SAND SPIT ELONGATION AND BREACHING AT THE LY HOA RIVER MOUTH, NORTHERN VIETNAM

Abstract

 Sand spit elongation is remarkable at the mouth of Ly Hoa river, located in northern Vietnam, and sudden migration of the river mouth has sometimes been induced by sand spit breaching. In order to understand the frequency of spit breaching and subsequent spit reformation process, a series of Landsat and Google Earth images which has been accumulated since 1976 were analyzed to clarify the characteristic change of the estuary topography. In order to quantitatively investigate such characteristics, the tip coordinate and the area of the sand spit on the left of the estuary were calculated. From the satellite analysis, it is found that the river opening has been moved consistently to the down-drift direction, and its traveling speed has reached 90m/year. In particular, the area of the sandbar has increased remarkably, and the increasing rate is almost constant. Using this value, the rate of sand volume intruded into the river mouth by waves was estimated and it is almost consistent with longshore sediment transport rate along the surrounding sandy beach.