TITLE:
Characteristics, Impacts and Risks of Dammed Lakes Induced by Debris Flows at the Wenchuan Earthquake Areas
AUTHORS:
Yonggang Ge, Xingzhang Chen, Jianqi Zhuang, Xinghua Zhu
KEYWORDS:
Dammed Lakes, Debris Flows, Outburst, Impacts, Risks
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.6 No.17,
November
28,
2014
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.