Wind tunnel measurements of sediment mass fluxes in different dense live plant canopies
Erosion, transport and deposition of soil or snow are processes that occur when the atmospheric turbulent boundary layer interacts with the ground. Vegetation on the ground is able to significantly modify these processes, usually resulting in reduced particle mass fluxes. Previous wind tunnel studies quantifying mass fluxes as a function of the wind speed mainly investigated bare sediment surfaces without vegeta-tion. However, studies investigating the sheltering effect of vegetation against wind erosion typically focused on the influence of the canopy density on the mass flux. We present a combination of both: Wind tunnel measurements of particle mass fluxes and vertical mass flux profiles in different dense live plant canopies as a function of the wind speed. The experiments were performed in the SLF boundary layer wind tunnel with an 8 m long test section and a cross section area of one square meter. Three canopies of different densities were investigated (0; 5 and 25 plants/m2). For the experiments, natural quartz sand was spread on the ground beneath the plants (ryegrass). A sediment sampler with 60 bins was used to measure the vertical mass flux profiles up to a height of 60 cm. The results are compared to previous measurements of the surface shear stress in similar canopies. First data analyses show an exponential decrease of the total mass flux Q as a function of the canopy density as found in many other studies. For the bare sand surface, Q shows the typical (uτ - uτ,th)3 increase with increasing wind speed or skin friction velocity uτ, where uτ,th is the threshold at the onset of particle erosion. Similar relations were found for the 5 and 25 plants/m2 setups, however, with significant differ-ences compared to the bare sand surface that can be explained by the strong spatial inhomogeneity of uτ for the canopy cases.
Record created on 2014-03-14, modified on 2016-08-09