Floodplain Map Library (FPML): Innovative Method for Flood Warning System for Urban Watersheds in Houston, TX

The next step in the development of flood warning systems aims to provide visualized information on floodplain inundation maps in addition to predicting hydrographs at various points in real time. The normal approach to this goal follows rainfall transformation and floodplain delineation using both a calibrated hydrologic model and an accurate hydraulic model (HEC-RAS) in real time. The hydrologic model (HEC-1) has been run for many years without problems in real time, but the standardized hydraulic model (HEC-RAS) has difficulty in handling large and intense hydraulic computation in real time. Because bridges can create serious problems with numerical instability in real-time applications, it is especially difficult for HEC-RAS to simulate elevations where numerous bridges can overtop during a major flood. In order to approach the goal of visualizing floodplains, the floodplain map library (FPML) as a new hydraulic prediction tool has been developed for White Oak, one of the major urban watersheds in Houston. The similar methodology was used to develop the Brays Bayou FPML, which is currently being created and integrated into an existing radar-based flood alert system (FAS2) for the Texas Medical Center (TMC) in Houston to provide inundation maps in near real time. The development of FPML includes three stages: designing rainfall patterns based on historical rainfall data over the watersheds, delineating 99 floodplain maps in Geographic Information System (GIS) based on design rainfalls for each watershed, and designing an algorithm to link real-time NEXRAD radar rainfall to the appropriate map. The FPML system can analyze rainfall intensities and patterns to quantify water surface elevations and delineate floodplains under various spatial and temporal conditions. This will allow the emergency personnel to begin flood preparation with as much lead time as possible, and the enhanced system can be used as a prototype for other flood-prone areas along the Gulf coast. The FPML method is also compatible with storm surge model outputs in order to predict inundation maps and evaluate severe inundation in non storm surge zones. For example, major evacuation routes from Galveston can be visualized during extreme coastal weather conditions. The FPML with storm surge data will improve emergency personnel's ability to initiate evacuation strategies at many levels.