الفهرس 
Geomorphology, Geology and Hydrogeology of the Nile Delta
Recharge-Discharge system of the Nile Delta aquiferOnly 14 pages are availabe for public view
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Abstract
Electrical resistivity and gamma ray logs were used for 34 wells to identify the petrophysical, chemical, and hydrogeological characteristics of the Nile Delta aquifer due to its significant importance. The Nile Delta reservoir consists of two formations. The upper is the Bilqas Formation, which is of a clay nature and the lower formation is of a sandy nature and called Mit Ghamr Formation. According to the calculations used, the thickness of Bilqas Formation ranges from three meters in the southwest direction to 31 m in the northeast direction. The shale content ranges from 54 to 97%. The porosity ranges from 21 to 55% with an average of 24.71%. This layer has low permeability values ranged from 16 x 10-9 to 78 x 10-9 mD with an average of 30.71 x 10-9 mD. The calculations showed that the hydraulic conductivity of this layer is weak and less than 2 x 10-9 cm/s. The water salinity of this layer ranges from 200 mg to 1600 mg/l. The increase in the thickness of this layer, the increase in porosity, the decrease in permeability and hydraulic conductivity, as well as the increase in the water salinity are to the north and northeast directions. Mit Ghamr is the main aquifer in the region where its minimum value of the shale content is 4.5% and the maximum value is 22%. Lenses from the clay are scattered in different places and increasing in intensity in the northeastern direction of the region. Porosity ranges from a minimum of 19% to a maximum of 39%. The permeability recorded high values in this formation where it ranged from 0.1 x 10-2 to 8.7 x 10-2 mD. The calculations also showed that the hydraulic conductivity values for this formation ranged from 5.082 x 10-10 to 2.134 x 10-8 cm/s. In this layer, the increase in the shale content, the increase in porosity, decrease in the permeability and hydraulic conductivity, as well as the increase in salinity are to the north and northeast. The annual means of air temperature from 1997 to 2017 at Tanta meteorological station was 22.74 oC. The air temperature in the study area increased about 0.0629oC/year since 1997 to 2017. This surface warming might impact the subsurface temperature by the effect of heat transfer. The values of therml gradient ranged in general from -0.009oC/m (well 4) to 0.0098oC/m (well 12) The vertical change in the thermal gradient of wells 1, 3, 4, 5, 6, 7, 9 and 11 is lower than 0 while that of wells 2, 8, 10 and 12 is higher than zero and decreases with depth due to the higher groundwater velocity in the shallow zone compared to the deeper zone. from the measured temperature logs in 12 boreholes in study area, vertical directions and velocities of the groundwater flow were estimated from the numerical analysis by comparing the type curves and the measured values. Based on the obtained result, the studied wells could be divided into three groups: group (1); wells dominated by upward groundwater flow and were represented by subareas of Damatt (well 2), Semella subarea (well 3), Sebrbay (well 5), Ekhnaway (well 9), El-karada (well 11) and Kafr El-Arab (well 12). In group (2); the groundwater mainly flows downward as detected in wells 1, 4, 7 and 8 in subareas of Tokh Maziad, Nawag, Belshaay and Hanoot, respectively. Wells of group (3) were characterized by downward groundwater flow in the shallow zone and upward flow in the deeper parts as shown in Khabatta subarea (well 6) and Tala subarea (well 10). The vertical groundwater flow velocities were calculated. The lowest downward groundwater velocity equals 11.53 cm year-1 was recorded at Tala subarea (well 10) at depth range 200-236m and the highest velocity is 69.20 cm year-1 and detected in Tokh Mazaid subarea (well 1) at depth 32m. The upward groundwater velocities varied from -498.26 cm year-1at El-Karada subarea (well 11) at depth below 60 m to -10.65 cm year-1 at Kafr El-Arab subarea (well 12) at depth below 115 m. The results of this study showed the analysis of the hydrochemical data using statistical techniques such as Box plots, cluster analysis, correlation matrix, Factor analysis and PCA to interpret the geologic factors controlling water chemistry. Box plot showed that the TDS in the shallow zones, the intermediate zones and deep groundwater vary from 210 to 8820 mg/l, 173 mg/l to 6430 mg/l and 180 to 1940 mg/l with average values 1146.495 mg/l, 794.33 mg/l and 640.71 mg/l, respectively. The pH values of the three zones are of average values 7.7, 7.74 and 7.7, respectively. The physicochemical analysis revealed that concentrations of majors (K, Na, Ca, Mg, HCO3, Cl and SO4) with some traces as NO3, Si, NH4 and Fe decrease from the shallow zone to reach its lowest values in the deep zone because of the surface hydrologic and anthropogenic factors affect the shallow groundwater. Correlation matrix showed different correlation relationships represented as very strong, intermediate and weak in the three zones. Geochemically, the cluster analysis classified the groundwater samples into five groups (G1-G5) in the shallow zone, five groups (G6-G10) in the intermediate zone and 6 groups (G11-G16) in the deep zone. To simplify the statistical classification of collected samples, the geochemically similar groups in the three groundwater zones were gathered in one series producing five series. Groundwater type of series one is Ca>Na>Mg and HCO3>Cl>SO4, series 2 is Na> Ca >Mg and HCO3>Cl >SO4, series 3 is Na> Mg>Ca and Cl >HCO3 >SO4, series 4 is Na>Ca>Mg and Cl> HCO3 >SO4 and series 5 is Ca>Mg>Na and Cl> HCO3 >SO4. According to Piper diagrams, Na and Ca are the major cations and Cl and HCO3 are the main anions in the majority of the shallow, intermediate and deep groundwater samples. It revealed that shallow groundwater characterized by four water types Na-Cl, Ca-HCO3, Na-Mg-Cl and Na-HCO3. Intermediate groundwater classified into four water types Na-Cl, Ca-Mg-HCO3-Cl, Na-Mg-Cl and Na-HCO3. The deep groundwater has three hydrochemical types Na-Cl, Ca-HCO3, and Na-HCO3. Factor analysis showed that the shallow groundwater was affected by surface hydrochemical process, soil salinity and water-rock interaction as main sources of groundwater salinity. Sea water is a secondary origin of the dissolved ions. The factor analysis revealed that there are two origins of the deep groundwater, one is fresh flowing from south to north and the other is affected by seawater intrusion in the northern part of the study area. Factor analysis also showed that the intermediate groundwater is a mix between the shallow groundwater (which is heavily affected by surface and soil zones) and the deep groundwater which mainly affected by seawater intrusion.