极端降雨下黄土高原草被沟坡浅层滑坡特征及其对产流产沙的影响

植被恢复作为黄土高原防治水土流失的重要措施，但极端降雨诱发的浅层滑坡在植被恢复的沟坡上频繁发生，影响流域的产流产沙过程。基于野外原位模拟降雨试验，在60 mm/h降雨强度下，研究草被沟坡浅层滑坡发生特征及其发生前后的产流产沙差异。结果表明：（1）极端降雨所诱发的草被沟坡上的浅层滑坡深度为14-36 cm，与自然强降雨所导致的浅层滑坡深度相贴合，均是低于50 cm。（2）植被根系与土壤容重、孔隙度等土壤性质显著相关（P<0.05），致使滑坡面上、下层土壤物理性质差异显著（P<0.05）。由于土壤性质的差异，在极端降雨下滑坡面上层土壤水分更快达到饱和（饱和度>90%），导致浅层滑坡的发生。（3）草被坡面浅层滑坡后的径流与产沙均显著增大（P<0.05）。三个小区的平均径流率在滑坡后增大了4.0-13.1倍，其平均含沙量和产沙率在滑坡后分别增大了9.9-54.9倍和70-841倍。研究结果有助于加深了解植被沟坡的侵蚀产沙机理，并为浅层滑坡防治提供科学依据。

Characteristics of shallow landslides under extreme rainfall and their effects on runoff and sediment on the Loess Plateau

Vegetation restoration is an important measure to prevent and control soil erosion on the Loess Plateau, but shallow landslides induced by rainfall occur frequently on the revegetation slopes, affecting the process of runoff and sediment production in the watershed. In order to quantify the impact of shallow landslides on the process of runoff and sediment and to study the difference in runoff and sediment yield before and after the landslide occurrence, the field simulated rainfall tests were carried out on the grasscovered slope in the Wangdonggou watershed on the Loess Plateau. Based on the field investigation, each experimental plot was 25 m long and 2.5 m wide, and the slope was 35°-40°. Rainfall intensity was 60 mm/h, rainfall time was 90 min, representing a typical heavy rainfall on the Loess Plateau. After the shallow landslide occurred, another rainfall test was carried out, and then the rainfall was stopped. Runoff and sediment samples were collected at the plot outlet at 5minute intervals from the beginning of the rainfall. After the test, a 100 cm³ ring knife was used to collect soil samples from different soil layers (10 cm, 30 cm, 50 cm) in the experimental plot to determine soil bulk density, soil porosity, and the saturated hydraulic conductivity. Three soil samples were taken from each layer. The drying method was used to determine the soil bulk density and soil porosity, and the doublering knife method was used to determine the saturated hydraulic conductivity. The results show that:(1) the depth of the shallow landslide on the grass cover slope induced by extreme rainfall was 14-36 cm, which was consistent with the shallow landslide depth (less than 50 cm) caused by the natural heavy rainfall. The shallow landslide depth was significantly correlated with the vegetation root depth. (2) There were significant differences in the physical properties between upper layer (rootsoil composite) and the lower layer of the landslide surface (P<0.05). The bulk density of the lower layer of the landslide surface was 20.6%-26.0% higher than the upper layer of the landslide surface. The saturated hydraulic conductivity of the upper layer of the landslide surface was 8.2-311 times higher than that of the lower layer of the landslide surface. Under extreme rainfall, the soil moisture on the surface of the landslide reached saturation sooner, and the soil moisture saturation exceeded 90%. (3) The runoff and sediment yield after a shallow landslide on the grass cover slope increased significantly (P<0.05). The average runoff intensity of the three plots was only 0.05-0.13 mm/min before the landslide, and as high as 0.62-0.69 mm/min after the landslide, an increase of 4.0-13.1 times. The average sediment concentration and average sediment yield rate were only 0.6-5.8 kg/m³ and 0.03-0.26 g m^-2 min^-1 before the landslide, respectively, and reached 30.0-111.5 kg/m³ and 18.6-21.9 g m^-2 min^-1 after the landslide, respectively, increasing of 9.9-54.9 times and 70-841 times. The research results are helpful to deepen the understanding of the erosion and sediment yield mechanism of revegetation slopes, and provide scientific basis for shallow landslide prevention and control.