Serious Erosion of the Southern Sendai Coast Due to the 2011 Tohoku Earthquake Tsunami and Its Recovery Process - Post-Tsunami Hazard: Reconstruction and Restoration - page 216

Chapter 15
Serious Erosion of the Southern Sendai Coast
Due to the 2011 Tohoku Earthquake Tsunami
and Its Recovery Process
K. Udo , Y. Takeda , M. Takamura , and A. Mano
Abstract We investigate morphology change of the southern Sendai Coast due to
the 2011 Tsunami by analyzing topography and aerial images before and after the
tsunami. The results show the characteristics such as erosion in the longshore direc-
tion behind seawalls, landward sediment transport during tsunami runup, seaward
sediment transport from shore during backwash especially through crevasses of the
seawalls, and coastal stabilization by coastal structures such as seawalls, breakwa-
ters and headlands. At the seriously eroded Yamamoto Coast, more than half of the
total amount of eroded shore sand above sea level was estimated to be transported
seaward due to backwash. After 1 year from the tsunami, the eroded coasts were
recovered to form pocket beaches. After another year, the coastal morphology had
not changed apparently but seawalls started to be reconstructed. At present, after
3 years from the tsunami, the seawalls with a height of 7.2 m have been recon-
structed along the coast. With the reconstruction, the foundation ground of the sea-
walls has been recovered, but the eroded beaches still remain disappeared. The coast
act in Japan was established in 1956 to protect the coast from disasters, and amended
in 1999 to also preserve both the coastal environment and its utilization. From the
perspective of long-term coastal management, it is strongly required to consider the
vision of the future coast.
Keywords Beach morphology ￿ Coastal structure ￿ Ecosystems ￿ Airborne laser
scanning data ￿ Bathymetry data