Abstract
On-going monitoring of deformation of dams is critical to assure their safe and efficient operation. Traditional monitoring methods, based on in-situ sensors measurements on the dam, have some limitations in spatial coverage, observation frequency, and cost. This paper describes the potential use of Synthetic Aperture Radar (SAR) scenes from Sentinel-1A for characterizing deformations at the Mosul Dam (MD) in NW Iraq. Seventy-eight Single Look Complex (SLC) scenes in ascending geometry from the Sentinel-1A scenes, acquired from 03 October 2014 to 27 June 2019, and 96 points within the MD structure, were selected to determine the deformation rate using persistent scatterer interferometry (PSI). Maximum deformation velocity was found to be about 7.4 mm·yr−1 at a longitudinal subsidence area extending over a length of 222 m along the dam axis. The mean subsidence velocity in this area is about 6.27 mm·yr−1 and lies in the center of MD. Subsidence rate shows an inverse relationship with the reservoir water level. It also shows a strong correlation with grouting episodes. Variations in the deformation rate within the same year are most probably due to increased hydrostatic stress which was caused by water storage in the dam that resulted in an increase in solubility of gypsum beds, creating voids and localized collapses underneath the dam. PSI information derived from Sentinel-1A proved to be a good tool for monitoring dam deformation with good accuracy, yielding results that can be used in engineering applications and also risk management.
Highlights
Earth fill dams, because of their low construction cost and relatively simple design, are the most common hydraulic structures built around the world
The Sentinel-1A mission was launched on 03 April 2014, with its payload of C-SAR (C-band Synthetic Aperture Radar) [46]
This study demonstrates the successful application of the Persistent Scatterer Interferometry (PSI) approach for mapping unstable areas and determining geo-hazard risks at Mosul Dam
Summary
Because of their low construction cost and relatively simple design, are the most common hydraulic structures built around the world. Several factors can contribute to dam deformation, such as hydrostatic loading from water storage, construction parameters, and site geology. The latter is associated with planes and zones of weakness in the foundation and abutment rocks. Some studies have been published on deformation monitoring of Mosul Dam (MD) in NW Iraq [21,22,23] using DInSAR techniques such as small baselines (SBAS) [1] and PSI [21,22], they lack validation of their results with in-situ data. We have been able to establish the cause and effect relationship of MD deformation with site geology
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