Experimental study on tsunami attenuation by mangrove forest

Abstract

Laboratory experiments on the effectiveness of mangroves to reduce tsunami energy were performed. A complex tree structure of Rhizophora sp. was parameterized using the stiff structure assumption (root system and trunk) for different submerged root volume ratios and frontal tree areas. The hydraulic resistance of the prototype and the parameterized models under steady flow conditions was compared and the most appropriate parameterized model in terms of both equivalent flow resistance and practical feasibility was selected for further investigation. The damping performance of the mangrove forest was determined from laboratory tests performed synchronously in a twin-wave flumes (with and without the forest model in 1 and 2 m-wide wave flumes, respectively) for varying incident height of solitary wave, water depth and forest width. The role of the different types of wave evolution modes on wave damping is discussed based on the measurements of the forces exerted on the single tree models along the entire forest width. A new approach for the wave transmission coefficient, which is based on the ratio of the forces exerted on the trees placed in the last and first forest row, is proposed. In the paper, the most important results of the tree parameterization procedure and the wave flume experiments are discussed.