Author(s): Akihiro Tominaga; Iehisa Nezu; Masashi Nagao
Linked Author(s): Iehisa Nezu, Akihiro Tominaga
Keywords: No Keywords
Abstract: Flow structures in compound open channels indicate complicated three- dimensional (3-D) behaviours. The most important feature of compound channel flows is a strong interaction between the main-channel and flood-plain flows. In a laboratory channel with smooth flood plains, this interaction is significant as the flow depth on the flood plain, h, is much smaller than that on the main channel, H. With an increase of h, the effects of these interaction on flow resistance becomes weaker, but the secondary currents become predominant. In natural rivers, the bed roughness of flood plains is often larger than that of main channel due to vegetation. An enlargement of roughness elements decelerates the flow over the flood plains and thus it enhances the difference between main-channel and flood-plain velocities. In this case, even when the depth ratio, h/H, becomes larger than about 0.5 in flood, the strong interaction may occur in the interface region. Therefore, the roughness of the flood plains increases the flow resistance and heighten the water level.
Year: 1993