Knowledge Resource Center for Ecological Environment in Arid Area
| 三种地表风沙流特性及沙丘近地表风速研究 | |
| 其他题名 | The research on the characteristics about three kinds of aeolian sediment and the near-surface wind speed of sand dunes |
| 马小明 | |
| 出版年 | 2017 |
| 学位类型 | 硕士 |
| 导师 | 吕萍 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 风和沙相互作用所形成的风沙流和沙丘是风沙地貌主要研究对象，风沙流和沙丘移动对农田、牧场、交通、工矿居民点等造成严重危害。因此，认识和掌握风沙流特性和沙丘的形成演变规律对沙漠化防治、风沙实践工程具有重要的意义。在野外环境下，由于地表属性、地表湿度、风的脉动和风程长度等因素的时空变化对风沙流特性及沙丘近地表风速产生一定影响，野外直接观测是研究风沙运动的重要基础。地表性质对风沙流特性有着重要的影响，沙丘近地表风速对沙丘的形成演变起着决定性的作用。本文选取腾格里沙漠东南缘中国科学院风沙观测场，直接观测三种典型地表1m高度内的输沙量及不同沙丘近地表风速特征，初步探究野外环境下不同地表风沙流特性及沙丘的形成演变过程，旨在掌握野外沙漠地区风沙运动规律，为腾格里沙漠特别是沙坡头景区的防沙工程提供理论基础。1、不同地表风沙流特性在腾格里沙漠东南缘中国科学院风沙观测场内人工平整一块面积为200m×115m的区域，通过人工设置，野外模拟三种典型地表（流沙地表、草方格地表、砾石覆盖地表），用相同规格的LDDSEG集沙仪野外同步观测三种地表1m高度内的输沙量，探究不同地表属性的风沙流特性。主要得出以下结论：（1）三种地表在相同环境条件下风沙流通量廓线均满足指数递减规律，相关系数在0.99左右，砾石覆盖地表在风速＞8m/s时，风沙流通量廓线呈现“象鼻”特征，风沙流通量最大值出现在距离地表约4cm处。（2）风沙流通量廓线参数a与单宽输沙率满足线性关系，参数b代表风沙流通量随高度的递减速率。他们大小显著受地表性质影响。草方格地表参数a随单宽输沙率增加的最快，流沙地表和砾石覆盖地表参数a随单宽输沙率增加的速度相似；砾石覆盖地表参数b最大，风沙流通量随高度递减速率最慢，草方格地表参数b最小，风沙流通量随高度递减速率最快。（3）沙粒运动是一种贴近地表的运动形式，砾石覆盖地表沙粒最大跃移高度达65cm，草方格地表沙粒最大跃移高度为40cm，流沙地表最大跃移高度为37cm，同一种地表，风速越大，沙粒获得的能量就越多，跃移高度就越大。（4）砾石覆盖地表平均跃移高度最大，草方格地表次之，流沙地表最小，沙粒平均跃移高度随着风速的增大而上升。随着风速增大，三种地表输沙率累积百分数随高度变化的差异越明显。2、沙丘近地表风速在腾格里沙漠东南缘中国科学院风沙观测场内选取6个高度不同的天然沙丘，沿沙丘横断面布置观测点，利用可移动的风速观测系统直接观测沙丘近地表7个高度的风速（最低高度确定在距沙丘表面5cm处），探究沙丘近地表风速变化与沙丘形成演变之间的关系。主要得出以下结论：（1）在沙丘风速观测时间段内，距沙丘地表不同高度处风速随观测时间不断发生变化，表现出一定的阵性。（2）贴近沙丘地表0.05m和0.1m高度的风速，由于直接受沙丘地形的影响，风速变化复杂。风速从0.3m到0.4m变化幅度较大，从0.4m到1m风速变化最小，风速加速率都小于1，越靠近地表，地表对风速的扰动越明显。（3）不同沙丘，其沙丘顶部位置，0.05m高度处的风速最大值位置以及0.6m高度处的风速最大值位置不在同一水平位置处，而是沿着风速方向发生一定的位移，此位移影响沙丘的形成与演变。 |
| 英文摘要 | The Aeolian sediment and sand dunes caused by interaction between wind and sand are the main research objects in the aeolian landforms. The aeolian sediment and movement of sand dunes bring devastating damage to farmland, pasture, traffic, and industrial and mining settlements. In the field, spatial and temporal variation of surface properties, surface moisture, wind turbulence, and fetch length affect the characteristics of aeolian sediment and the surface wind speed on dunes. Consequently, direct field observations are the basis of researches concerning wind and sands movement. Surface properties significantly affect the characteristics of aeolian sediment, and surface wind mainly contributes to the formation and development of dunes. The research site is located in the Aeolian Experiment Site, Chinese Academy of Sciences, in the southeastern edge of the Tengger Desert. In this study, we directly observed the sand flux within 1 m height above three typical land surfaces, and the characteristics of surface wind on different dunes. The main aims of this study are to determine the movement patterns of aeolian sediment under the field conditions, and provide theoretical basis for the sand prevention and control engineering in the Tengger Desert and especially the Shapotou tourism spots. 1. Characteristics of aeolian sediment on different land surfacesIn the research site, we smoothed a 200 m×115 m region and manually constructed three typical land surfaces (open shifting sand, straw-checkerboard sand, and gravel-covered sand). To explore the characteristics of aeolian sediment, the LDDSEG sampler of same specifications were used to synchronously monitor the sand transport in the field. The results are shown below.