Knowledge Resource Center for Ecological Environment in Arid Area
| 敦煌莫高窟风沙防护综合体系若干措施的环境效益监测研究 | |
| 其他题名 | The Monitoring Research of the Environmental Benefits about Several Methods of Aeolian Sand Comprehensive System |
| 李国帅 | |
| 出版年 | 2012 |
| 学位类型 | 硕士 |
| 导师 | 屈建军 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 敦煌莫高窟是我国乃至世界古代灿烂文化艺术的瑰宝，由于地处西北干旱荒漠地带，所以风沙危害一直是莫高窟保护面临的主要威胁之一。本文依据前人的研究，着重从机械防沙、植物防沙、化学防沙和防风固沙效应等角度简略介绍敦煌莫高窟风沙危害防治保护工作的主要科研成就以及科研成果在实际工作中的运用和效果，以此突出敦煌莫高窟保护工作的重要性。\n 莫高窟常年遭受风沙侵蚀，气候干燥，属于典型的沙漠气候带，其原始地貌由于人为扰乱和旅游开发改观，窟前为阻缓围岩的风蚀建立的防护林缓冲带和崖顶铺压的人造戈壁，取代原先的粗砾质戈壁，构成莫高窟独特的人工自然景观。近地层不同下垫面影响到风沙环境不同的局部区域，不同下垫面构成的局域风沙环境的不同气象要素可反映出莫高窟环境的具体变迁，为今后人们研究不同下垫面造成的小气候影响和效果提供定量的物理参数。\n 由莫高窟窟顶野外风速廓线试验依据合适的经过调整的风速廓线方程拟合1 m×1 m麦草方格的不同高度的风速廓线，得知麦草方格使得流沙原始地表上零风速高度变为7.274 cm，粗糙度增大为1.050 cm。此外结合鸣沙山原始地表野外风洞实验可进一步得出麦草方格使得流沙地表粗糙度由原先的0.003 cm变成1.050 cm，增加约350倍。而且发现，不同高度的风速与粗糙度的关系符合经过一定修改的增长曲线模型。综合以上研究可进一步推导出麦草方格的漩涡影响公式。\n 灌木林带植物防沙效益长期监测是一项比较重要的工作。对莫高窟顶灌木林带采用插扦法长时间监测四处不同的积沙断面，以蚀积量特征作为标准定性判断效益好坏，可以发现：莫高窟顶灌木林带年平均蚀积量一直处于风积状态，有增长加快的趋势。结合风沙堆积位置，花棒与红柳沿主风向相邻配置防沙效益最好，混交林带次之。花棒、柠条防沙效益最佳时期为6月、5月和11月，红柳可能为4月。花棒单一纯林带最适合用来做防沙物种首选。研究区段灌木林带以每年29.9万吨的速度积沙，而多年、逐年平均积沙变化间接证明莫高窟风沙综合防护体系已起到一定作用。\n 砾石压沙的防护机制的解决是一个比较复杂棘手的问题。我们通过对比莫高窟顶原始戈壁与经砾石压沙形成的人造戈壁的静压起动风速、不同高度的风速、吹蚀时间、粗糙度、含沙量、盖度和野外积沙等特征的变化，解释砾石压沙的防护机制，最终证实砾石压沙的有效性和通用性。我们得出的结论有：流沙表面、原始戈壁、人造戈壁的粗糙度和静压起动风速依次增大。夏季是原始戈壁上就地起沙风和挟沙风发生次数最多的季节。就地起沙是原始戈壁风沙流发生的主要原因。小砾石、中砾石、大砾石的粗糙度随盖度的增加均呈现出“四峰”的形状。随着砾石粒径和盖度的增加，含沙量随离地面高度的分布会不规则。人造戈壁上小砾石积沙效果随盖度的增加而增加，大砾石的积沙效果随盖度的增加反而降低。原始戈壁的积沙率的反常是导致莫高窟风沙严重的一个重要原因。砾石压沙除能防止就地起沙，积沙功能也非常重要。\n 1990年在莫高窟顶设置的A字形尼龙网一直以来是抵抗风沙的有效手之一。A字形结构疏导和沉积来自偏西风(主害风)的沙粒，但在一定程度上也阻碍了偏东风的向鸣沙山方向的反向输导和搬运作用。尼龙网戈壁一侧有较高的风速，易形成掏蚀坑，沙源丰富的情况下一般会形成“双峰”结构。如果尼龙网处于地表性质不同的戈壁的交界处，在不同季节下风沙蚀积形状类似，然而，两侧性质相似的话，不同季节的蚀积形状变得不规则。沿着尼龙网南侧和北侧易形成具有一长坡脚的蚀积曲线。由于空气流场的被扰乱，监测断面会形成“单峰”的形状。尽管尼龙网的设计寿命已经超过预期寿命(10年)，我们的观测显示出它在风沙防护中仍发挥一定的作用，不应该被拆除。 |
| 英文摘要 | Dunhuang Mogao Grottoes are ancient brilliant culture of China and the world of art treasures, while it is located in northwest arid desert, sandstorm damage has been one of the main threats to protect it. This article based on previous research, focusing on mechanical defense, vegetation defense, chemical defense, main effects of sand and sand-fixing angles brief description of Mogao Grottoes sand hazard control, protection of major research achievements and the use and effectiveness of research results in practical work, thus highlighting the importance of the protection of Dunhuang Mogao Grottoes.\n Understanding the variation of meteorological effects on these different earth surfaces will be helpful to devise protective strategies for this precious world cultural heritage. Extreme temperature response changes on the artificial gobi are greater than that on the original gobi, which suggests that the artificial gobi could be a good indicator of strong temperature amplitude oscillation. The average monthly air temperature, the average monthly relative humidity, and the average wind speed in the artificial gobi tend to first decrease and then increase with the increase of measurement height. The shelterbelts in front of grottoes retain heat longer than the other two locations and effectively decrease wind speed by 83.95%, compared with the artificial gobi (8.21%). The gravel layer in the artificial gobi loses heat between February and October and absorbs heat between November and January. The extreme of monthly average atmospheric pressure in front of the grottoes occurs 1 month earlier than in the artificial gobi.\n According to the test of contour line of the wild wind speed on the top of Mogao Grottoes and based on the right and adjusted equation of the wind speed contour line fits the contour line of the 1m×1m square of different height of wheat straw which makes the height of zero wind speed on the original surface of quicksand come to 7.274cm, the roughness increase to 1.050. In addition, combined with the wind tunnel test on the original surface of Mount Mingsha, we can know that the wheat straw makes the roughness of the original surface of quicksand change from 0.003 to 1.050, which increases about 350 times. And it is found that the relationship between different height of wind speed and roughness accords with the growth curve model which has been modified. It can be further deduced the whirlpool impact formula of wheat straw according to the upper researches.