Evaluation of groundwater mineralization processes and seawater intrusion extension in the coastal aquifer of Oualidia,
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ORIGINAL PAPER
Evaluation of groundwater mineralization processes and seawater intrusion extension in the coastal aquifer of Oualidia, Morocco: hydrochemical and geophysical approach Ahmed Fadili & Khalid Mehdi & Joëlle Riss & Saliha Najib & Abdelhadi Makan & Khadija Boutayab
Received: 25 August 2014 / Accepted: 20 January 2015 # Saudi Society for Geosciences 2015
Abstract Oualidia city is located on the Moroccan Atlantic coast. Groundwater is the only resource for agriculture irrigation in this area. This operation is done by intensive pumping mainly in the coastal fringe. In this study, hydrochemical and geophysical methods were conducted to evaluate both composition and processes which control groundwater mineralization in Oualidia. For this purpose, 19 samples of groundwater were analyzed in major ions. The results showed that the mineralization is mainly due to sea water intrusion, especially in the first kilometer over the ocean, with abundance of Na+ (651.3 mg/l on average) and Cl− ions (1,425 mg/l on average). Beyond this fringe, 1 km, the mineralization is low, with an abundance of calcium (190.4 mg/l on average) and bicarbonate (241.1 mg/l on average) indicating the rock nature effect. Data interpretation from six profiles of electrical resistivity tomography (ERT), performed in the region, has led to detect seawater intrusion extension. The level assigned to the marine effect is characterized by a resistivity lower than 30 Ω m. Moreover, hydrochemical and geophysical studies were provided information on the mineralization extension in the aquifer of this zone, which is limited to 1 km from the ocean.
A. Fadili (*) : K. Mehdi : S. Najib : K. Boutayab Marine Géoscience and Soil Science Laboratory (URAC-45), Faculty of Science, University of Chouïb Doukkali, El Jadida, Morocco e-mail: [email protected] J. Riss I2M UMR 5295 Laboratory, Environmental Civil Engineering Department, Bordeaux 1 University, Bordeaux, France A. Makan Water and Environment Laboratory, Faculty of Science, University of Chouïb Doukkali, El Jadida, Morocco
Keywords Groundwater mineralization . Statistical analysis . Ionic ratios . Electrical resistivity tomography Introduction The seawater intrusion in coastal aquifers leads to quality degradation of fresh waters. Excessive increasing groundwater exploitation lowering water tables is well known to be the primary cause of saltwater intrusion. The extent of saltwater intrusion is controlled mainly by geological characteristics of the area, hydraulic gradient, and the rate of exploitation with respect to the reload of the groundwater (Choudhury et al. 2001; Morgan and Werner 2014). Analyzing seawater intrusion in coastal aquifers requires multidisciplinary approach, combining several methods, such as geophysics and hydrochemistry. Electrical prospecting was applied by several authors to delimit the marine intrusion extension (Bugg and Lloyd 1976; Urish and Frohlich 1990; Vandam and Meulankamp 1967; Zohdy 1969; Frohlich et al. 1994; Nowroozi et al. 1999. Choudhury et al. 2001; Hodlur
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