Three models of sediment transport and contaminant distribution (CHARIMA, HEC-6, and TODAM) are being applied to the Clinch River/Watts Bar Reservoir system as part of a CERCLA remedial investigation. Planned uses of model results are to identify high deposition areas of the river, forecast the effects of various remedial actions and climatic events on contaminant distribution, and aid in the design of future data collection efforts. The three models share some similarities but also differ in several important details. All three models are one-dimensional and include similar processes for sediment deposition and resuspension. Differences among the models include steady-state versus unsteady flow, the complexity of the channel network permitted, and the level of detail of contaminant-related fate processes represented. As part of our multiple model strategy, some aspects of the three models are configured using common information on the system (e.g., spatial geometry), while other aspects of the models, including some modeler decisions and calibration methods, are allowed to differ. Comparison of results among the three models can lead to increased confidence in predictions and in recommendations for future data collection. The general approach of using multiple models is described and preliminary results of the Clinch River/Watts Bar application are presented to illustrate the utility of using a multiple model approach for complex environmental assessments.

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