ESTIMATING THE DISCHARGE CAPACITY IN STRAIGHT COMPOUND CHANNELS

A method for predicting the stage-discharge relationship in a straight compound channel is presented. The approach is developedps from an ex amination of the changes in the mean velocity of the main channel and the floodplain regions caused by the momentum interaction between the regions. Experimental results from the United Kingdom flood channel fa cility have been used to develop a method which is capable of more acc urately representing the component mean velocities. This results in an improved estimate of both zonal and the overall discharge values. The approach presented in this paper uses a single parameter (xi) which i s applied to the component velocities predicted by the vertical and ho rizontal division method to produce an intermediate velocity which mor e closely represents the observed velocity in both the main channel an d the floodplain. A value of xi = 0.5 has been found appropriate for s mooth compound channels and xi = 0.2 for compound channels with very r ough floodplains. Further validation of the approach has been undertak en by comparison with an alternative data set. The ability to predict the component velocities more accurately has significant advantages fo r numerical modelling and channel design.