Tsunami Bores in Kitakami River

TL;DR

This study analyzes tsunami bores in the Kitakami River following the 2011 Tohoku tsunami, applying shock wave theory to interpret water level data, estimate flow velocities, and validate shallow-water models for tsunami bore propagation.

Contribution

It applies classical shock conditions to real tsunami data in a river setting, validating theoretical models against measurements and testing shallow-water approximations.

Findings

Shock conditions successfully reconstructed flow velocities.

Wave heights ranged from 0.3 m to 4 m.

Shallow-water approximation was applicable for the observed bores.

Abstract

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 m to 4 m in a river segment with a depth of 3-4 m.