Author(s): Pedro J.M. Moreta; Juan Pedro Martin-Vide

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Keywords: Apparent friction coefficient; apparent shear stress; compound channel; momentum transfer; overbank flow

Abstract: In compound open channel flow, the strong interaction between the main channel and the shallow floodplains affects considerably the discharge capacity. Since this phenomenon was identified, many authors have estimated experimentally the flow interaction in terms of an apparent shear stress acting at the vertical interface between the main channel and the floodplains. Empirical formulae have been developed to quantify this apparent shear stress, yet without general applicability. Herein, a dimensionally sound expression, depending on the square of the velocity gradient between the main channel and the floodplains, and on the so called “apparent friction coefficient”, is proposed. Its variation with the geometrical and roughness ratios is analysed herein. A generalized formulation to predict the apparent shear stress is presented and validated for a wide range of laboratory data. These include small-scale flumes and the large-scale flood channel facility, with both smooth and rough floodplains.

DOI: https://doi.org/10.1080/00221681003704137

Year: 2010