Lessons Learned from the 2011 Tohuku Tsunami on Coastal Structures
Abstract
The 11 March 2011 Tohoku Tsunami caused devastating damage in coastal structures along the Japanese coasts due primarily to overtopping flows. Tsunami inundation depths exceeded substantially the design heights of the structures. A typical damage pattern of the mound-type sea dikes is the formation of severe scour holes along the landward side of the dikes; the crest portion was also blown away by tsunamis in some cases. A typical damage pattern of the upright-type seawalls is the rotational failure due to tsunami's lateral forces together with the undermined foundation. Such observations yield invaluable lessons learned from the Tohoku Tsunami, which allow us to evaluate the overtopping effects on seawalls, dikes, and levees. Storm surges can cause substantial overtopping flows and are most likely the cause to create serious flooding in the coastal zones when we consider the effect of fast-growing sea-level rise associated with the current climate change. Based on the observations of the tsunami damages, we analyze and seek an optimal seawall design so that the structures can have better chance to resist undermining and overtopping failure. It is shown that the slope of the lee-side surface is a critical factor to reduce the failure: the mild slope creates smaller overtopping-flow curvature at the top and also at the landward foot of the structure; thereby it decreases the centrifugal forces induced by the flow. To demonstrate this mechanism, the centrifugal forces are computed quantitatively for some example cases.Sea-dike damage in Isobe, Fukushima
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMNH23C..04Y
- Keywords:
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- 4564 OCEANOGRAPHY: PHYSICAL / Tsunamis and storm surges;
- 4304 NATURAL HAZARDS / Oceanic;
- 4313 NATURAL HAZARDS / Extreme events