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The Great East Japan Earthquake of March 11, 2011 generated a massive tsunami wave that severely damaged coastal areas of Japan. Furthermore, the wave propagated into rivers, causing damage upstream far from shore. Videos recorded during this tsunami event were collected and analyzed to estimate the celerity of tsunami propagation in river and on the land. The result shows good comparison with estimation based on theoretical approaches that use water level measurement data. It was found that the tsunami celerity in river is approximately 25–30 km/h, and moved upstream with gradual deceleration. However, wave celerity on land was decreased significantly due to debris and dominant ground friction. The propagation trend in river mainstream and floodplain behaves differently in the location where the mainstream is not parallel to the embankment. Tsunami discharge and velocity in a river induced by tsunami wave were estimated based on continuity equation using the measured water level variation along the Sunaoshi River. The maximum estimated discharge is approximately 152 m3/s with the maximum velocity of 1.4 m/s.

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This paper presents a numerical study on flow and local scour around two identical cylinders with diverse spacing ratios (s/D) and alignment angles (α). The spacing ratio of center-to-center distance between cylinders (s) to the cylinder diameter (D) varied from 1.25 to 5.0, including five alignment angles ranged from 0 • to 90 • . The detailed scour processes and information were obtained in a physics-based way by using large eddy simulation coupled with sediment transport in a Lagrangian framework and a morphodynamic model. Turbulent flow properties around two cylinders in staggered array are significantly concerned by the spacing ratio and the alignment angle which reflect complex features of evolution of scour and scour depth. The computed results exhibited the scour depth is associated with the spacing ratio and alignment angles especially at the rear cylinder. For small alignment angles, the growth rate at the rear cylinder increased as the spacing ratio increased, due to a decrease in shielding effect. As the alignment angle increased, the scour depth around the rear cylinder increased until the angle reached approximately 45 • -60 • . Subsequently, the scour depth decreased with the alignment angle. It also revealed that the spacing ratio was more sensitive to the maximum scour than that of the alignment angle. For (s-D)/D > 2.0, the maximum scour depth only depended on the spacing ratio.

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