Moraine Lake Debris Flow Disaster: Risk Evaluation And Numerical Simulation

The disaster caused by moraine lake outburst was a typical and important geological disaster in the Himalayas in Tibet in our contry. This paper researched major influence factors of moraine lake, and chose major evaluation indexes, built moraine lake outburst risk evaluation system, adopted Catastrophe Progression Assessment Method to determine the moraine lake risk level, researched the relation between moraine lake volume and inundation range, relation between moraine lake volume and valley cross-section through remote sensing method and numerical simulation combining with field investigation data. Using the imporved software of LAHARZ which was used to moraine lake outburst debris flow inundation in the Himalayas to simulate moraine lake, and get the range of moraine lake debris flow. The conclusions were as follow through this way:1. The glacier developed well because of the high altitude in the Himalayas, the moraine lake were formed by glacier and were supplied by melt water. With the global warming, the moraine lake outbursts disaster become more and more because of the glaciers melting and fading away. There were a lot of moraine and reckle in both of moraine lake downstream valleys, and provided well water conditions and material conditions for moraine lake debris flows.2. Summarized moraine lake outburst influence factors, included replenishment glacier snow cover area, glacier snow area average longitudinal slope, glacier tongue slope, front tongue distance from the moraine lake, moraine lake area, crest width of terminal moraine and downstream slope of terminal moraine seven factors, took these seven influence factors as the evaluation indexed, adopted Catastrophe Progression Assessment Method to assess maraine lake risk.3. Analyzed the dynamics characteristic of debris flow from the physical property, assumed the volume of moraine lake mud-rock flow is a constant in the process of flow, the volume density is not changed,by using the theory of fluid mechanics,deduce the mathmatical model of mud-rock flow volume and flood hazard area of the moraine lake,the volume of moraine lake mud-rock flow and the cross-sectional area of valleys,make this mathematical model as the equation of motion of the moraine lake mud-rock flow.4. Summarized the data of moraine lake in the Himalayas, and research the characteristics of 18 dangerous lakes and moraine lake debris flows. Used linear regression method to establish the math relation of moraine lake volume and Solving two coefficient of movement equation of moraine lake,take the equation of movement as reliability test to prove the reliability of the mathematical model.5. Put the math model into LAHARZ program to simulate the moraine lake debris flow in Sangwangcuo moraine lake and Jialongcuo moraine lake in the Himalayas. Comfirmed the elevation threshold, stream threshold, energy cone threshold and debris flow volume through calculation and research when LAHARZ was running. Sangwangcuo moraine lake elevation threshold was 4310 m, stream threshold was 6000, energy cone threshold was 0.15 and moraine lake debris flow volume was 2.5×108m3. Jialongcuo moraine lake elevation threshold was 2330 m, stream threshold was 6000, energy cone threshold was 0.55 and moraine lake debris flow volume was 1.05×107m3.6. Chose Sangwangcuo moraine lake total storage 2.5×108m3and Jialongcuo moraine lake total storage 1.05×107m3 as the basic value, and divided the moraine lake outburst into four conditions to consider: the whole burst, 80% burst, 60% burst and 40% burst, the moraine lake debris flow volume was equivalent to the burst water volume, and divided into four different volumes to perform numerical simulation.7. Chose four of different volumes of 2.5×108m3, 2×108m3, 1.5×108m3 and 1×108m3 as the moraine lake debris flow volume according to the four situations for Sangwangcuo moraine lake, and chose the volumes of 1.05×107m3,8.4×106m3,6.3×106m3 and 4.2×106m3 as the moraine lake debris flow volume of Jialongcuo moraine lake. Used LAHARZ to simulate the inundation hazard zone of Sangwangcuo moraine lake debris flow and Jialongcuo moraine lake, and the conclusion was as follow: for Sangwangcuo moraine lake, when the debris flow volume was 1×108m3, the accumulation area was strip in the middle of cheuch, the Dili village in downstream was in the range of accumulation zone, this area belonged to high dangerous region. When the debris flow volume was 1.5×108m3, the front of the accumulation area reached the turning of downstream. When the debris flow volume was 2×108m3, the accumulation area was far away from lake 25 km, and the accumulation zone was wide at the top and narrow at the bottom. Dili village had been covered. When the debris flow was 2.5×108m3, the accumulation zone was strip, and the furthest area was away from Sangwangcuo 27 km. In addition, the moraine lake debris flow may block the riverway and interdict the river, effect the Jiangzi contry downstream because of the second burst flood. For Jialongcuo moraine lake, the most dangerous inundation hazard zone was Nielamu town. The national road of 318 was also suffering seriously by the moraine lake debris flow. The furthest area of indunation hazard zone reached 8 km of Nielamu town downstream. So the government of Nielamu town shoud prepare and prevent for Jialonghu moraine lake debris flow because of its huge damage, and guarantee the safety of people’s lives and properties.