Application of embankment breaching model to simulate dam-break floods of barrier lakes
ZHU Yonghui, LV Qingbiao, CHEN Dong & ZHOU Jianyin
Key Laboratory of River Regulation and Flood Control of MWR, Changjiang River Scientific Research Institute, Wuhan, China

Results
The barrier lake refers to the lake formed by large-scale landslides or mudslides blocking
the river. The so-formed dam is a kind of natural embankment prone to breaching. Thereare currently relatively few studies specifically focused on natural embankment breaching
simulation. Application of an embankment breaching model previously developed tosimulate the dam-break floods of two high-risk barrier lakes are summarized.
The two barrier lakes (or natural embankments) are shown in Fig. 1 and Fig. 2, andsummarized in Table 1.

(1) Model applications during emergency response phase
According to the continuous accumulated and updated measured or inferred datatransmitted from the sites, over 100 possible scenarios of the dam-break floods have been
simulated for the two barrier lakes (see e.g. Table 2 and Fig. 3), providing important basis
for the emergency evacuation of the population at risk.
(2) Model applications to the back analysis
For the Tangjiashan Barrier Lake, it was artificially breached by a manual excavateddrainage channel about one month later after its formation. The model was also applied toback analyze the drainage process of the barrier lake. The modeled results agree well withthe available measurements (see Fig. 4).
Table 2 Some of the calculation conditions and results of the“10.10” Baige Barrier LakeNo.

Fig. 1 Tangjiashan embankment

Fig. 2 “10.10” Baige embankment before and after breaching

Table 1 Summary of the two barrier lakes (natural embankments)
Naturalembankment
Tangjiashan

Length river
direction (m)803Width valley
direction (m)611“10.10” Baige

2000

450-700

Height (m)82-12461-100Volume embankment Volume water(106 m3)
stored (108 m3)
20.4
2.5
25

1
2
3
4
56

Corresponding lake storage(108 m3)
3.0
3.0
3.0
3.0
3.0
3.0

Breach size
1/2 dam body
1/2 dam body
1/2 dam body
1/3 dam body
1/3 dam body
1/3 dam body

Breach duration(hr)36123612Calculated flood peak(m3/s)
21600
15600
9500
9500
8500
6900

2.9

Model
The embankment breaching model is previously developed based on the mechanism of
breach erosion as observed in various laboratory or field tests and prototype cases. The
model mainly simulates the coupling process of embankment failure, such as reservoir
water balance, embankment-breaching flow change, embankment-breaching morphology
development and embankment body erosion. For details readers are referred to Zhu (2006)
and Zhu et al. (2008).
The main difference between barrier embankment and artificial embankment is that thematerial grading of barrier embankment is wider and looser, and the embankment bodyalong the river is thicker. However, in terms of failure, the barrier embankment andartificial embankment still have similar failure process and hydraulic characteristics, andsimilar failure mechanism as well. Since the embankment body is thicker in the river
direction, the characteristics of headcut erosion of the failure of the barrier embankment
are more prominent.

Fig. 3 Predicted breach flow rates of
the “10.10” Baige Barrier Lake

Fig. 4 Predictions vs. measurements for the Tangjiashan
Barrier Lake (left: lake level, right: breach flow rate)

Conclusions• Non-engineering measures are the main means for emergency rescue and disposal ofbarrier lakes.
• The most basic requirement for the calculation of dam-break flood risk for theemergency treatment of barrier lakes is simple and fast.
• Due to the lack of data and the urgency of time, many assumptions usually have to beadopted in the flood simulation and prediction during emergency treatment of barrierlakes, so it is feasible to borrow embankment breaching model at this time.
References
Zhu, 2006. Breach growth in clay-dikes. Delft: Delft University of Technology.
Zhu et al., 2008. Dam break flood analysis and discharge scour simulation of the Tangjiashan Barrier
Lake. Yangtze River. 39(22): 79-82.