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 surface s, especially highways and agricultural lands. The Virginia experiments tes ted 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 d esign parameters as length, longitudinal slope, and the presence of check d arns. Minimum design guidelines for use of swales as a BMP are suggested.