Equations for discharge calculation in compound channels having homogeneous roughness

Although different methods for estimating the discharge capacity of compound channels have been developed, no entirely satisfactory method exists. However, a large body of experimental data has now been acquired covering small scale and large scale laboratory compound channels. In this paper, discharge characteristics in straight compound channels having homogeneous roughness are studied, and a method for discharge calculation in these channels is presented by analysing some experimental results from a United Kingdom flood channel facility (UK-FCF). The approach presented uses two correction coefficients, a and b, which are applied to the component mean velocities predicted by the traditional vertical division method in order to find more accurate values of the mean velocities in the main channel and floodplains. It has been found that a and b can be expressed in terms of two dimensionless parameters of the channel, coherence and the relative depth (ratio of the floodplain depth to the total depth). Although the procedure developed in this study is based on data from UK-FCF, it is simple and shows satisfactory results when compared to the recently developed method by Lambert and Myers, termed the weighted divided channel method, and when applied to the independent data set collected by others.