Urban Flood Scaling Using Hydrologic and Hydraulic Models with Inception for Early Warning

Abstract—Urban floods are generally characterized by surge in runoff volumes resulting in high flow peaks and water depths incurring huge socio- economic losses. Hydrologic and hydraulic simulation tools integrated with ground survey inputs can be effectively used to simulate the movement of flood waters in intricate urban environments. Integration of hydrological–hydraulic flood models supported by geospatial tools and hydro-meteorological analysis is one effective measure to comprehend urban flooding. Numerical Weather Prediction (NWP) models as WRF aided aided by Nowcasting DWR observations is one resourceful tool for urban flash flood forecasting. The NWP forecasted precipitation data is conglomerated to a distributed hydrological model to derive flood hydrographs. The theme of the study is to establish flood runoff thresholds in one of the most flood-prone urban region of India – Guwahati city, by simulating the spatial flooding extents, developing flood runoff thresholds and to scale the flood events. Database build up for actual flooding events, ground reconciliation using ETS-RTK survey, setting up of Base Flood Elevation (BFE) points for hydraulic model integration was done. The resulting hybrid DEM (1m resolution) was adopted for building the spatially-distributed hydrological model in HEC-HMS. Model runs were carried out to derive flood runoff hydrographs and peak discharges using time series NWP–WRF and AWS data. Drainage active areas, building footprints and blockages in storm drains were laid over the high resolution 1m bathymetric grid in hydraulic MIKE FLOOD model. Flood inundation simulation using runoff hydrographs were carried out under source/sink pairs. Schematization of the simulated flood inundation layers using threshold scales of flood discharges was used to develop a scaling of the urban flooding in Guwahati, with early warning inception