Présentations Colloques

    Oral Presentation
    Session 8.02: Groundwater Development and Protection in Coastal and Volcanic Environments with Complex Geological Structures
    Albert Folch
    Advanced techniques for groundwater investigation of seawater intrusion in a coastal sedimentary aquifer
    The characterization and monitoring of saline water interface is a key issue to understand the evolution of groundwater resources in coastal areas. In order to go beyond the current knowledge in this issue a new experimental site has been constructed in the lower part of an alluvial aquifer north of Barcelona (Spain). In this zone the seawater interface is being monitoring by different techniques and parameters to understand how the saline-fresh water interface behave along different seasons under different recharge-discharge conditions (wet and dry seasons, pumping, etc). The site, between 30 and 90 m from the seashore comprises 16 shallow piezometers with depths ranging between 15 and 25 m. All piezometers are equipped with Fiber Optic cable to perform distributed temperature measurements. Two single steel armoured fiber optic cable lines of around 600m length were installed in all boreholes. On the one hand, the cable is used as passive sensor for the continuous monitoring of temperature. On the other hand, as an active temperature sensor to monitor different in situ experiments. Furthermore, deepest piezometers are also equipped with electrodes in order to perform cross-hole electrical resistivity tomography (CHERT). Periodic CHERT measurements are carried out between the piezometer equipped with electrodes, resulting in parallel and perpendicular vertical cross sections of the site resistivity. The position of the fresh-salt water interface can be identified due to the resistivity contrast between the saline and fresh water. Together with the fiber optics and CHERT investigations, groundwater geochemical characterization (Rn, Ra isotopes, trace metals, nutrients) are analysed in different piezometers. Preliminary results indicated that the combination of both methodologies is a useful technique to investigate and monitor the discharge of groundwater into the coastal sea, which may have relevant implications for both groundwater resources and coastal biogeochemical cycles.**********


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