Land subsidence induced by groundwater extraction in the Alto

Guadalentín aquifer, SE Spain.

Land Subsidence induced by fluid extraction workshopMadrid, 14th November 2017

Pablo Ezquerro, Marta Béjar-Pizarro, Gerardo Herrera, José A. Fernández Merodo, Roberto Tomás, Carolina Guardiola-Albert, Roberta Bonì, Alejandra Staller

2Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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

3Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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.

4Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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. 2015

5Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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. 2016

6Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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 1961-2012 period.

7Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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.

8Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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 10426 REDNAP line, belonging to IGN.

• Build up of three permanent structures for GPS observations.

9Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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 2014. Its improved spatio-temporal resolution is very suitable for subsidence monitoring.

• C-band gap between ENVISAT period (2003-2010) and Sentinel-1 period (Since 2014) is filled with Cosmo-SkyMed data.

10Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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

11Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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 2016. One year and a half time series are now long enough to be accurate. Annual subsidence rate of 8.5 cm/year

12Land Subsidence Induced by Water Extraction Workshop Madrid, 14th November 2017

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.