The use of relatively small nonerodible elements (gravel) in stabilising a mobile surface was investigated. The aim of this study is to determine the different factors that affect the sand erosion due to the presence of small immobile rough elements. A regular array of spherical glass marbles was distributed on a nine metre length in the working section of a 12 metres long boundary layer wind tunnel. A bed of dune sand was spread over the marbles filling the gaps and covering the marbles. Four different shear velocities were used with two different marble spacings. The experimental results showed that the sand erosion and the sand flux along an isolated sand bed containing both mobile and immobile elements is neither uniform nor steady. The marbles start to be exposed at a certain position along the wind tunnel (the position of the maximum flux gradient and thus the maximum erosion). This is followed by a gradual exposure of the rows of marbles along the wind tunnel downwind of the initial exposure. This process continues until all the marbles are exposed downwind. The marbles are also exposed upwind of the initial exposure but this propagates at much lower rate and some marbles remain covered with sand at the end of the experiment. The sand flux measured at the downwind end of the working section remains constant for some time. When the marbles start to expose at some distance upwind, it starts to decrease rapidly. This indicates that the effect of the nonerodible elements on sand flux is not a local effect. A numerical model was developed to simulate the mechanism of the sand erosion observed in the wind tunnel experiments. The model helps in determining the different factors that influence the sand flux and sand erosion due to the exposure of the nonerodible elements. The model succeeded in simulating the erosion process and in providing a qualitative prediction of the sand level and sand flux distribution along the sand bed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:304938 |
| Date | January 1992 |
| Creators | Al-Sudairawi, Mane |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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