中都河流域“8·16”山洪致灾机理分析

我国西南地区地形地貌条件复杂,极端暴雨山洪灾害频发,显著制约地区社会经济发展。为科学认识暴雨山洪形成过程,揭示受灾地区致灾机制,构建符合区域特征的山洪灾害预警体系,以四川省屏山县中都河流域“8.16”山洪灾害为例,结合实地调查及基础资料,从地区降雨特性、洪水陡涨过程及人类活动三方面入手,系统分析了此次暴雨山洪的灾变响应过程,以及采用水位流量反推法和洪水上涨率判定法计算山洪灾害预警指标阈值。结果表明：此次山洪灾害成因主要在于上游马边县地区短时强降雨导致下游屏山县中都镇河水陡涨,极大缩短了沿河居民转移时间;当地居民围滩造地侵占河道,减少了行洪面积,属于典型的地区强降雨与人类活动综合影响下的突发性暴雨山洪灾害;对比上述两种预警方法的结果,发现水位流量反推法预警精度稍差且多次出现漏警,洪水上涨率法预警期显著延长,预警效果更为可靠。因此,建议中都河流域山洪灾害防御采用洪水上涨率法和传统预警相结合,以流域划分模式构建马边屏山两县行政联合的山洪预警体系,可为该区域乃至其他类似山洪灾害频发地区的防治提供科学依据。

Analysis on the disaster mechanism of "8.16" flash flood in Zhongdu River Basin

The complicated topographical conditions and rainstorms frequently lead to mountain flash flood disasters, which severely restrict the social and economic development in southwest China. It is very important to scientifically understand the process of flash flood, reveal the disaster mechanism, and construct the early warning system of flash flood considering the regional characteristics. Based on the field investigation and analysis of "8.16" flash flood disaster occurred in Pingshan County, Sichuan Province, this study systematically analyzed the catastrophic response of flash flood from three aspects of regional rainfall characteristics, flood steeply rising phases and human activities. This study took two methods including a water level discharge relationship and rising of flood level into account early warning values, respectively. The results showed that the heavy rainfall from the upstream Mabian County resulted in this flood disaster event, and the rising of flood level greatly shortened the transfer time duration of residents along the riverbank. On the other hand, residents made cultivated land through floodplain, which reduced the flood discharge capacity and increased the disaster risk. It belongs to a typical sudden flash flood disaster under the comprehensive interactions among regional heavy rainfall, topographical conditions and human activities. In short, the traditional early-warning method of inversions on water level/flow missed several alarms in selected sections, and has slightly poor accuracy. However, the water level rising rate early-warning method is a more reliable from the escape time. That is to say, it is useful to adopt the coupling methods such as rising of flood level and traditional ways to establish a county-to-county joint flash flood early-warning system.