integrated coastal zone management project west ... - Iczmpwb.org

165Figure 15: Possible sediment transport pathways around Sagar Island based onconfiguration of coastal landforms. A sediment convergence zone is proposed on the westcoast (Pethick, 2008).South coast erosion161. The overall erosion of the south coast of Sagar Island appeared to John Pethick(2008)to be a product of rising sea levels and is to be explained by the estuarine roll-over model.This general background erosion is however at a much slower rate (approximately 1m peryear) than the erosion rate at Dublat and Beguakhali where rates of 10m per year areexperienced at present. It is noticeable that both these erosional areas are located at the„corners‟ of the island: that is where sediment transport pathways must change directionabruptly. A possible explanation for these high erosion rates is therefore that sedimentcarried along the coast is temporarily moved offshore at these „corners‟ causing sedimentstarvation and erosion as they do so. This process may be exacerbated by the specificlandforms at each site.Figure 16 shows that the hard coastal defences at Beguakhali erected to protect the formerlighthouse and pilot station, although they have failed to arrest the erosion here, havesucceeded in slowing the erosion rate down relative to that of the earth embankments oneither side. The result is that the defended stretch now forms a headland along whichincreased current velocities prevent the deposition of fine sand. Figure 12 shows that at