Analytical Derivation of Urban Runoff-Volume Frequency Models

The analytical probabilistic approach has been investigated and occasionally applied in urban stormwater management for more than three decades. Many expansions and improvements have been made since its first appearance. However, there are still areas for the model to expand and improve. This study illustrates the derivation of the exact frequency distributions of the runoff-event volume considering both infiltration and saturation excess runoff generation processes. This new model is more accurate than the previously developed ones and can be used for the planning and design of certain stormwater management practices featuring water quality control, such as low-impact development practices. The model can effectively estimate the runoff volume of a small urban catchment with different return periods. It is applied to an actual small urban catchment under different soil saturation levels. The model was able to detect the minimal changes in the values of soil saturation; for a fixed return period, the model produced different runoff volumes under very close levels of soil saturation.