Abstract
After the Wenchuan Earthquake, many large-scale debris flows blocked rivers, generated dammed lakes, and produced outburst flood at the seriously hit areas. This paper mainly discussed the formation, outburst, impacts and risks of debris flow dammed lakes. The field investigation showed that the dammed lakes were created by debris flows from gullies and hill-slopes as well as the combination of debris flow and landslides, and also distributed along rivers step-by-step. The height of dams and the length of dammed lakes along river channel varied from 4 m to 18 m and from 400 m to 5000 m, respectively, and the reservoir capacity of dammed lakes were from 1.5 × 105 m3 to 3 × 106 m3. Due to geomorphological impact, dammed lakes commonly partially outburst along their front of debris flow deposition dams (1/4 - /3 outburst) or the suture between debris flow and landslide, and hardly completely outburst. Moreover, the subsequent debris flows continuously increased the magnitude and height of dams, not only increasing the stability of a single dam, but also improving the risks of outburst flood induced by intensive rainstorm. Dammed lakes produced steep rage in the sites of dams with the 4% - 9% of slope and rapidly raised river channel in the upstream due to a mass of alluvial sediment. As a result, the landscapes of step-dams and step-lakes dominate driver channels, significantly increasing the hazards of floods. Then the hazards, impacts and risk of debris flow dammed lakes along Min River from Dujiangyan to Wenchuan were analyzed. In order to mitigate dammed lakes induced by debris flows, the identification model of debris flow blocking rivers, the process of the formation, outburst and evolvement of dammed lakes, and the model of risk assessment for step-dammed lakes were strongly suggested to explore, and be used at the rivers of Min, Yuzi, Caopo, Longxi, Mianyuan, Jian, Shiting, Baishui and Jushui.
Highlights
Dammed lakes are generally generated by landslides from torrential rains, earthquakes, lavas from volcanic eruptions, or ice-jams and moraines from glacier [1], and have been concerned and deeply researched to explore the mechanism of dammed lake formation, assess and predict risk, and find the technical measures for mitigating [2]-[11]
The shape, height and volume of debris flow dam were in diversity which depend on the dynamic parameters of debris flow, the geomorphology of the outlet of debris flow gullies and river channel and the sediment that was delivered into river
After the Wenchuan Earthquake, dammed lakes are produced by slope debris flow, gully debris flow and the combination of debris flow and landslides
Summary
Dammed lakes are generally generated by landslides from torrential rains, earthquakes, lavas from volcanic eruptions, or ice-jams and moraines from glacier [1], and have been concerned and deeply researched to explore the mechanism of dammed lake formation, assess and predict risk, and find the technical measures for mitigating [2]-[11]. The intensive earthquakes at mountain areas generally result in a large number of geo-hazards, including landslides, rock falls, debris avalanches and debris flows, which block rivers and create dammed lakes so as to endanger mountain environment and local inhabitants’ security. The Wenchuan Earthquake in May 12, 2008, with MS 8.0, produced 40,000 - 50,000 landslides, rock falls and debris avalanches [15]-[17], which blocked river and formed 257 dammed lakes. Debris flows directly destroyed local environments and endanger reconstruction, and blocked rivers, formed dammed lakes, threatened the securities of its upstream and downstream, and posed more serious hazards. This paper concentrated on formation, outburst, impacts and risks of debris flow dammed lakes to give valuable measures for mitigating
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