Impacts of Rainfall Distribution on the Performance of Urban Storm Drainage Systems

The performance of an urban drainage system is sensitive to the rainfall quantity, duration, and distribution. Changes in the distribution for the same quantity and duration of a rainfall event can produce significantly different results in terms of flooding extent, depth, and duration. Assessing the performance of an existing storm drainage system under different rainfall distributions provide communities with another viewpoint that can be used when selecting/prioritizing projects or determining the best value during improvement design. This presentation will showcase the performance sensitivity of existing urban storm drainage systems using InfoWorks ICM, HEC-HMS, and HEC-RAS with different synthetic rainfall distributions along with actual rainfall events. The synthetic rainfall distributions include NOAA Atlas 14, Huff and the representative storm. The representative storm distribution is developed based on assessing historical rainfall events from gridded gauge adjusted radar rainfall (GARR), which produces hydrographs and peak discharges that more closely reflect actual storms experienced in an area. By running the same storm (quantity and duration) with different distributions, it allows us to see how the urban drainage system perform under different scenarios and help pinpoint the real high flood risk areas. Having more accurate flood risk evaluation information allows communities to make better decisions on how to spend finite resources where needed most while still providing the community's expected level of service.