Author(s): G. C. Christodoulou; W. R. C. Myers
Linked Author(s):
Keywords: Flood plain; Compound channel; Apparent shear stress; Friction factor; Flood hydraulics
Abstract: The paper aims at quantifying the apparent shear on the vertical interface between main channel and flood plain in symmetrical compound sections. The apparent shear stress is expressed in terms of an apparent friction factor fa and the square of the velocity difference between subsections. Experimental data from the large scale Flood Channel Facility in U. K., as well from a small scale facility are analyzed. The velocities of the subsections are estimated by means of Manning’s formula, thus incorporating any difference in roughness and allowing the applicability of the method in a predictive sense. The resulting fa is found to be well correlated to the width ratio B/b of the compound section and to the Reynolds number on the flood plain, Ref. These findings confirm that B/b is the most important geometrical parameter in compound channel flows, in agreement with earlier research, and show that flow in the least turbulent section, i. e. the flood plain, governs the interaction with the main channel. A plot similar to the Moody diagram is produced, where B/b takes the place of the relative roughness of pipe flow. This can be used to evaluate the apparent shear stress and consequently the discharge of the compound section.
Year: 1999