Sardoba Dam Failure—Uzbekistan Collapse InSAR Disaster Forensics

Great Hopes

After 7 years of construction, the dam was recently completed to provide irrigation water to the surrounding districts. Holding 922 million cubic meters of water, the dam was meant to improve the agricultural output of the area and provide a source of electricity; with electricity from a hydroelectric plant to be added in the future. This breach of the 30 meter high dam led to the evacuation of nearly 100,000 people. While the exact failure mode of the early morning breach of May 1 is still unclear, the current statements seem to point to overtopping of a lower section of the dam by wind driven waves.

Before Failure. Courtesy of NASA.
After Failure. Courtesy of NASA.

Forensic information from the InSAR Archive

A key strength of the Sentinel 1 and Copernicus platform is the ability to ‘go back in time’ and view the deformation of a structure with consistent over flights. Pulling a bit more than the past year of data on Sardoba showed some fascinating results. Sentinel provides some insight into the settlement of this structure over time. Recognizing that all new dam structures settle it is interesting to see rates of 100 mm per year continuing in some sections. The area of the failure did not have the greatest crest subsidence rate during this period. This failed section abuts a turn in the dam where there was significantly less subsidence in the past year. Looking closer at the settlement patterns, it seems there is noticeable differential movement along this stretch of the crest not as prevalent in others. Perhaps this played a role in the failure mode as the differential settlement could lead to weak zones or cracking. An alternative progressive slope failure mode would potentially demonstrate uplift at the toe of the embankment which was not noted in this data. However, erratic uplift and subsidence can be seen in the nearby field beneath the structure and could be a factor for consideration. We hope that this data, developed in conjunction with Ovela will be useful to Uzbek authorities in the disaster assessment and recovery process.

In the radar images from Sentinel 1 above, red indicates subsidence (down) and blue indicates uplift (up) over the year that the dam was observed. The color scale used is -50 to +50mm. This was obtained from the Ascending orbital data looking east. The failed section is noted by the circle.

Featured image (top of page) courtesy of NASA.

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