KMS XINJIANG INSTITUTE OF ECOLOGY AND GEOGRAPHY，CAS
| 新月形沙丘对荒漠化地区地表风蚀的影响机制研究 | |
| 蔡东旭 | |
| Subtype | 硕士 |
| Thesis Advisor | 李生宇 |
| 2018-06-01 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 新疆乌鲁木齐 |
| Degree Discipline | 农学硕士 |
| Keyword | 新月形沙丘 蚀积分布 风沙流饱和度 流场结构 风洞模拟 Barchan dune distribution of erosion and deposition sand flow saturation airflow structure wind tunnel simulation |
| Abstract | 新月形沙丘是风蚀荒漠化过程中伴随的重要风积地貌类型，在以往的研究中主要侧重于沙丘体表面动力学过程，而关于沙丘在风蚀荒漠化过程中的作用鲜有报道。本文选择风沙活动频繁的台特玛湖的干涸湖盆（曾经的塔里木河尾闾湖）为研究区， 实地测定了该区典型新月形沙丘形态参数，采用测钎法，监测了新月形沙丘的移动速度及周围地表的蚀积变化。 依据风沙运动相似理论，制作不同高度的新月形沙丘模型，在不同风速、不同沙源供给的条件下，进行风洞模拟实验，系统的探究了沙丘周围区域地表蚀积变化、气流分布模式、风沙流饱和度和输沙率等参数。 分析了风蚀荒漠化过程中新月形沙丘对地表风蚀的影响，揭示了新月形沙丘对地表风蚀影响的机理。 本文主要研究结论如下：（1）野外监测结果显示，新月形沙丘体对周围地表的风蚀和堆积产生了较大影响，出现了沙丘周围地表蚀积强度分布空间不均匀的现象：沙丘迎风坡前区、沙丘左翼和右翼蚀积强度较 CK 略大，沙丘背风坡以风积为主，而背风侧尾流区以风蚀为主。沙丘迎风坡前区风蚀量略大于风积量，左右翼角附近处于相对平衡状态（同 CK），背风侧尾流区以风蚀为主，其净风蚀量随着沙丘体积的增加而增大。沙丘体积越大，移动速度越慢，对背风侧尾流区的风蚀影响越明显，净风蚀量越大。将沙丘周边地表蚀积总量分摊到沙丘下伏压埋地面和周围影响区，单位面积的蚀积强度值与 CK 相仿。（2）通过风洞模拟实验对新月形沙丘周围区域的蚀积分布的变化进行探究，发现在新月形沙丘背风侧，存在 3 个相互关联的区域，依次为风蚀区（A）、相对平衡区（B）、尾流风蚀区（C） ， 其中尾流风蚀区（C 区） 加速了地表风蚀。沙丘高度、风速大小、沙源供给的改变，均会对沙丘背风侧尾流风蚀区（C 区）范围产生影响，其中尾流风蚀区的范围随着沙丘高度的增加呈倍数增大；随着风速的增加，其增加效果不明显；随着沙源供给充足，尾流风蚀区的范围略有减小。尾流风蚀区（C 区）的风蚀强度随着风速增加显著加剧；随着沙丘高度的增加，风蚀强度变化不明显；沙源供给充足时，风蚀强度明显减弱。 不同风速、不同沙丘高度、不同沙源供给条件下，沙丘影响区域整体地表的平均风蚀率与平沙地表（CK）较为接近。（3） 通过风洞模拟实验对新月形沙丘流场结构进行探究，根据风速廓线的变化特征，将沙丘背风侧分离气流分为外流区和内流区、内边界层。内流区又可分为涡流区、气流重附着点、保护区、尾流恢复区。 在沙丘迎风坡前区至坡顶，风速廓线呈对数分布；在沙丘背风侧涡流区，风速廓线呈分段函数；在保护区，呈复合函数；尾流恢复区，风速廓线呈对数函数。 风速的变化对沙丘周围流场结构的影响较为微弱，其主要影响沙丘背风侧保护区的长度，随着风速增加，保护区的长度将变短。在风速一定时，随着沙丘高度的增加，沙丘流场结构变化明显，其中背风坡涡流区、保护区、尾流恢复区的长度与沙丘高度呈正比， 背风坡涡流区长度为 4H 左右；保护区长度为 1-2H 左右；尾流恢复区长度为 9-10H 左右。（4）新月形沙丘主要通过改变周围区域气流分布、风沙流饱和度及输沙率来影响地表蚀积分布。 在沙丘背风侧涡流区（A 区），气流迅速衰减， 输沙率降低， 风沙流处于过饱和状态，同时受反向涡流的影响地表呈“先风积，后风蚀”现象。 在保护区（B 区），近地表气流附着并恢复，输沙能力较弱， 气流对地表沉积物的影响极小。 在尾流恢复区（C 区） ， 近地表气流加速率逐渐增加， 风沙流处于极度不饱和状态，且输沙率增强，地表风蚀发生。 沙丘高度越大，沙丘背风侧尾流恢复区的饱和路径长度增长，导致风蚀影响面积越大； 当风速增加时，尾流恢复区风沙流饱和路径长度变化明显， 床面输沙能力增强时，导致地表风蚀增加。 |
| Other Abstract | Barchan dune is an important type of aeolian landform, which is formed duringthe process of desertification. In the past researches, more researchers mainly focusedon the study of the surface dynamic process of barchan dune, but little research hasbeen done on the influence of barchan dune on surface erosion during desertificationprocess. In this paper, the playa of Taitima Lake with frequent aeolian activities(formerly the Talimu Lake in Talimu River) were selected as the study area. Theplugging-brazing method was used to measure the distribution pattern of erosion anddeposition on the surface of the peripheral region of barchan dunes, and the movingspeed of sand dunes. Based on the wind-sand motion similarity theory, barchan dunemodels with different heights was produced. Under the conditions of different windspeeds and supply of different sand sources, wind tunnel simulation experiments werecarried out to systematically explore the changes in surface erosion and deposition，flow distribution patterns surrounding barchan dune, the variation of sand flowsaturation, sediment transport rate and other parameters. The influence of barchandunes on surface wind erosion during wind erosion desertification was analyzed, andthe mechanism of the impact of barchan dunes on surface wind erosion was revealed.The main conclusions of this article are listed as follows:(1) Field monitoring results show that the barchan dune has a great influence onthe wind erosion and deposition around its the surface, and there is a phenomenon ofuneven distribution of the intensity of erosion and deposion around the dunes: theintensity erosion and deposition is slightly larger than that of CK in the front area of thedune windward slope, the left and right wing of the sand dune. The surface wasdominated by deposition in the leeward slope, while the leeward side wake area isdominated by wind erosion. The amount of wind erosion in the pre-wind slope of thedune is slightly larger than the amount of the deposion, and the balance between theright and left wing angles is in a relatively balanced state (with CK). The lee side wake area is dominated by wind erosion, and the amount of net wind erosion increases withthe increase of the dune volume. With the increase in dune volume, the the movingspeed of sand become more slower, and effect of sand dunes on wind erosion in the leeside wake area become more obvious, and the amount of net wind erosion amountbecome more larger. The total amount of surface erosion around the sand dunes wasapportioned to the buried surface and surrounding affected area under the dune, and theerosion intensity per unit area was similar to that of CK.