Natural coastal barriers, such as sandbars, provide protection against storm surges and flooding exacerbated by sea-level rise and climate change. Cigu sandbar, located on the southwestern coast of Taiwan, faces steady erosion problems due to global warming, extreme natural events, and unnatural events. A continuation of this may lead to habitat loss, job loss, and jeopardized ecosystem. A clear understanding of shoreline changes and sediment transport is helpful when trying to understand the reasons for coastal erosion. This study attempted to construct a visual and numerical representation of shoreline changes and sediment transport along a sandbar in the Cigu lagoon by combining the technology of remote sensing with the hydrodynamic model. Various datasets over different temporal scales were synthesized in an attempt to make a chronological series easy to understand. The results show that from 1986 to 2021, the shoreline changes indicate high erosion, especially on the north side of the Wangzailiao sandbar, with a maximum rate of -29.3 m/year (EPR) and -33.7 m/year (LRR). Results have indicated that in this particular case, the erosion in the Cigu sandbar has been caused by a series of typhoons and the coastal management decisions over the last century. In addition, The analysis of sediment transport revealed that in the winter season, the amount of sand transported is much higher than in the summer season, resulting in a high erosion along the sandbar and siltation inside the lagoon. Now the erosion indicates a stable state with an average of 6 m/year, but most geologists predicted that the sandbar would reach the land and the lagoon would disappear. In order to control the erosion into the stable state, sustainable solutions and adaptation strategies need to be taken into account with regard to the management of the Cigu sandbar.

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