Investigation of the landslide dam in Chin Hill, Myanmar, 15 July 2016

Investigation of the landslide dam in Chin Hill, Myanmar, 15 July 2016

Heavy rainfall (480mm) 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 landslide dam was formed by quick deposits of landslide materials, which lack of sufficient compaction in damming material.  In other hand it is lacking of seepage control and flood drainage facilities. For these reasons, the dam may breach and the consequent flood could create significant loss of life and downstream property. The stability of this landslide dam is a prime concern for local people.

In this regard the Ministry of Environmental Conservation and Forestry of Myanmar requested ICIMOD to undertake an assessment of investigation of landslide dam and to develop a comprehensive management plan to tackle the problem. The Director of the Chin State Forest Department had prepared a short field trip to the areas of landslide dams in order to assess the risk of the landslide dam. The ICIMOD team joined the group to investigate the landslide dam in May 2016. Most of the physical information was gathered through the study of satellite images, which was later verified in the field. Though the field trip was brief, the team was able to collect substantial data.

The mountainous provinces of Myanmar, primarily the western ranges and eastern highlands, have an unstable geologic structure: steep slopes and higher than average seismicity that, when combined with monsoon rains, makes the area extremely hazard—prone.

Landslide dams are natural dams formed by quick deposits of landslide materials. Since the landslide material are loose and lack of fines for cohesion, there is high possibility of dam breach. Knowing the extent of a dam’s stability is quite important for people living in the area and downstream of the dam.

Costa and Schuster (1988) studied an inventory of 73 landslide dams with the intention to investigate the longevity of dams that fail. They found that 27% of landslide dams fail within the first day, 41% within the first week, 80% within six months and 85% within the first year of existence.

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 of 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.

The present report is based on the analysis of available maps, satellite images, literature, and our related site investigations.

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