HYDROGRAPH SEPARATION TO DETERMINE STORM RUNOFF GENERATION IN AN URBAN WATERSHED IN THE SOUTHERN APPALACHIAN MOUNTAINS

Hydrograph separation techniques were used to determine contributions of surface runoff (i.e. event water) and groundwater baseflow (i.e. pre-event water) during storm events in a temperate urban headwater in the Southern Appalachian Mountains. Multiple preliminary storm hydrographs were successfully separated using a two endmember mixing model. Chemical signatures indicated groundwater baseflow was a significant component of storm runoff at this stream site on Boone Creek in Boone, North Carolina. Average contribution of groundwater baseflow throughout entire storm events was 56.4%, while average contribution of groundwater baseflow at peak discharge during storm events was 43.6%. Peak contribution of baseflow occurred earlier than peak of surface runoff during some storm events, which suggests rapid transmission of groundwater to streams. Surface runoff becomes more dominant with increasing amount of precipitation. Five-day antecedent rainfall for storm events may be a considerable indicator of how dominant the groundwater baseflow contribution will be during a given storm event. Overall, this study suggests baseflow contribution to storm runoff in urban watershed systems might be greater than we assumed.