Calculating Long-Term Shoreline Recession Rates Using Aerial Photographic and Beach Profiling Techniques
Keywords:Coastal erosion, shoreline position, survey methods, rate calculations, beach
Quantifying measurement error and precision may be the most difficult step of shoreline recession rate calculations. Calculation of long-term shoreline recession rates based on aerial photograph analysis reflect only the shoreline positions at the time of photography. Conventional methods of long-term recession rate calculation were combined with beach profiling techniques in order to quantify potential errors that can be produced by short -term variations in shoreline position. Monthly beach profiling of a typical northeastern/mid -Atlantic microtidal and wave dominated shoreline demonstrated short-term shoreline position changes of up to 20m over a one year period. Average long-term shoreline recession rates in this area were 1.2 m/yr ± 1.0 m/yr. Short-term shore line position changes were the largest source of error in the long-term recession rate measurements. This emphasizes that photographed shorelines do not necessarily represent the seasonal mean shore line position, particularly in locations where shorelines characteristically exhibit relatively large short-term variations in shoreline position.