Field test of grassed-swale performance in removing runoff pollution

The paper presents results of field tests, conducted in Taiwan and Virginia, of the pollutant removal efficiencies of grassed swales. Swales are a low-cost storm-water best management practice (BMP) that have been reported as a cost-effective method for controlling runoff pollution from land surfaces, especially highways and agricultural lands. The Virginia experiments tested a highway median swale, while the Taiwan experiments were conducted on an agricultural test farm. Average pollutant removal efficiencies reported for the test swales vary front 14 to 99% for total suspended solids;(TSS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The wide range of performance results indicates the importance of such design parameters as length, longitudinal slope, and the presence of check darns. Minimum design guidelines for use of swales as a BMP are suggested.