Author(s)

Y. Chen & B. C. Yen

Abstract

For most natural rivers and some artificial channels, their cross sections consist of subsections of different cross sectional shapes with overbank floodplains, defined as compound channels. Besides, the wall roughness of the channels usually changes along the wetted perimeter. It can be found that the way one divides the cross section into subsections would change the sub-cross sectional areas and the perimeters of the main channel and each side channel and would result in different overall roughness of the compound channels. This study presents a set of equations derived based on different assumptions, including those have been proposed previously, to estimate the overall compound composite channel resistance. To know how many of them are theoretically appropriate, in this study variation of Manning’s n over depth is evaluated for a series of hypothetical compound channels with different shapes based on two types of subarea division lines. The results of evaluation provide useful information for hydraulic engineers dealing with velocity and discharge of open charnels.

Keywords