Fluvial mobile models with light material

In this paper we analyze the problems of the fluvial mobile bed scale models. Particular atten-tion is paid to the choice of the material to reproducing the sediments, The possibility of using light material is discussed. In the paper is presented an application of this technique. The ap-plication concerned the modelization of a fluvial groynes field, reproducing a standard reach of the Po river in Italy. The bed material adopted in the model consists of light plastic mate-rial. The experimental analysis has shown the formation of a bar between two consecutive groynes. The flow field between the groynes were analysed with a 3D acoustic Doppler ve-locimeter. The direction of the secondary circulation depends on the curvature of the path lines. Moreover, the formation of the bar is likely related to the suspended load. In fact, the material is entrained into suspension by the longitudinal vortex responsible for the local scour at the head of the dike. The distribution of Reynolds stresses in a horizontal plane confirms this mechanism. The vertical axes secondary circulation inside the groyne field, is responsible for the formation of the bar. Part of the material brought into suspension by the longitudinal vortex, is entrapped in the groyne field, thus forming the bar.