Calculation of cross-section average flow velocity in vegetated compound channels

The formulae of cross-section average flow velocity of main channel and floodplain in vegetated compound channels are derived by establishing horizontal force balance formula. The value of momentum transfer coefficient is chosen by relative flow depth. The experimental data of different density of floodplain vegetation in compound channels are applied. When the vegetation density m=0, series of no floodplain vegetation experimental date are taken to measure the formulae of cross section average velocity and find good agreement; when the vegetation density m>;0, the other series of experimental date measured in compound channels with floodplain vegetation are taken to evaluate the formulae and compare that with Liu peiqing method. The computed results show the formulae are more accurate than Liu peiqing method.