Judgement and analysis of dam-break possibility and final breach shape
TAN Guangming1，WANG Jingwen1，ZHANG Chong2，WANG Rui2，SHU Caiwen1，MA Zihao1，ZHANG Guangyue1，HAN Shasha3，4
(1. State Key Laboratory of Water Resources Engineering and Management，Wuhan University，Wuhan，Hubei 430072，China；2. PowerChina Chengdu Engineering Corporation Limited，Chengdu，Sichuan 610031，China；3. Key Laboratory of Lower Yellow River Channel and Estuary Regulation，Ministry of Water Resources，Yellow River Institute of Hydraulic Research，Zhengzhou，Henan 450003，China；4. State Key Laboratory of Hydro Science and Engineering，Tsinghua University，
Beijing 100084，China)
Abstract：Judgement regarding the possibility of a dam-break is critical for deciding whether engineering measures should be taken. Fast access to final breach geometry parameters is also essential for peak-flow prediction. In this study，data from 49 landslide cases and natural dam-breaks from the year of 1654 to the present were collected. Then，the landslide dams after emergency response were regarded as “new dams” according to on-site disposal measures，and data about their upstream lake and dam characteristics were re-classified. Then，statistical and test analysis were combined to select factors that influenced dam-break possibilities and final breach shape from case characteristics，dam-break process and mechanical analysis；the rapid prediction method was summarized. Results showed that the dam-break possibility was related to upstream inflow，barrier lake volume，dam materials and the length-to-height ratio. The influence of length-to-height ratio on the dam-break possibility was only reflected on the dam composed of Class IV and V materials，and this influence was constrained by upstream inflow. The vertical dam-break degree was found to be mainly related to the material of the dam and length-to-height ratio. Based on the above factors，two quick-judgment methods met the needs of predicting dam-break possibility and vertical dam-break degree were proposed during the emergency response process. In addition，the prediction error of the vertical dam-break degree is caused by a vertically inhomogeneous dam structure，especially the binary and ternary stacked structures with “pseudo bedrock” at the bottom. They exerted a significant impact on the vertical dam-break degree. Therefore，such uneven distribution should be considered to reduce the error in prediction. Furthermore，breach width was influenced by the vertical dam-break degree；when one-half of a dam was washed away vertically，the breach width was limited to the river width. From the principles of sediment transport，empirical formulas for calculating top and bottom breach width were derived based on actual discharge storage capacities and vertical erosion depth data obtained from model tests and field cases(R2＞0.86). This research combined scientific，practical and systematic aspects of dam-break prediction；the resulting rapid assessment methods can provide effective references for field decision-makers in preparing emergency plans and preparing peak-flow predictions by assuming suitable breach parameters.
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2024, Vol. 43 
