几种不同材料机械沙障防风效应研究
Effects of Different Sand Barriers on Wind-break and Sand Fixation

机械沙障是降低近地表土壤风蚀的重要措施,其主要通过改变下垫面的性质,增加地表粗糙度来实现降低风速、减弱风蚀,进而达到防风固沙的目的。然而,以往的实验主要以风洞模拟为主,野外实验结果稀少。本研究选取毛乌素沙地南缘作为样地,通过大量野外实验,观测不同沙障措施(麦草、芦苇杆、聚酯纤维沙袋、塑料网)下近地表风速变化规律和土壤的蚀积特征,探讨沙障措施对土壤风蚀影响的机理,找出各项沙障技术利用目前存在的问题,并提出有效的解决办法,以期能为制定防治土壤风蚀的对策提供科学的依据,结论如下:(1)对于塑料网沙障,本试验选取了规格为1m×1m、2m×2m、3m×3m及4m×4m,高度分别为20cm、30cm、40cm和50cm,孔隙度为20%、30%、50%及70%的64种组合方式。经过对比分析得出:沙障规格为1m×1m,高度为50cm,孔隙度为20%时,塑料网沙障在四种材料中防风固沙效果最佳。在同一高度条件下,所有规格沙障当沙障高度为40cm时,防风固沙效果和高度为50cm时的相差很小,而且当沙障孔隙度为30%时,防风固沙效果和孔隙度为20%时的相差不大。综合考虑沙障的设置成本等因素,沙障在相同的条件下,选择高40cm,孔隙度为30%较为适宜。(2)沙袋沙障的防风固沙效果分析结果表明,在1m×1m、1.5m×1.5m、2m×2m、3m×3m及4m×4m等5种规格当中,1m×1m规格的防风固沙效果最佳。不足之处为该材料跟其他材料沙障相对比较,防风固沙效果最差。这是由于沙袋沙障的高度固定为10cm,相对较低,从野外试验结果来看,增大粗糙度的效果不明显。从野外试验结果分析得出,当野外平均风速达到8m/s以上时,沙袋方格内部的沙粒大部分被吹出,使得沙障内部的风蚀程度大于裸地,沙袋沙障的设置反而加强了沙障内部的风蚀。同时,从野外观察发现,在铺设沙袋沙障后,迎风面的沙袋的底部首先遭到大风的‘掏蚀’,之后沙袋自然下塌,从而使得该沙障达不到理想的防风固沙的作用。沙袋沙障的优势是能就地取材,以沙治沙,布设办法简易,费时短,效率高,成本低廉,在一定面积里需要的材料量比其他材料少。不足之处为生产费用和运送费比其它材料贵。(3)对1m×1m、1.1m×1.1m、1.2m×1.2m、1.4m×1.4m、1.5m×1.5m、1.6m×1.6m、1.8m×1.8m及2m×2m 8种规格麦草沙障防风固沙效果进行了分析。分析结果为:随着麦草沙障规格的增大,相对风速逐渐降低,防风固沙效果降低。麦草沙障的地面粗糙度分析结果显示,1m×1m规格麦草沙障的地面粗糙度最大,2m×2m规格的最小。随着麦草沙障规格增大,地面粗糙度逐渐降低。在麦草沙障内部的蚀积量观测结果显示,1m×1m到1.4m×1.4m的麦草沙障与其他规格的沙障相比,稳定区范围较大,侵蚀区的范围较小。试验的8种规格当中,1m×1m麦草沙障蚀积量最小。麦草沙障的成本在这四种材料当中最低。(4)对规格为1m×1m、2m×2m及4m×4m的芦苇杆沙障防风固沙效果分析结果为:1m×lm和2m×2m芦苇杆沙障的防风固沙效果差别不大。4m×4m芦苇杆沙障的平均粗糙度最小,防风固沙效果最差。防沙效果对比分析结果表明,1m×1m和4m×4m芦苇杆沙障在第一个方格中粒径为0.25mm以上的输沙量比旷野的输沙量多。从粗糙度分析,1m×1m和2m×2m规格芦苇杆沙障的平均粗糙度为0.1009m和0.0925m,差别不大。从防风固沙效果、输沙率和粗糙度综合分析表明,1m×1m沙障效果最好。而2m×2m沙障的防风固沙效果、输沙率和粗糙度则与1m×1m沙障的差别不大。芦苇杆沙障的成本仅次于麦草沙障。(5)从上述结论可以看出,沙障的防风固沙效果与高度和孔隙度均有密切关系。在以往布设格状沙障时,通常只考虑材料和沙障规格,而忽视了孔隙度的重要性。因此,今后实施固沙措施时,除了材料本身以外,沙障孔隙度也是一个关键指标。在沙区布设沙障,不仅要考虑防风固沙效果,还要尽量控制沙障成本,只有综合考虑生态和经济因素,才能从根本上解决治沙问题。

