Topographical Change in Coastal Areas Arising from Soil Erosion in the Riparian Zone

Sedimentary inputs into coastal estuaries because of activities upstream can lead to rapid bathymetric and topographical changes, which may affect coastal functions such as habitat or fisheries. In South Korea, the Four Major Rivers Restoration Project was initiated in 2008 to address environmental problems arising from dredging and land reclamation, and a number of ecological parks were created. This study analyzed: 1) the land cover of each period using land cover maps before (2007), immediately after the project (2012), and after five years (2017); 2) the average annual amount of soil loss from the riparian zone of the Nakdong River using the revised universal soil loss equation (RUSLE); and 3) the change in the area of barrier islands in the estuary of the Nakdong River from 2008 to 2017. In order to generate the factors required for RUSLE, various spatial data, such as land cover maps, national spatial information, aerial photographs, a soil map, and average annual precipitation data were used. The results showed the percentage of annual soil loss from classes 4, and 5 (severe and very severe levels of soil erosion, respectively) increased immediately after the project finished in 2012 but decreased by 2017. The digitized aerial photographs confirmed that the area of Maenggeummeori-do, one of the barrier islands located in the estuary of the Nakdong River, decreased by more than 20 % as sediment inputs declined. Thus, it was confirmed that changes in soil loss in riparian zones arising from river maintenance projects can affect the area of barrier islands in coastal estuaries. Through this study, it was revealed that large-scale river refurbishment projects indirectly affected soil erosion in the waterfront area of the Nakdong River, which eventually affected the area change of the barrier island at the mouth of the Nakdong River.