Effects of Inappropriate Beach Nourishment on the Coastal Sand Dune Resilience

Kang, J.H., Lee, J.H., and Choi, K.H., 2024. Effects of inappropriate beach nourishment on the coastal dune resilience. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 453-457. Charlotte (North Carolina), ISSN 0749-0208. Beach nourishment is an alternative and supplementary method to hard protection for coastal erosion, achieved by increasing the volume of beaches or dunes through sediment filling. However, nourishment that does not consider the location of sand filling, type of sand, and particle size may cause problems with the geomorphic process and dynamics of the coast. This study analyzes the changes in dune topography caused by a case of inappropriate nourishment and discusses what should be considered. Okjukdong Sand Dune, located on an island in the Yellow Sea, was highly active and dynamic in the past, but after afforestation for the windbreak, sand erosion is seriously progressing in the hind dune. In this area, nourishment was carried out by directly filling sand into the eroded hind dune. As a result of nourishment, the sand dune topography was temporarily restored, but after one year, about 14% of the filling sand was eroded, confirming that the sand trapping effect was minimal. In addition, as a result of comparing the sand particle size in 2008 before and in 2023 after the nourishment, it was confirmed that the particle size was increased from fine to very coarse, and the sorting was lowered. The cause is that the mixed sediments of sand and gravel deposited in the port were used as a source of nourishment. It has been observed that the wind blowing from the coast has decreased due to the pine vegetation planted as a windbreak, and the wind speed has also weakened. This is the result of selectively moving only small-sized sand that can be moved by the wind among filling sand. In order to restore the function of coastal dunes, the coastal dynamic process is very important through thinning and removal of the pine forest and recovery of wind flow to increase nature resilience.