泥石流多发区蒋家沟流域的下渗与产流特点

Infiltration and Runoff Yield Characteristics in Jiangjia Ravine

在云南东川蒋家沟泥石流源区多个典型点,进行野外下渗试验得出蒋家沟流域宽级配土的下渗特征。试验发现:1.下渗曲线皆较好满足霍顿下渗公式;2.下渗率比较大,主要土壤红黄壤的各种土地利用类型的稳定下渗率都在0.08 mm/s以上;3.不同土壤类型的稳定下渗率按大小排序依次为:砾石土>红黄壤>燥红土,红黄壤的各种土地利用类型的稳定下渗率按大小排序依次为:耕地>林地>灌木丛>裸地(滑坡后壁)>草地。蒋家沟流域宽级配土决定了降雨时壤中流产流占有很大比例,在径流场进行人工降雨,采集前期土壤水、壤中流和降雨样品,通过测试其中的稳定同位素浓度,利用同位素分割径流的原理,发现前期土壤水在壤中流产流中起着不可忽略的作用。降雨时,大量雨水下渗入土体,使孔隙水压力增加,前期土壤水位于湿润峰的前端,因此壤中流产流初期,前期土壤水占有很大的比例,达到86.46%,随着降雨时间的持续,雨水逐渐取代前期土壤水的作用,导致产流中本次降雨的比例逐渐升高,试验结束时达到85.63%。可以推断,短历时暴雨时,降雨强度大于下渗率,该流域以超渗产流为主,易发生坡面泥石流;长时间小强度降雨时,该流域以蓄满产流为主,壤中流占有很大比例,本次降雨是泥石流暴发的诱发因素,但不一定是水量的主要供给源。

Infiltration characteristics were obtained by outdoors experiments on various typical points in debris flow source region in Jiangjia Valley. Some basic characteristics were presented, including 1 ） The infiltration capacity curve can be preferably fitted by Horton formula. 2） The infiltration intensity in this area is relatively hard. Satu- rated stable infiltration rates in all kinds of land use types in Red - Yellow soil which is the main soil type in this area are bigger than 0.08 mm/s. 3 ） To the three soil types, infiltration coefficient form great to small ： gravelly soil --~ Red -Yellow soil ---＊ Dry Red soil; to different land use types in Red -Yellow soil, the sequence is： plowland --~ woodland --＊ shrubbery --~bare land（ landslide back wall）--~ grassland. The interflow in this area plays an im- portant role in the runoff because of the big infiltration capacity. An isotope separating interflow runoff during the artificial rainfall experiment was carried out in one plot. The samples of antecedent soil moisture, rainfall and inter- flow were collected, measured and analyzed. During the rainfall, infiltration increased the soil water content which made pressure to push the antecedent soil moisture migrate downward. So, it was possible that the antecedent soil moisture peak at the wetting front during the infiltration. Therefore, in the early stage of the runoff, the antecedent accounted for a very large proportion （86.46%）. As the time last, rainfall water gradually took the place of the antecedent soil moisture to be main part of water in the soil, meanwhile, the proportion of rainfall water in the un- derground water was also gradually increasing （85.63 % in the end of the experiment）. It was deduced that during a short duration rainstorm, over-infiltrating runoff dominated and slope debris flow is easily to occur; during a long- time drizzle, stored-full runoff dominated the antecedent soil water plays an non-negligible role meanwhile, slump debris flow and landslide debris flow are easier to occur instead. This paper contributes the runoff producing and debris flow starting mechanism in this area.