Catastrophic flooding from an orographic thunderstorm in the central Appalachians

[1] An orographic thunderstorm system in Pendleton County, West Virginia, produced 125 - 150 mm of rainfall in less than 1 hour on 9 August 2003. Rainfall and fluvial impacts were concentrated in the ungauged 2.1 km(2) Saul's Run watershed. Despite the short duration of the event the flood produced significant fluvial impacts and abrupt changes in the extent of incision and channel widening. Hydrometeorological analyses of the storm are based on WSR-88D radar reflectivity observations and rain gauge observations. The small multicell thunderstorms that produced the Saul's Run flood were not markedly different from other storms in the central Appalachian region on 9 August 2003. Detailed surveys of high watermarks and channel/floodplain geometry are used for hydraulic analyses of the Saul's Run flood, including estimation of peak discharge at four locations. Peak discharge estimates at the 1 km(2) scale cluster around 18 m(3) s(-1), placing this event on the flood envelope curve for the mid-Atlantic region. Observed rainfall, estimated peak discharge, and observer notes on timing of peak discharge are used along with a distributed hydrologic model to reconstruct hydrographs at multiple locations. Hydrologic modeling indicates that land use effects may have significantly influenced extreme flood response in Saul's Run. The wide range of fluvial impacts is consistent with patterns of boundary shear stress and unit stream power derived from a simulation of the Saul's Run flood using a 2-D depth-averaged hydraulic model.