\n By using erosion pins for long-term monitoring of four ecologically different sections on top of the Mogao Grottoes from 1999 to 2009, here we show that aeolian sand erosion and deposition have been increasing in quantity and intensity. Analyzing the positions of aeolian sand deposits, we determined that Hedysarum scoparium planted adjacent to Tamarix ramosissima Ledeb. could best resist sand deposition in the primary harm wind direction, followed by mixed shrub belts. This configuration model is extended and used in other desert region. Combining the aeolian sand condition in different seasons in different desert region with the optimal timing of plant emergence for sand protection, different kinds of shrub belts are selective. Tamarix ramosissima Ledeb. appears in April, Hedysarum scoparium in June, and Caragana korshinskii Kom. in May and November. Single Hedysarum scoparium belts are the most suitable plantings for sand protection systems. Shrub belts in the study area accumulated an average of 299,000 tons of sand every year between 1999 and 2009, and analysis of the average accumulating sand change year by year suggests that protection measures against aeolian sand movement have made progress.\n The protective mechanism of gravel paving on top of original gobi is complicated and difficult to elucidate. In this study we assess a variety of relevant parameters, such as the static pressure starting wind speed, wind speed at different heights, wind abrasion time, gravel roughness, sediment concentration, paving coverage, and field sand accumulation in original gobi and artificial gobi after gravel paving on top of the Mogao Grottoes. We prove the validity and general protective benefits of gravel paving, and demonstrate that the roughness and static pressure starting wind speed increase by turns on the surface of drifting sand, original gobi, and artificial gobi. The summer season has the highest frequency of sand-driving threshold wind and sand-carrying wind. Sand-driving wind on the local gobi is the main cause of dust storms in the original gobi. The roughness curves of small, medium, and large gravel present four peaks related to the increase of the coverage. The distribution curve of sediment concentration with the increase of height becomes irregular with the increase of gravel diameter and coverage. The effect of sand accumulating on small-sized gravel increases with increase of coverage, whereas sand accumulation on large-sized gravel decreases with increase of coverage on artificial gobi. A certain abnormality of accumulating sand rates in the original gobi is discussed, which is an important cause of severe aeolian sand in the Mogao Grottoes. In addition to preventing sand-driving wind on the local gobi, the function of sand accumulating in gravel paving is also demonstrated to be very important.\n A A-shaped nylon net fence installed in 1990 on top of the Mogao Grottoes is shown to be effectively resisting aeolian sand damage to the grottoes. The structure guides and causes deposition of sand from westerly wind (the primary hard wind), but to some extent hinders the inverse function of easterly wind carrying sand away from the grottoes toward Mount Mingsha. The gobi side of the fence experiences higher wind speeds and easily forms undercutting pits, and deposited sand in that area generally forms double-peak structures due to the abundant sand source. Also, in gobi areas on both sides of the fence, if the earth surface characteristics are quite varied, the forms of erosion and deposition of accumulating sand are similar in different seasons. However, if the earth surface characteristics in the gobi are similar to each other, the forms of erosion and deposition of accumulating sand become irregular in different seasons. Curves of accumulating sand with long slope feet are formed along the south and north sides of A-shaped nylon net fence. Where the air flow field is disrupted by the fence, monitoring sections develop sand accumulation in the form of single peaks. Although the design life of the A-shaped nylon net (10 years) has now been exceeded, our observations indicate that it is still effective in reducing wind-driven sand harm to the Mogao Grottoes, so it should not be withdrawn. |
| 中文关键词 | 莫高窟 ; 麦草方格 ; 灌木林带 ; 人造戈壁 ; 尼龙网栅栏 |
| 英文关键词 | Mogao Grottoes wheat grass checkboard shrub belts artificial gobi nylon net fence |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287083 |
| 推荐引用方式 GB/T 7714 | 李国帅. 敦煌莫高窟风沙防护综合体系若干措施的环境效益监测研究[D]. 中国科学院大学,2012. |
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