Wave Reduction by Mangroves during Cyclones in Bangladesh : Implementing Nature-BasedSolutions for Coastal Resilience

• Published in: IDEAS Working Paper Series from RePEc
• Main Authors: Gijón Mancheño, Alejandra, Vuik, Vincent, Wesenbeeck,Bregje K van, Jonkman, S N, Bas, Moll, Roelof, Kazi, Swarna, Urrutia Duarte, Ignacio M, Mathijs Van Ledden
• Format: Paper
• Language: English
• Published: St. Louis Federal Reserve Bank of St. Louis 01.01.2022
• Subjects: Bangladesh

This paper investigates how mangrove foreshores can be integrated into embankment designs inBangladesh. The effect of mangroves on surges has already been studied for the design conditions of Bangladesh.However, the impact of wave attenuation by mangroves on embankment designs is not known. A model is thus developedto estimate the wave height reduction by a mangrove forest, and how such wave attenuation would influence the design ofa landward embankment. Model simulations suggest that mangrove belts with a width between 100 and 1,000 meters(perpendicular to the coast) could provide wave attenuation rates between 7 and 55 percent (compared to a situationwithout mangroves) at potential afforestation sites identified in previous studies. Such wave attenuation rateswould reduce the embankment height by 0.09–0.30 meters, diminish the slope revetment thickness by 13–46 percent, anddecrease the wave shear stresses at the embankment toe up to 25–70 percent. Relatively wider mangrove belts not onlycause a larger reduction of the embankment design requirements, but also host larger biodiversity and are moreresilient against pests and extreme events. The model results are highly sensitive to the mangrove properties, andcollecting data on the local mangrove species is recommended to reduce uncertainty in the predictions. Moreover, theresults also suggest that trees older than 10–20 years might collapse during storms. Expanding the mangrove stabilitymodel, including other pioneer species in the analysis, and exploring the option of canopy pruning are thus advised toensure the integrity of any future afforestation efforts. Overall, this paper provides a methodology that could beapplied to design nature-based solutions in Bangladesh.