LAND SUBSIDENCE ANALYSIS CAUSED BY AQUIFER OVEREXPLOITATION USING GEP TOOLS: A-DINSAR ON THE CLOUD

Groundwater is a vitally important resource for humans. One of the main problems derived from the overexploitation ofaquifers is land subsidence, which in turn carries other associated natural risks. Advanced Differential satellite radarinterferometry (A-DInSAR) techniques provide valuable information on the surface displacements of the ground, whichserve to characterize both the deformational behaviour of the aquifer and its properties. RESERVOIR is a research projectbelonging to the European PRIMA programme, whose main objective is to design sustainable groundwater managementmodels through the study of four areas of the Mediterranean subjected to water stress. One of the main tasks of the projectis the integration of the terrain deformation data obtained with satellite remote sensing techniques in the hydrogeologicaland geomechanical models of the aquifers. In the present work, a first evaluation of the deformation of the ground in eachstudy area is carried out using the tools contained in the Geohazards Exploitation Platform (GEP). This is a service financedby the European Space Agency (ESA) that allows processing directly on its server, without need to store data orapplications locally.

Towards an increase of flash flood geomorphic effects due to gravel mining and ground subsidence in Nogalte stream (Murcia, SE Spain)

Transition from endorheic alluvial fan environments to well-channelized fluvial systems in natural conditions may occur in response to base-level fluctuations. However, human-induced changes in semi-arid regions can also be responsible for similar unforeseen modifications. Our results confirm that in-channel gravel mining and aquifer overexploitation over the last 50 years in the case study area have changed the natural stability of the Nogalte stream and, as a result, its geomorphic parameters including channel depth and longitudinal profile have begun to adapt to the new situation. Using interferometric synthetic aperture radar (InSAR) data we obtain maximum values for ground subsidence in the Upper Guadalentín Basin of ∼ 10 cm yr−1 for the period 2003–2010. In this context of a lowered base level, the river is changing its natural flood model to a more powerful one. A comparison of the 1973 flood event, the most dramatic flood event ever recorded in the area, with the 2012 event, where there was a similar discharge but a sediment load deficit, reveals greater changes and a new flooding pattern and extension. In-channel gravel mining may be responsible for significant local changes in channel incision and profile. This, together with the collateral effects of aquifer overexploitation, can favour increased river velocity and stream power, which intensify the consequences of the flooding. The results obtained here clearly demonstrate an existing transition from the former alluvial pattern to a confined fluvial trend, which may become more pronounced in the future due to the time lag between the drop in aquifer level and ground subsidence, and introduce a new scenario to be taken into consideration in future natural hazard planning in this area.

Towards an increase of flash-flood geomorphic effects due to gravel mining and ground subsidence in Nogalte stream (SE Spain, Murcia)

Transition from endorheic alluvial fan environments to well-channelized fluvial systems in natural conditions may occur in response to base-level fluctuations. However, human-induced changes in semi-arid regions can also be responsible for similar unforeseen modifications. Our results confirm that in-channel gravel mining and aquifer overexploitation over the last 50 years in the case study area have changed the natural stability of the Nogalte stream and, as a result, its geomorphic parameters including channel depth and longitudinal profile have begun to adapt to the new situation. Using interferometric synthetic aperture radar (InSAR) data we obtain maximum values for ground subsidence in the Upper Guadalentín basin of ~ 10 cm yr−1 for the period 2003–2010. In this context of a lowered base level, the river is changing its natural flood model to a more energetic one. A comparison of the 1973 flood event, the most dramatic ever recorded in the area, with the 2012 event, where there was a similar discharge but a sediment load deficit, reveals greater changes and a new flooding pattern and extension. In-channel gravel mining may be responsible for significant local changes in channel incision and profile. This, together with the collateral effects of aquifer overexploitation, can favor increased river velocity and stream power, which intensify the consequences of the flooding. The results obtained here clearly demonstrate an existing transition from the former alluvial pattern to a confined fluvial trend, which may become more pronounced in the future due to the time-lag between the drop in aquifer level and ground subsidence, and introduce a new scenario to be taken into consideration in future natural hazard planning in this area.

Aquifer recharge for securing water resources: the experience in Llobregat river

The Llobregat Delta Aquifer has historically been a strategic water supply resource to the Barcelona metropolitan area. The use of river water combined with the exploitation of groundwater resources during dry periods has enabled the demographic and economic growth of the Barcelona area during the last fifty years. The aquifer overexploitation has entailed the decrease of groundwater level and the penetration inland of seawater intrusion. The main consequences have been the salinization of several wells and the deterioration of the groundwater quality. In this context, aquifer recharge has been practiced during nearly 40 years with the following objectives: (i) storing excess of water for times of less water availability, (ii) introducing an additional barrier for purification of water for a specific use and (iii) preventing the degradation of groundwater resources due to overexploitation or seawater intrusion. These methods, jointly with an efficient management of well extractions, have enabled to recover groundwater quality and therefore to guarantee the sustainable exploitation of such a vulnerable aquifer.