Kyu-Tae Shim

Along the West Coast of Korea, many reclamation projects are being carried out to expand the country’s territory for various business developments. When creating new sites through reclamation projects, it is necessary to precede the work by blocking seawater. This closure work becomes the most difficult process involved in reclamation as the water velocity increases due to the narrowing gap at both ends. However, even after the completion of the final closure work, the embankment can be destroyed due to various factors such as the piping phenomenon resulting from the difference in water levels between the sea and landward side of the revetment or the occurrence of abnormally high tides and waves. This study analyzed the process and causes of the collapse of embankments after the final closure has been conducted.

Problems caused by abnormal climate conditions are developing into major issues that are having adverse societal impacts. The rise in sea level, one of the representative problems associated with an abnormal climate, not only increases the reach and energy density of waves, but also negatively affects the stability of port facilities and the maintenance of tranquility. This study examines the increase in overtopping and the frequency of wave run-up occurring at small and medium-sized fishing ports due to the rise in sea level. In addition, wave overtopping and run-up are major factors that increase the fluctuation of the seawater surface at the port, and by analyzing the correlation between sea level rise, wave overtopping, and wave run-up, this study aims to prepare for any potential issues that may arise.

The study area was Anin Beach, where a 1.48-km-long breakwater, consisting of a non-porous caisson, was constructed over 16 months. During this process, significant erosion occurred over a wide area behind the coast, with a maximum reduction in the beach width of 36 m observed in the central part of the coastline. As a countermeasure to prevent erosion, a submerged breakwater was installed that consisted of concrete blocks and had a length of 600 m. Following the implementation of this submerged breakwater, the beach behind it increased in width by 64 m, in proportion to the installation length, while erosion phenomena, such as the loss of coastal roads, were observed at both ends of the structure. In this study, the topographical changes caused by waves and currents were analyzed to identify their causes and establish countermeasures. Additionally, the planned measures, established before structure installation, were closely examined against the actual occurrences observed onsite through a coastline survey.

In a coastal area where the water depth changes rapidly, waves developed in the offshore propagate to the coast, with a massive energy without any dissipation. Particular attention should be paid to the occurrence of damage in an island, where the land is open towards the ocean, in the event of abnormal wind wave, and design of structures in such region requires thorough examination. The southern and northern coasts of Hongdo Island located in the western coast of South Korea face the ocean side, and are directly affected when a typhoon or a high wave occurs. Therefore, structural damage due to wave generation frequently occurred in the coasts, and repair and reinforcement work were carried out several times.

This study investigated the beach nourishment effect and topographical changes when using nourishment sand with relatively large particle diameters to perform beach nourishment on a beach subject to erosion. A physical model test was conducted in a 2D wave flume with an installed wind tunnel. The experiment examined the sediment transport mechanism under conditions with wind and waves. Although applying nourishment sand with large particle diameters attenuated sediment transport, the increase in particle diameter was not always proportional to the reduction in topographical changes. Increasing the particle diameter of the nourishment sand increased the friction force between particles, resulting in large-scale erosion and accretion around the coastline, and this trend increased with winds. Also, with wind, the wave run-up height increased, the undertow became stronger, and large-scale scouring occurred at the boundary between the nourishment sand and the existing beach. Increasing the particle diameter of the nourishment sand played a role in reducing the run-up phenomenon (d₅₀: 1.0 mm with 24–50%, d₅₀: 5.0 mm with 59–83%), and the range of particles moved by winds also decreased (d₅₀: 1.0 mm with 10–38%, d₅₀: 5.0 mm with 5–37%).

The purpose of this study is to analyze the applicability of a sunken vessel as an artificial reef in a high wave energy area in a shallow water zone. Artificial reefs in general shapes are unlikely to be installed and maintained stably in high-energy wave zones. To solve this problem, a method for using a large 2000-ton class sunken vessel as an artificial reef was proposed in this study. Accordingly, we analyzed the applicability, including stability, of the sunken vessel as an artificial reef on the east coast of South Korea, where high-energy waves and swells are observed frequently. In the analysis process, various methods, such as numerical simulation and a hydraulic model experiment, were utilized. 2D and 3D numerical simulations were conducted to simulate the wave energy in the area where the sunken vessel was installed as an artificial reef to identify wave force applied to the vessel. Moreover, a hydraulic model experiment using a sunken vessel model as an artificial reef was performed to compare the stability and motion properties of the vessel model. The experimental results indicated that the stability and motion properties of the sunken vessel differed depending on the water depth. Additionally, the water depth that ensured the stability of the sunken vessel was identified.

A physical model test was carried out to evaluate a measure of reducing sediment transport in a condition of erosive wave incidence. The erosion trend was analyzed in a beach profile consisting of 0.1 mm sand, and a scenario in which 1 mm and 5 mm materials were applied to the erosion section was conducted. The effects of beach nourishment profiles with different sand diameters were verified by comparing the results when the submerged breakwater was installed. In addition, because high waves are usually accompanied with strong wind, to determine the wind effect, morphological change was examined under waves only and the coexistence of waves and wind together. The experimental results showed that sediment transport around the shoreline decreased in a condition of nourishment with 1 mm grains, and the total amount of morphological change was similar to the case in which the submerged breakwater was installed. The results illustrated that a change in wind velocity increased the wave energy density, as well as the range of morphological change.