黄土高原勺状沟壑特征及发育过程

沟谷是黄土高原物质交换最频繁,形态变化最剧烈的区域。在内外营力的共同作用下,不同发育阶段的各类沟谷塑造了黄土高原“千沟万壑”的独特地貌景观。在黄土高原沟壑系统中,广泛分布着一类特殊的黄土勺状沟壑,目前对其成因、发育过程与机理以及空间分布特征等的认知明显不足。本文以高分辨率遥感影像和DEM数据作为数据源,在大量野外调查和专家知识的基础上,首先提出了黄土勺状沟壑的概念,指出黄土勺状沟壑是独立发育于黄土坡面上的永久性沟谷。其次,从沟壑形态、汇流关系、侵蚀过程、分布特征等方面分析了黄土勺状沟壑区别于其他已有沟壑的特点。进而,从发育形态、发育规模、发育部位等角度对黄土勺状沟壑进行了分类,深化了对勺状沟壑的认识。再次,基于空代时理论,定量分析了黄土勺状沟壑发育过程的形态演变特征,进一步探讨了黄土勺状沟壑发育过程,论证了黄土勺状沟壑是黄土切沟的初期阶段。最后,在系统梳理总结勺状沟壑的特征及分类的基础上,提出了黄土勺状沟壑的发育过程设想,指出勺状沟壑的形成离不开黄土陷穴和暗穴的生成和发育,勺状沟壑的进一步发育伴随着水力侵蚀和重力侵蚀过程。勺沟尾部变细甚至消失,不能发育成更大规模的切沟,与地下暗穴、黄土渗透率、降雨条件以及地表覆盖有关。本文成果期望为进一步完善黄土沟谷地貌发育和侵蚀过程与机理等认识做出贡献,同时对黄土高原水土保持工作提供参考。

Characteristics and development process of spoon-shaped gully in the Loess Plateau

Gully is characterized by the frequent material exchanges and strong morphological changes in the Loess Plateau. Under the combined action of internal and external forces, various kinds of gullies in different development stages have shaped the unique geomorphologic landscape in the Loess Plateau. And a special loess gully, namely, the spoon-shaped gully is widely distributed in this plateau. At present, there is limited research on its formation, development process, mechanism, and spatial distribution characteristics. Using high-resolution remote sensing images and DEM data, and based on the sufficient field investigation and expert knowledge, this paper put forward the concept of loess spoon-shaped gully, and pointed out that the loess spoon-shaped gully is a kind of permanent discontinuous gully independently developed on the loess slope. Then, the characteristics of loess spoon-shaped gully were analyzed from the aspects of gully shape, confluence relationship, erosion process, and distribution characteristics, which were different from other existing gullies. Furthermore, the loess spoon-shaped gully was classified from the perspectives of development morphology, development scale and development location. Based on the space-for-time substitution theory, the morphological evolution characteristics of the spoon-shaped gully were analyzed quantitatively, and the development process of loess spoon-shaped gully was further discussed. It was proved that loess spoon-shaped gully was the initial stage of loess bank gully. Finally, on the basis of systematical summary on the characteristics of spoon-shaped gullies, the development process of spoon-shaped gullies was deduced, and it was pointed out that the formation of spoon-shaped gullies was closely related to the formation and development of loess sinkholes and dark caves. The further development was accompanied by the process of hydraulic erosion and gravity erosion. The reason for the shrinkage or the disappearence of the tail of the spoon-shaped gully can be attribute to the underground caves, loess permeability, rainfall conditions and surface cover. The results of this paper are expected to contribute to the further understanding of the landform development, erosion process and mechanism of the loess gully, and to provide references for soil and water conservation in the Loess Plateau.