This study was conducted in ShaQuanWan, YanChi County, Ningxia Hui autonomous region, which is located in the southern border of Mu Us Sand Land in China, and the effect and the mechanism of windbreak and sandbreak differently installed by size, by height, and by porosity using four kinds of sand barriers including straw, reed, polyester sand sausage, and rubber net were examined. The results are as follows:(1) The study on the windbreak and the sandbreak for the rubber net sand barriers was conducted by combining the four sets of sizes including 1m×1m,2m×2m,3m×3m and 4mx4m, the four heights such as 20cm,30cm,40cm and 50cm, and four porosities such as 20%,30%,50% and 70%. The research results are as follows:In case of size of the sand barrier lmxlm, the height 50cm, and the porosity 20%, the effect of windbreak and sandbreak for the rubber net sand barrier was the greatest. The comprehensive result was that except lmxlm, the sizes of 2m×2m,3m×3m and 4mx4m with the sand barrier height of 40cm showed the similar results to those with the sand barrier height of 50cm. Also, the windbreak and sandbreak effect of porosity 30% for 1m×1m,2m×2m,3m×3m and 4m×4m was similar to that of porosity 20% for each responding size. Accordingly, I conclude that it is the most effective to build up the sand barrier with the height 40cm and the porosity 30% in a desert site. The installation of rubber net sand barrier is simple and easy, and saves installing time and labor. However, as the production cost is high presently, it is considered that the mass production in a factory should contribute to overcoming the poor price competiveness and becoming good material for windbreak.(2) The results of analyzing the effect of the sand sausage sand barrier are as follows: The best effect of windbreak was shown by 1m×1m of the sand barrier sizes among the five sets of sizes including 1m×1m,1.5m×1.5m,2m×2m,3m×3m and 4m×4m. The weakness of this material was that it was the least effective sand barrier comparing with the others. The major cause of this was that the height of the sand sausage was fixed to 10cm, which was relatively lower than the others. I found from the results of field experiment that the surface roughness showed no big differences regardless of the sizes of sand barriers. According to the results of field experiment analysis, on condition of the average wind speed of 8m/s or above at the height of 2m on the ground, most of the sand particles inside the sand sausage were blown away by the wind, and this phenomenon formed the major cause that made the wind erosion of the interior of the sand barrier severer than an open land. Also, according to the observation result of the experiment, when strong wind hit the lower part of the sand sausage facing the direction for the wind after the installation of the sand barrier, the’Undercutting’occurred and a hole was created leading the sand sausage to collapse naturally. Therefore, this sand barrier failed to show ideal effect of windbreak and sandbreak. The strengths of the sand sausage sand barrier lie in that it can be built up with the environment-friendly material which uses the on-site sand and that its installation is simple and easy and takes short time to be installed. However it has the weakness that the production cost and the transportation expenses are more expensive than the others.(3) The windbreak effect of straw sand barrier was analyzed after subdividing the sizes between 1m×1m and 2m×2m into eight categories including 1m×1m,1.1m×1.1m, 1.2m×.2m,1.4m×1.4m,1.5m×1.5m,1.6m×1.6m,1.8m×1.8m and 2m×2m. The analysis results of the windbreak effect of straw sand barrier are as follows:The more the sizes of the straw sand barrier grew, the slower wind velocity became. This means that the bigger the size of the straw sand barrier gets, the less the windbreak effect gets. According to the analysis of the surface roughness of the straw sand barrier, the surface roughness of the straw sand barrier with the size of lmxlm was the greatest, and that of the straw sand barrier with the size of 2mx2m was the lowest. As the sizes of the straw sand barrier became larger, the surface roughness grew less. The observation results of the wind erosion inside the straw sand barrier showed that the erosion of the straw sand barrier with the size of lmxlm was the smallest out of the eight categories. Also, the stabilized zone was the widest for the straw sand barrier with the sizes between 1m×1m and 1.4m×1.4m, and the range of erosion area for it was relatively small. The straw sand barrier had the merits that the price was the most competitive of all the four materials for sand barriers and it was environment-friendly material. On the other hand, it had the defects that the windbreak effect could last short depending on the geographical features and the strength of wind.(4) The study on windbreak, the sandbreak, and the mechanism of reed sand barrier by the three sizes categories of 1m×1m,2m×2m and 4m×4m was conducted. The analysis results of windbreak effect and sandbreak effect of the reed sand barrier are as follows: There was no significant difference in the windbreak effect of the reed sand barrier between the sizes of lmxlm and 2m×2m. For the reed sand barrier with the size of 4m×4m, the average surface roughness was the lowest and both the windbreak and sandbreak effect were the lowest as well. As a result of the comparative analysis of sand barrier effect, the quantity of sand particle with the diameter of 0.25mm or above in the first grid of the reed sand barrier with the sizes of lmxlm and 4m×4m is larger than that of the wilds spot. The analysis results of surface roughness of reed sand barrier by sizes showed that the surface roughness of the sand barriers with the sizes of lmxlm and 2m×2m was 0.1009m and 0.0925m respectively, displaying not much difference. According to the general analysis of windbreak effect, sand quantity, and surface roughness, the reed sand barrier with the size of 1m×1m was the most excellent. However, the windbreak effect, the sand quantity and the surface roughness of the reed sand barrier with the size of 2m×2m were little different from those of the reed sand barrier with the size of lmxlm. In terms of the installation cost, the reed sand barrier was the second cheapest of the four kinds of materials.(5) As you can see from the results of the experiment, the windbreak effect and the sandbreak effect of sand barrier are closely correlated with the sand barrier height and the porosity. In the previous installation of sand barrier, only the materials for sand barrier and the sizes of the sand barrier were considered but the height of sand barrier and the porosity were almost ignored. Therefore, in addition to the material selection, the porosity also should be selected as the critical criterion. In particular, this experiment was focused on the installation cost as well. The radical solution to sand control includes the comprehensive consideration of economical fields such as installation cost including the cost of materials for sand barrier, the transportation expenses, and labor cost as well as the ecological fields such as the windbreak effect and the sandbreak effect of materials for sand barrier installation.

毛乌素; 机械沙障; 沙障配置; 土壤风蚀; 防风效益;

Mu us sand land; Mechanical sand barrier; Configuration of Sand Barrier; Wind erosion; Windbreak effect;

吴斌; 丁国栋;

X171

101716515875K