Damages to River Dikes Due to Tsunami in South-central Coastal Area of Iwate Prefecture in 2011 off the Pacific Coast of Tohoku Earthquake

Abstract

Numbers of river dikes were damaged by the earthquake motion and tsunami in 2011 off the Pacific Coast of Tohoku Earthquake. This paper summarizes the damages on river dikes in middle and southern coastal part of Iwate Prefecture, with the intention of obtaining physical properties of embankment materials to mitigate the damage on river dikes due to tsunami. Damage configurations such as erosion and collapse were investigated along some rivers in the region of tsunami run up from the estuary. The spots, shapes, soil materials and the damage configurations of the river dikes are highlighted. Damages on embankments at the crossing with road bridges or railway bridges were also surveyed. These investigations have revealed that the river dikes protected with concrete facings will suffer less damage, and that even the three-face-armored banks will be subject to erosion in the upstream of the structures such as abutment or water gate.