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At 14:46 local time on March 11, 2011, a magnitude 9.0 earthquake occurred off the coast of northeast Japan. This earthquake generated a tsunami that struck Japan as well as various locations around the Pacific Ocean. With the participation of about 300 researchers from throughout Japan, joint research groups conducted a tsunami survey along a 2,000 km stretch of the Japanese coast. More than 5,200 locations have been surveyed to date, generating the largest tsunami survey dataset in the world. The inundation height and run-up height were surveyed by laser, GPS, and other instruments, and the tidal correction has been accurately adjusted using a tidal database and a numerical simulation for Tohoku, an area where tide gauges were destroyed by the tsunami. Based on the survey dataset, the regional and local scale analyses were conducted to understand the basic characteristics of this event. Maximum run-up heights greater than 10 m are distributed along 500 km of coast in direct distance. The affected area of this event was several times larger than historically recorded in Tohoku. The mean inundation height in the southern Sanriku region is 10–15 m and there are several peaks of inundation along the coast from the northern to middle part of Sanriku.

Extensive studies have been carried out to study the performance of mangrove forests in wave height reduction. In this study, the reduction of the inundation and run-up of leading tsunami waves by mangrove forests was investigated through a series of laboratory experiments conducted in a long wave tank. The inundation and run-up were measured using a high speed CCD camera. Solitary waves were used to model the leading tsunami waves. Five vegetation models representing three forest densities and two tree distributions were examined on an impermeable sloping beach, and they were compared with the non-vegetated slope in view of wave reflection, transmission, and run-up. Results show that both incident wave height and run-up could be reduced by up to 50% when the vegetation was present on the slope. Dense vegetation reduced the wave transmission because of the increased wave reflection and energy dissipation into turbulence in vegetation. Normalized wave run-up on the beach decreased with the increase of both normalized incident wave height and forest density. Effect of forest density on the wave run-up on the sloping beach was further examined, and an empirical formula with the density incorporated was proposed. The study also highlighted the importance of tree distribution to wave interaction with vegetation on the slope when the forest density was unaltered, and run-up reduction difference between tandem and staggered arrangements of the trees could reach up to 20%.

In this study, a series of dam-break laboratory experiments were carried out to investigate the run-up process of breaking bores under dry- and wet-bed conditions. Detailed measurements were conducted to reveal differences in the run-up hydrodynamic characteristics under these two conditions, e.g. the bore front profile, the maximum run-up height and duration, and the instantaneous bore front velocity. Two successive bores were observed under the wet-bed run-up process, while multiple bores (three bores in general) were generated during the dry-bed run-up process due to the significant bottom friction effect. A linear relationship with the uniform gradient is found between the maximum run-up height and the initial water head for both dry- and wet-bed conditions, indicating that difference in the maximum run-up height between the dry- and specified wet-bed cases or among various wet-bed cases is not sensitive to the initial water head. Under the same initial water head, although the dry-bed run-up process takes a longer duration than that of wet-bed cases, the maximum run-up height is smallest for the dry-bed case and gradually increases with the increase of the initial downstream water depth for wet-bed cases. Under the wet-bed conditions, temporal variation of the bore front run-up velocity can be classified into two stages, i.e. the acceleration stage induced by the relatively large incident bore front water depth (large onshore hydrostatic pressure gradient) and the deceleration stage governed by the offshore-directed gravity force and bottom friction. Nevertheless, due to the small incident bore front water depth, run-up process under the dry-bed conditions does not show the acceleration stage.

Tsunamis, such as the 2004 Indian and 2011 Japan tsunamis, routinely cause severe damage along coasts. Coastal vegetation serves as an excellent, naturally occurring protection from tsunamis. However, prior studies focusing on the wave attenuation by vegetation assumed that solitary waves would adequately represent the major aspects of tsunamis. However, there are substantial differences between solitary tsunami waves with regards to their wave profiles and how it evolves with time. This study aims to improve our understanding of the wave-vegetation interactions by employing a more realistic wave profile (tsunami-like instead of solitary). This work uses measurements obtained during the 2011 Japan tsunami to parameterize the observed tsunami-like wave profile, which is then used to investigate the wave-vegetation interaction on a sloped beach, using a nonhydrostatic wave (NHWAVE) model. The work investigates the efficiency of vegetated sloped beach in mitigating the maximum run-up height and total wave energy as function of wave height, water depth, vegetation width, vegetation density and wave model (solitary vs. tsunami-like). Results show that a vegetated sloped beach is effective in reducing the wave energy of both kinds of waves. However, when a solitary wave is used, the vegetation patch is shown to be relatively better at attenuating wave energy and in reducing maximum run-up heights. The findings indicate that the solitary wave model overestimates protections afforded by coastal vegetation, and that it underestimates maximum run-up heights. The findings drawn from this study further broaden our understanding on the wave attenuation of tsunami surges and waves by a vegetated sloped beach.

Hydrodynamic properties of the breaking bore run-up process were investigated under a sloping dry bed condition. A series of laboratory experiments were performed using a 1:7.5 stainless steel slope and a dam-break type PVC-made flume. Under the dry bed condition, different flow velocities were generated by adjusting initial water levels from 8cm to 24cm in the upstream reservoir. The bore propagation velocity and the maximum run-up height were obtained from images recorded using a high speed video camera. Existing models underestimate the present measured maximum run-up height, which is ascribed to the phenomenon that multiple ensuing bores generated by the water mass compression overpass the preceding bore front during the run-up process. Nevertheless, water depth of run-up front under the dry bed condition is much smaller than that of the wet bed condition which contributes to the generation of multiple ensuing bores.