Hydraulic Modeling of Extreme Hydrologic Events: Case Study in Southern Virginia

A comprehensive hydraulic modeling effort that was applied to two rural watersheds in southern Virginia is presented in this paper. The 10-, 50-, 100-, and 500-year storms and the probable maximum flood (PMF), are considered in this study with the objectives of assessing the impact of extreme hydrologic events through the generation of inundation maps, characterizing the sediment transport process under severe flooding conditions, and quantifying the uncertainty associated with the floodplains boundary roughness and its influence on the results. The employed methodology includes the construction of a river terrain model that combines geospatial and field-collected data, a calibration procedure based on regression equations and developed stage-discharge predictor curves, and unsteady flow simulations utilizing discharge hydrographs produced by an event-based hydrologic model. The results highlight the severe flooding conditions associated with the PMF and the necessity of considering it as the worst-case scenario in regions with relatively wet and humid climate. The modeling effort presented in this paper aims to serve as a reference framework for the development, implementation, and validation of hydraulic models intended to simulate extreme hydrologic events, as well as to provide guidance for the interpretation of the results for similar studies. (C) 2014 American Society of Civil Engineers.