REGIONAL MODELING OF SAN ANTONIO RIVER BASIN IN TEXAS

For millions of South Texas residents, quality of life is linked inextricably to the San Antonio River. More than 220 miles long, the river flows through five counties and comprises six major watersheds, with numerous jurisdictions, agencies and organizations dependent on the river's quality and quantity.An Inter Local Agreement (ILA) was established among the San Antonio River Authority (SARA), the City of San Antonio (COSA), and Bexar County to establish a collaborative, regional approach toward flood control and storm water management, including both water quantity and quality. The ILA partners created the Bexar Region Watershed Management Coalition (BRWMC). The BRWMC focuses on the development of a comprehensive Regional Watershed Modeling System (RWMS) that will act as a single repository of spatial and modeling data for the entire San Antonio River Basin (SARB). The goal is to improve the quality of life, protect life and property, provide safe transportation during heavy rain and flood events, and provide a tool for the management of water quality (WQ) in storm water runoff and ambient waters.The regional modeling effort is centered on the development and incorporation of new and existing models in a Geographical Information System (GIS) platform that will assist in flood mitigation planning, capital project prioritization, floodplain management, and other applications.As a part of this effort, existing WQ data and models were inventoried, reviewed, assessed, and recommendations were made regarding existing studies and supporting geospatial data. Procedures for establishing watershed geo-databases using the Arc Hydro data management system were also developed. This system provides spatial, time and flow linkages between the selected hydrologic and hydraulic (H&H) models such as HEC-RAS and HEC-HMS models, and the WQ models, such as HSPF and QUAL-TX. The developed WQ models are to link with the H&H models to ensure consistency in H&H simulations.The GIS-based models will be continuously updated and used to evaluate proposed development, revise FEMA maps, prioritize capital improvement projects, support permit and standard compliance, support the removal of stream segments from the 303(d) list and avoid unwarranted TMDL studies, assess impacts from upstream developments and agricultural runoff, evaluate effectiveness of Best Management Practices (BMPs), identify site-specific WQ issues, evaluate needs for biomonitoring, and support WQ trend analysis.