Impact of an emergent model vegetation patch on flow adjustment and velocity

This study achieved three goals to clarify the impact of a vegetation patch on flow adjustment and velocity. First, a valid equation for the interior adjustment distance (L_d) inside a model patch was developed for a wide range of velocities and flow depths. Second, the minimum distance inside a patch beyond which the resuspension of fine sediment is suppressed (L_min) was found to be related to the position at which the local velocity decreases to the threshold for generating stem-scale turbulence. L_min primarily depends on the flow blockage (C_dab) and the stem diameter (d): a shorter L_min is a result of a larger C_dab and a smaller d. An equation was formulated for estimating L_min. Third, for the fully developed flow region inside a patch (L > x > L_d), an equation was developed to estimate the increase in the mean velocity in the bare channel relative to the overall mean channel velocity. For C_dab < 2, this fraction is controlled by both the patch density (ad) and the patch blockage (b/B) whereas, for C_dab > 2, this fraction is controlled by only b/B. A suggestion for choosing the patch size in future flow and sediment research projects is presented.