Report
Teaser, summary, work performed and final results
Periodic Reporting for period 1 - STEADY (SaTEllyte synthetic Aperture radar interferometry to model Dam stabilitY)
Teaser
The aim of STEADY project is to identify new tools to support monitoring and managing of dams, particularly when gruelling safety situations do not allow adopting tradition monitoring techniques. Structural health assessment is an important practice to guarantee the safety of...
Summary
The aim of STEADY project is to identify new tools to support monitoring and managing of dams, particularly when gruelling safety situations do not allow adopting tradition monitoring techniques.
Structural health assessment is an important practice to guarantee the safety of infrastructure in general. In case of dam monitoring, it is necessary to control the structure itself and the adjacent water reservoir, to pledge efficient operation and safety of surrounding areas. Ensuring the longevity of the structure requires the timely detection of any behaviour that could deteriorate the dam and potentially result in its shutdown or failure. The monitoring and maintaining of existing dams garnered even more importance regarding the European 2020 Energy Strategy aimed to increase the use of renewable energy. Considering that most of the largest hydroelectric power stations were built in the ‘70s, ‘80s, it is easy to understand the importance of monitoring and planning all the necessary maintenance works to guarantee the efficiency and stability of these structures.
The detection and monitoring of surface displacements is increasingly performed through the analysis of satellite Synthetic Aperture Radar (SAR) data, thanks to the non-invasiveness of their acquisition, the possibility to cover large areas in a short time and the new space missions equipped with high special resolution sensors. Nevertheless, the availability of SAR satellite acquisitions from the early 1990s enables to reconstruct the historical evolution of dam behaviour, defining its key parameters, possibly from its construction to the present. Furthermore, the progress on SAR Interferometry (InSAR) techniques through the development of Differential InSAR (DInSAR) and Advanced stacking techniques (A-DInSAR) allows velocity maps and displacement time-series to be obtained.
There are some attempts of using Space-borne Synthetic Aperture Radar data on civil engineer infrastructures but they are not generally considered as common practices.
The importance of these techniques emerges when environmental or logistic conditions do not allow to monitor dams applying the traditional geodetic techniques. In such cases, multi-temporal DInSAR (MT DInSAR) constitutes a reliable diagnostic tool of dam structural health to avoid any unforeseen failure that may lead to a dramatic disaster. Results of STEADY projects proved the great capability of interferometric techniques on giving important information for dam monitoring, particularly showing how precursor deformation could be identified reducing the occurrence of hazards and disasters. Outcomes of STEADY showed how the proposed analyses should become a common practice on the infrastructure monitoring.
Work performed
The project development was based on some real cases, each of them characterized by particularities and specific issues.
Five cases have been considered: Mosul dam, Iraq; Mullaperyiar dam, India; Ataturk dam, Turkey; Oroville dam, USA; Brumadinho tailing dam, Brazil.
All the cases have been analysed through MT DInSAR. Mean velocity maps and time-series of deformation have been retrieved for the sites.
In case of Mosul dam, results highlight the ongoing deformations affecting the dam, and a sliding surface on the coastline, on the basin upstream the dam itself, and some sinkholes in the area downstream the dam. Additional analysis have been performed on the temporal evolution of deformation time-series, to identify areas affected by similar behavior, considering the ongoing deformations but also seasonal effects that induce oscillations connected to the groundwater level variation.
Mullaperyiar dam analyses has been performed using high resolution data, which emerges to be necessary considering the size of this dam, approximately 300 m. Available TerraSAR-X scenes were spanning year, 2012. During the analysed period no deformation has been identified over the structure.
Analysis of Ataturk dam allowed a deeper comparison between traditional monitoring techniques (GPS and leveling) and the potential of MT DInSAR analysis of SAR data. MT DInSAR shows the big advantage of providing spatially continuous information over the dam but also over the surrounding basin, supplying measures every 6 days, proving the potential of these innovative techniques. In addition, several datasets were processed on this dam, from 1992 up to now. Therefore, it was possible to reconstruct almost all the consolidation history of the dam since its completion up to present. The use of interferometric techniques also allowed the analysis of the dam stability after a magnitude 5.2 earthquake occurred in April 2018, which epicenter was located 30 km far from the dam.
The last two cases Oroville dam in California, and Brumadinho tailing dam in Brazil, have been selected because of their catastrophic failures. Oroville main spillway collapse in February 2017, causing the evacuation of more than 200’000 people during the emergency. Brumadinho case has been definitely more dramatic as the tailing dam of the Córrego do Feijão iron ore mine near Brumadinho collapsed in January 2019, causing approximately 300 fatalities.
In both of the cases, MT interferometric techniques have been applied to verify the capability on identifying precursor deformations that could have been used on defining a monitoring and alert system. Temporal evolution of deformation showed, in both of the sites, deformations going on during the analysed period, starting from 2015, and an increase of the deformation rates before the tragic events, that actually was more evident in Brumadinho tailing dam, which started to accelerate indicatively four months before the failure.
Dissemination activities of STEADY results, participation at conferences and business events, allowed to share the project outcomes, even reaching the World Bank that identified the proposed application ad innovative ones on the domain of water resources management.
Final results
Results of STEADY project highlight the great importance of the proposed techniques, MT DInSAR, as an essential diagnostic tool in monitoring dams. The numerous applications deepened in the framework of the project proved the great advantages and the essential information retrieved though space-borne SAR data. Moreover, the free availability of some datasets, as Sentinel-1 data, and their worldwide acquisition plan, guarantee the usability on most of the world big dams. Results demonstrate the capability of detecting eventual increase on the deformation rate and localizing where material failures are affecting the structures. Dissemination of results was finalize on spreading the advantages of these techniques, addressing this information to who is designing and monitoring dams, some private companies working with dams, students of Civil Engineering, international organisations as the World Bank or the Swiss Development Cooperation. The socio-economic influence of STEADY results could have a strong impact if the integration of the proposed tools on the common dam monitoring practices can contain costs but above all reduce disaster frequency and possibly saving human lives.