Coastal erosion trend analysis using a combination of remote sensing and hydrodynamic models: Case study of Ca Mau Cape, Mekong Delta

Background: Coastal erosion and the loss of protective forest areas have recently become serious problems in the Ca Mau Cape (CMC) area of the Mekong Delta. Specifically, in 2016–2020, the rate of erosion in some subsections of the east coast reached 25–37 m/year and the forest area decreased significantly. Objectives: To analyse erosion and accretion trends in the period 2016–2020 and to determine the mechanism underlying erosion in the CMC using a hydrodynamic model focused on tides, currents, waves, and sediment transport. Methods: Satellite images (Google Earth), remote sensing images (Landsat 8 OLI/TIRS C1 Level-1), and a combination of hydrodynamic modules were used to evaluate the combined effects of tides, currents, waves, and sediment transport on erosion. Results: Remote sensing image analyses revealed that the east coast has a very high rate of erosion, with the highest erosion rates of 35 m/year in both 2016–2018 and 2019–2020, while the west coast showed an accretion trend in 2016–2018, followed by strong erosion in 2019–2020, with a rate of 10 m/year. Hydrodynamic models showed that hydrodynamic factors, such as tides, currents, waves, and a low suspended sediment concentration (SSC), directly contribute to the erosion trend in the area. The differences in water level between the high tide and low tide on the east coast, reaching 2 m (dry season) and 0.8 m (wet season), were consistently two times higher than those on the west coast, i.e. 0.9 m (dry season) and 0.4 m (wet season). The flow rates on the east coast (i.e. 0.4–0.6 m/s, on average) were significantly higher those on the west coast (0.2 m/s, on average). Wave heights on the east coast, reaching 1.5–2 m in the dry season and 0.6–1 m in the wet season, were consistently higher than those on the west coast, reaching 1–1.2 m (dry season) and 0.4–0.6 m (wet season). In addition, the SSC was lowest under strong erosion, with average concentrations of 0.04–0.06 kg/m3 in the wet season and 0.02–0.04 kg/m3 in the dry season. The SSC was highest in the sections showing accretion trends, with concentrations of >0.3 kg/m3 in the wet season and 0.08–0.1 kg/m3 in the dry season. Conclusion: Evaluating shoreline changes using remote sensing technology and validating these results using hydrodynamic models provides a better understanding of the mechanism underlying coastal erosion and its development and provides a basis for the development of a coastal protection strategy. © 2022 Elsevier B.V.