Comparisons of sand accumulated at different locations along the fence demonstrated the effectiveness of the windbreak fence. Examples are shown in Tables 4-6. As indicated in Table 4, when there were northeasterly winds in Section I, comparatively small amounts of sand transport took place 1 m in front of and in back of the fence and 20 m in back of and in front of the fence, due to insufficient sand sources, even though there was a strong wind force. The small quantity of sand transport at 20 m in back of the fence was also a result of the sand-blocking effectiveness of the fence. This is congruent with the state of sand accumulation described above. The effectiveness of this type of sand control is clearly reflected in Sections III and IV At distances of 10 and 20 m in back of the fence, the quantity of sand transport was only 0.7-2.7% of the quantity of sand transport at the corresponding distances in front of the fence. It can be said that less than 5% of the windblown sand will be able to reach the top of the cliff after it has passed through the protection system. At present, most of the sand that has gathered in front of the caves is the product of many years of accumulation. There were very great differences in the quantity and composition of the accumulated sand, particularly under the influence of easterly winds.
In summary, comprehensive measures against damage by windblown sand are necessary, especially in the Mogao grottoes region. The diversity and complexity of windblown sand activity makes comprehensive control even more necessary A comprehensive, overall sand-control program is dependent on a thorough understanding of the patterns of windblown sand movement.
Conclusion
Different frequencies and intensities of winds from multiple directions characterize the average flow field in the Mogao region. Serious sand accumulation and severe wind erosion are two major forms of windblown sand damage to the Mogao grottoes brought about by this type of flow field.
On the basis of test data on patterns of windblown sand activity in this region, the triangular windbreak fence was capable both of blocking the drifting sand carried in the dominant winds and of diverting fixed quantities of accumulated sand in the secondary wind directions. This multifunctional fence system has effectively controlled windblown sand (decreasing it by about 95%) and has prevented accumulation of sand in front of the caves (reducing it by about 75%).
World History
