Author(s): Daisuke Kobayashi; Tatsuhiko Uchida; Kazuyuki Ota

Linked Author(s): Daisuke Kobayashi, Tatsuhiko Uchida, Kazuyuki Ota

Keywords: Undular bore; Soliton fission amplification; Bore head’s line; Sinuosity; Non-dimensional width

Abstract: It is important to understand the propagation characteristics of hydraulic bore in the meandering part of rivers in order to mitigate the damage from the inundation due to tsunami run-up. The form of the tsunami run-up in rivers is divided into breaking bore and undular bore. The undular bore propagates with a phenomenon of soliton fission, due to non-hydrostatic pressure and includes the risk that the water surface profile increases rapidly in rivers. Therefore, it is important to clarify an amplification characteristic of the undular bore in meandering rivers. In this study, we conducted the experiment in straight and two meandering channels and compared the results with two- and three-dimensional calculations. Focusing on the difference of the sinuosity of two meandering channels, the amplification characteristics of undular bore in meandering channels were investigated. In the experiment, the wave height was measured three times at center point in the straight channel, near both banks in the meandering channels. We used the averaged values as experimental results. The governing equations of two- and three-dimensional calculation are the shallow water equation and the Reynolds-Averaged Navier-Stokes equations, respectively. In the straight channel, the wave height of soliton fission was not changed in longitudinal direction as presented by many researchers. On the other hand, the soliton fission amplification was investigated in the meandering channel, indicating the longitudinal increase in the wave height along the outer bank. The amplification in small sinuosity channel is larger than that in the large sinuosity channel. The difference in the longitudinal tendency of the amplification is explained by the two-dimensional calculation results. However, the two-dimensional calculation results could not reproduce the difference in the location of maximum amplification between two meandering channels. The three-dimensional calculation results explained experimental results of the initial wave height and reproduced the amplification characteristic. We confirmed the bore impinging on the outer wall of meandering channel and the wave height along the outer bank increased which induces the soliton fission amplification. Both calculation results are coincident with the profile of bore head’s line in meandering channels and can express the mechanism of the soliton fission amplification. The soliton fission amplification along the outer bank occurs in the meandering channel of small non-dimensional width in the numerical experiments.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022950

Year: 2022