Development of Appropriate Synthetic Design Storms for Small Catchments in Gauteng, South Africa

Synthetic design storms are often used as input in dynamic rainfall-runoff simulation models. A number of methods to generate synthetic design storms are described in the literature. However, the selection of an inappropriate synthetic design storm will generate unrealistic simulations. Therefore, the aim of this study was to develop appropriate synthetic design storms for small urban catchments in Gauteng, South Africa. This study evaluated the applicability of the SCS method adapted for South Africa (SCS-SA), the Chicago Design Storm method and the Rectangular Hyetograph method. The performance of each method was evaluated compared to observed rainstorm events. Storm shape and intensity were used for the evaluation. As expected, the Rectangular Hyetograph was the least representative of naturally occurring storm events. The Chicago Design Storm and SCS-SA distribution curves initially performed poorly. Adjustment of the timing of the peak storm intensity to the start of the event resulted in a significant improvement for both methods. A novel approach was used to generate intermediate site-specific SCS-SA rainfall distribution curves anywhere in the study area.