Numerical simulation estimating effects of tree density distribution in coastal forest on tsunami mitigation

To control river regime from ship wave attacks, porous structure have been built along the riverbank. The results are not as good as expected at all locations even though same structures are applied. This study firstly investigated the interaction between porous structure and waves under different volumetric porosity of structure (θ) by conducting physical experiments. Based on that, relationship between θ and drag coefficient was established by using a 1-D model. The optimal θ to mitigate wave attacks was then determined by a 2-D model taking into consideration not only cross slope behind groins (i) but also the gap between two neighboring groins (G). In cases of i =1/100, the combination of  = 0.4 and L/G = 5 (L is the stream-wise length of a groin) could bring out the best wave energy reduction. It is necessary to consider both of i and G for designing stream-wise groins.

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“…6 as the drag coefficient decreases with the increase of porosity. This result agrees well with the study of Iimura and Tanaka 14) …”

Section: (2) Numerical Simulation A) 1-d Model Validation and Applicasupporting

confidence: 94%

The Optimal Porosity of Stream-Wise Groins for Wave Attenuation Under Different Cross Slope Conditions

2015

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“…In fact, a number of field surveys conducted after recent major disasters such as the 2004 Indian Ocean Tsunami and the 2013 Typhoon Haiyan have confirmed the mitigation effect of mangroves against tsunamis, storm surges, and high waves (e.g., Wolanski et al, 2009;Ellison, 2009;Teh et al, 2009;Narayan et al, 2010;Rasmeemasmuang 5 and Sasaki, 2015;Mikami et al, 2016). Such function of vegetation has also been confirmed by laboratory experiments that imposed tsunami-like bores in a wave flume (Irtem et al, 2009;Iimura and Tanaka, 2012;Strusinska-Correia et al, 2013). Takagi et al (2016a) demonstrated that the impact of a type of tsunami induced by a sudden dyke failure would be substantially mitigated by planting a mangrove belt in front of the dyke, through two mechanisms: (1) a reduction in floodwater velocity and inundation depth and (2) a flow smoothing 10 effect, which reduces strong turbulence.…”

Section: Introductionmentioning

confidence: 81%

Design Considerations of Artificial Mangrove Embankments for Mitigating Coastal Floods – Adapting to Sea-level Rise and Long-term Subsidence

Takagi

2017

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Abstract.Mangrove plantation belts are expected to act as natural infrastructural buffers against coastal hazards. However, their performance will not endure over time if the platform is not appropriately designed. In fact, despite massive funds dedicated to the rehabilitation of mangrove forests, the long-term survival rates of mangroves are generally low. This paper investigates the function of mangrove embankments in attenuating the amplitudes of ocean tides 10 through a coupled numerical model that reproduces shallow-water wave propagations under the progress of soil consolidation. The developed model is capable of simulating tidal propagation over an artificial embankment, which will inevitably change its ground surface elevation with the passage of time because of sea-level rise, land subsidence, vegetation growth and sediment accretion. A parametric analysis demonstrates that high tides could be effectively mitigated only if the embankment is appropriately designed to maintain an equilibrium state among 15 these multiple influences over the long term. On the other hand, an embankment designed without considering geomorphological transitions will become submerged under the rising sea level, resulting in no significant effect on tidal damping. Therefore, the artificial mangrove embankment must be carefully designed to function not only during the initial stage of its lifetime but also over time, to avoid system failure in the future. 20

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“…Coastal vegetation can significantly aid in reducing the severity of tsunami waves, diminishing the amount of energy generated by the tsunami (Tanaka et al 2007). Therefore, research has focused on the interaction between a uniform flow (a tsunami wave) and a submerged object, where the resulting loss of tsunami height causes simultaneous decreases in the flow velocity and hydrodynamic forces (Iimura and Tanaka 2012).…”

Section: Introductionmentioning

confidence: 99%

Field study on planted forest structures and their role in protecting communities against tsunamis: experiences along the coast of the Biobío Region, Chile

et al. 2015

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A field study using satellite images was carried out to analyze the effect of coastal vegetation in mitigating the impact of a catastrophic tsunami on coastal villages in the Biobío Region, Chile, in February 2010. Two types of stand, Pinus radiata D. Don forests and Cupressus macrocarpa Hartw. shelterbelts, appear to have protected coastal areas behind them from the direct impact of the tsunami. The impacts of the horizontal and vertical structures of these coastal forests on the drag forces were analyzed by observing the characteristics of Pinus radiata forests and Cupressus macrocarpa shelterbelts. The stands absorbed the impact of the tsunami without incurring broken stems or uprooted trees due to their diverse horizontal structure, as they contained short trees with various diameters. However, small areas of the stands were damaged by salinity after the tsunami. For this tsunami, which was less than 3 m high, the horizontal and vertical structures of the P. radiata and C. macrocarpa stands provided effective protection for coastal villages since they reduced the velocity and height of the tsunami. A shelterbelt consisting of three rows of C. macrocarpa in front of the tsunami and a P. radiata forest with a density of 11 trees/100 m 2 and a width of[50 m immediately behind the shelterbelt are suggested as a means of protecting communities along the coastline of the Biobío Region against tsunamis.

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Numerical simulation estimating effects of tree density distribution in coastal forest on tsunami mitigation

Cited by 112 publications

References 16 publications

The Optimal Porosity of Stream-Wise Groins for Wave Attenuation Under Different Cross Slope Conditions

The Optimal Porosity of Stream-Wise Groins for Wave Attenuation Under Different Cross Slope Conditions

Design Considerations of Artificial Mangrove Embankments for Mitigating Coastal Floods – Adapting to Sea-level Rise and Long-term Subsidence

Field study on planted forest structures and their role in protecting communities against tsunamis: experiences along the coast of the Biobío Region, Chile

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