Simplified formulae for designing coastal forest against tsunami run-up: one-dimensional approach

Thuy, Nguyen Ba; Nandasena, N.A.K.; Dang, Vu Hai; Tanaka, Norio

doi:10.1007/s11069-018-3197-z

Cited by 23 publications

(12 citation statements)

References 18 publications

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“…When the width of the coastal vegetation increases, it can reduce both the hydrodynamic force and the inundation depth downstream of the vegetation [22,25]. A few studies have clarified the effect of vegetation density and its relation to energy reduction [22,24,26], but the effect of vegetation density within a hybrid and/or compound mitigation system is unknown. Hence, in the present study, a series of model scale experiments was conducted to introduce a compound mitigation system comprising a seaward embankment model (E) followed by landward coastal vegetation model (V) over a mound model (M) (EMV) under varying conditions of different mound heights.…”

Section: Introductionmentioning

confidence: 99%

Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

2021

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As a countermeasure against tsunami inundation, the present study conducted a series of laboratory experiments using a compound mitigation system in which a seaward embankment (E) followed by landward coastal vegetation (V) over a mound (M) (EMV) was investigated in supercritical flow conditions. The changes of flow around the mitigation system and energy reduction were clarified under varying conditions of mound height and vegetation density. Cases of an embankment followed by only a mound (EMNV) were also considered for comparison. Experimental results showed that three basic types of flow structures were observed within the mitigation system in EMV cases. A water cushion was created within the mitigation system mainly due to the combined effects of the mound and vegetation. It significantly reduced the maximum total energy in EMV cases by approximately 41%66%, whereas in EMNV cases, the maximum energy reduction was found to be 23%65%. Increments in both mound height and vegetation density increased the intensity of the water cushion within the mitigation system by offering more drag and reflecting the flow, and hence, significantly reduced the energy of the flow.

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Section: Introductionmentioning

confidence: 99%

Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

2021

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“…This type of tree was found in the natural coastal vegetation zone in Sri Lanka [20]. In case of a tsunami less than 5 m high in a real scale, a P. odoratissimus tree belt was found to be effective in reducing the tsunami force due to its high density and complex aerial roots [20,35]. In the current study, a coastal forest (SLM or DLM) was considered as a secondary defense structure behind a sea embankment.…”

Section: Physical Model Of the Hybrid Defense Systemmentioning

confidence: 84%

“…Thus, the DLMs were constructed by considering the combination of widely spaced tall trees and densely grown trees similar to P. odoratissimus in its effective height (5 m in real scale). Considering the vertical configuration, the real P. odoratissimus tree was scaled down to a rigid circular cylinder like the previous study [35]. The tall forest model was considered with lower density and thickness so that the tree trunk was large in diameter and the crown height was relatively high compared to the heights of the tsunami inundation and the short trees.…”

Section: Physical Model Of the Hybrid Defense Systemmentioning

confidence: 99%

Energy Reduction of a Tsunami Current through a Hybrid Defense System Comprising a Sea Embankment Followed by a Coastal Forest

Muhammad

Tanaka

2019

Geosciences

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The 2011 Great East Japan tsunami revealed the limit of using natural or artificial infrastructures as a single tsunami countermeasure. In recent tsunami mitigation strategy, interest in a hybrid defense system (combination of natural and artificial infrastructures) rather than a single defense structure is growing, and a pilot project has already started in Japan. Clarification of flow structures within the hybrid defense system is necessary for designing an improved mitigation system. In addition, when a hydraulic jump is expected, its position should be restricted to a protected area for the resilience of the hybrid defense system. This study performed flume tests to elucidate the mitigation effect of a hybrid defense system comprising an embankment model (EM), followed by different types of single-layer emergent forest models (SLM) or vertical double-layer forest models (DLM). Different types of hydraulic jumps were observed within the defense system, jump position and their characteristics dominated the energy reduction downstream of SLM or DLM. Experimental results showed that this hybrid defense system reduced the flow energy to 30% and 40% of maximum for SLM and DLM, respectively, compared to only the single EM. Moreover, the position of the hydraulic jump was near the EM in the combination of EM and DLMs.

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“…In Pakistan alone, around 12,330 people lost their lives, 197,273 villages were damaged or destroyed and an area of more than 616,598 km 2 was flooded during the last 71 years (Flood Forecasting and Warning Centre, 2017). The 2010 floods can be considered the worst of all in Pakistan's history as they resulted in substantial loss of lives and economic output (Tariq and Van de Giesen, 2012). The main reason behind these severe storms is because most of the river cross‐sections in lowland areas are incapable of carrying storm flows, resulting in overflowing riverbanks (Buijs et al ., 2018).…”

Section: Introductionmentioning

confidence: 99%

Development of ecosystem‐based flood mitigation approach – investigations by experiments and numerical simulation

Tariq

Pasha

Tanaka

et al. 2020

Water & Environment J

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The purpose of this research was to understand how to minimise the destructive effects of floods by establishing a bio‐shield of natural vegetation. Experiments were conducted in a water flume to determine the flow properties under different vegetation conditions whereas; volume of fluid (VOF) multiphase approach with a standard k‐ɛ turbulence model was developed for a simulation. The study involved comparative analysis of flow structures and loss of energy in a single patch of finite length, layered (single or double layer with gaps) and continuous (full width) vegetation models. The results showed that, for a single patch, the increase in vegetation density and aspect ratio increased the backwater rise in front of vegetation, reduced velocity and enhanced energy dissipation. Furthermore, in the case of horizontally layered vegetation models (single and double horizontal layers), the loss of energy was higher in double horizontally layered vegetation layouts. Gaps between vegetation patches of a single horizontally layered vegetation model possessed high flow velocity, which was countered by providing a second horizontal layer of vegetation with an alternate gap. The findings from this research are critical in designing optimum vegetation layouts for flood mitigation.

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Simplified formulae for designing coastal forest against tsunami run-up: one-dimensional approach

Cited by 23 publications

References 18 publications

Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

Energy Reduction of a Tsunami Current through a Hybrid Defense System Comprising a Sea Embankment Followed by a Coastal Forest

Development of ecosystem‐based flood mitigation approach – investigations by experiments and numerical simulation

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