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SWASH: a New Method for Quantifying Coastal Change

Buggy used to collect dataCoastal erosion is a serious national problem with long-term economic and social consequences. Developed areas are threatened with billions of dollars in property damage as a result of storm impacts and long-term erosion. Over the last few decades, data on the position of the shoreline has emerged as the principal source of information for local, state, and federal government agencies charged with managing coastal erosion. This measure of the shifting land/water interface is also an important source of information for scientific investigations of coastal change, for determinations of the sediment budget, and for conducting numerical simulations of shoreline change.

Despite the importance of this measure of coastal change, the methods available for collecting shoreline position data are very limited. The most commonly applied method-shoreline interpretation from aerial photography-is expensive, labor-intensive, and involves a considerable amount of subjectivity in identifying the shoreline. There is a significant need for a method that can provide an unambiguous and repeatable measure of shoreline position, can cover large sections of coast within a single low tide period, is inexpensive to operate, and can be used for both long-term monitoring and rapid-response surveys of storm impacts. In response to this need, the USGS developed SWASH, a vehicle-based system for measuring shoreline position which utilizes recent advances in the Global Positioning System (GPS). SWASH stands for "Surveying Wide-Area Shorelines."

SWASH methodologyMethods:

The SWASH system is mounted on a six-wheel amphibious all-terrain vehicle (click here for image of the buggy and details of instruments used). As the vehicle transits the coast, an array of GPS sensors are used to make high-accuracy measurements of horizontal position, vertical position, and beach slope. Following the field survey, position and slope data are combined to compute shoreline position, defined as the horizontal location of a target elevation contour's intersection with the beach. See the displayed SWASH schematic for more details (click on thumbnail of image to access a larger one). In keeping with historical sources on shoreline information, the Mean High Water (MHW) contour is usually chosen as the definition of the shoreline.

In contrast to shorelines derived by most previous methods,SWASH shorelines have well-defined error bars, important for determining the statistical significance of shoreline change. Error bars are calculated on a point-by-point basis as a function of beach slope and the deviation between the elevation driven and MHW. SWASH can survey more than 70 km of shoreline within a single low tide period and provide near real-time information on shoreline changes during storms. SWASH is also very inexpensive to operate relative to previous methods for obtaining shoreline position.

All information pertaining to SWASH on this page was taken from the SWASH Methodology page, with permission.

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