Space geodetic monitoring of engineered structures: The ongoing destabilization of the Mosul dam, Iraq

Abstract

We present a detailed survey of the ongoing destabilization process of the Mosul dam. The dam is located on the Tigris river and is the biggest hydraulic structure in Iraq. From a geological point of view the dam foundation is poor due to a site geology formed by alternating strata of highly soluble materials including gypsum, anhydrite, marl and limestone. Here we present the first multi-sensor cumulative deformation map for the dam generated from space-based interferometric synthetic aperture radar measurements from the Italian constellation COSMO-SkyMed and the European sensor Sentinel-1a over the period 2014-2016 that we compare to an older dataset spanning 2004-2010 acquired with the European Envisat satellite. We found that deformation was rapid during 2004-2010, slowed in 2012-2014 and increased since August 2014 when grouting operations stopped due to the temporary capture of the dam by the self proclaimed Islamic State. We model the inferred deformation using a Markov chain Monte Carlo approach to solve for change in volume for simple tensile dislocations. Results from recent and historical geodetic datasets suggests that the volume dissolution rate remains constant when the equivalent volume of total concrete injected during re-grouting operations is included in the calculations.

Figure 1. InSAR measured subsidence rates on the Mosul dam, Iraq.

Negative values indicate motion away from the satellite, consistent with subsidence. (a) Envisat ascending track DInSAR stacked interfergrams covering May 2004–August 2010. Horizontal/Vertical Profile O-O’ is shown in Fig. 2(b) Envisat descending track DInSAR stacked interfergrams spanning May 2004–August 2010 (c) CSK ascending track covering December 2014–July 2015 (d) Sentinel descending track covering December 2014–July 2015. Time-series analysis generated using the SARPROZ Software (http://www.sarproz.com January 26 2016 Version). Map data: Google, CNES/Spot Image, Basarsoft (https://www.google.com/earth/).

Figure 2. Up-down (left) and east-west(right) displacement at the Mosul dam, Iraq.

Negative values indicate downward and westward motion respectively. The data have been resampled on a common grid calculated using the coherence maps from the interferograms (Envisat) and time-series analysis (CSK-Sentinel-1a). Formula (7) and (8) have been applied to the LOS displacements to calculate the up-down and east-west motion respectively. Time-series analysis generated using the SARPROZ Software ((http://www.sarproz.com. January 26 2016 Version). Map data: Google, CNES/Spot Image, Basarsoft (https://www.google.com/earth/).

Figure 3. Subsidence profiles.

(a) Vertical and east component of surface velocities along the Mosul Dam from Envisat 2004-2010 2D deformation (b) velocity components from CSK, Sentinel-1a velocity maps obtained using data spanning the same time period (December 2014–July 2015). The results confirm that the vertical velocities greatly exceed the horizontal contribution typical of subsidence patterns. (c) CSK LOS cumulative displacement profiles.

Figure 4

(a) CSK/Sentinel-1a Time series of subsidence at the center of the dam assuming negligible North-South motion (b) CSK/Sentinel-1a amplitude derived shoreline location on the dam face calculated from amplitude measurements calibrated with JASON-1 altimeter data.