Researchers: Pietro Milillo, Paul Lundgren, and Eric Fielding, NASA Jet Propulsion Laboratory; Roland Bürgmann, University of California, Berkeley; Jacqueline Salzer, GFZ German Research Center for Geosciences; Daniele Perissin, Purdue University; Filippo Biondi, University of L’Aquila; and Giovanni Milillo, Italian Space Agency.
Written by Linda Rowan
26 June 2017
The Mosul Dam on the Tigris River in Iraq was built on weak rock that is dissolving due to water infiltration since it was built. Satellite imagery shows the dam subsiding over 6 years at variable rates with different mitigation strategies. The subsidence rate increased starting in 2014 when mitigation and maintenance stopped. The increasing subsidence increases the risk of dam failure, which would affect more than a million people living nearby and everyone who relies on the dam for energy and water.
The Mosul Dam was built on weak rocks. The rocks include anhydrite/gypsum, sand, silt and clays. The rocks are layered and interbedded with each other and the whole sequence is dipping to the east. The anhydrite/gypsum is soluble in water and is being dissolved by water leaking through the dam and from the river. Grouting to fill the holes has been done since the dam was built in 1984. The U.S. government tried to establish a more effective grouting technique in 2007 with modest results. The dam was captured by the self-proclaimed Islamic State for a short period in 2014 and since that time, no maintenance or cement grouting has been done. Space-based synthetic aperture radar (SAR) measurements have been made from 2004 to 2014 to estimate the amount and location of deformation at the dam. Observations were acquired from the European Envisat satellite from 2004 to 2010, from the Italian COSMO-SkyMed from 2014 to 2016 and from the European Sentinel-1a from 2014 to 2016.
The satellite data show that the dam subsided at a linear rate of 12.5 millimeters per year from 2004 to 2010. The rate of subsidence increased to 15 millimeters per year from 2014 to 2016. There has also been a 300-meter shift to the east of the peak subsidence toward the dam’s main spillway when the profiles from 2004-2010 and 2014-2015 are compared. The rate of subsidence and the shifting of the peak subsidence provides information about the unseen risks of dam failure and may help with mitigation strategies.
Milillo, P. et al. Space geodetic monitoring of engineered structures: The ongoing destabilization of the Mosul dam, Iraq. Sci. Rep. 6, 37408; (2016), doi:10.1038/srep37408.
synthetic aperture radar, interferometric synthetic aperture radar
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Last modified: Wednesday, 28-Jun-2017 21:48:02 UTC