Horry County Schools

Abstract Many small streams in coastal watersheds in the southeasternUnitedStates are modified for agricultural, residential, and commercial development. In theSouthCarolina Lower Coastal Plain, low‐relief topography and a shallow water table make stream channelization ubiquitous. To quantify the impacts of urbanization and stream channelization, we measured flow and sediment from an urbanizing watershed and a small forested watershed. Flow and sediment export rates were used to infer specific yields from forested and nonforested regions of the urbanizing watershed. Study objectives were to: (1) quantify the range of runoff‐to‐rainfall ratios; (2) quantify the range of specific sediment yields; (3) characterize the quantity and quality of particulate matter exported; and (4) estimate sediment yield attributable to agriculture, development, and channelization activities in the urbanizing watershed. Our results showed that the urban watershed exported over five times more sediment per unit area compared with the forested watershed. Sediment concentration was related to flow flashiness in the urban watershed and to flow magnitude in the forested watershed. Sediments from the forested watershed were dominated by organic matter, whereas mineral matter dominated sediment from the urban stream. Our results indicated that a significant shift in sediment quality and quantity are likely to occur as forested watersheds are transformed by urbanization in coastalSouthCarolina.

This report is the first of two open-file reports describing the collection and preliminary analysis of digital seismograms recorded by the U.S. Geological Survey during the Mammoth Lakes, California, earthquake sequence of This first report describes the details of data collection and processing, and contains a summary of data gathered. The second report, by