基于床面蚀积定量分析的新月形沙丘向沙丘链演变研究

The morphological evolution of sand dune was normally caused by the interaction of wind erosion and aeolian deposit process between wind-drift sand and its bed surface. The essence was the sand dune morphological transformation and migration, which was caused by the difference of surface erosion- deposit process. Researching the mutual feedback relationship between erosion-deposit differences and sand dune morphological transformation process is the key to clarify barcan evolution. Taklimakan desert hinterland is a typical area where the barchan dunes develop to barchan chain. This project proposal intends to use comprehensive approach such as sand geomorphology, sand physics method and GIS technology, and to adopt sand observation, topographic survey and imagery interpretation, precisely measuring the barchan dune (barchan chain) surface erosion-deposit dynamics and monitoring the dune morphology changes. With the support of erosion-deposit observation data and topography repeated measurement data, we will analyze the sand dune surface erosion and deposit difference and influence factors, establish the interaction relationship between sand dune surface erosion-deopsit difference and airflow, sand dune morphology evolution. And then, we will analyze the effect of sand dune surface erosion-deposition differentiation influencing on sediment particle size distribution, so that to reveal the erosion-deposit difference on sand dunes form evolution to understand the influence of the migration direction and speed, and to quantitatively express the relationship between erosion-deposit difference and sand dunes local height, width, migration rate and direction of movement. Finally, we try to clarify the dynamic mechanism of the morphological evolution of barchan dunes transform to barchan chain until dissipation.

沙丘形态演变是风沙流与床面侵蚀-堆积相互作用的过程，其实质是表面侵蚀-堆积差异，引起沙丘形态转换与迁移。研究侵蚀-堆积差异与沙丘形态转换过程的互馈关系，是阐明新月形沙丘演变的关键。塔克拉玛干沙漠腹地是新月形沙丘（群）向沙丘链演变过程发育的典型区，本项目拟运用风沙地貌学、风沙物理学方法和GIS相关技术，采取风沙观测、地形测量和影像解译分析综合方案，精确测量新月形沙丘（链）表面侵蚀-堆积动态和监测沙丘形态变化。在侵蚀-堆积观测和地形重复测量数据的支持下，分析沙丘表面侵蚀-堆积差异及其影响因子，建立沙丘表面侵蚀-堆积差异与气流、沙丘形态演变的互馈关系，分析沙丘表面侵蚀-沉积分异对沉积物粒度分布的影响，揭示侵蚀-堆积差异对沙丘整体演变形式、迁移方向和移动速率的影响，定量表达床面侵蚀-堆积差异与沙丘局部高度、宽度、迁移速率和移动方向的关系，阐明新月形沙丘向沙丘链演变直至消散过程的形态-动力学机理。

在塔克拉玛干沙漠腹地建立新月形沙丘演变监测区，通过高精度三维坐标测量、数据处理、分析建模及沙丘属性参数提取分析，研究了新月形沙丘演变过程，获得以下研究进展与结果：（1）采用华测X90 GNSS RTK测量，获取4期空间分辨率小于50 cm×50 cm的沙丘演变监测区高精度三维坐标数据；（2）采用CASS 与ArcGIS相结合的方法，建立了基于DEM的沙丘形态属性及演变参数（沙丘高度，脊线长度，坡长，坡度，宽度，体积，表面积，投影面积，两翼走向，翼间距离和夹角以及移动距离与方向等）提取技术，为风沙地貌演变量化研究提供了精确方法；（3）应用SPSS 21.0逐步线性回归分析方法，建立了沙丘主要形态特征及演变参数之间的关联函数。新月形沙丘演变过程中属性参数均发生变化且相互关联，沙丘移动速度受其高度、坡长、坡度、宽度、面积和体积等属性参数的综合影响，并不单受沙丘高度的控制；脊线长度与沙丘宽度及翼间距离，沙丘宽度与翼间距离，沙丘走向与两翼走向均呈线性正相关；脊线长度与迎风坡角，沙丘宽度与迎风坡角，背风坡长与背风坡角之间均呈弱线性负相关；沙丘移动方向与左翼走向密切正相关，具有“左翼走向形态效应”。（4）沙丘表面坡度坡向变化主要受侵蚀堆积格局控制，而侵蚀堆积过程主要受风和沙源因素影响。监测区沙丘高度在2.0 m以下，对风沙过程响应敏感，侵蚀堆积平衡的稳定性差，受上风向高大沙垄对流场的干扰及垄间粗砂地表的影响，高度不饱和态风沙流引起沙丘沙侵蚀量大于堆积量。（5）多期DEM模拟显示的沙丘演变特征表现为两翼退化收缩，迎风坡与落沙坡变缓，沙丘高度有所降低，沙丘轮廓清晰度下降，沙丘群雁阵排布格局变差，沙丘群密度降低，新月形沙丘的逆向演变趋势明显。沙源匮缺所导致的高度不饱和风沙流是产生新月形沙丘逆向演变的主要原因。（6）此项研究的方法与结果对于风沙地貌演变的形态-动力学定量化探索具有重要促进意义。