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Abstract Summary and Conclusions The present thesis concerns with detailed geomorphologic, geologic, hydrogeologic and hydrogeochemical settings of wadi Qena basin. It also deals with the effective factors on the development of water resources in the study area. Wadi Qena basin occupies an area of 15455 Km2 and extends in northeastsouthwest direction discharging its water in River Nile. It lies between latitudes 26° 15´ 00” & 28° 15´ 00” North and between longitudes 32° 15´00” & 33° 30´33”East. The average annual precipitation over Wadi Qena basin was extracted from 3-hourly, Tropical Rainfall Measuring Mission (TRMM), precipitation data over a period of 15 years (from 1998 to 2013). It decreases from 13.43 mm/y on the eastern part of the study area to 2.78 mm/y on the western parts. Geomorphological features, the study area is divided into several land features. These features are the high lands (watershed areas) and low lands (water collectors). The first includes; the Red Sea mountainous terrains, the high plateaus (El Maaza limestone and El Ababda sandstone), the low plateau and hilly area. The low lands include the morphotectonic depressions, piedmont plain and drainage networks. The general characteristics and hydrogeological significance of these units are explained. Wadi Qena main basin and its tributaries are morphometrically analyzed. Assessment of the flood strength and hazard degrees of the studied sub-basins relative to each other is also calculated. Geologic setting: Stratigraphic succession, in the present study, special attention has been paid to the stratigraphic setting of the water bearing formations especially Nubia sandstone and Quaternary deposits where both of them represents the main aquifers in the study area. The lithologic sequence and rock exposures along Wadi Qena basin range in age from Precambrian to Quaternary. Summary and Conclusion 141 The stratigraphic succession (250 m thick) at Qena-Safaga road was measured and sampled. The petrographic studies, twenty-five samples have been petrographically examined. Based on Pettijohn’s classification (1972), four microfacies associations have been defined, described and illustrated. These microfacies are Quartz arenite represents 52% of the studied samples, Sub-litharenite represents 32%, Quartz wacke represents 8% and Pebbly Quartz wacke represents 8% from the studied samples. Compaction and cementation are the most common diagenetic process that detected in the studied sandstone samples of the Nubia Formation. Generally, the studied sandstone thin sections have well developed intergranular porosity in most studied samples ranging between 10-21%. The pores are interconnected giving good permeability favorable for development of good groundwater aquifers in the studied area Structural settings, Wadi Qena basin was intensively affected by structural discontinuities, i.e. shear zones, faults, folds and fractures. Two prominent shear zones were reported in the study area including: Qena-Safaga shear zone and the Najd shear system. Landsat TM ratio images (e.g. 5/7, 5/1 and 5/43/4 in RGB) were created Delineating surface structural features. Based on interpretation of these Landsat ratio mosaic together with geologic maps and field investigation, three major zone belts of Najd shear zone were mapped (NJ1, NJ2 and NJ3). While, The Qena-Safaga shear zone was mapped on the basis of its NE-SW trend and right-lateral displacement. Mapping subsurface structures is based on separation of the total intensity magnetic map into its regional and residual components. This was conducted using the fast Fourier transform technique in the Oasis Montaj TM package (version 7.1, 2010). Summary and Conclusion 142 The major structural trends in the study area includes the NE-SW (Qena-Safaga trend) and the NW-SE trends (Najd shear system). Locations of the inferred basins and uplifts are consistent with the borehole data obtained from deep wells drilled along N-S traverse in the study area. The structural features (e.g. shear zones and faults) in Wadi Qena basin indicates a striking similarity in the trends of surface and subsurface structures. Spatial analysis of these structures indicate that the surface shear zones and faults extend deeply through the subsurface succession and could be interpreted as a reactivation of the pre-existing structural weaknesses in the basement rocks during the Red Sea opening. Hydrogeological conditions: The groundwater in Wadi Qena basin is available from different water bearing formations under different hydrogeologic conditions. The water bearing formations are (from the younger to the older): The Alluvium Quaternary Aquifer, is formed of sand, gravel, and boulders filling the courses of the hydrographic basins. They vary laterally and vertically in the lithological composition and thickness according to the dominated rock exposures. The thickness of these deposits generally