On the initial development of shear layers in partially vegetated channels

Linear stability analysis of flows in open-channels with vegetation at one of their sides is performed. The lateral gradient of the streamwise velocity induced by the drag difference between the vegetated zone and the adjacent non-vegetated zone may result in flow instability in the shear layer around the edge of the vegetated zone, causing the generation of discrete horizontal vortices. We assume that the base state flow field before the occurrence of instability is characterized by a sub-depth-scale turbulence which is mainly generated by bottom friction. By introducing perturbations to the flow depth as well as the streamwise and transverse velocities in the base state, the conditions re-quired for perturbations grow in time were studied over a wide range of hydraulic parameters. The theory is validated by means of its application to experimental data.