Vegetation altering hydrodynamic conditions of an open channel flow controls the exchanges of sediment, nutrientsand contaminants. Thus, the knowledge of the hydraulic characteristics of flow over vegetation is very importantto support the management of fluvial processes. But, the analysis of the hydrodynamic conditions is complexbecause vegetation is flexible in varying degrees and it oscillates in the flow changing position. Furthermore,because of temporal changing of roughness due to natural vegetative growth, the response of vegetation to theflow can change in time. Many theoretical and experimental investigations have been performed in order toanalyze both the mean flow and turbulence structure of open-channel flow (Nezu and Rodi 1986; Lemmin andRolland 1997; Shvidchenko and Pender 2001; Ghisalberti and Nepf, 2002). Recent experimental runs carried outin laboratory channels with flexible vegetation, realized by using artificial filaments (Kutija and Hong 1996; Ikedaand Kanazawa 1996), investigated some peculiar characteristics of flow turbulence structure and revealed thegeneration of periodic organized vortices whose center is located slightly above the top of the vegetation layer.On the other hand, recent experimental studies conducted by Termini and Sammartano (2012) in a mobile-bedlaboratory channel, and in absence of vegetation, have demonstrated that the formation of coherent turbulencestructures plays an important role in sediment transport and in scouring evolution. In particular, ejection andsweep events contribute significantly to erosion, deposition and sediment suspension.In this paper, in order to give a contribution to the understanding of the rule of vegetation on the analyzed erosionprocess, experimental results obtained in the same laboratory channel, but with bed covered by flexible vegetation,are presented. Attention is paid to interaction vegetation/erosion both along the vegetated-bed channel reach anddownstream of it. In particular, different vegetation patches are experimentally tested and how such vegetationpatches serve to obstruct the erosive action of water is discussed.
|Numero di pagine||1|
|Stato di pubblicazione||Published - 2012|