半隐蔽格状沙障的综合防护效益观测研究

Study on Comprehensive Sand-protecting Efficiency of Semi-buried Checkerboard Sand-barriers

半隐蔽格状沙障,特别是麦草和碾压芦苇方格沙障,是近地风沙流边界层防止风沙危害的一种经济实用、功能独特、效果显著而应用最为广泛的固沙措施。它增大了下垫面的粗糙度,明显降低了底层风速,进而减弱了输沙强度,使流沙表面得以稳定。在格状边框内,由于气流的涡旋作用,使格内原始沙面充分蚀积最后达到平衡状态,即稳定的凹曲面形成。这种有规则排列的凹曲面,对不饱和风沙流具一种升力效应,而形成沙物质的非堆积搬运条件,这是格状沙障作用的关键。试验证明1m×1m,1.5m×1.5m和2m×2m草方格防沙效果都是显著的,0.5m×0.5m的方格不仅费工费料,而且防风固沙效果很不理想,并很快地被沙堤失去防护功能。同一规格的格状沙障往往由于设置的地形部位不同,其防护作用可能产生很大的差异。因此,应该根据一个地区的风沙流场性质和沙障功能综合评价半隐蔽沙障防护效益。

The semi-buried checkerboard sand-barrier mainly made from wheat straw or rolled reed, is an economic, effective and widespread-used method of sand fixation (stabilization) in China. It can stabilize the shifting sand by increasing the roughness height of underlaying surface, decreasing the wind velocity near the ground surface and thus weakening the intensity of sand transportation. Due to the eddy action of airflow, the sand in sand-barriers can reach a state of equilibrium between erosion and accumulation, and finally form a stable concave surface. These regular-arrayed surfaces in sand-barriers have a lift force effect, which causes unsaturated sand flow pass it over totally. This is the key mechanics of sand protecting of checkerboard sand-barriers. The tests in Shapotou show all of 1 m×1 m,1.5 m×1.5 m and 2 m×2 m girds have marked function to sand-protecting, whereas the sand-protecting efficiency of 0.5 m×0.5 m checkerboard sand-barriers is not ideal as the two formers, they lost their function of sand-protecting soon after being buried. Moreover, the making of 0.5 m×0.5 m sand-barriers wastes a lot of manpower and materials. In addition to dimension of sand-barriers, the topographic location has also a direct effect on sand-protecting efficiency. So in order to evaluate the integrated sand-protecting efficiency of sand-barriers objectively, both the wind field characteristics of investigated area and the function of sand-fence must be considered simultaneously. Recently, we used some new techniques and materials (such as nylon, polyester and plastic net) to sand protecting, and obtained some fruits during tests. These measures cannot only provide the material sources to sand protecting, but also extend their operational life span.