MAPPING ESTUARINE SHORELINES IN SOUTH CAROLINA: METHODS, PROBLEMS, AND ANALYSIS

A pilot project is being done to develop a standardized methodology for digitizing estuarine shorelines and complements existing coastal shoreline digitization projects. The project shares similar ideas of development, but the estuaries are complex areas with their own unique challenges. In cooperation with coastal geologists, geomorphologists, GIS analysts, and other concerned partners, the methodology was progressively developed. A first step focused on creating an inventory of data sources that could be used to digitize shoreline positions. We were interested in both a temporal and spatial data set. Data sets inventoried include old nautical charts (T- and H-sheets), coastal topographic maps, aerial photography of various ages, ortho-rectified imagery, satellite imagery, and lidar. Results of the inventory will be made available through a web application. Shoreline contacts are, and will be, digitized using heads-up techniques. Autovectorization may be feasible for paper maps, but it seems unusable for imagery at this time. Efforts also are being made to extract shorelines from lidar datasets using tidal gauge information. The methodology will include a means to identify and delineate uplands, marshes, mudflats, water courses, and recognition of a new feature in the estuarine system, the fringe. We interpret fringe as collapsed upland areas – a result of the modern transgression. Another requirement of this project is to identify and capture locations of manmade structures such as docks, walkways, revetments, and seawalls. Understanding the distribution of these features is important to planners. The final aspect of the project will take a temporal series of shorelines to evaluate rates and vectors of physical change. Established software packages (DSAS), however, have known limitations when applied to highly tortuous shorelines. The recognition of the fringe unit adds to this overall complication, and alternative methods will be needed to evaluate rates of change.