Abstract: A series of experiments was carried out in a largesymmetric compound channel composed of a rough main channel and roughfloodplains to investigate the resistance characteristics of inbank andoverbank flows. The effective Manning, Darcy-Weisbach, Chezy coefficientsand the relative Nikuradse roughness height were analyzed. Manydifferent representative methods for predicting the composite roughness weresystematically summarized. Besides the measured data, a vast number oflaboratory data and field data for compound channels were collected and usedto check the validity of these methods for different subsection divisionsincluding the vertical, horizontal, diagonal and bisectional divisions. Thecomputation showed that these methods resulted in big errors in assessingthe composite roughness in compound channels, and the reasons were analyzedin detail. The error magnitude is related to the subsection divisions.