الفهرس 
Submarine Groundwater DischargeOnly 14 pages are availabe for public view
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Abstract
The study area is located in Dakahliya Governorate, Egypt and is bounded by latitudes 31.39° & 31.51° N and longitudes 31.28° & 31.51° E. Generally, the area is characterized by long hot summer and short warm winter. The mean annual rainfall is about 40.4mm, the mean relative humidity is 65.4% and the average evaporation rate is about 7.7mm/d. The area of study exhibits certain desertification features because the surface Nile water does not adequately reach to the ends of canals. The investments were in a need to supplementary water sources for irrigation and the other investment fields. Groundwater is a good complementary source. Investments drilled arbitrarily a group of wells. Although the area of study is a coastal area the surprise was to find an artesian aquifer with low brackish salinity. Therefore, the area of study was in demand for detecting the groundwater resources and its origin. In this study, electrical resistivity measurements were integrated with hydrogeological and hydrochemical data to explore the origin and characteristics of low salinity brackish groundwater in Abu Madi coastal area in the northern part of the Nile Delta, Egypt. The stable isotopic composition of oxygen and hydrogen and the chloride concentrations strongly suggest that the deep groundwater in Abu Madi coastal area is dominated by inland freshwater with about 4.5-16.7% seawater. The freshwater composing the major part of this groundwater is derived mainly from the River Nile water before the High Dam construction. The higher percentage of freshwater compared to the low percentage of seawater produces a water mixture that is saturated with carbonate minerals but unsaturated with sulfates and chloride minerals. This sulfate depletionresulted in high dissolution effects of sulfates in clay-rich sediments. According to graphical and statistical classifications, Sulin’s diagram, ionic relationships and ionic ratios; the deep groundwater is classified into two main groups: A and B. group A water samples are characterized by higher sulfate and bicarbonate concentrations, higher-than-unity Na/Cl, NaHCO3-water type and reverse ion exchange and dissolution processes. This group characterizes the inland groundwater flowing toward the sea. On the other hand, group B water samples are characterized mainly by NaCl-water, having lower values of SO4 due to gypsum precipitation, MgCl2 according to Sulin’s diagram, lowerthan-unity Na/Cl, ion exchange and mineral precipitation processes. The latter group represents the seawater component inter mixed with the inland fresh groundwater. Although the fraction of inland fresh water is higher than the seawater, most water samples have high specific conductance and high sodium hazards, rendering the groundwater unsuitable for irrigation purposes in the study area. The current consumption of the groundwater for irrigation and domestic uses should be preceded by special treatment practices such as mixing it with surface water from canals. The field data of the resistivity soundings have been interpreted qualitatively and quantitatively to delineate the subsurface sequence of the geoelectrical layers in the area. from the qualitative interpretation, the dominant field curves in the study area are; KHKA, KQQHA, QQHA, QHA and KHA, types. The results of the quantitative interpretation of geoelectrical resistivity surveying confirmed that the groundwater resources in the study area are represented by a group of ‘geoelectrical’ layers. The first water-bearing layer(the 2ndgeoelectrical layer) lies near the earth surface with a limited thickness. It has resistivity values ranging from less than 1 to 14.2 Ohm.m. This layer varies in lithology from sandy clay to sand. The depth to water is equivalent to the thickness of the first layer (1-5.8 m). The thickness of this layer itself ranges from 2.5 to 11.4 m .The source of the water of this layer is the surface water of canals and drains. The second water-bearing layer (the4thgeoelectrical layer) is present under confined conditions but has low resistivity values dueto the high water salinity. It has resistivity values ranging from less than 1 to 8.0 Ohm.m. The thickness of this layer ranges from 21.8 to 31.4 m. The main aquifer in the study area is represented by the sixth geoelectrical layer, which is also under confined conditions and thus represents an artesian aquifer where the water flows over the earth surface. This aquifer has relatively high resistivity values ranging from 6.1 to 33 Ohm.m, and consists lithologicallyof sandy clay to water-bearing sand with a low tomedium porosity (7.5-9.6%) and large thickness (72.8 - 99.8 m). These results are consistent with the hydrochemical characteristics indicating the slight/moderate brackish nature of the studied groundwater samples (with average TDS of 3566 mg/l). Moreover, stable isotopic contents, saturation indices, ionic relationships and the low seawater salinity in front of the area in the depth range of 30 -200m, indicate that groundwater is mainly composed of inland freshwater with a minor seawater component as well as the possibility of submarine groundwater discharge. The interpretation results of the first 2D ERT profile that was carried out perpendicular to El Salam drain at the northern part of study area revealed that the water bearing layer extends from a depth of 3 to 8 m and its resistivity values vary from 16.5 to 3.5 Ohm.m due to the effect of drain water. On the other hand, the interpretation results of the second 2D ERT profile that was carried out near to hand-dug well with fresh water at the southern part of study area revealed that the water bearing layer extends from a depth of 1.5 to 6 m, and its resistivity values vary from >65 to 12 Ohm.m corresponding to water-bearings and dunes recharged from rain water, and is underlain by a clayey layer.