INTERRELATIONSHIP BETWEEN SERIOUS SHORELINE RETREAT AND SAND TERRACE FORMATION ON CUA DAI BEACH, CENTRAL VIETNAM

Abstract

 Morphology of Cua Dai River mouth and adjacent sandy beaches in Hoi An City, central Vietnam has been being eroded severely in recent years. Results of Landsat image analysis reveal that morphology of river mouth in the period from 1975 to 1991 is highly similar to one in the period from 2003 to 2015; long sand spit on the left side and cuspate shoreline (cuspate foreland) on the right side. Meanwhile, welding of two sand spit occurred in the period from 1995 to 2002. The river mouth topography formed during the 40-year long period are classified into three types. The right bank of river shifted to the south about 250m. That is corresponded to the period with elongation of sand spit on the left after welding from offshore sandbar. The tip of cuspate shoreline on the right side was also observed to move to the south during the period that right river bank shift to the south. The shifting to south of main river channel resulted in more sediment deposit on the right side of the river mouth, resulting in serious erosion on the left beach.