abstract
The characteristics of scoured regions behind embankments generated by the 2011 Great East Japan
tsunami were investigated along the Abukumagawa River, where severe erosion by overtopping of river
embankments had occurred, and four other locations. To quantitatively estimate the relationship
between the damage and hydraulic parameters, the tsunami was simulated by non-linear long wave
equations and a fault motion model. The maximum energy head and momentum express the maximum
scoured depth and length, but the overflow type, free or submerged, also greatly affects the scour
characteristics. Even on the far side of the river mouth, the scoured depth and length were large because
propagation of the tsunami in the river was faster and overflow occurred as a free type affected by the
local conditions of the river, i.e., a meandering course and damming by the bridge girder. The relationship
obtained by this real-scale study can be utilized to estimate the maximum scour depth and length behind
the embankment, to design footings for embankments, and to estimate the extent of the tsunami in posttsunami
surveys.
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