By Karl McArthur, P.E., Senior Water Resources Engineer, and Donna Huey, Vice President, Information Solutions Division, PBS&J

With its headwaters in the flood-prone Balcones Escarpment hill country area of central Texas, the San Antonio Basin receives some of the world's most intense rainfall events. The combination of frequent severe storm events and one of the largest urban centers in the country is a recipe for significant property damage and loss of life.

In an effort to better manage flooding issues, general drainage problems, and stream water quality, three government agencies—the San Antonio River Authority (SARA), the city of San Antonio, and Bexar County—came together to form the Bexar Regional Watershed Management (BRWM) Committee. This partnership brings together people, resources, and technology to more effectively manage water resources issues.

A key component of the management program being developed by the committee is the San Antonio River Basin Regional Watershed Modeling System (RWMS), a comprehensive regional watershed management system that will act as a single repository of spatial and modeling data.

Arc Hydro, Esri's water resources data model, provides the underlying framework that will tie all water-related data into that shared repository. As a standardized template, Arc Hydro helps users more easily and quickly link a wide variety of data through relationships between features by tracing and connecting elements along the path of water movement.

The core design of the Arc Hydro framework supports the full integration of spatial, modeling, and time series data for water resources management. The benefits of this standardized framework are easy access to common data, no redundancy or differing representations, quality assurance as the relationships are automatically maintained between data layers, widespread access to results through a shared environment, and ease of use.

On behalf of BRWM, SARA selected Esri Business Partner PBS&J in 2002 to support the regional watershed management program development and subsequently implemented RWMS as an enterprise GIS based on the Arc Hydro data model. Working with Dr. David Maidment, director of the Center for Research in Water Resources at the University of Texas, Austin, and Dr. Francisco Olivera of Texas A&M University, the project team is developing extended, model specific geodatabases and data management tools and procedures that work in concert with the basic Arc Hydro framework.

The result is an integrated system that combines the power of GIS and hydraulic/hydrology modeling capabilities to track and predict the actual flow of water from its origin to final outfall, thereby creating the opportunity to effectively manage resources in the best possible way. When complete, this robust data management system will "publish" its GIS and hydraulic and hydrology modeling data, as well as standards, procedures, and productivity tools, through a Web portal. The Web portal will also allow BRWM members to manage data requests and submittals as well as track the approval and denial of submitted drainage studies.

According to Steve Graham, SARA's director of Watershed Management, "This technology brings to life the shared vision of linking and managing models through a GIS-based framework. Through it, we can assimilate a variety of local, regional, and national data into one system that can be used by everyone from GIS experts to government agencies to the engineering community as well as the general public."

The initial phase of the development project included the creation of a prototype application to demonstrate the potential linkage and automation aspects of the final RWMS. This application, called Map2Map, incorporates several key components of the overall system and illustrates the vast potential of RWMS for flood forecasting and automated flood inundation mapping. The Map2Map application takes advantage of the new ModelBuilder tools available in ArcGIS 9 Desktop to automate hydrologic and hydraulic modeling from the processing of NEXRAD radar data, through the HEC-HMS and HEC-RAS applications, to the creation of a flood inundation map.

RWMS, built on the core framework of Arc Hydro and extended, application specific data models, will provide BRWM with a powerful set of tools that will help efficiently manage the sharing and updating of models and data throughout the San Antonio River Basin. The system will also provide the platform for effective flood forecasting applications, water quality modeling and management, and distribution of information and data to both the engineering community and the general public.

For more information, contact William Sadang Burmeister, watershed engineer, San Antonio River Authority (e-mail: rwms@sara-tx.org, tel.: 210-227-1373); Karl McArthur, P.E., senior water resources engineer, PBS&J (e-mail: kemcarthur@pbsj.com, tel.: 512-342-3295); or Donna Huey, vice president, Information Solutions Division, PBS&J (e-mail: dmhuey@pbsj.com, tel.: 1-800-284-5182).