甘肃省小陇山林区降雨型浅层滑坡汇水面积-坡度关系及其影响因素

沟头发生侵蚀的地形临界模型可有效预测侵蚀沟的形成条件,浅层滑坡失稳形成的洼地也是沟头形成的方式之一。为探究浅层滑坡临界起动模型的特点,以甘肃省天水市小陇山林区的降雨型浅层滑坡为研究对象,运用汇水面积-坡度关系,构建临界起动模型,与黄土高原典型侵蚀沟(浅沟、切沟)的临界起动模型进行对比分析,并探讨土地利用类型、植被类型和土壤质地对该模型的影响。结果表明:(1)浅层滑坡临界起动模型为S=3.50A_s^-0.34,其侵蚀阈值为3.50,大于黄土高原典型浅沟(0.96)和切沟(1.54)的侵蚀阈值。研究区浅层滑坡一般发生于土层较薄的陡坡地带,其平均坡度(S=1.26)大于浅沟(S=0.35)与切沟(S=0.46),单位汇水面积(A=89.08 m²/m)小于浅沟(A=920.93 m²/m)和切沟(A=1 129.82 m²/m)。(2)汇水面积与坡度平方的乘积(AS²)代表了沟头产生侵蚀的能量指标值。研究区浅层滑坡AS²值在269.1~5 703.2 m²,平均值为1 772.97 m²,黄土高原浅沟AS²值在4.74~892.66 m²,切沟在41~814 m²,启动能量值方面,浅沟<切沟<浅层滑坡。(3)土地利用类型、植被类型和土壤质地通过影响土壤的抗冲力、渗透性和黏粒含量,从而对浅层滑坡的起动难易程度产生影响。在不同的土地利用方式中,农地最易发生侵蚀,其次是林地。油松林附近浅层滑坡的抗侵蚀能力高于日本落叶松林。研究结果为探究浅层滑坡的起动条件提供理论依据。

Research on the Area-Slope Relationship of Typical Rainfall Shallow Landslides in Xiaolong Mountain Forest Area of Gansu Province and Its Influencing Factors

The topographic critical model for the occurrence of erosion at gully head can effectively predict the conditions for the formation of erosion gullies, the depression formed by shallow landslide instability is also one of the ways of gully head formation. In order to explore the characteristics of the critical initiation model of shallow landslides, the rainfall-type shallow landslides in the Xiaolong mountain area of Tianshui City, Gansu Province was taken as the research project. We used area-slope relationship to construct the shallow landslide critical initiation model, and compared with the critical initiation model for typical erosion gully ephemeral gullies and permanent gullies located in the Loess Plateau. The effects of land use type, vegetation type and soil texture on the critical initiation model were also discussed. The results showed that: (1) The critical initiating model of shallow landslides was S=3.50A_s^-0.34, and its topographic threshold was 3.50, which was larger than ephemenral gullies (0.96) and permanent gullies (1.54) in the Loess Plateau. Shallow landslides in the study area generally occurred on steep slope area with thin soil layer, and the average slope (S=1.26 m/m) was higher than ephemeral gullies (S=0.35 m/m) and permanent gullies(S=0.46 m/m). The unit upslope drainage area (A=89.08 m²/m) was less than the ephemeral gullies(A=920.93 m²/m) and permanent gullies (A=1 129.82 m²/m). (2) The product of upslope drainage area and the square of the critical slope gradient (AS²) was used as an important energy index for gully formation. The AS² value of shallow landslide in the study area ranged from 269.1 to 5 703.2 m², with an average value of 1 772.97 m². The AS² value of ephemeral gullies in the Loess Plateau ranged from 4.74 to 892.66 m², and that of permanent gullies in 41 to 814 m². In terms of starting energy value, ephemeral gullies < permcnent gullies < shallow landslides. (3) Land-use type, vegetation type and soil texture had an effect on the initiation of shallow landslide by affecting the resistance, permeability and clay content of soil. Among different land use modes, agricultural land was the most vulnerable to erosion, followed by forest land. The erosion resistance of landslides near Pinus tabulaeformis forest was higher than those in Larix kaempferi forest. The results of this study provide a theoretical basis for exploring the initiation conditions of shallow landslides.