A simple method for estimating bed shear stress in smooth and vegetated compound channels

Instead of a large number of measurements of the streamwise velocity, a simple method is proposed to estimate the bed shear stress in smooth and vegetated compound channels, based on the Darcy-Weisbach equation. This method contains a dimension-less parameter Ai, to represent the relationship between the bed shear stress and the velocity close to the channel bed (Ub), which is determined in each divided domain. This method is verified in two smooth compound channels with different geometries, and in one compound channel with emergent floodplain vegetation. The comparison of predicted and measured bed shear stresses indicates the good predictive capability of this method, particularly in the mixing region. This method is further discussed for a channel with submerged vegetation. Once the values of Ai in the main channel and the floodplain are determined, this method is a practical tool for estimating the bed shear stress based on a small number of measurements of Ub in compound channels.