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Bangladesh: Can mangroves mitigate catastrophic consequences of cyclone-induced storm surges?
By Susmita Dasgupta
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To get a deeper insight into the design issues, I conducted research in collaboration with the Institute of Water Modeling in Bangladesh – one of the world’s most vulnerable countries to tropical cyclones. The study focused on seven coastal locations. We used a hydrodynamic model for the Bay of Bengal based on the MIKE21FM system to replicate the category 4 Cyclone Sidr, which generated a 12-15 ft storm surge along the Khulna-Barisal coast of southwest Bangladesh in 2007. Recently published in PLOS One, our study estimated surge height and water flow velocity, first without mangroves and then with various forest widths and planting densities of different mangrove species.
Our findings show varying levels of protection from mangroves for different tree species and forest widths and densities across the seven locations. Sonneratia apetala was the species that provided the greatest protection. Mangroves generally reduced surge height by 4cm to 16.5cm with mangrove belts of 50m to 2km width, and reduced water flow velocity by 29 to 92 percent with forest widths of 50m or 100m. The findings also highlighted that the range of protection is location-specific.
Quantifying the protective capacity of mangroves from storm surges in coastal Bangladesh, our study emphasizes the important role mangroves can play in a multi-dimensional approach for protection against cyclonic surges. For protection from cyclones, mangroves may be particularly effective in protecting rural areas where populations are widely dispersed and the construction of built infrastructures like seawalls may not be economically feasible over long coastlines. In contrast, for densely populated coastal regions, mangroves alone will not fully protect population, assets, and activities at risk considering the reduction of surge height from mangroves is generally modest. However, even a modest reduction in surge height provided by healthy mangroves in the foreshore of embankments will allow embankment heights to be lower, thereby reducing the cost of construction considerably.
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