STREAM CHANNEL RESPONSE TO URBAN LAND-USE IN THE COASTAL PLAIN OF NORTH CAROLINA

Urban land-use and impervious area commonly alter stream hydrology by changing the hydrologic response to precipitation. Land-use trends suggest that North Carolina streams are at risk for alteration; by 2030 projections indicate that 27% of the state's watersheds will have greater than 5% total impervious area. Watershed imperviousness has modified stream channels in a variety of settings with the in-stream response varying depending on land-use and geomorphology. One common response is enlargement of the channel dimensions. Urbanization effects on Coastal Plain stream channels are not well known. In the Coastal Plain blackwater streams are common, characterized by gently sloping, meandering channels that flood frequently and carry suspended loads. In this study we quantified the effect of urban land-use on Coastal Plain stream channel morphology. The channel dimensions and sediment characteristics of 20 rural and 20 urban streams were compared across a range of watershed areas (0.18 – 4.0 km2) within the North Carolina Coastal Plain. Preliminary results indicate that urban land-use has resulted in stream channel widening (0.69 m) and deepening (0.12 m). Urban streams consistently had larger cross-sectional areas (0.39 m2) than rural streams. Channel grain size distribution also varied between urban and rural streams, the 84th percentile grain size for urban streams (0.64mm) was larger than that for rural streams (0.45mm). Sediments within urban stream channels typically contained a greater percentage of gravel (7.38%) when compared with rural streams (0.28%). Rural stream channels contained a greater percentage of sand (93.3%) than urban streams (82.5%). These data suggest that discharge alterations related to urban land-use have affected Coastal Plain stream morphology. Common in-channel responses to urbanization included enlargement of channel dimensions and fluvial sorting that resulted in coarser channel sediments.