Comparison of Targeted Replacement and Vegetative Filter Strips for Sediment Control and Cost Effectiveness

Abstract

Two erosion control methods are compared for cost effectiveness in reducing sediment loading into the streams; targeted replacement of agricultural crops and placement of vegetative filter strips (VFS) along field drains. The first method implements an optimization approach for reducing sediment load through targeting and replacement of row crops in sensitive areas with switchgrass, such that watershed income is maximized while maintaining sediment load at a desired level. In the second approach, the soil and water assessment tool (SWAT) was used with simplified grass filter model , a filter strip model, to estimate sediment load. The sediment load predicted for each hydrologic response unit in SWAT was input to a filter strip model which calculates the sediment trapped as flow passes through the filter strip. The study shows that placement of VFS along field drains is more cost effective compared to targeted replacement approach in reducing sediment load. However, the targeted replacement approach renders in situ soil conservation, because it reduces the amount of sediment generated on site compared to placement of VFS along field drains to trap sediment that has already been displaced. Further analysis was made to evaluate the relative benefits of placing vegetative filter strips on selected fields based on the sediment yield. The comparison was made between placing a VFS in all fields and placing VFSs on 75, 50, and 25% of the fields with the greatest sediment loads. It was found to be more effective to place small sized filter strips in as many land units as possible, as opposed to placing larger size VFSs on a few selected fields. It was also found to be slightly more beneficial to vary the width of the VFS in proportion to the size of the field contributing to the sediment inflow. In addition, the relative benefits of harvesting the VFS instead of designating the areas as the Conservation Reserve Program lands was evaluated. It was found that producers could obtain more income from harvesting the VFS than they would earn from water quality incentive payments while maintaining the same level of sediment reduction, resulting in a savings of conservation expenditures.