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ARS Home » Research » Publications at this Location » Publication #198685
Title: FIELD DATA AND PRELIMINARY MODELING TO DEMONSTRATE MODEL ABSTRACTION TECHNIQUES USING THE OPE3 FIELD SITE

Author
item Pachepsky, Yakov
item Gish, Timothy
item Guber, Andrey
item NICHOLSON, T - U.S. NUCLEAR REG. COM
item CADY, R - U.S. NUCLEAR REG. COM.

Submitted to: Government Publication/Report
Publication Type: Government Publication
Publication Acceptance Date: 8/24/2006
Publication Date: N/A
Citation: N/A

Interpretive Summary: It has been amply demonstrated that the increase in complexity of a model does not necessarily mean an increase in its accuracy. If the complexity is not inexorably linked with the accuracy, there may exist an opportunity to simplify the model. Model abstraction is defined as the methodology for reducing the complexity of a simulation model while maintaining the validity of the simulation results with respect to the question that the simulation is being used to address. The model abstraction can serve as the device to determine whether a simple model can be used that is easy to understand and communicate to regulators, stakeholders, and the general public, and can adequately represent their site. The implementation of the model abstraction methodology provides a context for more efficient use of modeling in the regulatory process. The model abstraction addresses the uncertainty of model structure and model parameter determination, and facilitates transparency and realism with respect to site-specific features, events and processes. The objective of this report was to analyze available data and software with respect to the feasibility of building a base flow and transport model that explicitly accounts for preferential pathways and small-scale heterogeneities at waste disposal sites, and abstracting this model to simpler commonly used models. The Beltsville USDA-ARS OPE3 experimental watershed and the hydrologic database developed from surveys and monitoring were utilized in this model abstraction case study. The HYDRUS and GMS-FEMWATER software were successfully tested to assure their applicability to building a suite of abstracted models. Overall, the availability of an unique extensive dataset supplemented with task-related experiments allowed us to develop the case study to apply the systematic model abstraction process at the watershed scale and to demonstrate how the model selection process affected long-term solute transport simulation results.

Technical Abstract: This report describes the data and preliminary modeling to develop a case study of model abstraction application at the watershed scale. Model abstraction is defined as the methodology for reducing the complexity of a simulation model while maintaining the validity of the simulation results with respect to the question that the simulation is being used to address. The model abstraction can serve as the device for the NRC licensees to determine whether a simple model can be used that is easy to understand and communicate to regulators, stakeholders, and the general public, and can adequately represent their site. A review of model simplification techniques developed in subsurface hydrology is included. Abstractions of both model structure and model parameter determination are described. A systematic and objective approach to the model abstraction is outlined. The objective of this report is to analyze available data and software with respect to the feasibility of building the base flow and transport model that explicitly accounts for preferential pathways and small-scale heterogeneities at the waste disposal sites, and abstracting this model to simpler commonly used models. The Beltsville USDA-ARS OPE3 experimental watershed and the hydrologic database developed from surveys and monitoring are characterized. The design of model abstraction case study is described. The HYDRUS and GMS-FEMWATER software are successfully tested to assure their applicability to building a suite of abstracted models. The software can be used with some modifications. Overall, available unique extensive dataset supplemented with the task-related experiments will allow us to develop the case study to apply the systematic model abstraction process at the watershed scale and to demonstrate how the model selection, using hydrogeophysical data sources in parameter estimation, and the temporal averaging scale can affect long-term solute transport simulation results in the uncertainty context.