| When large-scale tsunamis propagate into rivers、 situations such as inundation inside levees due to bank overtopping and/or emergency stoppage of intake at water supply facilities to prevent salinity intrusion can be expected. With a main focus on the topographical conditions of Kushiro Marsh upstream of the Shin Kushiro River to the north of urban Kushiro、 this paper proposes a disaster mitigation measure involving the installation of a retarding basing with a storage capacity of approximately two million cubic meters downstream of the marsh. Numerical analysis was conducted to determine the impact of this measure on a tsunami propagating up the river. It was found that the water level would be reduced by up to 0.74 m for a 3.4-m-high tsunami (approximately 42% of the water level rise) upstream of the urban area compared to a situation with no retarding basin. Results also indicating a reduction in the volume of flooding and the distance of propagation further highlighted the potential for disaster mitigation based the use of local topographical characteristics. |
