Estimation of Small Rainfall Events Impact on the Urban Runoff by Analytical Model

The amount of impervious area in urban catchment increases because of developed conditions, resulting in the increase of peak discharge rate and runoff volume. The estimation of runoff quantity helps to design stormwater control facility. This research considers analytical model for urban runoff estimation in the test catchment located in semiarid region based on efficient impervious area. To study the significance of small rainfall events, the rainfall events less than 10 mm was considered in the analytical model. The results of this study revealed that the omission of rainfall volume less than 6 mm does not change the maximum relative error value remarkably and the analytical model is not sensitive to the rainfall events less than 6 mm. This omission will simplify the statistic calculations for providing rainfall characteristics parameters of analytical model