Impact of earthquake-induced-landslides on hydrologic response of a steep mountainous catchment: a case study of the Wenchuan earthquake zone

Earthquake-induced-landslides will change the underlying surface conditions (topography, vegetation cover rate, etc.), which consequently may influence the hydrologic response and then change the flash flood risk. The Jianpinggou catchment, located in the Wenchuan earthquake (occurred in Sichuan, China, 2008) affected area, is selected as the study area. The distribution of the landslides is obtained from the remote sensing image data. The changes of topography are obtained from the comparisons among digital elevation models (DEMs) during different periods. A physical-based model, the integrated hydrology model (InHM), is used to simulate the hydrologic response before and after the landslide. The influence of the underlying surface conditions is then discussed based on the simulation results. The results reveal that landslides cause significant effects on the hydrologic response, and the impact is proportional to the proportion of surface flow in the total runoff. The effect of landslides on the runoff is insignificant at the outlet, but obvious in the local area. The larger the rainfall, the more visible the impact, and the impact of landslides will increase rapidly at the threshold of the runoff (the total rainfall of 235 mm in 6 h in the study area), but there is a limit with the further enlarged rainfall. The improved understanding of the impact of landslides on the hydrologic response provides valuable theoretical support for storm flood forecasting.摘要目的明确汶川地震所引发的滑坡对震区小流域水文响应过程的影响, 推进震区洪水过程的准确预报。创新评估汶川地震对碱坪沟流域的下垫面条件的破坏, 并在此基础上利用先进的分布式水文模型定量评估地震事件对小流域产汇流过程的影响。方法1. 选取四川省龙溪河地区的碱坪沟小流域作为研究区域, 利用遥感影像数据以及数字高程数据获得滑坡区的分布以及高程变化情况; 2. 运用基于物理概念的综合水文模型 (InHM) 对该流域水文过程进行模拟精度验证; 3. 对滑坡发生前后的降雨产流过程分别进行数值模拟, 探讨在同样降雨条件下, 由于滑坡所引起的下垫面特性变化对产流过程的影响。结论1. 震后滑坡灾害所带来的下垫面变化导致了流域内的山洪特性变化, 且在流域内局部地区的表现更为明显, 局部山洪危害增加; 2. 与震前相比, 随着暴雨规模的增强, 震后下垫面变化所致的流量峰值增量也随之增加, 峰值的增加比例在 6 小时雨量达到 235 mm 时急剧增大, 但降雨持续增强后趋近于稳定值 (约 87%)。

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