Effect of open gap in coastal forest on tsunami run-up—investigations by experiment and numerical simulation

• Published in: Ocean engineering Vol. 36; no. 15; pp. 1258 - 1269
• Main Authors: Ba Thuy, Nguyen, Tanimoto, Katsutoshi, Tanaka, Norio, Harada, Kenji, Iimura, Kosuke
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-11-2009; Elsevier
• Subjects: Applied sciences; Bioshield; Buildings. Public works; Coastal; Coastal forest; Computer simulation; Drag; Drag force; Earth, ocean, space; Exact sciences and technology; External geophysics; Flow velocity; Forests; Gap; Hydraulic constructions; Marine; Mathematical models; Pandanus; Pandanus odoratissimus; Physics of the oceans; Port facilities and coastal structures. Lighthouses and beacons; Surface waves, tides and sea level. Seiches; Tsunami run-up; Tsunamis; Turbulence induced shear force; Vegetation; ISEW, Southeast Asia; Drag force; Tsunami run-up; Gap; Pandanus odoratissimus; Bioshield; Turbulence induced shear force; Coastal forest; Validation; Monocotyledones; Forests; Turbulence; Tsunami; Shear force; Experimental study; Pandanaceae; Coastal zone; Drag; Angiospermae; Numerical simulation; Flow velocity; Spermatophyta; Mathematical model
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2009.07.006

The objective of this study is to investigate the effects of an open gap, such as a road, in a coastal forest on tsunami run-up. A numerical model based on two-dimensional nonlinear long-wave equations was developed to account for the effects of drag and turbulence induced shear forces due to the presence of vegetation. Experiments were conducted on a forest simulated with vertical cylinders by changing the gap width. The numerical model was validated in good agreement with the experimental results. The numerical model was then applied to a wide forest of
Pandanus odoratissimus, a tree species that is a dominant coastal vegetation on a sand dune in South and Southeast Asia. The effect of vertical stand characteristics of
P. odoratissimus with aerial roots was considered on the drag resistance. A straight open gap perpendicular to the shoreline was used to investigate the effect of gap width. As the gap width increases, the flow velocity at the end of the open gap first increases, reaches a maximum, and then decreases, while the run-up height increases monotonously. The maximum velocity in the present condition is 1.7 times the maximum velocity without a coastal forest. The effects of different gap arrangements in the forest on tsunami run-up were also investigated in this paper. The flow velocity at the end of an open gap can be reduced by a staggered arrangement.