive to the subsurface-related parameters and sediment yield was additionally sensitive to the channel-related parameters. Changes in crop rotation influenced both surface and subsurface regimes. Although the differences in total stream flow and recharge were not significant, substantial temporal and spatial variations were detected by the model. The results indicated that DANSAT could be a useful tool for watershed managers who are interested in simulating the effectiveness of spatially and temporally variable BMPs on hydrology and water quality.