Présentations Colloques

    Oral Presentation
    8.02
    Session 8.02: Groundwater Development and Protection in Coastal and Volcanic Environments with Complex Geological Structures
    Tal Adi
    The interaction between surface reservoirs, multi-layered coastal aquifer and the sea
    The hydrological relations between a multi-layered coastal aquifer and the sea and the impact of surface reservoirs (fish ponds) on the aquifer were studied in the coastal aquifer of Israel. The Quaternary aquifer in the studied site is sub-divided into three units – a shallow, phreatic unit (A) and two confined units (B and C). Chemical measurements suggest that there is infiltration of water from the fish ponds into the phreatic unit A, while the connection with the confined units B and C is very limited. The phreatic unit is OM-rich (TOC=3.8 mgl), characterized with low oxygen concentration (1.1 mgl) and high concentration of ammonium and phosphate (713 and 17 IM, respectively), and it is isotopically-enriched, with +18O of -1‰, +D of -4.6‰ and +13C = -8.6‰, probably due to enhanced evaporation. On the other hand, the water in the confined units is OM-poor (0.5 mg l TOC), having low concentration of NH4 (6 IM) and P04 (0.3 IM) and depleted isotopic composition (+18O = -4.3‰, +D = -20.4‰, +13C = -11.2‰). **The CHIRP mapping suggests that the sub-seafloor extent of the clay, which separates the confined from the phreatic units, is variable from 100 m to more than 1000 m offshore. In the numerical model, this resulted in different extent of seawater intrusion into the shallow confined unit. In places, where the clay is limited to 100 m offshore, the interface reached the Shoreline just a few years after pumping commenced, while the water is fresh at the area where the clay layer extends farther offshore, and seawater intrusion is expected (by the simulation) only some years later. These results are consistent with those of the TDEM, which shows relatively fresh groundwater in unit B where the clay extends 1,000 m offshore, while saline water in the site with limited clay extension offshore.**
    Israel

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