| Disasters such as floods, landslides and debris flows take place in a valley is called as mountain torrent disaster which has the characteristics of sudden and destructive. Geological features and terrain styles in China are complex, area of mountain takes 66 percents of the total land area, and is larger than world average. In addition, the rainfall distribution is unequal in time, distribution range is wide in space, and heavy rain is relatively concentrated, thus formed the characteristics of high frequency for mountain torrent disaster in China, which has caused great losses of people’s life and property.At present, prevention and control work for the mountain torrent disaster has make great progress in preplan, county-level monitoring and early warning platform and monitoring and prevention system construction. This system meets China’s national conditions. The Construction for engineering measures such as monitoring and prevention has been implement, however, the research of mountain flood prevention work which focus on non-engineering measures appeared later relatively, especially in quantitative of torrent disaster early warning indicators. This study used GIS, satellite remote sensing, hydrological analysis and calculation, combined site survey about mountain torrent disaster, analyzed the storm and flood in small watershed, evaluated defense capabilities for mountain torrent disaster, and divided the danger zone; and analyzed the critical rainfall of flood, which can support the control capacity and sustainable socio-economic development. Based on the solid brain cooking basin in west of Lanzhou as the research object, the main research content is as follows:(1) We analyzed the existing forms and characteristics of mountain torrent disaster, the characteristics of mountain torrent disaster are high storm intensity, large flood peak, short flood process, small total flood volume, difficult defense and large disaster extent. The development characteristics of mountain torrent disaster are mainly shown in the two aspects of space and time, spatial feature is closely related with regional tectonics, rock types and human activity and other factors. Time characteristics is consistent with rainfall periodicity in Xigu zone.(2)Based on the parameters such as disaster level, storm duration, critical flow and warning period, we consider the survey data and compared the Lanzhou empirical formula and rational formula, and we selected the Lanzhou empirical formula to calculate the mountain torrent disaster. We determined the stage-discharge relationship of disaster control section using manning formula, and got the disaster level elevation of research area using measured data about residential housing elevation in disaster range, and determined the critical flow, storm duration and warning period.(3) According to the actual situation of Xigu zone and the characteristics of mountain torrent disasters, the complete situation of basic data, the accuracy of the practical application and operational conditions, we consider that disaster and frequency of rainfall with the law- Inverse Method is appropriate to determine the warning index in Xigu.The basic idea is that we assume that the frequency of rainfall and flood is the same, then analyze the disaster objects, determine the warning period, draw the storm frequency curve and flood frequency curve, and determine critical flow using control section and disaster level, we also look for the corresponding frequency, and calculate the corresponding rainfall. This paper determines the research of early warning index of small watershed in different times.(4) In this paper, we choose Naodigou basin of Lanzhou Xigu District as a typical area, specific operation of mountain torrent disaster was displayed, characteristics of mountain torrent disasters was expounded, peak flow at different frequency were determined using appropriate methods, the critical flow of Naodigou basin is 21.5m3/s, through the heavy rain lasted and flow analysis, warning period of 1h, 3h, 6h, 12 h and 24 h were determined, warning index value of Naodigou at different time scale were calculated by Disaster and rainfall same frequency-inverse method. |
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