Improvement of the Lateral Distribution Method based on the mixing layer theory

•We revisited an analytical solution of the depth-averaged streamwise momentum equation.•Experimental data was used to calibrate the coefficients.•A compound channel division based on the width of the mixing layer is proposed.•Accurate predictions of depth-averaged streamwise velocity were obtained.•The proposed method was validated against experimental data. The accurate prediction of depth-averaged streamwise velocity, boundary shear stress and lateral shear stress are important requisites for the estimation of the flow depth associated with flood events in compound river channels composed of main channel and floodplain. This engineering problem may be tackled through the analytical solution of the depth-averaged momentum equation. Under uniform flow, this solution relies on the calibration of three descriptors of the bottom friction, secondary currents and lateral shear stress. In this paper, the analytical solution materialized in the Lateral Distribution Method is revisited through the consideration of a new panel division. Accurate measurements of streamwise and spanwise velocities as well as of boundary shear stress are used to obtain new predictors of the coefficients describing the effects of bottom friction, secondary currents and lateral shear. The new lateral division of the compound channel into four panels is physically based on the mixing layer width, which is computed by an iterative procedure easily implemented in practical applications.