Shoreline Change Analysis After Construction of Coastal Structures in Wonpyeong-Chogok Beach by Satellite Image Process

As the number and quality of satellite data detecting the Earth increases, a significant number of research fields are using these images, providing increasingly interesting results that were previously unimaginable. In this study, we extract the coastline from satellite images captured over a long period of time and analyze how the location of the coastline has changed in time and space.

Recently, many studies have attempted similar analyzes. However, the resolution of the image is low, so the results tend to be unreliable, as they often produce trend results of less than cm per year. Therefore, in this study, we first analyzed how reliable the trend results are depending on the amount of data, even if the resolution is low.

We also present a method to obtain the location of the coastline from reference points fixed behind the coast by linearly fitting nearby coastline points to reduce the error of coastline points extracted from satellite images. This method obtains the coastline position as the distance to the intersection of the base line and the fitting line and obtains the coastline gradient as the angle of the fitting line.

This method was applied to Wonpyeong-Chogok Beach located in the East Sea of the Korean Peninsula to analyze how the coastline has evolved over the past five years from 2019 to 2023, when coastal structures were built. On this beach, which has a total length of 2.9 km, three submerged detached breakwaters, two emerged detached breakwaters, and three groynes were built to reduce beach erosion. Reference points are located about 100 m behind the circular line that best fits the coastline, and the direction of base line is fixed to face the center of the fitting circle. Behind the emerged detached breakwater, the rate of change is up to 6.2m per year, and even in areas where structures have not yet been installed, there is a slight forward trend (0.4m/yr) due to the influence of beach nourishment. The standard deviation of the coastline position data for each base line ranges from 4.0m to 10.6m. Recently, Lim et al. (2022) presented the relationship between the standard deviation of the coastline data and sand grain size, and compared to the sand grain size results collected in the field, the grain size value was shown to be larger. The reason is that if the annual mean coastline is not maintained and continues to advance, the standard deviation increases. Considering this effect, the results are compared with observed sand gain size data. Therefore, it will be interesting to see how feasible it is to estimate the sand grain size from the analysis of long-term shoreline data obtained from satellite data, as in the results of this study.

 

 

Reference

Lim, C., Kim, T.-K., Kim, J.-B., and Lee, J.-L. (2022). A study on the influence of sand median grain size on the short-term recovery process of shorelines. Front. Mar. Sci. 9. doi: 10.3389/fmars.2022.906209