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Flash Flood Risk Management – A Training of Trainers Manual
Figure 20: a) Bhairabkunda Khola a few days after the LDOF; b) debris deposited by the LDOF;
c) large boulders trapped at the highway bridge; d) Larcha village destroyed by the flash flood
a
b
Session 14
c
d
Source: NR Khanal
RM 14.3: Case studies of landslide dam outburst floods
Case 1: The Budhi Gandaki and Larcha Khola landslide dam outburst flood
In recent memory, the Budhi Gandaki River in Nepal was twice dammed near Lukubesi (Shrestha et al.
2008). In 1967, the river was dammed for three days after slope failure at Tarebhir. Another landslide in
1968 again dammed the river with a huge amount of displaced material. After the landslide dam was
breached, the water level rose by 14.61 m. The peak flow was estimated to be 5,210 m 3 /sec, which is
significantly higher than the mean annual instantaneous flood (2,380 m 3 /sec). After the breach, one bridge
and 24 houses were swept away at Arughat Bazaar which is located about 22 km downstream from the
damming site (Figure 20).
The Bhairabkunda Khola (river) was dammed in 1996. The subsequent landslide dam outburst flood
destroyed 22 houses and killed 54 people in Larcha village. The highway bridge was swept away by the
flash flood.
Case 2: The Tsatichhu landslide dam outburst flood
Another example of an LDOF in the HKH region is the Tsatichhu LDOF in Bhutan (Shrestha et al. 2008)
(Figure 21). On 10 September 2003, material with an estimated volume of 7–12 x 10 6 m 3 failed on the
wall of a valley and slid into the Tsatichhu River. The tremor cause by the landslide was felt as far away as
Ladrong village some 2.5 km away. According to the inhabitants of nearby areas, the main slide occurred
over a period of 30 minutes. The slide formed a river-blocking dam 110 m high. The deposited material
had an estimated volume of 10–15 x 10 6 m 3 . The dam crest extended approximately 580 m across the
valley (Dunning et al. 2006), and the deposited material spread a distance of 200 m upstream and 700 m
downstream.
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