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Accelerating Displacement Detected 2 Months Before Dam Failure

Bokeo Province, Laos
Water Management
Historical Analysis

Project Overview
On July 23, 2018, Saddle Dam D of the Xe-Pian Xe-Namnoy power project in south eastern Laos collapsed, releasing 5bn cubic litres of water. The flash flood resulted in many deaths and forced several thousands of victims to lose their homes. 3vG conducted a historical analysis of Sentinel-1 SAR data over the site to examine whether cutting edge multi-temporal InSAR could have provided an early indication of displacement within the dam structure.


Time evolution of the volume of the reservoir (lower left), as measured from SAR amplitude images (top left) and the corresponding displacement (bottom right) detected on Saddle Dam D (shown in the top right).


3vG processed 37 archival C-band, descending pass, Sentinel-1 SAR images taken between May 11, 2017, and July 17, 2018. A tailored processing chain was used for isolating and utilizing only high quality coherent points in and around the dam. This processing was repeated for variable end dates to simulate the sequential acquisition of each scene.

SAR amplitude images taken July 17 (left) and July 29th, 2018 (right), immediately before and after the collapse of Saddle Dam D. Water appears dark in the amplitude images.
Optical images of Saddle Dam D taken on April 11, 2018 (left) and October 23, 2018 (right), showing the dam before and after collapse. Saddle Dam D is outlined with a red box. (Middle) The colour scale shows the cumulative detected displacement from the S1 images, with the white and cyan contours denoting areas with displacement detected with 3-sigma (99.7%) and 4-sigma (99.99%) confidence. The black contour denotes the area with significant acceleration detected at a 95% confidence level.

Within an effective dam instrumentation and monitoring program, InSAR has the ability to monitor subtle movements of all dams, reservoir slopes, and subsidiary dams on a 2 to 12 day frequency. 3vG would likely have been able to have provided early warnings that Saddle Dam D was undergoing accelerating subsidence if 3vG were to have been monitoring the dam.

3vG provides rapid reports within 24 hours of image acquisition showing displacement and acceleration, providing actionable intelligence to enable immediate remediation or the issuance of evacuation notices.

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