| Luanchuan is a mountainous county that located in west of Henan Province. It’s known as "Two valleys surrounded by four rivers and three mountains, One space contained half-tenth water, half-tenth plough and nine-tenth mountain", for having YiHe river, XiaoHe river, Mingbai He river, YuHe river and Xionger mountain, Eyuling mountain, Funiu mountain. Meanwhile, Luanchuan has many mountains and valleys, abundant rainfall in summer and autumn. Yet it is located in Gushi-Luanchuan-Queshan Fault zone and lifting area, which leaded to erosion landform and gravity landform developing. Moreover, Luanchuan environment are strong interfered by human beings, especially in1950th and1960th, the vegetation destruction heavelly. And the emergence stratum mainly are metamorphic rock and igneous rock, which belong to easily weathered rocks. These are creating conditions for regional debris flow breaking out, in Luanchuan. According to "County Annals of Luanchuan (1994)", Luanchuan has been broken out several serious rainstorms, floods and debris flows in history. On July24th,2010, heavy rain was occurred in Luanchuan area, the precipitation of Taowan, Luanchuan and Miaozi reach to149.4,147.8and100.1millimeter respectively. That resulted many towns of Luanchuan County broken out debris flows, such as Luanchuan, Chitudian, Taowan, Shimiao and so on, which left68people dead,21people missing and caused a total direct economic loss of19.8billion yuan.Luanchuan County has2715streams that their length more than500meters, yet much more streams’ length less than500meters. Among them, some have abundant source that could be a potential debris flow gully. According to historical data and investigation data, the watersheds are different of Luanchuan debris flow gully, the biggest can exceed50kilometers, but the smallest can less than0.1kilometers. The gully type, such as Danangou Gully, Qigugou Gully, Taowannangou Gully and Washiyangou Gully’s basin area are more than10kilometers, but slope type, such as Shirengou debris point, Zhuyuancun2Zu debris point and Taowan8Zu debris point’s watersheds are less than0.15kilometers.As Luanchuan’s debris flow gullys with different characteristics, in order to analyze the debris flow breaking out conditions and to find out theirs common factors, the source condition, gully morphology, precipitation condition and soil strength are analyzed. Based on previous achievements and project investigation results, these debris flow points were divided into seven types based on start-up model. They are dragging and busting joint action model, punching and slumping joint action model, impacting induced liquefying model, slope slumping model, slope washing and gully start-up joint action model, tailings busting model and combinational model, respectively. Moreover, detailed analysis of seven typical debris points, which belongs to the seven debris types, was conducted. Then combined with statistics data, the source accumulating condition, runoff kinetic energy condition and soil strength weaking condition are picked out, which included11factors that theirs values are assigned by TAHP method. Finally, the hazard zonation real-time dynamic model is structured by combinating source accumulating condition, runoff kinetic energy condition, soil strength weaking condition and hazard bearing body condition. And the model were assessed by Luanchuan "7.24" rainstorm debris disaster points (without tailings busting type) with GIS techniques.Main conclusions of the article as follows:1, Luanchuan County has conditions of breaking out regional debris flow, and it has been developed different types, such as mudflow, debris flow and water-rock flow.2, Luanchuan’s debris flow points could be divided into seven types based on start-up model. They are dragging and busting joint action model, punching and slumping joint action model, impacting induced liquefying model, slope slumping model, slope washing and gully start-up joint action model, tailings busting model and combinational model, respectively.3, Based on GIS techniques and "7.24" rainstorm debris data, fault density, gully density, slope aspect values, slope values, apparent source amount, watershed were extracted. Then referencing previous achievements and project investigation results, the debris real-time dynamic division model with Luanchuan characteristics, was established. The model includes four conditions and12factors, such as source accumulating condition (petrofabric, fault density, gully density, slope aspect values, slope values and apparent source amount), runoff kinetic energy condition (physiognomy, watershed, hour rainfall density and gully gradient), soil strength weaking condition (120hours rainfall before and24hours rainfall before), and hazard bearing body condition. Moreover the model can be divided into two parts, one is debris risk index and the other is net debris risk index. The region that may break out rainstorm debris flow can be warned by integration judgement, through debris risk index and net debris risk index eonbinated model.4, Hazard zonation models were established that based background conditions, hours rainfall, start-up mechanism respectively. Facts proved that the models can reflect Luanchuan County debris lability areas objectively and can playback "7.24" rainstorm debris perspective with time.5, Assessed with18rainstorm debris data in the conbinated model, Luanchuan rainstorm debris warning values are confirmed that the risk index value more than0.216and the net risk index value more than0.05. Meanwhile, Luanchuan County debris harzad zonation was researched, based on background conditions (physiognomy, watershed, petrofabric, fault density, gully density, slope aspect values, slope values and apparent source amount) that without rainfall factor. Results show that Luanchuan rainstorm debris high lability areas are located in Funiu Mountain section between Miaozi and Taowan, the section between Yihe River section above Luanchuan Town and Eyu Mountain, part of Shizimiao and Baitu section that between Eyuling Mountain and Xionger Mountain, and some small pockets of Tantou and Daqinggou.Certainly, as the weather is different in Luanchuan different towns, the model can’t be exactly assessed when only used Luanchuan weather station data. Yet, the model is critical to rainfall data that arrounded evaluation object. So there need more exact samples to complete the model. And hazard bearing body condition is also worthy of attention, especially the aspect of vulnerability quantization. That to say, the model and its conclusions in the article, are preliminary results, just for referencing.Otherwise, follow-up study of Luanchuan County harzad zonation can reference the article idea. And the real-time harzad zonation system should to make the best of computer and GIS techniques, for inputing the whole town’s rainfall data of Luanchuan County to system database real-timely and dynamicly displaying zonation results on screen. Then the model can play a more important role in Luanchuan County debris prevention and reduction, and that is also the ultimate goal of this article. |
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