Flow-induced vegetation uprooting in a meandering bend : experimental investigation

Abstract

Vegetation uprooting is a complex process which depends on many interrelated factors. In this paper, attention is focused on the flow-induced uprooting in river bends, where the flow characteristics vary as effected by the channel's curvature and its continuous changing in the downstream direction. Results are presented by an experimental work done in a high-amplitude meandering flume with mature herbaceous vegetation on the bed. In the first part of the paper, the variation along the bend of the geometrical (length, thickness, and radical architecture) and the mechanical (resistance force) characteristics of the roots are analyzed. In the second part of the paper, the transition from the condition of vegetation distributed on the bed to the condition of vegetation uprooted by the flow is experimentally examined. The results show that the flow-induced uprooting varies along the bend depending on the roots' geometrical and mechanical characteristics which are, in turn, influenced by the variation of the water surface elevation along the bend itself. It has been found that lower values of the resistance force occur at the apex section where the roots are characterized by higher values of length and lower values of thickness and have radical apparatuses characterized by limited encumbrance, a high number of roots, and low bushyness. The flow-induced uprooting especially develops close to the outer bank along the channel reach between the bend entrance and the apex section, where the root resistance force and the water surface slope tend to decrease in value.