(1) The aeolian sediment flux density profiles above the three surfaces decreased with height, following an exponential function under the same environmental condition, with correlation coefficient around 0.99. When the wind speed exceed 8m/s above the gravel-covered sand, the flux density profile exhibited a shape of elephant nose, and the maximal flux density occurs at the 4 cm height above surface. (2) There was a linear relation between parameter a in the flux density profile and streamwise sand transport rate, and parameter b represented the decrease rate of aeolian sediment flux density by height. These two parameters were significantly affected by surface properties. The parameter a showed a highest increase rate by streamwise sand transport rate in the straw-checkerboard sand , and similar increase rate between the open shifting sand and the gravel-covered sand. The parameter b was the highest in the gravel-covered sand, and the decrease rate of aeolian sediment flux density by height was minimum. While in the straw-checkerboard sand, the parameter b was minimum, the decrease rate of flux density with height was maximal. (3) The movement of sand particle was close to surface. The saltation height of sand particle reached to 65 cm in the gravel-covered sand, 40 cm in the straw-checkerboard sand, and 37 cm in the shifting sand. Above the same surface, larger wind speed contributed to higher energy of sand particle, and consequently higher saltation height. (4) The average saltation height was maximal in the gravel-covered sand, lower in the straw-checkerboard sand, and minimum in the shifting sand. The average sand saltation height increased with increasing wind speed. In addition, as the wind speed grew, the difference of cumulative percentage of surface sand transported rate between land surfaces enlarged. 2. Near surface wind speed above dunesIn the research site, we totally selected 6 natural sand dunes with different heights. The monitoring sites were located along the cross section of dunes. To explore the variation of wind speed near the dunes surface and its relation with the formation and development of dunes, the wind speeds at 7 heights were monitored with mobile wind speed monitoring systems. The results are shown below.(1) Within the monitoring period, the wind speed at different heights varied with time, and showed turbulence.(2) The wind speed at heights from 0.05 m to 0.1 m, affected by topography of dunes, showed large variability. The variation of wind speed at heights from 0.3 m to 0.4 m was large, while minimum from 0.4 m to 1.0 m. The accelerating rate of wind speed was less than 1, and the role of surface in disturbing wind speed was more significant at positions closer to land surface.(3) At the summit position of sand dunes, the horizontal position of maximal wind speed at height of 0.05 m did not coincide with that at 0.06 m, while moved downwind. This movement affected the formation and development of sand dunes. |
| 中文关键词 | 风沙流 ; 沙丘 ; 野外观测 ; 风沙流特性 ; 近地表风速 |
| 英文关键词 | Aeolian sediment Sand dunes Field observations Characteristics of aeolian sediment Near surface wind speed |
| 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/2XILL650/287845 |
| 推荐引用方式 GB/T 7714 | 马小明. 三种地表风沙流特性及沙丘近地表风速研究[D]. 中国科学院大学,2017. |
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