Land subsidence induced by groundwater extraction in the Alto Guadalentín aquifer, SE Spain.

Transcription

1 Land subsidence induced by groundwater extraction in the Alto Guadalentín aquifer, SE Spain. Pablo Ezquerro, Marta Béjar-Pizarro, Gerardo Herrera, José A. Fernández Merodo, Roberto Tomás, Carolina Guardiola-Albert, Roberta Bonì, Alejandra Staller Land Subsidence induced by fluid extraction workshop Madrid, 14th November 2017

2 Alto Guadalentín Basin Alto Guadalentín Basin is a tectonic depression of 250 km2 created during the Alpine orogeny. Alhama de Murcia fault bounds the basin on its Northern side. Alto Guadalentín aquifer-system is formed by Tertiary and Quaternary sedimentary materials over the metamorphic basement. Sedimentary materials are organized in the typical alluvial fan distribution, generating sand and gravel lenses structures embedded in a clay or silt-clay matrix Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November

3 First studies Alto Guadalentín basin deformation is being monitored since 2011 using historic SAR datasets from ERS 1/2, ENVISAT, Cosmo- SkyMed y ALOS satellites This first studies revealed an area with a high deformation rate above 10 cm/year centered in the NE side and covering about 40% of the basin area. 3

4 Geology review Detected deformation leaded to the reinterpretation of the 23 well logs existing on the Plio-Quaternary materials. Analysis revealed the existence of an important clay layer where highest subsidence rates were detected. Clayed materials could be responsible of the subsidence due to groundwater level changes. Bonì et al Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November

5 Geology review A Kriging with External Drift (KED) approach was implemented to interpolate sparse measurement variables (GPS and compressible soil thickness) using high density InSAR measurements The compressible deposits thickness map is significantly improved The resulting continuous GPS velocity map shows maximum subsidence rates above 10 cm/year in the center of the basin, in agreement with previous studies Béjar-Pizarro, M. et al

6 Aquifer-system modeling Alto Guadalentín aquifer-system is a strategic water resource which correct management is important. CHS in 1991 and 2005, and IGME in 1994 developed numerical models in order to reproduce the aquifer-system behavior. Taking into account previous information and new defined layers, a new three layered model was developed using MODFLOW for the period. 6

7 Groundwater modeling results Model results show a general declining trend in the groundwater levels, changing from near surface (290 m a.s.l.) in 1960 to an important depth in 2012 (110 m a.s.l.). Model calibration was carried out using the limited existing piezometric information. Derived error was under 10% of the ground water level change. 7

8 Developing a subsidence monitoring network During the last three years works in this area have been intensified A new monitoring network has been established using different measurement techniques. Two geometric leveling field campaigns in January 2016 and May 2017 in REDNAP line, belonging to IGN. Build up of three permanent structures for GPS observations. 8

9 Developing a subsidence monitoring network New permanent GPS station. Processing of new SAR images over the basin. Sentinel-1A/B new constellation allow to continue monitoring from Its improved spatiotemporal resolution is very suitable for subsidence monitoring. C-band gap between ENVISAT period ( ) and Sentinel-1 period (Since 2014) is filled with Cosmo-SkyMed data. 9

10 New SAR Results Previous deformation data show a declining subsidence rate from 11.8 cm/year in the ERS period to 9.2 cm/year in the Cosmo-SkyMed period. Preliminary results from new Cosmo-SkyMed and Sentinel-1 processings also show the same declining trend, 8.1 cm/year in the Cosmo-SkyMed period and 7.5 cm/year in the Sentinel-1 10

11 In-situ network results Leveling benchmarks measured in 2016 and 2017 field campaigns support the SAR displacements with rates around 8 cm/year GPS permanent station began its operation in February One year and a half time series are now long enough to be accurate. Annual subsidence rate of 8.5 cm/year 11

12 Conclusions and future works SAR images were used to detect and monitor during 25 years the subsidence anomaly in the Alto Guadalentín basin. Deformation results were used to update the geological settings, allowing the development of a new hydrogeological model. Model results are a valuable constraint for geo-mechanical modeling Continue with the InSAR processing, especially with the Sentinel-1 data. Upgrade the leveling and GPS monitoring network. Generate a geo-mechanical model defining the relationship between groundwater and deformation. 12

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