Quantifying the protective capacity of mangroves from storm surges in coastal Bangladesh.

Susmita Dasgupta,Md Saiful Islam,Zahirul Huque Khan,Md Raqubul Hasib,Mainul Huq,Ismael Aaron Kimirei

doi:10.1371/journal.pone.0214079

Susmita Dasgupta, Md Saiful Islam + Show 4 more

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https://doi.org/10.1371/journal.pone.0214079

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Abstract

Mangroves are an important ecosystem-based protection against cyclonic storm surge. As the surge moves through the mangrove forest, the tree roots, trunks, and leaves obstruct the flow of water. Damage to adjacent coastal lands is attenuated mainly by reducing (i) surge height, which determines the area and depth of inundation and (ii) water flow velocity. But the extent of mangrove protection depends on the density of tree plantings and the diameter of trunks and roots, along with an array of other forest characteristics (e.g., floor shape, bathymetry, spectral features of waves, and tidal stage at which waves enter the forest). Making efficient use of mangroves’ protective capacity has been hindered by a lack of location-specific information. This study helps to fill that gap by estimating reduction in storm surge height and water flow velocity from mangroves at selected sites in cyclone-prone, coastal Bangladesh. A hydrodynamic model for the Bay of Bengal, based on the MIKE21FM system, was run multiple times to simulate the surge of cyclone Sidr (2007) at the Barisal coast. Estimates of surge height and water flow velocity were recorded first without mangroves and then with mangroves of various forest widths and planting densities, including specific information on local topography, bathymetry, and Manning’s coefficients estimated from species’ root and trunk systems. The results show a significant reduction in water flow velocity (29–92%) and a modest reduction in surge height (4–16.5 cm). These findings suggest that healthy mangroves can contribute to significant savings in rehabilitation and maintenance costs by protecting embankments from breaching, toe-erosion, and other damage.

Highlights

Coastal managers increasingly recognize the protective role of mangroves as a disaster riskreduction tool. This recognition reflects the emphasis that recent scientific literature has placed on the role of mangroves in protecting adjacent coastal lands from the impacts of inundation and erosion, both during natural disasters and through their longer-term influence on coastal dynamics [1,2,3,4,5,6]
Field observations considering minimum distance between mature trees conclude that planting of S. apetala at 5 m spacing, A. officinalis at 4 m spacing, and H. fomes, E. agallocha, and C. decandra at 5 m spacing in
Some researchers skeptical about the ability of mangroves to protect against tsunamis note that mangroves might be more capable of protecting against tropical storm surges [34,35], given that surges have comparatively shorter wavelengths and more of their energy near the water surface [36]

Summary

Introduction

Coastal managers increasingly recognize the protective role of mangroves as a disaster riskreduction tool. This recognition reflects the emphasis that recent scientific literature has placed on the role of mangroves in protecting adjacent coastal lands from the impacts of inundation and erosion, both during natural disasters and through their longer-term influence on coastal dynamics [1,2,3,4,5,6]. Numerous modeling and mathematical studies have shown that, during. Mangroves protective capacity from storm surges in Bangladesh manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section

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Conclusion