Guadalentín slumps at 100 milimeters per year, raising the risk of economic impact, flooding and infrastructure of the area.
The recent publication of a scientific paper on the issue in Murcia can help prevent collapse in the future.
Experts are monitoring and modelling the land subsidence in Orihuela, Murcia and Guadalentín thanks to two projects of the Ministry.
Alicante. 22 July 2016
Murcia is the city where most damage has occurred in the early 90s of the twentieth century, with fifty million Euros spent in repairs due to land subsidence by overexploitation of groundwater.
Researcher Roberto Tomás Jover, from the University of Alicante Polytechnic School Department of Civil Engineering warns on the risk for Spain of this land subsidence.
This progressive surface subsidence is due to massive extraction of water from underground. This extraction generates soil consolidation, resulting in soil settlements that may affect infrastructure leant on therein. In this sense, Guadalentín Valley in Lorca is the most affected area in Europe followed by Murcia in the Spanish geography.
The drought between 1995 and 2008 in the region of Murcia, along with the overexploitation of the aquifer left this problem in the metropolitan area. Nowadays, the latest study published by the team led by University of Alicante researcher Roberto Tomás Jover notes how the land has been gaining height thanks to the recovery of the aquifer level in recent years after stopping water extraction. These data are published on article Comparison of water-level, extensometric, DInSAR and simulation data for quantification of subsidence in Murcia City (SE Spain) from Hydrogeology Journal.
The lifting off the ground, however, leads to other problems. Tomás Jover explains that <<a ground settlement over 2.5 centimetres is already a problem; another one is the fact of this settlements being irregular>> with the consequent height deviation from one façade to the other on the same building. The aforementioned study analyses the recovery of groundwater that has occurred since 2008 and then determines the cause of the land deformation.
The researcher cites the case of the church of Santa Justa and Rufina in Orihuela as an example, which << had to be underpinned>> due to this problem of subsidence.
The research group with Tomas Jover as the main researchers are studying the land subsidence or progressive surface collapse in medium and lower basins of the Segura river. There are many regions affected by land subsidence in Spain, especially in southern and southeastern regions, where water demand is higher that water resources and, therefore, water shortfall is supplied with groundwater. In all cases studied, the most alarming is the Guadalentín valley in Lorca where the largest land subsidence in Europe occurs due to water extraction. In 2015, Tomás Jover and his reserach team have published the article Twenty-year advanced DInSAR analysis of severe land subsidence: the Alto Guadalentín Basin (Spain) case study on the scientific journal Engineering Geology, and they are now working on a Spanish Ministry project on this. Murcia is next with registered values up to 7 millimetres a year
UA reserach groups in Soil Engineering and its Structures (INTERES), with Tomás Jover as the main researcher (MR), and Signals, Systems and Telecommunication, with Prof. Juan Manuel López Sánchez as MR, are using Interferometry SAR (INSAR) since 2003 to study land subsidence in medium and lower Segura river basins. Experts have conducted a study by the SAR Interferometry (INSAR) technique to detect movements of the Earth surface over time with pinpoint precision through the use of remote sensors for space platform, that is, taking data from satellites orbitin the Earth further than 700 kilometres. In this case, they have used satellites of the European Space Agency (ESA) and the German Space Agency (DLR).
Works of land subsidence that have been carried out in Spain have been developed through collaboration between the UA research groups in Landscape Engineering and Structures (INTERES), conducted by Roberto Tomás Jover; Signals, Systems and Telecommunication, the head f which is Juan Manuel López Sánchez; Geohazards InSAR laboratory and Modelling Group, conducted by Gerardo Herrera from the Geological and Mining Institute of Spain (IGME); the Unit associated to research ground movements by radar interferometry (UNIRAD), between UA and the Geological and Mining Institute of Spain (IGME), directed by Gerardo Herrera (IGME) and Roberto Tomás (UA), of which Juan Manuel López is part. As stated by Roberto Tomás, <<they are multidisciplinary specialising research groups in SAR, geohazards, modeling and civil engineering, which are actively involved in research related to land subsidence and remote sensing since 2002>>.
UA researcher notes that they have now two active projects from the Ministry, under which we are monitoring and modeling land subsidence in Orihuela, Murcia and Guadalentín Valley by SAR Interferometry (InSAR), other than being assessing the effect of land subsidence on buildings and other infrastructure>>.
Other case studies being developed by this multidisciplinary team are Orihuela, with values registered of 5 millimeters per year; north of Madrid, where subsidence occurs during periods of extraction, which is almost fully recovered when pumping ceases; and parts of Barcelona, such as El Vallés and Santa Perpetua de Mogoda, with maximum rates of 6-10 millimeters per year. Also, this UA expert stresses that they are collaborating with international reserach groups in Leeds, Glasgow, Newcastle (as a result of this collaboration the Beijing work was drafted), Federico II di Napoli, Florencia, Padova, Liverpool, etc., and a good number of national reserach works (Granada, UPV, UPC, UPM, Zaragoza, CSIC, Oviedo, etc.)>>.
An environmental world economic and logistic issue
Land subsidence has great economic impact as it can affect linear structures such as the high-speed train (AVE), roads, building etc. On the other hand, by descending the ground surface, the risk of flooding increases. Moreover, the effect is even more damaging in cities near the sea when the water level raises due to climate change. Deformations induced land subsidence also produce some mile long cracks in the ground surface that can affect many infrastructures. Given the relevance of the problem, UNESCO created the l Working Group on Land Subsidence, of which the UA researcher is a member.
There are more than one hundred fifty major cities affected by the phenomenon of land subsidence worldwide, as confirmed by this researcher. One case is China <<It is a major problem as it affects over forty five cities in an area of around 49.000 km2>>, Tomás Jover notes. Indeed, within this context of subsidence, UA researchers have collaborated on the Beijing work with researchers from the University of Newcastle (UK), the GFZ German Research Centre and various research centres in China (Imaging Land Subsidence Induced by Groundwater Extraction in Beijing (China) Using Satellite Radar Interferometry, published on the journal Remote Sensing.) Subsidence is due to massive extraction of water from underground. This extraction generates soil consolidation, resulting in soil settlements that may affect the infrastructure leant on therein.
Some other examples worth stressing are Mexico, with registered values up to 280 mm per year, San Joaquin Valley (United States), with subsidence of up to 270 mm per year and Jakarta, with values up to 260 mm per year, which exceeds the data detected in Beijing, as reported by Roberto Tomás Jover.
Research have also been carried in some China cities by Tomás Jover as a collaborator with the University of Newcastle (UK), a research group conducted by Prof. Zhenhong Li where subsidence was due to water extraction in the cases of Sanghai and Tianjin. They are also working jointly with Professor Li in the Yangtze Delta and updating information on Beijing with new data to study the effects of subsidence in infrastructures, such as in the high-speed line that operates through the valley.
Since the problem in Spain is becoming worrying, researcher Jover reports that they have also created a dependent subgroup within UNESCO subsidence group that he leads with the participation of experts and researchers from Spain>>. The Spanish Work group on Land Subsidence (SUBTER) has been hosted within the UA website where all the studies in Spain carried out by its members in recent years has been published.
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