Vegetative Filter Strip Design for Grassed Areas Treated with Animal Manures

Abstract

Vegetative filter strips (VFS) are a low-cost management option that have been demonstrated to be effective in reducing runoff transport of fertilizer constituents applied to grassed areas (pasture or meadow). Runoff quality studies involving fertilizers applied to grassed areas suggest that VFS can be designed by assuming that (1) only infiltration is responsible for pollutant removal, (2) the first post-application runoff event is most important from a water quality perspective (enabling a design event approach), and (3) no pollutant build-up that degrades VFS performance will occur. The purpose of this study was to develop a VFS design algorithm for grassed areas that uses available information on the water quality dynamics of these systems to simplify the design process to the greatest degree practical. The design algorithm consists of the SCS (1972) Curve Number method for runoff estimation and the Overcash et al. (1981) equation for predicting concentrations of pollutants exiting a VFS as a function of VFS and runoff parameters. The procedure can be used to determine the VFS length required to meet either an allowable pollutant runoff concentration or allowable pollutant mass transport. As an alternative, the process can be used to determine VFS length required to achieve given relative reductions in incoming pollutant runoff concentrations and mass transport. This algorithm can be used quickly and with minimal data to determine the VFS length requirement necessary to provide any desired degree of effectiveness given inputs such as incoming pollutant runoff concentration, background pollutant runoff concentration, soil hydrologic properties, and design storm parameters. Charts are presented that eliminate the need for computations in selected cases.