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  TMDL Model Evaluation and Research Needs (EPA/600/R-05/149) November 2005

This review examines the modeling research needs that support environmental decision making for the 303(d) requirements for development of total maximum daily loads (TMDLs) and related programs, such as 319 Nonpoint Source Program activities, watershed management, storm water permits, and National Pollutant Discharge Elimination System discharge evaluations. By examining the currently available models and considering the needs for TMDLs and related watershed programs, a comprehensive list of modeling research needs can be developed.

More than 65 currently available models were evaluated for their capabilities and applicability to TMDL development and related watershed management activities. Evaluation tables were developed to facilitate comparison of models and to inventory the potential gaps in model capabilities. Fact sheets were developed for models to provide more detailed information on the capabilities of each model. Existing integrated model systems were also evaluated and compared, based on data processing, modeling tools, and model linkages supported. The review of available models demonstrates that many of the dominant pollutant types and water bodies can be simulated using available technologies. However, many specific technical gaps remain, especially in linkages between air, surface water, ground water, and receiving water models.

The model reviews and emerging trends in technology were considered in developing a comprehensive list of research needs that include a variety of sources, processes, water bodies, data, systems, and integration needs. This diversity of needs is consistent with the current development of TMDLs across the country. Initially, TMDL development focused on dominant source and pollutant types, but more recently, emphasis has shifted to completing TMDLs under a variety of site-specific conditions and supporting more detailed implementation planning. Because of the specialized and diverse characteristics of the needs, an equitable prioritization of specific needs cannot be defined.

Applications that could benefit from this review include:

  • Integrated best management practice modeling systems
  • More physically based representations of watersheds
  • Support for linkage of watershed and receiving water models

The review recommends that this diverse set of technical needs should be supported by new and more flexible modeling systems and tools. Development of integrated modeling systems can provide the commonly needed tools and support adoption of new techniques, source representation, and algorithms. Providing integrated system platforms, ideally Internet-based, can help minimize duplication of effort (shared on-line data management, data display, shared resources), while maximizing resources for more fundamental development and research of key components.

The use of Internet-based technologies has emerged as a viable and practical medium for management of data, analysis techniques, and tools to support TMDL and more generalized watershed analyses. Development of a standardized Internet-based framework could provide significant cost savings for the management and application of models. In addition, a standardized and open framework, with clearly defined linkage capabilities, could encourage research and continuous testing and update of new components.

Future development of models and the supporting infrastructure of data and guidance can support informed environmental decision making, improve understanding of the physical systems in our world, and ultimately provide information to support the effective restoration and protection of the nation's waters.


Mohamed Hantush

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