Tsunami Bores in Kitakami River

摘要

The 2011 Tohoku tsunami entered the Kitakami river and propagated there as atrain of shock waves, recorded with a 1-min interval at water level stations atFukuchi, Iino, and the weir 17.2 km from the mouth, where the bulk of the wavewas reflected back. The records showed that each bore kept its shape andidentity as it traveled a 10.9-km-path Fukuchi-Iino-weir-Iino. Shock handlingbased on the cross-river integrated classical shock conditions was applied toreconstruct the flow velocity time histories at the measurement sites, toestimate inflow into the river at each site, to evaluate the wave heights ofincident and reflected tsunami bores near the weir, and to estimate propagationspeed of the individual bores. Theoretical predictions are verified against themeasurements. We discuss experiences of exercising the shock conditions withactual tsunami measurements in the Kitakami river, and test applicability ofthe shallow-water approximation for describing tsunami bores with heightsranging from 0.3 m to 4 m in a river segment with a depth of 3-4 m.