Coastal Services Center

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Establishing Beach Setback Lines

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State law requires that South Carolina's beach setback lines be revised every 10 years. In 1998, the state's coastal managers began using LIDAR (Light Detection And Ranging) data for this purpose. They were able to map the entire state's shoreline with fewer resources and in less time than previously possible using traditional survey methods.

The Project: Revising South Carolina's Beachfront Jurisdictional Line

South Carolina's beachfront jurisdictional line (setback line) is located a minimum of 20 feet behind the crest of the primary dune system. The line is established to help preserve natural dune systems, minimize the impacts of erosion, and reduce the risk of damage or destruction of buildings and structures from waves and storm events. All the land seaward of the setback line is under authority of the state, and development is restricted. The precise location of the line can be worth millions of dollars to property owners, builders, and the state. It is critical that South Carolina develop a legally defensible, accurate, and up-to-date line for nearly 200 miles of beach.

In the past, South Carolina's Office of Ocean and Coastal Resource Management (OCRM) measured dune elevation from stereo pairs of aerial photographs (3-dimensional views); however, questions arose about the accuracy of the resulting information. In 1998, the state tested a method using Global Positioning Systems (GPS) to measure elevation. This method produced highly accurate results, but required staff to walk along the crest of the dune for the entire coast. It was estimated that two staff working all day could survey about three miles of coast per day. Under ideal conditions that equates to about 66 days of fieldwork for each surveyor, not including the post-processing and analysis of the data.

LIDAR data for Pawleys Island, South Carolina, are displayed as a color grid and elevation contour lines. The grid is colored based on elevation: the blues indicate land that is at or below sea level, the greens and yellows are above sea level, and the reds are features with higher elevations, such as houses and boardwalks. To help visualize elevation, a shading effect (hillshade) was applied. Technicians use the elevation data to designate the primary dune crest, which in this example is a pink line. OCRM places the setback line a minimum of 20 feet landward of this dune crest. The distance of the setback line from the crest varies for each area depending on the local erosion rates.

Deriving the Beachfront Jurisdictional Line with LIDAR Data

In 1997, working with the NOAA Coastal Services Center, OCRM acquired LIDAR data for the entire state of South Carolina. The data are accurate both vertically and horizontally, meaning that the data accurately represent the position and height of the ground.

To update the state's setback lines, the elevation points were processed into elevation contour lines. From these contours, the crest of the dune was delineated, and the setback line was established a minimum of 20 feet landward. It was estimated that one technician at a computer with the data could map an average of 10 miles of beach a day. That amounts to about 20 days of work per year, as compared to the 132 manpower days required using the GPS technology.

The Result

Today, OCRM is using beachfront jurisdictional lines developed using LIDAR and will continue to do so until 2007, when it will be time for a remap. OCRM plans to use LIDAR data, collected during December 2005 and January 2006 by the U.S. Army Corps of Engineers', to remap the beachfront jurisdictional lines. The U.S. Army Corps of Engineers LIDAR data is available from the NOAA Coastal Services Center's Web site and can be downloaded using the LIDAR Data Retrieval Tool (LDART).

For More Information

• South Carolina Department of Health and Environmental Control (DHEC) Office of Ocean and Coastal Resource Management (OCRM)
• NOAA Coastal Services Center Topographic Change Mapping Project

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