A recent erosional problem around a river delta on the Cox's Bazar coast was analyzed in this study. The coastline extends from south to north. Rapid erosion has affected some portions of a 24-km road along the coast, and local authorities have attempted to protect the road via revetment. However, the structure was soon buried with sediment because of a growing sand spit along the river delta, and a new area was eroded. Shoreline positions for a 44-year (1972-2016) period were digitized using Landsat images. From the time stack images, we observed a sand spit growing in a northward direction from 2000 to 2015, and the adjacent erosion area extended in the same direction. We employed a numerical model (MIKE21FM SM) for the computation of wave-driven currents and sediment transport along the coast, and attempted to reproduce recent erosional processes. The numerical result shows that net littoral drift is dominant in the northward direction along the coast, which is the same direction of the spit growth observed in the satellite images. A higher amplitude spit induces higher sediment transport compared to a low amplitude spit because of the difference in local incident wave angles resulting in greater positive gradient of the longshore sediment flux distribution, causing erosion in the downcoast.
This paper describes the long-term shorelines variability of Cox's Bazar coast which is located south-east part of Bangladesh in terms of spatial and temporal over a period of 40 years. Recently the coast is experiencing severe erosion and it is becoming more vulnerable in some specific location. The spatial and temporal variability of the shorelines position is split by Empirical Orthogonal Functions (EOFs) decomposition. The result of EOF analysis shows the first five modes explains 86% of the variance and the recent erosion problem may have some relation with the variation around the Reju Khal area. The dominant modes of shoreline variability were correlated with the wave energy flux components estimated by MIKE21 SW model. The large variation around the Reju Khal may be due to longshore sediment movement, and the erosion problem at Marine Drive Road may have some connection with a growing spit.
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