The Characteristics of Dam Break Flows in a Meandering Channel

The form of the tsunami run-up in rivers is divided into breaker bore and undular bore. It is important to understand the propagation characteristics of hydraulic bore in the meandering part of rivers in order to prevent the damage from the inundation due to tsunami run-up. In this study, hydraulic bore is investigated by opening the gate rapidly in a meandering channel. With the aim of clarifying the characteristics of bore propagation, the temporal variations in wave height are measured.

Those are measured three times with a servo type wave height meter and averaged for each measurement point.

One-dimensional theoretical analysis of temporal variation in the water level due to dam break flow in a straight channel is compared to cross-sectional averaged experimental value in meandering channel. The experimental value of hydraulic bore shows good agreement with the theoretical value. There is little effect of the channel meander on the cross-sectional averaged value of temporal variation in wave height.

The time-averaged experimental value of the water surface profile in the transverse direction is compared with the theoretical value that is obtained by assuming the hydrostatic pressure distribution in a steady flow. The experimental value of breaker bore corresponded with that of theoretical analysis. The experimental value of undular bore is not reproduced by the theoretical analysis near the outer bank when it flows downstream. This is caused by the amplification of soliton fission in the outer bank. The soliton fission even affects the time averaged water surface profile.

It is found that the temporal variation in the water surface profile of breaker bore in an experimental meandering channel can be explained by the theoretical analysis of one-dimensional dam break flow and water surface profile in steady flow in a uniform curved channel. However, because the wave height due to soliton fission is amplified along the outer bank in a meandering channel, the theoretical analysis underestimates the wave height.