Urban flooding has come into a national focus in recent years following intense and prolonged rainfall events that resulted in widespread flooding in Houston, Ellicott City, Washington DC, Dallas, and Las Vegas, among others. Stormwater infrastructure designed to carry a 10-year to 25-year rainfall event is inadequate when the city experiences a 100-year rainfall. Cities are taking note of these flooding experiences and taking initial steps to save lives and mitigate damages, and engineers are tasked with evaluating the adequacy of the stormwater infrastructure’s performance for a larger than design storm. NOAAAtlas 14 duration-frequency estimates for rainfall are used to generate stationary storms, which are translated to floodplains through hydrologic and hydraulic models. However, real storms centers move across a watershed. Therefore, floodplains estimated using a stationary storm system will not be the same as that of a moving system. Gridded quantitative precipitation estimates can conveniently be used with these hydraulic models.There is some guidance available to generate watershed-specific probable maximum precipitation but extending this guidance to frequency storms needs specific meteorological expertise. Tools exist in the public domain (HEC-MetVue) to model observed storms and paths, but are inadequate to generate the frequency relationships for storm paths and intensities a pluvial floodplain model needs. In addition, pluvial flood modeling of generally flat, urban areas requires 2D hydraulic modeling. This presentation summarizes methodologies available to estimate pluvial floodplains and highlights areas where availability of storm frequency information for tracks and intensities will improve the analysis.
