The 2011 Tohoku Tsunami Flow Velocity Estimation by the Aerial Video Analysis and Numerical Modeling

When a tsunami reaches the coast and penetrates inland, its characteristics change significantly from water wave to strong inundation flow which causes damage on infrastructures, buildings and humans. Measuring flow velocities of tsunami inundation on land is quite rare but is important for understanding how tsunami penetrates inland and improving tsunami numerical models. In order to clarify the tsunami inundation flow characteristics on land with particular regard to velocity, we analyzed the aerial videos which captured the 2011 Tohoku tsunami attacking Sendai coast, Miyagi Prefecture. Consequently, the tsunami front and flow velocities reached approximately 8 m/s within 1 km inland from the shoreline, and they decreased as penetrating more inland. The results were used for verification of the numerical tsunami inundation model that is performed in Sendai city. We found that the present model results are consistent with the observed inundation characteristics when the bottom roughness distribution is sufficiently incorporated according to the land use conditions. This implies the capability of the present tsunami inundation model which is now used for the evaluation of post-disaster reconstruction plan of Sendai city.