Effect of rainfall characteristics on removal efficiency evaluation in vegetative filter strips

The efficiency of a facility to remove non-point source pollution is likely to fluctuate according to conditions such as facility type and rainfall events; therefore, it is required to use a proper method to estimate removal efficiency. This study was conducted to estimate the efficiency of a facility with vegetative filter strips to remove pollutants by using methods previously used for the estimation of removal efficiency and compensate for weaknesses of the known methods. Other ways were presented to estimate an efficiency by which rainfall events were classified according to meteorological condition and amount of rainfall. Rainfall of frequency and summation of load as rainfall of frequency, where the frequencies per rainfall class were considered in efficiency ratio and summation of loads, respectively, seemed to have higher removal efficiencies than those estimated with the previous methods. Although it rained at the basin site, often in small quantity (below 10 mm), the rainfall events of below 10 mm were less frequent, during the monitored rainfall events, which accordingly resulted in low removal efficiencies. However, if the frequencies per rainfall class were considered, overall removal efficiencies of VFS might be increased because the removal efficiencies of the rainfall class under 10 mm was higher than other rainfall classes. Therefore, it is desirable to take into account such factors as effects of rainfall when it comes to measuring the removal efficiency of a non-point source pollutant of a factor, because those facilities are likely to be influenced by meteorological conditions including rainfall characteristics.