Articles | Volume 17, issue 11
Nat. Hazards Earth Syst. Sci., 17, 1871–1883, 2017
Nat. Hazards Earth Syst. Sci., 17, 1871–1883, 2017

Research article 06 Nov 2017

Research article | 06 Nov 2017

High-resolution modeling of tsunami run-up flooding: a case study of flooding in Kamaishi city, Japan, induced by the 2011 Tohoku tsunami

Ryosuke Akoh1, Tadaharu Ishikawa2,*, Takashi Kojima3, Mahito Tomaru3, and Shiro Maeno1 Ryosuke Akoh et al.
  • 1Graduate School of Environmental and Life Science, Okayama University, Okayama, 700-8530, Japan
  • 2Tokyo Institute of Technology, Kanagawa, 226-8503, Japan
  • 3TOKEN C. E. E. Consultants Co., Ltd., Tokyo, 174-0004, Japan
  • *retired

Abstract. Run-up processes of the 2011 Tohoku tsunami into the city of Kamaishi, Japan, were simulated numerically using 2-D shallow water equations with a new treatment of building footprints. The model imposes an internal hydraulic condition of permeable and impermeable walls at the building footprint outline on unstructured triangular meshes. Digital data of the building footprint approximated by polygons were overlaid on a 1.0 m resolution terrain model. The hydraulic boundary conditions were ascertained using conventional tsunami propagation calculation from the seismic center to nearshore areas. Run-up flow calculations were conducted under the same hydraulic conditions for several cases having different building permeabilities.

Comparison of computation results with field data suggests that the case with a small amount of wall permeability gives better agreement than the case with impermeable condition. Spatial mapping of an indicator for run-up flow intensity (IF = (hU2)max, where h and U respectively denote the inundation depth and flow velocity during the flood, shows fairly good correlation with the distribution of houses destroyed by flooding. As a possible mitigation measure, the influence of the buildings on the flow was assessed using a numerical experiment for solid buildings arrayed alternately in two lines along the coast. Results show that the buildings can prevent seawater from flowing straight to the city center while maintaining access to the sea.

Short summary
A numerical model was developed to simulate tsunami run-up in a densely built-up area by introducing internal hydraulic conditions on building footprints. Computation showed good agreements with observation on maximum wave heights and wavefront speed in streets in the 2011 Tohoku tsunami. An indicator for tsunami impact was introduced based on observed distribution of washed-out houses, and a numerical experiment suggested that building array improvement would reduce damage of houses remarkably.
Final-revised paper