Scour profiles downstream of wood structures in vegetated channels

Low-environment impact structures for river restoration are the answer for many river design project. Among them, log-frame structures can be often found in natural streams, where they create suitable habitat for fish species. They contribute to the formation of pools in which fishes can rest and find suitable conditions in terms of flow velocity. Nevertheless, such structures contribute to deeply modify the local sediment transport and results in localized erosion processes, which need to be carefully controlled in order to avoid structure and bank stability problems. In addition, natural rivers are also characterized by other two important elements which should be taken into serious consideration, when designing these structures: 1) the river curvature; and 2) the presence of vegetation. Based on these observations, dedicated experimental tests were conducted by using log-frame structures located in a curved channel. Furthermore, plastic fibres (simulating in a very simple and preliminary way the natural vegetation) were placed downstream of the wood control structures in order to investigate their effect on the erosive mechanisms. Tests were conducted by varying hydraulic conditions, location of the structure within the channel bends, and different vegetation density and spatial distribution. Experimental evidence allowed us to highlight the effects of tested parameters on the localized scour process. In particular, this preliminary analysis focuses on scour morphology and non-dimensional longitudinal and transversal scour profile similitude and is conducted by comparing the main scour features obtained in the presence of downstream vegetation with those relative to reference tests where the vegetation was absent in the channel