Critical evaluation on different methods for predicting zonal discharge of straight compound channels

Correct prediction of flow discharge in different parts of a compound river channel is increasingly important in river flood mitigation, environment design, restoration, sediment transport, etc. This paper compares four recently developed 1-D methods, namely Interacting Divided Channel Method (IDCM), Energy Concept Method (ECM) and Modified Divided Channel Method (MDCM) and Apparent Shear Stress Method (ASSM), against a wide range of our experimental data and the data available in the literature. The 26 datasets used include symmetric channels (22 datasets) and asymmetric channels (4 datasets) with various aspect ratios (channel total width (B) at bankfull divided by main channel bottom (b) = 1.5~15.8), and bed slopes (S_o = 4.3 × 10^-4~1.3 × 10^-2). It was found that none of the methods performed well against all the datasets. All the methods predicted both the total discharge and zonal discharge reasonably well within 5% for symmetric channels, but they had large errors for the prediction of the zonal discharge for asymmetric channels compared with that in symmetric channels. The ASSM has shown the best overall performance on both the total and zonal discharge prediction, but none of the methods are suitable for a channel with very wide floodplains.