Revised system for shallow-water design wave estimation on the coast of the Republic of Korea based on numerical model data

In this study, a new approach to calculate the shallow-water design wave (SWDW, design wave at the coastal structure) applied in the Republic of Korea is introduced and evaluated. Accurate estimation of the SWDW is crucial in designing port and coastal structure. In the Republic of Korea, the deep-water design waves (DWDW, design wave at depths greater than 20 m) are provided by the government, by which the DWDW heights are calculated at 210 grid points in the waters around the Korean peninsula using numerical models with wind fields and through extreme value analysis. For the SWDW estimation, two approaches were suggested. Case 1 was the conventional method by which the SWDW was calculated using the DWDW parameters as boundary conditions for SWAN wave modeling over a small-computational domain around target location. Case 2 was a new approach as it used the wind fields selected from the typhoon and extratropical cyclone events that had significant impacts on the target areas. By running the SWAN model for the large computational domain around the Korean peninsula, wave spectra were generated during selected storm events and these spectra were used as the boundary forcing conditions for the small-computational domain simulations around the target areas. The results of the two model cases were compared with those based on wave observations at four wave stations where the extreme value analysis were applied for the SWDW height estimation, showing that the newly developed approach was in better agreement with the observations for the typhoon events than the extratropical cyclones. In particular, the greatest SWDW height calculated Case 2 was 7.7 m which was much closer to the observation value (8.32 m) than the value by Case 1 (6.8 m), indicating that the error of SWDW estimation could be reduced by the new approach under severe conditions although the overall errors were similar between the two case. The results suggests that the SWDW estimation error could be reduce by combining the results of both approaches. The SWDW estimation and evaluation system in this study could be applied usefully in regions with similar conditions where long-term wave observational data are not sufficient to estimate the SWDWs at the targeted coastal structures.