Landslide Dam Outburst Flood in Chin Hill, Myanmar

Landslide Dam Outburst Flood in Chin Hill, Myanmar

Heavy rainfall (480 mm) on 16 July 2015 triggered a huge landslide (DGSE and GDKU, 2016) that dammed the Tui Lam Lui River approximately 52 km upstream of Yazagyo Dam near Hangken Village, Falam District in the Upper Chin hill region in northwestern Myanmar.

The Chin Hill range is composed of fractured brown and gray shale with subordinate of brown sandstone. The steep slopes of the region combined with intense monsoon rains make the mountainous region one of the most hazard-prone areas in Myanmar. The dammed lake from the July 2015 landslide grew rapidly during the monsoon to 50 Ha by August 2015 and then reduced down to 41 Ha in the dry season. The lake contains 15.5 million cubic meters of water (DGSE, 2016). The landslide dam was formed by quick deposits of landslide materials, which lack sufficient consolidation. Hence, the stability of this landslide dam was a prime concern for local people.

The Ministry of Environmental Conservation and Forestry of Myanmar requested ICIMOD to assess the landslide dam and develop a comprehensive management plan to tackle the problem. The Director of the Forest Department of Chin State organized a short field trip to the landslide dam and lake area in May 2016 and the ICIMOD team led the investigation group. The team used remote sensing data and field data to be analyzed in a geographic information systems environment. Based on collected data, the ICIMOD team concluded there was a strong probability this landslide dam would breach.

As predicted, the landslide dam did breach in July 2016. After the burst, the remaining lake area measured 19.6 Ha with 4 million cubic meters of water stored. To confirm the future stability of the lake, the Ministry requested ICIMOD to conduct additional investigations of the lake. This began in December 2016 and the details are presented in the remainder of this report.

The report was co-funded by the Royal Norwegian Embassy in Nepal.