关键词: 黄土坡面, 细沟侵蚀, 发育平稳, 水动力学特性

Abstract:

: Rill erosion is the main way of slope erosion on farmland of the Loess Plateau. Rill erosion on slopes accounts for 70% of the total amount of erosion and plays an important role in soil erosion process on loess hillslopes. It is the beginning of qualitative change in the process of soil erosion. Studies of rill erosion can help control soil erosion on slopes, facilitate the development of agricultural production, and serve as the foundation of study of the development process of soil erosion. Natural rainfall may occur intermittently and rills may go through a second rainfall within a short time period. But studies on the dynamic characteristics of rill flow under these circumstances have been few. This research was carried out in the rainfall simulation lab of the State Key Laboratory of Soil Erosion and Dryland Farming on Loess from March to May 2010. Artificial rainfall was applied on a loess slope at an interval of 24 hours under two rainfall conditions, with the first rain that formed relatively stable rill followed by a light rainfall. The results show that: (1) rill flow velocity was impacted by slope length indistinctively. Average velocity of rill flow on slopes of different lengths was not very different. On the other hand, rill flow velocity was greatly influenced by rill morphology. Compared to 20° slope, rill density of 25° slope was higher, while its flow velocity was lower; (2) shear stress is jointly affected by flow discharge and slope. The Reynolds number and Froude number were significantly associated with flow shear stress-the Reynolds number is positively correlated with flow shear stress, but the Froude number had negative correlation with flow shear stress; (3) As the distance from the top of the hill increases, the Darcy-Weisbach resistance coefficient tends to increase as well. With the same rainfall intensity at the second time, the resistance coefficient of steep slope is higher. This indicates a close relationship between resistance coefficient and runoff and slope. There is a significant positive correlation between resistance coefficient and the Reynolds number. Higher Reynolds number means greater average flow rate and intensity. As a result of increased intensity of water flow, rill morphology is more complex and the flow resistance increases. Although the increased Reynolds number also means that the flow depth is larger, the test results show that the drag coefficient under the condition of steep slope is mainly affected by the velocity of flow.

Key words: loess slope, rill erosion, stable growth, hydrodynamic characteristics