| Quantifying resistance in open-channel flow, although typically represented mathematically as a one-dimensional problem, can be complicated by the two- and three-dimensional nature of flow in natural or man-made channels. Despite years of research, there is much that is still unknown with respect to channel boundaries comprised of multiple degrees of hydraulic roughness. Resistance in composite channels, where the roughness of the channel sides differs from that of the channel bed, is one such area where the majority of the theoretical predictive relationships for hydraulic roughness have not been verified experimentally.; The primary goal of this research was to experimentally determine the composite hydraulic roughness coefficient for a variety of channel roughness materials and compare the experimental results with composite roughness predictive methods previously published. To achieve this, 16 composite roughness formulas were compared with experimental data collected using an artificially-roughened rectangular flume. This study provided recommendations and limitations for composite roughness formulas that can be related to practical design of composite channels of simple geometry. Formula predictive results for the 16 formulas ranged from the reasonable accuracy of the Colebatch (8.7%) equation to the poorer accuracy of the Lotter Equation (23.0%). Experimental data, analysis summary, and formula recommendations are presented in detail. |
