Rainfall estimates for the event indicate that 8-10”, or in a few cases > 10”, of rain fell during the event in the central and southeastern portions of the state. The National Weather Service (NWS) defined this rainfall event as having a 1000-year return period in the heaviest precipitation areas, including Greenbrier County and within the Greenbrier River Basin. Preliminary data from US Geological Survey (USGS) stream gaging stations at four locations along the heavily impacted Greenbrier River indicate that flooding was most severe in the lower reaches of the watershed, where the flood preliminarily qualifies as the third largest peak annual flow at both Alderson and Hilldale, WV. However, the middle and upper Greenbrier River Basin received less total precipitation, which resulted in peak flows that do not rank in the top twenty peak annual flows at either Buckeye or Durbin, WV.
This project focuses on the hydrometeorology and flood hydrology of the Greenbrier River Basin associated with the June 2016 extreme precipitation event to identify the primary causes of the rainfall and associated flooding. Although both the rainfall and associated flooding are considered extremely low probability events, additional external factors led to difficulty in forecasting the severity of the event. These include the difficulty of forecasting mesoscale convective systems (MCSs) that cross the Appalachian Highlands, the complex and steep topography of the region, which influenced the hydrologic response of the watersheds and impacted the spatial validity of surface rainfall estimates, as well as antecedent soil and vegetation characteristics that influenced the rate and volume of surface runoff. Results of this study will help to highlight critical factors in flood forecasting within regions of complex topography during extreme rainfall events, leading to improved methods of diagnosis and prediction.