In this study, general characteristics of dynamic behavior of stormwater runoff from a small impervious catchment
was investigated from a series of simulations for a radial type surface runoff. Based on the simulation results, a better
placement strategy for stormwater inlets to improve performance of a structural best management practice (BMP) was
suggested. The degree of pollutant first flush from an ideal radial type impervious catchment was simulated using a
1-D diffusion wave equation coupled with a pollutant transport equation. The results showed that the first flush of
the chemical oxygen demand was the strongest when the catchment length ranged 30-50m at a bed slope of 0.02.
This result suggested that a required degree of the first flush can be intentionally obtained by just changing the
locations and numbers of stormwater inlets, and thereby adjusting the catchment length. Particularly, the overall
performance of a structural BMP in reducing pollutant load can be improved by placing the stormwater inlets at
locations for obtaining a required first flush strength.