Abstract
This study was to estimate the reduction effect of nonpoint source pollutants according to the rainfall intensity and drainage of infiltration grate inlet. Soil infiltration flow was measured on-site and SS load by the filter part was calculated by the experimental data in laboratory reactor test. Soil infiltration flow was measured to be about $1m^3/hr$ in soil condition saturated with water. The filter part of the infiltration grate inlet was a hydraulic equipment unhindered by soil infiltration on the bottom of the storage tank, because the infiltration flow was measured to be about $3m^3/hr$ continuously in the closing infiltration hole condition. Infiltration flow and SS load were over about $1m^3/hr$ and 1.71 kg according to laboratory results by the filter part using the artifical sample. Therefore, the above values could be presented as the limitted value to start the reduction of filtration effect. Reduction efficiencies of SS load by the filter part for the rainfall intensity were about 87 % at 5 mm/hr and about 61 % at 10 mm/hr in consideration of one infiltration grate inlet got the drainage area about $200m^2$. The reduction efficiency of nonpoint source pollutants was very effective in the first flush rainfall. However, the reduction efficiency by rainfall density was higher than by flow.