increases toward the River Nile Valley, where the thickness exceeds 100 m. Its groundwater is characterized by unconfined conditions where the depth to water ranges from 2.7m to 35.95 m. The total dissolved solids (TDS) value varies greatly between 586.71 mg/l to 36507.38 mg/l due to the circulation of irrigation water. The Carbonate and Sandstone aquifer (Eocene-Pliocene), is formed of undifferentiated sandstone and carbonate rocks of Eocene-Pliocene age. The water in this aquifer occurs under free water table where the depth to water ranges between 25 m to 65 m from the ground surface. Locally, the aquifer is bounded with clay layers (wells no. 27and 44). So, the groundwater exists under semiconfined to confined condition in these two wells. The total dissolved solids range between 2275 mg/l to 11401.45 mg/l, the Summary and Conclusion 143 variation in salinity values is attributed to the lithologic composition of water bearing formation. The Nubia Sandstone Aquifer (Turonian-Santonian): consists of sandstones and gravels with shale intercalations and it has 200m thick. The groundwater in this aquifer occurs under confined condition where it is overlain by the impervious Quseir variegated shale. The groundwater flow in this aquifer is from the northeast to southwest. The water salinity ranges between 1300 mg/l to 2251mg/l. The low salinity value is attributed to the closeness of wells from a watershed area and mixing with surface water or other shallow aquifers. On the other hand, high salinity value is due to the leaching processes and the stagnancy of the water. Upward leakage of the groundwater of this aquifer through Deep seated faults occurs and recharges the shallow Post Nubia and Quaternary aquifers. The Fractured basement aquifer (Precambrian), occupies the eastern portion of Wadi Qena basin and represented by the Red Sea Mountains. They are highly weathered and fractured. Most of the water points were detected in areas where extensive drainage network intersected by long and thick dykes. Thirteen water points tapped this aquifer which is mainly formed of granite. The groundwater in this aquifer occurs under unconfined condition. The TDS in this aquifer range between 504 mg/l to1801 mg/l. Hydrogeochemical characteristics: The Hydrogeochemical aspects of the groundwater in the study area were discussed through the following topics; groundwater salinity (TDS), major ions concentration, hypothetical salts combinations, hydrochemical coefficients (ion ratios), geochemical classification of the groundwater, evaluation of groundwater quality and stable isotopes. The salt assemblages in the groundwater of the different water bearing formations are calculated. They reflect different Summary and Conclusion 144 controlling factors (e.g. the effect of leaching and dissolution processes with the aquifer matrix) The geochemical classification of groundwater samples shows that most of the Quaternary, Post Nubia and Nubia aquifers exhibit secondary salinity properties. On the other hand, most of the groundwater samples of the fractured basement aquifer refer to primary alkalinity. Thirty-six groundwater samples were analyzed for isotopic compositions (O, H). The investigated samples were classified into two end members, one mixed group and one mixed with evaporation group. The groundwater samples collected from the Quaternary and Post-Nubia aquifers show a strong mixing signature between the deep, highly depleted Nubia waters and the modern meteoric waters. These samples are located proximal to deep-seated faults which act as vertical conduits along which groundwater upward leakage from the deep Nubia sandstone occur and recharge the overlying Post-Nubia and Quaternary aquifers. Furthermore, some of these samples show deviation from the mixing line between meteoric and Nubia waters indicating that the modern meteoric waters were subjected to high evaporation prior to infiltration. On the other hand, samples tapping the Nubia sandstone aquifer (NAS) in the northern part of the study area (i.e. near the outlet of Wadi Fattera sub-basin) show a strong mixing between Nubia and meteoric waters (without evaporation). The mixing ratio ranges from 28 % meteoric waters to 36%. The hydrogeologic evaluation of the study area reveals that the best sites for groundwater extractions in Wadi Qena basin should be around the delineated deep-seated faults. Future plans for land reclamation in the Egyptian deserts (96% of the total area of Egypt) should take into consideration the role of structure control (e.g. shear zones, faults and fractures) on the groundwater flow and accumulation. The integration of remote sensing data sets, with geophysical, stable isotopes, field and GIS technologies is effective in improving our understanding of the role of Summary and Conclusion 145 structural control and modern recharge in exploration for aquifer potential in arid environments and could be applicable for similar regions worldwide |