物源条件对震后泥石流发展影响的初步分析

强震过后一定时期内,泥石流的活跃性增强,即数量增多、规模增大、频率增加。而随着松散物质储量的减少,泥石流的活跃性会随之衰减。为了具体考察物源条件对震后泥石流活动的影响,使用震后泥石流逐年平均输沙量作为刻画泥石流活跃性的指标,在云南蒋家沟和西藏古乡沟泥石流数据的基础上,定量地分析了震后泥石流活跃性的变化过程。分析表明存在降雨控制型和物源控制型两种泥石流流域。前者的泥石流在震后很长一段时间内都不衰减,其发生主要取决于降雨条件。后者最大规模的泥石流发生于地震过后的短时间内,尔后泥石流活动随时间显著减弱。泥石流规模和频率的关系与暴雨不一致。当物源控制型流域的无量纲化活跃性指标值降为0.12左右时,可以认为泥石流进入了稳定或者衰弱期,不会再有大规模的泥石流事件发生。数据拟合结果表明,整个泥石流活跃性的衰减过程可以用幂函数来描述。其衰减指数与剩余物质储量和总物质储量之比存在密切的关系。这为定量预测震后泥石流发展趋势提供了一个初步的模型。

Influence of debris supply on the activity of post-quake debris flows

The influence of debris supply on the activity of post-quake debris flows was quantitatively examined by two cases： Jiangjia basin in Yunnan province and Guxiang basin in Tibet,southwestern China.Mean annual sediment discharge was served as the index of activity.According to the temporal behavior of the mean discharges,the two basin systems were identified.One is the rainfall-dominated basin of which debris-flow activity has not decayed even forty years after earthquake.The occurrence of debris flow in the first basin is determined by rainstorm,and then its return period is equal to that of rainstorm.The other is the supply-dominated basin in which the activity of debris flow decreases significantly along with the decreasing volume of loose materials.The latter should be in inactive or decline phase when the value of the dimensionless activity index reduces to 0.12 in the case of Guxiang.After that,there is no more large scale debris-flow accident.The decay process of debris-flow activity was described well by a power function,and the function’s exponent showed a close relationship with the ratio of the volume of the remaining loose material to the original materials,which provides a start point for developing a quantitative model to predict the trend of post-quake debris flow activity.