2000 Volume 53 Issue 2 Pages 22-33
In order to control wind-blown sand on beaches foredunes have commonly been constructed using sand fences.
Recently artificial embankments are often employed instead foredunes because construction of the embankment can be rapidly and economically done by using large earth-moving construction machines. However, the functioning of embankments for wind-break effect and wind-blown sand control is not fully understood yet. Thus, using a blown-off type wind tunnel, which was 1.1 m high, 1.0 m wide and 20 m long, the wind field around model embankments was examined. Two series of embankments were included in the experiments. One series involved trapezoidal type embankments where the foreslope was changed between 1:0, 1:0.5, 1:1, 1:2, 1:3, and 1:5 keeping the ratio of B/H=1.0 (where B is the crown width and H is the height of the embankment) and a backslope of 1:1. The other series encompassed rectangular type embankments with varying ratios of B/H=0.05, 0.5, 1.0, and 2.0.
Two main types of measurements were carried out, namely a tracer experiment to visualize the flow pattern and measurements of the wind speed field. The experiments produced the following main results : To keep a large area where the wind speed decreases on the downwind side of the embankment, the foreslope of the embankment should be steeper than 1:1 and the ratio of B/H should be smaller than 1.0. An area where the wind accelerated appeared behind the embankment within elevations from H to 5H. The area of acceleration considerably decreased when the foreslope became gentler than 1:1 and ratio of B/H became larger than 1.0. The wind speed amplification at the upwind edge of embankment crown was the largest when the foreslope of embankment had 1:1 and the width of crown did not give influence to the wind speed amplification.