(2) The wind tunnel simulation experiment was conducted to investigate thedistribution pattern of erosion and deposition around the barchan dunes. It was foundthat there were three interrelated areas on the leeward side of barchan dunes, followedby wind erosion areas (A) and relative balance areas (B), Wake wind erosion area (C),where the wake wind erosion area (C) accelerates surface wind erosion. Changes indune height, wind speed, and supply of sand source all affect the wind erosion area (Carea) of the dune leeward side. The range of wake wind erosion area increases with theheight of sand dune; With the increase of wind speed, the effect of increasing windspeed is not obvious; with the abundant supply of sand source, the range of wake winderosion area is slightly reduced. The wind erosion intensity in the wake wind erosionarea (C area) is significantly increased with the increase of wind speed; with theincrease of the height of sand dunes, the change of wind erosion intensity is not obvious;when the supply of sand source is sufficient, the strength of wind erosion weakenssignificantly. Under different wind speeds, different sand dune heights, and differentsand supply conditions, the average wind erosion rate of the entire surface of the sanddune impact area is close to that of the sandy land (CK).(3) Wind tunnel simulation experiment was conducted to investigate thedistribution pattern of airflow on the surface of barchan dune According to thecharacteristics of wind speed profile, the dune lee side air flow was divided into outflowarea, inflow area and inner boundary layer. The inflow area can be further divided intoa vortex area, an airflow reattachment point, a protection area, and a wake recovery area. In the front area of the dune upwind to the top of the slope, the wind speed profileis logarithmic. In the eddy area of the sand dune leeward, the wind speed profile is apiecewise function. In the protected area, it is a complex function. The wake recoveryarea, the wind speed profile is presented the logarithmic function. The change of windspeed has little influence on the structure of the flow field around the dune, and it mainlyaffects the length of the protection zone on the leeward side of the sand dune. Thehorizontal scale of the protected area will become shorter as the wind speed increases.When the wind speed is constant, with the increase of the dune height, the structure ofthe dune flow field changes significantly. The length of the eddy zone in the leewardslope is about 4H; the length of the protected area is about 1-2H; the length of the wakerecovery area is about 9-10H.(4) Barchan dune mainly affect the distribution of surface erosion by changingthe air distribution in the surrounding area, the sand flow saturation, and the sedimenttransport rate. In the dune lee side vortex area (A zone), the airflow rapidly decays, thesediment transport rate decreases, and the wind-sand flow is in an oversaturated state.Affected by the reversed eddy currents, the surface of the area A presents thephenomenon of “pre-wind accumulative, post-wind erosion”. Near-surface air flowattaches and recovers in the protected area (B zone), the sediment transport capacity isweak, and the air flow has minimal impact on surface sediments. In the wake recoveryzone (C zone), the near-surface airflow speed increases gradually, the wind-sand flowis in a state of extreme unsaturation and the sand transport rate increases, and thensurface wind erosion occurs in C zone. The greater the dune height is, the longer thesaturated path length of the dune leeward wake recovery area is, resulting in a largerarea affected by wind erosion. When the wind speed increases, the length of thesaturated sand path in the wake recovery area changes significantly, and the bedsediment transport capacity increases. Caused increased wind erosion on the surface. |
| Subject Area | 水土保持与荒漠化防治 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xjlas.org/handle/365004/14957 |
| Collection | 研究系统_荒漠环境研究室 |
| Affiliation | 中国科学院新疆生态与地理研究所 |
| First Author Affilication | 中国科学院新疆生态与地理研究所 |
| Recommended Citation GB/T 7714 | 蔡东旭. 新月形沙丘对荒漠化地区地表风蚀的影响机制研究[D]. 新疆乌鲁木齐. 中国科学院大学,2018. |
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