Canal de Isabel II Gestion is the company responsible for the integral cycle of water management in the Community of Madrid. The intensive exploitation of the underground waters by Canal began in 1992 (due to a period of important drought). The underground waters are considered to be a strategic resource that is used exclusively during situations of shortage. In 2011, Canal de Isabel II Gestion prepared to execute a few pilot tests of non-natural recharges in wells of Madrid. Although there was no precedence, subsidence or uplift of the terrain due to the operation in the wells of the Canal de Isabel II was not previously discarded.
To monitor this activity and to have evidences of no impact on the terrain, Canal de Isabel II Gestion contracted TELESPAZIO a subsidence monitoring project of the area, by interferometry technique, in the detritic tertiary well of Madrid, for the period of 1992 up to the end of the non-natural recharge tests. The used technology was PSP InSAR (Persistent Scatterer Pairs) developed by e-Geos, a Telespazio Group company. Geomática’s Institute (IdeG) and Geological Institute of Catalonia (IGC) also collaborated in the project. The tasks executed in the context of this project were:
Analysis of the historical period 1992-2010, by PSP InSAR technique, to evaluate the historical evolution of the movements of the terrain. Existing images were used: SAR ERS mission (1992 – 2000) and SAR ENVISAT mission (2003 – 2010).
Monitoring of the non-natural recharge tests in the period 2011 – 2012. Using COSMO-Skymed data and PSP InSAR technique, able to measure superficial slow movements of the area, due to collapses, landslides, seismic and volcanic phenomena, etc, with millimeter precision.
Comparative study of different subsidence detection techniques: the PSP InSAR technique is compared over other measurements on the terrain (high precision geometric leveling, GPS data and extensometers) as well as with the piezometric data, in order to evaluate its precision and suitability for an operative vigilance service.
The project allowed to check the suitability of the methodology to measure this type of phenomena, as well as to confirm its results among the rest of technologies. Likewise there was stated the null effect on the surface of the terrain for the non-natural recharge tests. Finally it also allowed to fix a suitable methodology to approach future terrain movements monitoring, in those areas affected inside the whole wells domain, with precise indications of goals, resources and costs.
Canal de Isabel II Gestión published a booklet with all the details of the work performed, which can be found in:http://www.madrid.org/bvirtual/BVCM018113.pdf