Tsunami Bores in Kitakami River
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The 2011 Tohoku tsunami entered the Kitakami river and propagated there as a train of shock waves, recorded with a 1-min interval at water level stations at Fukuchi, Iino, and the weir 17.2 km from the mouth, where the bulk of the wave was reflected back. The records showed that each bore kept its shape and identity as it traveled a 10.9-km-path Fukuchi–Iino–weir–Iino. Shock handling based on the cross-river integrated classical shock conditions was applied to reconstruct the flow velocity time histories at the measurement sites, to estimate inflow into the river at each site, to evaluate the wave heights of incident and reflected tsunami bores near the weir, and to estimate propagation speed of the individual bores. Theoretical predictions are verified against the measurements. We discuss experiences of exercising the shock conditions with actual tsunami measurements in the Kitakami river, and test applicability of the shallow-water approximation for describing tsunami bores with heights ranging from 0.3 to 4 m in a river segment with a depth of 3–4 m.
KeywordsTohoku tsunami 2011 shock wave shock conditions bore undular bore Kitakami River
The water level measurements were provided by the Kitakamigawa-Karyu (Downstream region of Kitakami River) River Office of the Tohoku Regional Bureau, Ministry of Land, Infrastructure and Transport of Japan. The Kitakami River bathymetry was developed in the National Institute for Land and Infrastructure Management, Japan, for their collaborative research with the Tohoku University, using bed elevation data acquired by the Kitakamigawa-Karyu River Office. Authors thank two reviewers for their careful reading and helpful suggestions on improving the paper’s presentation.
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