Selection of interface for discharge prediction in a compound channel flow

Abstract

River engineers often analyze the overbank fl ows using subdivision techniques through the selection of assumed interface planes. A wrong selection of interface planes between the main channel and fl oodplain accounts for transfer of improper momentum, which inculcates error in estimation of discharge for compound channel section. Distribution of apparent shear stress between the main channel and fl oodplain gives an insight into the magnitude of momentum transfer based on which the discharge estimation using divided channel methods is decided. In the present study, experimental results of momentum transfer at various interface plains for straight and meandering compound channels are presented. Momentum transfer and boundary shear distribution are found to be dependent on the dimensionless parameters viz., overbank fl ow depth ratio, width ratio, sinuosity, and the orientation of the interfaces. The developed equation helps to predict the discharge carried by compound channels of different geometry and sinuosity. The present study indicates that for a straight compound channel, the horizontal division method provides better discharge results for low overbank fl ow depth and diagonal division method is good for higher overbank fl ow depths. The best discharge results for a meandering compound channel are obtained through diagonal division method for low overbank fl ow depths and vertical division method is good for higher overbank fl ow depths. The adequacies of the present results are verifi ed using present experimental data, and the data collected from the large channel facility (FCF) at Wallingford, UK. These methods agree well when applied to some natural river data.

Energy and momentum coefficients for wide compound channels

“…This has been well reported in literature [15][16][17][18][19] etc. On account of this momentum transfer, the lateral distribution of velocity becomes non uniform in addition to natural non uniform velocity distribution of flow between the channel bed and free surface in a vertical direction.…”

Composite roughness for rough compound channels

“…So early investigations by Sellin (1964), Wright and Carstens (1970) have pointed to the existence of momentum transfer between the subsections, which is, in fact, more intense for small flow depths over the flood plain due to this a mixing shear layer is developed at the interaction region and apparent shear stresses appear. Wormleaton and Merret (1990) and Khatua et al (2013) proposed another empirical formula to estimate the apparent shear stress in straight compound channels. Posey (1957) and Ackers (1993) deduced a design formula for straight two stage channels by taking into account the interaction effects between floodplain and main channel.…”