暴雨山洪灾害预警指标计算方法比较研究

山区河流受地形地貌及降雨过程影响,洪水具有显著的陡涨陡落过程,这种短历时陡涨过程极大缩短了沿河居民的有效安全转移时间,给山洪灾害防治带来了极大困难。山洪预警预报是山洪灾害防治非工程措施的重要组成部分,一般分为水位预警和雨量预警。由于山区洪水历时短且监测站不足,水位预警在国内应用较少,传统流量反推法常以雨洪同频计算预警雨量,预警结果多出现漏警,不能满足防御山洪灾害的实际需求。为提高暴雨山洪的预警精度及预警时长,提出了基于洪水上涨率判定法和实时累积雨量法两种计算预警指标的新方法。以四川省金沙江支流中都河流域“8.16”山洪灾害为例,根据预警准确性及预警时长对三种预警方法的效果,探讨了与传统水位流量反推法的差异。结果表明：传统水位流量反推法的预警精度较低,难以达到预期的预警效果;洪水上涨率判定法的预警精度较高,但该方法的预警时长受洪水涨退特性影响,对延长预警时长有一定影响;采用基于小流域场次洪水与降雨过程变化关系的实时累积雨量法其结果均未出现漏警,且有效延长了预警时长,若以山洪灾害技术要求的30分钟为准,提出的新方法延长预警时长基本超过30%,满足预警要求。因此,建议在设定累积雨量阈值的基础上结合洪水上涨率进行灾害预警,以便更为有效地提高山洪灾害的预警准确率。

Comparative Study on Methods of Early Warning Index of Flash Flood Disaster Induced by Rainstorm

Affected by topography and rainfall process, mountain rivers have a significant steep rise and fall hydrograph, which greatly shortens the disaster response time of residents along the river and challenges the high-precision early warning and forecasting of flash floods. Flash flood early warning is an important part of non-structural measures for disaster prevention and damage reduction, and generally divided into water level early warning and precipitation early warning. Due to the short duration of mountain flood and the lack of monitoring stations, water level early warning is seldom used in China. In addition, the critical rainfall calculated by inversion on water level/flow is based on the assumption of the same frequency of rain and flood, the results of early warning are often missed, which cannot meet the actual needs of mountain flash flood prevention. In order to improve the early warning accuracy and the period of flash flood, two new methods for calculating the early-warning indexes are proposed respectively, which are based on methods of rising rate of flood level and real-time accumulated precipitation. Taking the "8.16" flash flood disasters in Zhongdu River Basin, a tributary of Jinsha River in Sichuan Province, as an example, the early-warning indexes are calculated by the methods of above-mentioned and inversion on water level/flow, and the calculation of the three methods are compared according to the accuracy and the duration of the early-warning. The results show that the early-warning accuracy of inversion on water level/flow is limited, and it is difficult to achieve the expected early-warning effect; the precision of the method of flood rise rate is higher, but the early-warning period is greatly affected by the flash flood characteristics and relatively short, which still has an effect on duration of flash flood early warning; the calculation of the real-time accumulated precipitation has no missed alarm and is a more successful on flash flood early warning compared with the above two methods. Therefore, it is suggested to set the threshold of accumulated rainfall combined with the rising rate of flood for disaster early warning, so as to improve the early warning accuracy of flash flood disaster more effectively.