Urban Land Use, Channel Incision, and Water Table Decline Along Coastal Plain Streams, North Carolina1

This study evaluates the effects of urban land use on stream channels and riparian ground-water levels along low-order Inner Coastal Plain streams in North Carolina. Six sites with stream catchments of similar size (1.19-3.46 km(2)) within the Tar River Basin were selected across an urban land use gradient, as quantified by a range of catchment total impervious area (TIA; 3.8-36.7%). Stream stage and ground-water levels within three floodplain monitoring wells were measured manually and using pressure transducers from May 2006-June 2007. Channel incision ratio (CIR), the ratio of bank height to bankfull height, was also measured at each monitoring site and along stream reaches within the study area (12 urban and 12 rural sites). Riparian ground-water levels were inversely related to catchment TIA (%). As TIA (%) and stormwater runoff increased, the degree of stream channel incision increased and riparian ground-water tables declined. In urban floodplains (> 15% TIA), the median ground-water level was 0.84 m deeper than for the rural settings (< 15% TIA). This has resulted in a shift to drier conditions in the urban riparian zones, particularly during the summer months. CIR was found to be a reliable surface indicator of riparian hydrologic drought in these settings.