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United Arab Emirates University (2001)

APPLICATION OF GEOPHYSICAL, HYDROGEOLOGIC L AND GIS TECHNIQUES FOR INVESTIGATION OF GROUNDWATER RESOURCES IN THE AL DHAID AREA, UAE

MOHAMED MUSTAFA MOHAMED AL MULLA

Titre : APPLICATION OF GEOPHYSICAL, HYDROGEOLOGIC L AND GIS TECHNIQUES FOR INVESTIGATION OF GROUNDWATER RESOURCES IN THE AL DHAID AREA, UAE

Auteur : MOHAMED MUSTAFA MOHAMED AL MULLA

Université de soutenance : United Arab Emirates University

Grade : Master of Science (MS) 2001

Résumé
In this thesis, geophysical, hydrological and GIS techniques were applied for. evaluation of groundwater potentiality and land use planning for agricultural purposes In the Al Dhaid area, United Arab Emirates. The gravity anomalies yielded three fault trends ENE-WSW NNWSSE and E-W .. The fault displacements range from 70 m to 320 ’ m, with downthrown sIides towards the northwest. The saturated thickness of sedimentary section above the ophiolite series varies between 700 m in the northwest and more than 3500 m at the northwest. The result of the resistivity and TDEM surveys produced a four-layers model based on thickness resistivity, and total dissolved solids (TDS) contents. The four layers, from top to base, are : the surficial layer (thickness = 1.5 to 5 m resistivity = 500 to 2000 ohm.m and IDS = 10 to 50 ppm), the upper aquifer (thickness = 5 to 5 m, resistivity = 205 to 605 ohm.m and IDS = 200 to 2000 ppm) the aquiclude (thickness = 28 m ot 150 m, resistivity = 10 to 1000 ohm.m and TDS = 100 ppm to 300 ppm) and the lower aquifer (thickness = 80 to 450 il,l resistivity = 20 to 100 ohm.m and TDS = 100 - 7500 ppm). Analysis of well logs indicated that porosity values ranges from 5% in some limestones to 47% in fractured dolomities. Temperature, conductivity and hydrochemistry logs showed the directions of groundwater flow and saline-water intrusion. The hydrogeologic units identified in the Al Dhaid area include an upper free to semi-confined aquifer, an aquiclude and a lower confined aquifer. The regional groundwater flow direction is from the main recharge area in.Northern Oman Mountain in the east torward the natural discharge area·the Arabian Gulf in the west. Between 1984 and 1999, a 20 km diameter cone-of-depression centered around the observation well GP-15 resulted from excessive groundwater pumping for all purposes. The average hydraulic gradient varies from 0.025 in the east to 0.005 in the west. The TDS content in groundwater of the Al Dhaid area changes from <750 mg/l in the northeast to 3000 mg/I in the central area and >7500 mgtl in the southwest. The sequence of cation dominance is Na+> Mg2+> Ca2+ and the sequence of anion dominance is CI> sol> HC03-. The IDS content and total hardness show that the groundwater in some localities at the study area is not suitable for drinking and domestic purposes. Because of the agricultural activity at and around the Al Dhaid area, the concentration of N03 - in some samples is above the WHO recommended limit for drinking water (10 mg/l N03—N). The results of GIS modeling indicate that the eastern strip of the study area has a high groundwater potentiality because of the intersection of more than one structural trend and low salinity (IDS =1500 gm/l). The areas of the Al Dhaid city and its surrounding and the south central area are most favorable for agriculture because groundwater in both areas has moderate salinity (TDS =3000 mg/I), low SAR « 10), shallow depth to groundwater « 4 5 m) and soil types suitable for agriculture

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Page publiée le 30 novembre 2016, mise à jour le 8 novembre 2017