The flood hydrology of small forested central Appalachian watersheds

This study seeks to determine the dominant controls on flood response for high-gradient, forested Appalachian watersheds. The work reported here focuses on two headwater sites in the central Appalachians. One is an established research site (the Fernow Experimental Forest near Parsons, West Virginia); the other site is an ungaged watershed (Saul's Run in Pendleton County, West Virginia) that experienced catastrophic flooding from an orographic thunderstorm in August 2003. The data sets obtained from these two sites are dramatically different, but both sites yield insight into the runoff production mechanisms controlling flood response. At the Fernow Experimental Forest, streamflow and rainfall observations are combined with observations from a network of crest-stage piezometers to examine storm event response. Surface channel response and subsurface saturation response are examined in the context of antecedent conditions, rainfall accumulations, and rainfall rates. Observations show pronounced heterogeneity of subsurface saturation even within the unchannelized swales of headwater watersheds. A conceptual model of runoff processes on these watersheds includes the formation of localized perched water tables due to decreased macropores and increased flaggy stones with increasing depth in the soil column. The conceptual model is used to examine key features of catastrophic floods in the central Appalachians. The use of historical streamflow data from the Fernow Experimental Forest highlights the importance of forest management practices on flood response at the headwater scale. On Saul's Run, a 2.1 km2 mixed land use watershed, an orographic thunderstorm system produced 150 mm of rainfall in less than one hour on 9 August 2003, and the resulting flood produced major fluvial impacts. Detailed surveys of high water marks and channel/floodplain geometry were used for hydraulic analyses of the Saul's Run flood, including estimation of peak discharge at four locations. Hydrologic modeling indicates that land use effects may have influenced extreme flood response in Saul's Run. This combination of observations on gaged and ungaged watersheds leads to a better understanding of the processes important for determining flood response on small forested central Appalachian watersheds.