The practical aim of the project is to assist in the better management of unvegetated or thinly vegetated terrain, so as to avert desertification where possible. The scientific objective is to develop an integrated model of the creep, saltation and suspension processes in aeolian transport. This implies an improved understanding of the interaction between air flow and the bed condition and in particular, the feedback mechanism which establishes the equilibrium level of each process in a given wind. The study will investigate the degree to which collision replaces direct wind dislodgement, changes in texture and morphology of the bed, changes in the near bed wind structure, and the response of moving grains to turbulence.
The specific areas of study are as follow:
surface texture (this involved the examination of the texture at the grain scale using a stereo photographic method) studies of the surface at the ripple scale (to examine the development of the ripple pattern) using a Moire photographic technique and for field studies of aeolian roughness, the use of back scatter radar signals transmitted and redetected from aircraft and spacecraft);
near bed air flow structure (there are readily measurable differences in turbulence structure within 2 cm above the bed between the flow approaching a mobile sand sheet and that 1.5 m downwind of its leading edge and as peak instantaneous velocities are known to have a particular influence on the transport process the observation of turbulence modification in the developing saltation layer is a significant finding);
grain transport models (the numerical model is based on a statistical account of collision based on the direct observation and an analytical model based on the same physical principles, gives explicit formulae for the transport rate and for the flux of sand grains from the surface into the air);
grain motion (a technique involving the use of colour film exposed at high speed has been adopted and is being use d to generate splash functions in which 3 size fractions are identified);
dust cloud generation (work on the dispersion of dust introduced into the atmosphere at ground level).
It is proposed to study the changes of soil constitution and surface texture which accompany wind erosion and, in particular, the dependency of thesechanges on the process mechanics of grain transport Both theoretical and experimental methods will be used, including spatial statistics and detailled examination of sand-laden wind structure and of grain dislodgement. The skills of two centres are necessary to the programme which coordinates mathematical statisticians and geologists at Aarhus with engineers at Aberdeen. The outcome will be better understanding of sand mobility, of desertification, and of milder forms of soil deterioration.
Funding SchemeCSC - Cost-sharing contracts
8000 Aarhus C