Tidal inlets with attached sand spits are a very common coastal morphology. Since the evolution of the sand spits along the coastline have greatly affected on the social-economic development of local coastal areas. However, previous studies mainly focused on the sand spits which are usually in the scales of hundred meters in width. Therefore, in this study, morphological change of a smaller and unexplored sand spit located in the west coast of Phu Quoc Island, will be investigated. It was found that there is a seasonal variation in the evolution of the sand spit at Song Tranh Inlet. The Longshore sediment transport rates (LSTR) along the spit are in the order from 104 to 105 m3/year. LSTRs of fourteen inlets in the literature were reviewed and the LSTRs at Song Tranh Inlet are higher than half of the LSTRs along the fourteen reviewed inlets. This study aims at contrib-uting to the growing literature on sand spit morphological changes as well as the sustainable coastal management for Phu Quoc Island which is well known as the Pearl Island of Vietnam.

Coastal erosion is threatening the infrastructures of coastal community at the Ma River mouth in Thanh Hoa province, Vietnam. When coastal erosion happens, people try to prevent it by emergency solutions like hard structures. However, this approach usually leads to more severe problem since the mechanism for coastal erosion is not investigated and understood properly. In this study the long-term configuration of Ma River mouth in Thanh Hoa Province, Central Vietnam has been investigated using Landsat imagery from 1987 to 2023. An analytical solution of one-line model for shoreline change was also employed to calculate the sand discharge from Ma River as well as the diffusion coefficient for sand transported along-shore by breaking waves. There was an asymmetric configuration of the Ma River mouth during the last 37 years. The sand supply from the Ma River is around 350,000 m3/year. This amount of sand is going mainly to the northern beach of the Ma River delta (from 55% to 75%). The asymmetric morphology of the Ma River mouth delta is the trigger for severe coastal erosion reported recently. This study provides a quick and easy method to investigate the morphological change of cuspate deltas where measured data is limited.