280
K. S. Gemail et al.
to reach its minimum value of 11 .m at VES 17 with increasing to the north and
reach the maximum value of 337 .m at VES 11. Decreasing of resistivity can be
explained by embedding of clay lenses in that formation and also to the increasing
of total dissolved salts in the groundwater from surface infiltration of preached water
and absence of the upper clay cap.
Based on the plotted TDS versus water resistivity relationship (Fig. 16b), it was
shown that the water samples in the northern part of the Taref water bearing zone are
characterized by high resistivities and low TDS to indicate a good water quality in this
part, while most samples of the southern parts are characterized by low resistivities
and high TDS. As mentioned before, low TDS values are primarily recorded along
the faulting zone on the depression surface (Fig. 16e), to indicate the direct hydraulic
joining between the low TDS deeper aquifers of Sabaya and Six Hills formations.
According to Mohamed et al. (2017), the groundwater flow from the south of Dakhla
sub-basin is impeded by the Uweinat-Aswan uplift.
5 Conclusions
This study was conducted to evaluate the groundwater potentialities and recharge
system in the shallow Nubian aquifer (Taref Formation) at the eastern part of Dakhla
depression. Geophysical, hydrogeological and borehole data exposed that the NSAS
is the foremost groundwater aquifer in Western Desert including Dakhla basin. The
groundwater aquifer is considered as the only natural resource for freshwater supply
in this area. However, the most water wells suffer from water level reduction in last
decades due to over extraction and unplanned pumping from the topmost aquifer
zone.
Based on the constructed resistivity sections and borehole data, the shallow aquifer
(Traef Formation) is covered the northern parts and originated along the normal fault
zones, which are possibly linked with the deeper formations of Sabaya and Six
Hills aquifers with permeable pathways. The water quality in the Traef aquifer is
degraded to the south due to the decreasing in sand and gravels in contrast with shale
and evaporate contents in the water-bearing zone. These lithologic variations led to
decrease the aquifer transmissivity and increase the salt leaching to the south of the
surveyed area. However, the constructed resistivity sections and distribution maps
indicate that groundwater might be of good quality in the northern and northwestern
parts than the central and southern parts.
The established 2D resistivity sections and 3D maps of shallow aquifer zone is
a helpful tool for understanding the conceptual flow model in the area and controlling the future wells drilling for freshwater purposes. The DC resistivity sounding
technique is widely contributed in delineating the place of such interface, and can be
easily employed in similar arid regions. Furthermore, geophysical investigations are
suggested by utilizing different techniques with more prominent examination depth
to evaluate and study the relationship between deep and shallow aquifers.
K. S. Gemail et al.
to reach its minimum value of 11 .m at VES 17 with increasing to the north and
reach the maximum value of 337 .m at VES 11. Decreasing of resistivity can be
explained by embedding of clay lenses in that formation and also to the increasing
of total dissolved salts in the groundwater from surface infiltration of preached water
and absence of the upper clay cap.
Based on the plotted TDS versus water resistivity relationship (Fig. 16b), it was
shown that the water samples in the northern part of the Taref water bearing zone are
characterized by high resistivities and low TDS to indicate a good water quality in this
part, while most samples of the southern parts are characterized by low resistivities
and high TDS. As mentioned before, low TDS values are primarily recorded along
the faulting zone on the depression surface (Fig. 16e), to indicate the direct hydraulic
joining between the low TDS deeper aquifers of Sabaya and Six Hills formations.
According to Mohamed et al. (2017), the groundwater flow from the south of Dakhla
sub-basin is impeded by the Uweinat-Aswan uplift.
5 Conclusions
This study was conducted to evaluate the groundwater potentialities and recharge
system in the shallow Nubian aquifer (Taref Formation) at the eastern part of Dakhla
depression. Geophysical, hydrogeological and borehole data exposed that the NSAS
is the foremost groundwater aquifer in Western Desert including Dakhla basin. The
groundwater aquifer is considered as the only natural resource for freshwater supply
in this area. However, the most water wells suffer from water level reduction in last
decades due to over extraction and unplanned pumping from the topmost aquifer
zone.
Based on the constructed resistivity sections and borehole data, the shallow aquifer
(Traef Formation) is covered the northern parts and originated along the normal fault
zones, which are possibly linked with the deeper formations of Sabaya and Six
Hills aquifers with permeable pathways. The water quality in the Traef aquifer is
degraded to the south due to the decreasing in sand and gravels in contrast with shale
and evaporate contents in the water-bearing zone. These lithologic variations led to
decrease the aquifer transmissivity and increase the salt leaching to the south of the
surveyed area. However, the constructed resistivity sections and distribution maps
indicate that groundwater might be of good quality in the northern and northwestern
parts than the central and southern parts.
The established 2D resistivity sections and 3D maps of shallow aquifer zone is
a helpful tool for understanding the conceptual flow model in the area and controlling the future wells drilling for freshwater purposes. The DC resistivity sounding
technique is widely contributed in delineating the place of such interface, and can be
easily employed in similar arid regions. Furthermore, geophysical investigations are
suggested by utilizing different techniques with more prominent examination depth
to evaluate and study the relationship between deep and shallow aquifers.