Influence of vegetation Height and Density on a turbulent Boundary Layer

In last years vegetated surfaces problems are becoming more and more important in hydraulic research, whereas boundary layer problems are always a very important topic of fluid mechanics. In this paper the influence of submerged rigid vegetation on the development of a water equilibrium boundary layer in a rectangular channel is experimentally investigated. Vegetation is modelled through vertical cylinders inserted in the channel bottom: two different cylinders heights and two different cylinders densities have been considered, so that four different vegetation conditions have been investigated and always compared with the same boundary layer without vegetation. Local mean velocity distributions in four subsequent test sections have been measured through an LDA system. The main results obtained are the following ones: 1) vegetation presence increases boundary layer thickness; 2) with the investigated cylinders heights and densities the boundary layer behaves yet as an equilibrium one; 3) the equilibrium characteristics depend on either cylinders height or cylinders density; 4) it is possible to define an index which summarizes the aforementioned equilibrium characteristics.