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Iida, T.; Kure, S.; Udo, K.; Mano, A., and Tanaka, H., 2016. Prediction of the 2011 Tohoku Tsunami scouring near structures. In: Vila-Concejo, A., Bruce, E., Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 872-876. Coconut Creek (Florida), ISSN 0749-0208. The 2011 Tohoku Tsunami left innumerable sites with large scale scouring near failed coastal structures. This was a major cause of failure, and the reconstruction of these structures in a robust way requires determination of the mechanisms and prediction of the scouring. Two mechanisms are known for tsunami scouring: erosion by the bottom shear stress and liquefaction by the pore pressure, however, these mechanisms have not been compared yet in their effects. This study aims to quantify these mechanisms and predict the scouring by the 2011 Tohoku tsunami. For this approach, we developed a numerical model by the quasi-3D finite volume method by meshing horizontally in water and vertically in ground. After validating our model, we have applied it to the breach point of a coastal levee hit by the tsunami. We can conclude that erosion by the bottom shear stress has the major role, however, the fluidisation still has innegligible effect in 28% to the maximum erosion depth. [ABSTRACT FROM AUTHOR]

Mano, A., IIda, T., Udo, K., and Tanaka. H., 2013. Breaking process and mechanism of coastal levees on Sendai Bay Coast hit by 2011 mega tsunami The 2011 mega tsunami induced by the East Japan Earthquake, Mw 9.0 hit the Sendai Bay Coast, overtopped the coastal levees and intruded deeply onto the Sendai and Ishinomaki plains by flushing people, houses, trees, etc. The levees with 6 to 7 m height had been constructed along 65 km-long sandy beach to protect the hinterland from the storm surges and wind waves. Eighty percent of the levees were broken by the tsunami in various degrees ranging from scatter of the surface blocks to the complete disappearance. The government decided to rebuild the levees with the target of the local major hazards as the storm surges but in a durable way even for the tsunami overtopping. Based on this background, this study aims to find the breaking process and mechanism of the coastal levees especially for the destructive cases. We conducted field survey, and collected aerial photos, tsunami records and videos, blue prints of the levees, etc. We integrated information of the tsunami records and videos, and matched the spatial information of the various data by GIS. These analyses enabled well understanding on the breaking process and mechanisms composed from two steps: (1) The impact of the leading bore with the maximum amplitude of 6 to 7m broke weaker parts like structural joints, parapets, landward soil slopes. (2) Return flow concentration to the broken parts in the first step or to the channels and swamps expanded erosion to make tsunami channels and bays and to lead levee breach. [ABSTRACT FROM AUTHOR]