| Recent developments in GIS interfaces have greatly improved hydrologic water quality modeling; larger watersheds can accurately be assessed at higher spatial resolutions for prioritizing site-specific areas where best management practices, such as vegetative filter strips, would be most effective. In this study, the AGNPS model in conjunction with the AGNPS GIS interface was used to prioritize locations of vegetative filter strip effectiveness within areas of a 45,000 ha (111,000 ac) agricultural watershed located in mid Michigan. Vegetative filter strips alone were found to be relatively inefficient (<25%) especially in areas where concentrated flow occurs (drainage area > 4 ha or 10 ac), which are areas of primary concern in terms of sediment load. Therefore conservation efforts should focus on reducing sediment load in areas of concentrated flow.; In addition, an unconditional stochastic simulation was preformed to identify the uncertainty in the AGNPS model due to errors in 30 m USGS DEM. Comparing the AGNPS sediment yield at the outlet of a 107 ha (264 ac) watershed when using 30 m USGS DEM and 10 m simulated elevation data resulted in a 37% decrease. However, the analysis also identified that change in cell size (from 30 m to 10 m) reduces the sediment load by 41%. These uncertainties are profoundly affecting the AGNPS estimates of sediment yield, which may dramatically influence the analysis of prioritizing conservation practices within watersheds. |
