Reduction of scouring downstream of a rigid bed by means of a vegetated carpet: experimental investigation in a laboratory flume

Vegetation is a critical component of aquatic ecosystems and exerts an important role in river morphodynamics. This paper describes the results of laboratory study carried out to investigate the role of vegetation on flow field and erosion process developing in non-equilibrium situations. Particular attention is paid to scour evolving downstream of a rigid bed and to the effect of a vegetated carpet used as a protective measure against scouring. The reported experimental study shows that the introduction of the vegetated carpet results in a more favourable configuration than in its absence determining reduced values of flow velocity, turbulence intensity and bed shear stress, and modifying their patterns, downstream of the rigid bed. Consequently, the vegetated carpet protects the bed against the erosive action of flow and determines a beneficial effect with respect the stability of the structure. Experiments also show that a scour hole forms downstream of the vegetated carpet but the geometrical characteristics (length and depth) of such a scour hole are reduced by about 50 %compared to those obtained downstream of the rigid bed in absence of vegetation.