Effects of Different Sand Barriers on Wind-break and Sand Fixation
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.