Effect of nearshore structures on reduction of wave energy along different locatons of coastline of Bangladesh

Abstract

The natural shape of Bangladesh coastal and marine areas is controlled by dynamic processes such as tides, wave actions, strong winds and it faces continuous land erosion and accretion. This study prioritizes the most vulnerable locations on the Bangladesh coast and finally selected the two most erosion-prone areas at the Cox Bazar coastline along the marine drive. Although there are few measures have been taken by the local authority using geotubes, tetrapods, and concrete block, but this does not stand appropriately against wave action; as a result, all previous measures are futile. This study is based on mathematical modeling to simulate the nearshore complex hydrodynamic and wave conditions. To analysis, the real-world nearshore scenarios, a two-dimensional model named Delft3D is used to set up the Bay of Bengal model. The coupled model is fully calibrated and validated to simulate the nearshore structures to examine the wave height, wave energy reduction rate with associated sediment transport patterns in the structures' vicinity. A series of Breakwater and Groins have been used at two different sites along the Cox Bazar coastline. The analysis shows that at site one, which is 1.7 km, Breakwaters are less capable of trapping sediment. The intervened series of Breakwater has a wave height reduction rate between 27 % - 53 %, wave energy reduction rate between 47%-78% and two of the Breakwater shows continuous erosion among three. On the other hand, series of Groin has wave height reduction rate between 9 % - 76 %, wave energy reduction rate between 17%-91%, and six groins shows continuous sedimentation within seven where one Groin shows continuous erosion. The analysis from site two, which is about 3 km shows, Groins are more capable of trapping sediment compare to Breakwater. The series of Breakwater at site two has a wave height reduction rate between 30 % -53 %, wave energy reduction rate 51% -78%, and all the eleven Breakwater shows continuous erosion; whereas, a series of Groin has wave height reduction rate between 15% - 53 %, wave energy reduction rate 51% -78%, and eleven groins show continuous sedimentation within thirteen where two Groin shows erosion. Moreover, the beach and sea view are also very important for the study areas, and Groins can be the best solution where no sand nourishment is required for long-term sustainability. This study is one of the first in Bangladesh to examine the nearshore structural intervention with Breakwater and Groin, can be used as a reference for field implementation or further research work.