On the evening of July 23rd, an auxiliary dam of the Xe-Pian Xe-Namnoy project in southeast Laos collapsed sending almost 18 billion cubic feet of water towards Attapeu Province to the south, killing over two dozen people. This collapse was the result of large rain events before July 23rd and ongoing construction operations.
Initial analysis performed by entities such as Maxar’s DigitalGlobe and MDA and UNOSAT, a program within the United Nations Institute for Training and Research, found that many villages were inundated with floodwaters. Nearly 6,000 hectares were covered with water, washing away people, homes, livestock and crops.
Comparing the analysis from Maxar and UNOSAT, which covered the period of July 10th to July 24th, PlanetWatchers is able to provide a more up to date analysis of this event. The UNOSAT analysis utilized RADARSAT-2, a satellite from MDA, with a resolution of three to five meters per pixel. PlanetWatchers used data from the Sentinel-1 satellite of the European Space Agency Copernicus Programme with a spatial resolution of about 20 meters. We are using radar imagery captured on July 29th and highlighting the flooded areas at that date as well as a comparison to the flooded area status on July 29th
Saddle Dam D (marked with a star), is the location where the water breached and began flooding south towards Attapeu Province. This was an auxiliary dam that was unable to withstand the force of water behind it.
The Xe Namnoy Reservoir (labeled A), the reservoir next to the saddle dam that failed, was designed to hold over 35 billion cubic feet of water at a height up to 80 yards and a length of one mile. The dam collapse led to a decrease in the surface area of this reservoir by over 50%, from 6,810 acres on July 17th to 3,260 acres on July 29th.
The Vang Ngao River (labeled B), shows increased water levels even six days after the collapse of Saddle Dam D. This river carried billions of cubic feet of water south towards the populated areas of Attapeu Province.
The populated areas in red only a couple miles northwest of Sanamxai (labeled C) were flooded as a result of this dam failure. PlanetWatchers estimates that areas of flooding have extended by up to one mile in the populated areas between July 17th and July 29th.
We at PlanetWatchers hope that our analysis of this tragic event will assist in the rescue efforts and might shed some light on where the water has been moving since it breached the dam. We will continue to monitor this situation and provide updates as necessary. For more information, please visit planetwatchers.com.