Landslide Dam Assessment in Chin State, Myanmar

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Field observation and measurements.
Photo: Sudan Bikash Maharjan/ICIMOD

A team of scientists recently visited the landslide dam in Chin State, Myanmar to assess the risk associated with the dam and to develop a comprehensive management plan. Conditions of the lake, landslide dam features, dam materials, the river course and river bed materials were studied. The team observed the landslide dam is composed of loose and highly shattered shale with scattered sandstone boulders — materials easily eroded by rain water and highly permeable. 

Experts Samjwal Bajracharya and Sudan Maharjan from the International Centre for Integrated Mountain Development (ICIMOD) and Vishnu Dangol from Tribhuvan University joined with the team from Chin State Forest Department. The group was invited by Dr Nyi Nyi Kyaw, ICIMOD Board member, Director General of Forest Department, Ministry of Environmental Conservation and Forestry and Dr Tint Swe, Director, Watershed Management Division, Forest Department Ministry of Natural Resources and Environmental Conservation.

Discussion with DG of Forest Department
Photo: Sudan Bikash Maharjan/ICIMOD

At present, the lowest freeboard, the height above the recorded high-water mark of the dam, is only 9 m and is expected to decrease rapidly during the monsoon season. Erosion and compaction will result in further reduction of the freeboard. The meteorological department forecasts at least one storm will occur in each month of this monsoon period and there is a strong probability of the dam breaching in this monsoon. 

Most physical information was generated through remote sensing or collected in the field analysed through geographic information system (GIS). Combining and analysing remote sensing data and the field investigation, the ICIMOD team sees a strong possibility of dam breach during the monsoon. If the Chin Hill landslide dam breaks and causes a flash flood, additional land-slides may occur within 10 km downstream and debris deposits may continue further down-stream. Fortunately, no settlements or infrastructure exist along the river down until Yazagyo dam and reservoir, 52 km from the landslide dam. Damage should be minimal, however, the possibility of additional sedimentation is high. 

The team recommended the installation of an automatic weather station (AWS) and an  automatic water level station (AWLS) with real-time satellite connection to monitor the precipitation and lake water level. Immediate installation of a flood warning system was recommended to keep people away from the river valley bottom down to the Yazagyo reservoir. Monitoring of lake water levels and dam conditions using web camera with an image feed is also needed to reduce risk. The team made a presentation to officials of Myanmar and briefed them on the their findings and recommendations.