Effect of Rigid Vegetation on Equilibrium Bed Morphology

Vegetation in waterways is effective in providing suitable ecological habitat for several fish species. Many studies investigated the effect of vegetation on hydro-morphological conditions in rivers. However, very few focused on induced localized scour processes. Therefore, this study aims to investigate the effect of different, rigid vegetation configurations on equilibrium bed morphology. Tests were conducted in a straight channel, where vegetation of various heights, diameters and densities were simulated in different arrangements. A total of 14 tests were conducted varying water depth and discharge, under clear-water condition. Experimental results showed that the maximum scour depth occurs inside an isolated vegetated patch, with the scour hole extending symmetrically downstream of it. Furthermore, a dune forms in the vicinity of the vegetation in the wake region. In the case of adjacent vegetated patches, a symmetric scour hole formed between them, and it is characterized by a more prominent depth and longitudinal extension with respect to the isolated configuration. Moreover, different deposit zones form downstream of every vegetated patch. Importantly, the effect of vegetation submergence on equilibrium scour features was found to be negligible in the tested range of parameters. However, additional tests are needed to better understand the scour mechanism occurring in the presence of vegetated areas in a straight channel.