Author(s): A. Vargas-Luna; A. Crosato; L. Collot; W. S. J. Uijttewaal
Keywords: Grass-type vegetation; Rigid cylinders; Baptist method; Laboratory experiments; Morphodynamics
Abstract: The morphological evolution of river systems is strongly influenced by the presence of vegetation. On vegetated beds, velocity fields are spatially heterogeneous at different scales according to vegetation density and hydraulic conditions. Plants affect velocity profiles that deviate from those commonly found in non-vegetated flows, changing the local sediment transport rates and the morphodynamic trends. To simulate the effects of vegetation on hydrodynamics and sediment transport, plants are often treated as uniform arrays of rigid cylinders characterized by diameter, height, density and drag coefficient. Given the vast variety of plant shapes and considering that plants may be flexible, it is important to define the key parameters that characterize plants in rigid-cylinder representations. In this work, artificial grass is characterized in a laboratory setup considering emergent and submerged conditions, three densities, and two sediment types. The same flow discharges are used in all the tests in order to be able to compare the cases. The results show the effectiveness of a selected rigid-cylinder representation in reproducing the measured vegetation effects. The results suggest a non-linear relationship between the total shear stress, the bed-shear stress and the drag exerted by plants.