Modeling and Master Drainage Planning of a Virginia Coastal Plains Watershed

The 1,988-acre Crestwood (CW) 2&3 watershed is a Virginia coastal (Atlantic) plains watershed that is prone to flooding because such watersheds are typically low-lying areas with less relief, have high groundwater tables, experience heavy rainfalls and high tides. In addition, such watersheds often contain old urban cities with more imperviousness, aged infrastructure lacking maintenance, and stormwater infrastructure not meeting current standards. In this study, a Master Drainage Plan (MDP) was developed for the CW-2&3 watershed to examine the current flooding problems and develop solution measures through improvements to the drainage infrastructure. PCSWMM, based on the US EPA’s Storm Water Management Model (SWMM), was used in developing the MDP. An existing conditions model was developed using topographic, stormwater infrastructure, and survey data. The model was calibrated using Weather Underground Station rainfall data, USGS tide gage data, and high-water levels measured at 11 monitoring stations during a significant rainfall event. The calibrated model was then run with six design storms for developing drainage improvements adequate for the required design storms at known and model dictated flooding areas. The presentation and the paper summarize the study alluding to the level of efforts and details going into these kinds of numerous studies by practicing engineers and scientists for municipalities (local governments) having limited resources that could be far from ideal elaborate research studies. It also shows the challenges that needed to be overcome while developing and calibrating the model and developing the MDP for this Virginia coastal plain and similar watersheds anywhere.