Modeling and Master Drainage Planning of a Virginia Coastal Plains Watershed

Abstract Submission: The Crestwood (CW) 2&3 watershed consisting of the 290-acre Hodges Creek and 1,535-acre Newton Creek basins, both discharging into the Southern Branch Elizabeth River, and 165 acres discharging directly into the river is a Virginia coastal plains watershed. Coastal watersheds are prone to flooding as those are low-lying areas with less relief, high groundwater table, heavy rainfalls, high tides, and old urban cities with more imperviousness, aged infrastructures, lack of maintenance, and stormwater infrastructure not meeting current standards. A Master Drainage Plan (MDP) was developed for the CW-2&3 watershed to examine the flooding problems and develop solutions. The PCSWMM based on U.S. EPA’s Storm Water Management Model (SWMM) was used. An existing conditions model was developed using stormwater structure data from construction plans and surveys. To calibrate the model, daily precipitation was taken from four Weather Underground stations, tide gage readings at Money Point, VA, and placing 13 monitoring stations within the watershed to measure high water levels resulting from a significant rainfall event. The model was calibrated with the 9/18/2020 rainfall event within an average 0.07 feet of the eleven reliable high-water marks. The calibrated model was then run with design storms and develop alternative solutions to alleviate flooding at known locations under various design storms. Significant improvements included paved ditches, upsizing existing pipes, and adding inlets and special structures. The presentation and the proceeding paper will elaborate the challenges and lessons learned during the model calibration process and while developing the MDP of the CW-2&3 watershed.

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