Abstract
Downdrift coastal erosion has occurred at natural or man-made groynes on Korea’s eastern coast, caused by oblique high waves in winter months. The resulting shoreline planform has a sagging shape with a maximum indentation point within the eroded shoreline. This study focused on solving the frequent and severe coastal erosion problem of this type at the Jeongdongjin review of wave data over 40 years from the National Oceanic and Atmospheric Administration (NOAA), as well as analyzing shoreline monitoring images for identifying the yielding line of maximum indentation points. An analytical method was developed to verify the eroding shoreline in a sagging shape and its maximum indentation by applying the conservation principle of sediment transport and the empirical model of equilibrium shoreline. To examine how well the empirical formula is suitable for the Jeongdongjin coast, the annual directional spectrum of the observed wave data was applied to the simple diffraction wave model for the gamma breakwater, and satisfactory agreement was obtained by comparing it with the shoreline results. Breaking wave height and angle, duration, longshore sediment transport coefficient, and protruding length of the groyne were the inputs. The theoretical results are in good agreement with those of the shoreline monitoring program. The factors mitigating downdrift coastal erosion of this type were identified by applying the obtained theoretical solution, and the engineering solutions were examined via factor analysis.
Highlights
On the eastern coast of Korea, low waves from the ENE direction prevail in summer, whereas high waves from the NE direction dominate in winter
This study focused on solving the frequent and severe coastal erosion problem of this type at the Jeongdongjin review of wave data over 40 years from the National Oceanic and Atmospheric Administration (NOAA), as well as analyzing shoreline monitoring images for identifying the yielding line of maximum indentation points
To examine how well the empirical formula is suitable for the Jeongdongjin coast, the annual directional spectrum of the observed wave data was applied to the simple diffraction wave model for the gamma breakwater, and satisfactory agreement was obtained by comparing it with the shoreline results
Summary
On the eastern coast of Korea, low waves from the ENE direction prevail in summer, whereas high waves from the NE direction dominate in winter. In areas where seasonal wave direction changes, local shoreline orientation responds to changes in 25 wave direction (for example, Sokcho and Jeongdongjin Beaches in Korea; Kim and Lee, 2015). Coastal erosion of more than 30-m in length has occurred often along the eastern coast of Korea because of seasonal high waves at the downdrift of natural groynes. A typical case of erosion of this type occurred in 2016 at downdrift of the northern groyne in Sokcho Beach (128o36’14”E, 38o11’25”N) in Gangwon-do Province, caused by winter high waves.
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