Manning's Roughness Coefficient in Alluvial Channels Affected by Seepage

Abstract

Seepage flow through alluvial channel bed can affect significantly the Manning's roughness coefficient, n. Both downward seepage (suction) and upward seepage (injection) through the alluvial channel bed can either increase or decrease Manning's n when compared to its no-seepage value. Such variations in Manning's n due to seepage are presented quantitatively so as to bring awareness among design engineers and researchers that seepage should be considered as a parameter while estimating the value of Manning's n even for a given size of bed material.

Design of plane sand-bed channels affected by seepage

“…The present theoretical and experimental investigations [13], [34], [35], [6] do not give an unequivocal answer to the question about the effect of seepage flow on the main flow. Chen and Chiew [34] showed that the customarily used law of the wall (logarithmic law) is also not applicable to open channel flow subjected to bed suction.…”

“…Chen and Chiew [34] showed that the customarily used law of the wall (logarithmic law) is also not applicable to open channel flow subjected to bed suction. Sitaram and Rao [35] have ascertained that Manning's n values are significantly affected from the seepage, thus there is a need to have a different kind of equation. Hence it has become necessary to develop a new resistance equation for plane sediment beds affected by bed suction.…”