定西于家山黄土洞穴的分布特征与侵蚀临界研究

黄土洞穴与滑坡、沟蚀等侵蚀过程联系紧密并加剧了黄土高原的水土流失程度,但目前黄土洞穴发育的分布特征与侵蚀临界暂未明晰。利用无人机获得了研究区高分辨率影像与数字表面模型,基于影像标识了黄土洞穴并统计了其土地利用类型与洞穴直径,利用标识点在数字表面模型上提取了黄土洞穴的坡度、坡向、曲率和汇水面积等地形数据并分析了黄土洞穴的分布特征。结果表明,黄土洞穴直径大多4 m。黄土洞穴在耕地上发育较少,多发育于牧草地区域流水汇聚的凹形坡,且在阴坡更为发育。同时,黄土洞穴坡度正切值范围集中于0.4～1.0,汇水面积一般不超过3 000 m~2。依托统计的坡度正切值与汇水面积数据绘制了黄土洞穴的侵蚀临界图并对比了黄土洞穴与浅沟、切沟的侵蚀临界。黄土洞穴的侵蚀临界边界分别为SA~(0.150)=0.368与SA~(0.135)=7.580,分布较广且覆盖了浅沟与切沟的侵蚀临界。浅沟、切沟的演化与黄土洞穴的发育有关,黄土洞穴通过连通与坍塌促进了浅沟、切沟的发育、转换与扩展,并因此加剧了黄土高原的水土流失。研究量化了黄土洞穴发育的分布特征,建立了黄土洞穴与浅沟、切沟的联系并深化了对黄土洞穴侵蚀过程的认识。

The Study of the Distribution Characteristics and Erosion Threshold of Loess Cave at Yujia Mountain in Dingxi

Loess cave is closely related to other erosion processes,such as landslide and gully erosion,and aggravates the degree of soil and water loss in the loess plateau. However,the distribution characteristics and the erosion threshold of loess cave are not clear yet. This study uses unmanned aerial vehicle (UAV) to acquire the high resolution image and digital surface model (DSM) of the study area. Identifying the loess cave,collecting its land use type and measuring its average length based on image as well as extracting its terrain data such as slope,aspect,curvature and drainage area,we analyze the distribution characteristics of the loess cave. The results show that the average length of loess cave is mostly shorter than 4 m. The loess cave tends to develop in pasture area rather than in arable land and requires certain terrain,mostly develops in the concave slope with water converges. The number of loess caves that develop on shade slope is more than that on sunny slope. Also,the area exits loess cave is usually with the tangent value of slope between 0.4 to 1.0 and the drainage area less than 3 000 m². Drawing the erosion threshold of loess cave rely on the statistics data of the tangent value of slope and drainage area and comparing the erosion threshold of loess cave with that of shallow ephemeral gully and gully,the erosion threshold of loess cave can be applied as formulas SA^0.150=0.368 and SA^0.135=7.580,which is widely enough to cover the erosion threshold of shallow ephemeral gully and gully. The evolution of shallow ephemeral gully and gully is related to that of loess cave. The development and transformation of the shallow ephemeral gully and gully are promoted by the collapse and connection of the loess cave,thus aggravates the degree of soil and water loss in the loess plateau. This study quantifies the distribution characteristics of the loess cave and establishes the contact among loess cave,shallow ephemeral gully and gully. It deepens the understanding of the process of the loess cave.