Water Resources Research Act Program

Details for Project ID 2007NC75B

Stable Isotope Tracers to Quantify Impervious Area Effects on Baseflow to Coastal Plain Streams

Institute: North Carolina
Year Established: 2007 Start Date: 2007-03-01 End Date: 2008-02-29
Total Federal Funds: $23,707 Total Non-Federal Funds: $47,414

Principal Investigators: Michael ODriscoll, Mark Brinson

Project Summary: North Carolina is the 6th fastest growing state in the U.S. (1990-2000). Statewide 18.1% of watershed area is affected by greater than 5% total impervious area. By 2030 projections indicate that 27% of North Carolinas watersheds will have greater than 5% total impervious area. Urban land-use has been shown to alter and degrade streams by changing their hydrologic response to precipitation. Current land-use trends and previous studies suggest that streams in North Carolina are at significant risk for degradation due to increases in impervious area. Ground water recharge in urban areas is complex because normal recharge pathways are often altered. Variable responses of baseflow to increased urban land-use have been observed in a variety of settings. Currently it is not known what threshold percentage of watershed impervious area will begin to affect stream baseflow. Stream responses to increased imperviousness may vary across physiographic regions. The relationship between impervious area and in-stream response must be established for the common physiographic settings in North Carolina: the Mountains, Piedmont, and Coastal Plain. The effect that watershed impervious area has on baseflow to Coastal Plain streams will be quantified in this study. Quantification of impacts on Coastal Plain baseflow is important because over 50% of annual average streamflow of Coastal Plain rivers is derived from baseflow and the Coastal Plain comprises 45% of the land area of North Carolina. Typically, stormwater management is dealt with on a site by site basis and the cumulative effects to the entire watershed are not measured. In humid temperate settings, where precipitation temperature varies seasonally, the stable isotopic composition of rainfall and stormwater should vary from that of ground water. This allows for quantification of baseflow and stormwater runoff using stable isotopic tracers. In this study, we propose to determine thresholds of baseflow impact and to evaluate a stable isotope approach to quantify the watershed-scale effects of stormwater runoff on Coastal Plain streams. The value of this proposed approach is that stable isotope measurements can reveal the cumulative effects of upstream land-use changes at a watershed outlet and provide estimates of the threshold levels of watershed impervious area that result in baseflow alterations to Coastal Plain streams.