Clear water scour at eco-friendly wood-based structures in vegetated channels

Worked Wood Piles (WWP) belong to the category of low-head eco-friendly restoration structures made from large woody debris that are often placed in the vicinity of riverbanks to realign the flow towards the central part of the channel, thereby stabilizing river embankment. Moreover, significant growth of in-stream vegetation usually occurs in the downstream wake region of WWPs, affecting the scour and dune morphology formed around such structures crucial for promoting biodiversity. To model these phenomena, we conducted experiments under clear water condition with isolated and multiple WWPs in series in the presence and absence of in-stream vegetation in horizontal channels under a large range of hydraulic, structural and vegetation configurations. The results captured the effect of growing stages of in-stream natural vegetation on the scour process in correspondence with WWPs. It was observed that inflow conditions and structure geometry greatly affect the equilibrium scour morphology whereas the number and height of vegetation impacts the maximum scour and dune lengths. In addition, different scour morphology types were distinguished and their fields of existence were established based on flow, structure and vegetation parameters. Finally, we derived empirical equations allowing practitioners to quantify the maximum scour depth and length as well as the dune height.