A method for predicting the stage-discharge relationship in a straight compound channel is presented. The approach is developedps from an examination 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 facility have been used to develop a method which is capable of more accurately 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 is applied to the component velocities predicted by the vertical and horizontal division method to produce an intermediate velocity which more closely represents the observed velocity in both the main channel and the floodplain. A value of xi = 0.5 has been found appropriate for smooth compound channels and xi = 0.2 for compound channels with very rough floodplains. Further validation of the approach has been undertaken by comparison with an alternative data set. The ability to predict the component velocities more accurately has significant advantages for numerical modelling and channel design.