Probabilistic rainfall‐runoff transformation considering both infiltration and saturation excess runoff generation processes

Many rainfall‐runoff models consider only the infiltration excess runoff generation process. The use of green roofs, bio‐retention areas, and pervious pavements for urban storm water management purposes requires the modeling of surfaces where both infiltration and saturation excess runoff generation mechanisms need to be considered. Expanded from previous results of probabilistic rainfall‐runoff transformation, analytical equations transforming the input rainfall frequency distribution to output runoff frequency distribution are derived to incorporate both runoff generation processes. These analytical equations can be used to calculate the average annual runoff volume and runoff event volume return period. Results from deterministic continuous simulation of various urban surfaces were compared to those from the analytical equations and satisfactory agreement was obtained. The analytical equations are therefore proposed as a complement to continuous simulation models for the modeling of urban catchments where both runoff generation processes occur.