Composite roughness for rough compound channels

Abstract

Accurate estimation of roughness in a compound channels is an important aspect in River hydraulics. Researchers have suggested equations for estimating composite roughness of an open channel flow which are good for simple channels and do not incorporate the interaction mechanisms that exist in a compound channel. An experimental investigation is performed to study the dependency of geometry, roughness and flow parameters for predicting composite roughness of non-homogeneous compound channels. Standard methods of predicting the composite roughness of compound channels are reviewed and applied to the new experimental rough compound channels for different flow conditions. Effectiveness of these methods is discussed and modification to the standard method is proposed. The new approach is found to give better results as compared to the other approaches when applied to the experimental data sets, large channel of FCF data sets and some natural river data sets.

Extension of the two‐component pressure approach for modeling mixed free‐surface‐pressurized flows with the two‐dimensional shallow water equations

“…However, in pressurized regions both values are modified in order to account for the effect of the solid roof. Several formulas have been proposed to compute a composite roughness in compound channels 37 . Here, we have used the formulation proposed in Reference 38, in which the composite roughness is computed as a wet‐perimeter weighted average of the different Manning coefficients.…”