鄂西长江三峡库区产流降雨特征的研究

Study on the Characteristics of Rainfall Excess in the Reservoir Area of Three Gorges of Yangtze River in Exi Region

鄂西山地连绵起伏，在暴雨作用下。坡面花岗岩风化层流失的大量粗沙在河流沟谷网中堆积起来，随时间推移逐步进入长江。根据坡面径流小区资料，在一次产流降雨中，降雨量（Ｈ），最大１０分钟（ｉ＿（１０））、３０分钟（ｉ＿（３０））和６０分钟（ｉ＿（６０））雨强对产流的作用都比较显著，它们的极值分布可用于估计不同频率Ｈ、ｉ＿（１０）、ｉ＿（３０）和ｉ＿（６０）设计值。对于林地、荒坡地和梯田，降雨侵蚀力指标以组合结构Ｅｉ＿（１０）。较适宜，而坡耕地则以组合结构Ｈｉ＿（１０）较好。根据天然降雨观测资料分析，鄂西地区的降雨类型基本上可分为均匀型、递降型、突发型和峰值型四种雨型，洪水过程和降雨过程相对应，实验流域的输沙量随Ｅｉ＿（１０）增大而增大。但对长历时降雨来说，在以蓄满产流为主的花岗岩风化土体上，Ｅｉ＿（１０）组合结构还是掩盖了降雨过程中一部分非侵蚀降雨的累积效应。

Exi hilly area is uninterrupted rise and fall.The impact of the storm against the soilbody formed by decayed granite in sloping face can preduce a lot of coarse sediment which is piledup in a network of river and gradually transported into Yangtze river with time. By the analysis ofrunoff data from sloping face plots,precipitaton(H)and the maximum rain intensities of 10(i_(10)),30(i_(10))or 60(i_(60) )minutes all play an obvious part in rainfall excess. Their probability distribution ofextreme value can form an estimate of the values of H,i_(10),i_(30),i_(60) with various designed frequence.Rainfall erosion index Ei_(10) is suitable for woodland ,terrace field and waste land. Hi_(10) is suitable forsloping cultivated land.By analysing the observed data from natural rainfall,rainfall patterns can bedivided into even raining,gradually droping raining,suddeuly raining and peak raining,etc. Floodprocess accords with rainfall proress.The higher Ei_(10),is,the higher sediment delivery ratio is in theexperimental watershed. As to long duration rainfall,the index of Ei_(10)can not reflect the accumulat-ed effect of some no-erosive rainfall in soil body formed by decayed granite with the mechanism ofsaturation overland flow.