Research Units Snow and Permafrost Staff Snow Physics Permafrost and Snow Climatology Snow Cover Industrial Projects and Snow Sports Projects Wind forces on plants

Duration: 2008 - 2012

Wind forces on plants and soil surfaces

Erosion, transport and deposition of soil and snow are only a few among a large number of processes that occur when the atmospheric wind interacts with the ground. These processes, however, have considerable influence on desertification and land degradation. Plants are able to modify these processes simply by reducing the surface exposed to the wind, by trapping particles in motion and by absorbing momentum from the flow.

	Fig.1: Turbulent boundary layer over a vegetated surface. U is the mean velocity, τ the total shear stress and τs the shear stress acting on the surface.

The overall goal of the project is to understand and quantify the basic mechanisms governing the sheltering effect of vegetation against soil erosion and snow transport. In order to have full understanding of the physical mechanisms, it is of crucial importance to investigate the very inner layer of the atmosphere, the turbulent surface layer close to the ground. Here, wind forces are transferred to the ground by turbulent shear stress, resulting in a force acting on the surface. In vegetation covered surfaces, parts of the downward transferred shear stress are absorbed by the plants. The ratio of the total shear stress τ above the plants and the reduced shear stress acting directly on the soil surface τ_s quantifies the sheltering effect of vegetation (Fig. 1). This “shear stress partitioning” is the main objective of the current research project.

The novelty of our approach lies in the use of real living plants for the experiments. So far, imitations instead of real plants have been used in most wind tunnel studies. However, real plants display a highly irregular structure that can be extremely flexible and porous in contrast to the often rigid and non-porous artificial plant imitations.

The final goal of the study is the development of a model which predicts the shear stress acting on the ground for given vegetation cover density and wind velocity. Such information can be used as an input for sediment, e.g. soil, sand or snow transport models as well as to develop suitable safety precautions to avoid sediment transport in arid regions.

Contact

• Benjamin Walter
  

Participants

• Christof Gromke
  

• Michael Lehning
  

Wind tunnel facility