Map to map: converting a NEXRAD rainfall map into a flood inundation map

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Robayo, Oscar

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The spatial nature of flood hazards makes GIS a proper means to address and integrate flood damage assessment components. Geography, relational databases, and engineering models are proposed as central elements to develop an end-to-end integrated and dynamic regional watershed modeling system for flood information support: the Map2Map application. Using ArcGIS 9 customization language and visual environment for batch geoprocessing, ArcObjects and ModelBuilder, respectively, a methodology for converting a NEXRAD rainfall map time series into a flood inundation map has been developed. The methodology integrates HEC-HMS and HEC-RAS modeling systems through flow exchange points in the stream network georeferenced in the Arc Hydro data model for water resources. The georeferenced flow change points allow the transfer of simulated runoff hydrographs from HEC-HMS into HEC-RAS by means of spatial relationships between hydrograph entry points in HEC-HMS and their closest downstream cross sections in HEC-RAS. To support this integration, spatially-referenced time series exchanges were achieved via custom designed applications for the two way transfer of time series between the HEC-DSS system and the Arc Hydro data model. The system achieves integration, not only by means of data exchange, but also by means of a centrally managed and unified execution of chained tasks representing the modeling workflow of the involved processes and datasets. The coupling of these external modeling systems (HECHMS and HEC-RAS) via a common geographic framework enables streamlined dynamic and seamless end-to-end simulations for historical, real time and planning analysis that overcomes a conventionally tedious and error-prone stepwise approach. The aforementioned integrating approach was implemented in the San Antonio River basin, Texas as part of a regional watershed modeling system being developed by the San Antonio River Authority, the City of San Antonio, and Bexar County. In particular, the Salado and Rosillo creeks have been used to test a prototype version of the proposed geographically based modeling integration.