Detecting and Controlling the Waterlogging in Dakhla Basin
251
2004). Dakhla Oasis is one of several structural depressions in the Western Desert
(Fig. 6), where Pleistocene pluvial sediments occur as iron-rich spring deposits as
well as carbonate spring and lacustrine sediments (Churcher et al. 1999). Dates from
Dakhla lacustrine deposits indicate pluvial conditions ranging from 100 ka to 200 ka
(Osinski et al. 2007). Nevertheless, a specific geochemical environment from that of
the lake high stand has been identified in these previous investigations.
Dakhla Oasis is a depression surrounded on its northern side by a steep escarpment
running in a generally south-east to north-west direction over a length of approximately 250 km. The Nubian Sandstone complex has a broad geographic distribution
within Dakhla Oasis. Shale and clay beds and lenses are needed at the local or
sub-regional level for water containment. A thick layer of clay overlays the aquifer
network, which acts as an aquiclude, an impermeable layer of water. The field is
characterized at a depth of about 1,000 m by rocks in the basement. In general,
the composition of rock layers is important to learn about the highly variable water
storage potential of various types of rock. The number of wells in Dakhla Oasis is
large: over 650 shallow water wells hit the upper aquifer in Dakhla Oasis and over
236 deep wells hit the lower aquifer (Ebraheem et al. 2004). The transmissivity is on
average 950.4 m
2 /day and the hydraulic conductivity 5.3 m/day (Bakhbakhi 2002).
The depth of groundwater throughout the Dakhla Oasis area will not hit the current
economic level of 65 m in the next 100 years, even if the current rate of extraction
is higher than expected (1.71x10
6 m
3 /day). The economic level gives an idea of the
drilling costs associated with the pumping speed. Because of the high drilling and
pumping costs, e.g. from electricity prices, the pumping rate limit in the Dakhla
Oasis is estimated to be 65 m before it is irrigated economically. In the middle of
the oasis, the aquifer’s permeability and thickness are strongly affected by a NorthSouth fault and an anticline bounding from East and West respectively. New well
fields should therefore be established in the western part of the oasis (Ebraheem et al.
2004). It is understood that a long-term increase in groundwater extraction is feasible
at the Dakhla Oasis. Nevertheless, Ebraheem et al. models predict multiple places
to dewater the first aquifer in Dakhla Oasis before the year 2100. Therefore, wells
reaching the first aquifer will be dried up (Ebraheem et al. 2004). In Dakhla Oasis,
the groundwater quality is generally good and below the safety levels of national and
international standards except for enhanced Pb occurrence. The concentration levels
of Pb in groundwater samples ranged from 0.06 to 0.17 mg L
−1 relative to acceptable
values (0.01–0.05 mg L
−1 ). The water is slightly acidic (pH 6.09–6.71), whereas the
soil is somewhat alkaline (pH 7.95–8.27). When used for medicinal purposes (as per
national and international standards), Pb can cause some problems. Consequently,
water quality can cause problems with the wells as drinking water sources (Soltan
1997).
There are huge areas appropriate for agriculture the western sector represents
about three-quarters of the area grown in the oasis, many wells, and land reclamation
has spread to the western region of West Mawhub. A lot of villages are scattered in
the western region. There are much less developed areas in the eastern sector than
the western sector and the number of wells. Dakhla is one of the richest oasis with
freshwater resources. In the far east of Dakhla, there are three sites with arable fields
251
2004). Dakhla Oasis is one of several structural depressions in the Western Desert
(Fig. 6), where Pleistocene pluvial sediments occur as iron-rich spring deposits as
well as carbonate spring and lacustrine sediments (Churcher et al. 1999). Dates from
Dakhla lacustrine deposits indicate pluvial conditions ranging from 100 ka to 200 ka
(Osinski et al. 2007). Nevertheless, a specific geochemical environment from that of
the lake high stand has been identified in these previous investigations.
Dakhla Oasis is a depression surrounded on its northern side by a steep escarpment
running in a generally south-east to north-west direction over a length of approximately 250 km. The Nubian Sandstone complex has a broad geographic distribution
within Dakhla Oasis. Shale and clay beds and lenses are needed at the local or
sub-regional level for water containment. A thick layer of clay overlays the aquifer
network, which acts as an aquiclude, an impermeable layer of water. The field is
characterized at a depth of about 1,000 m by rocks in the basement. In general,
the composition of rock layers is important to learn about the highly variable water
storage potential of various types of rock. The number of wells in Dakhla Oasis is
large: over 650 shallow water wells hit the upper aquifer in Dakhla Oasis and over
236 deep wells hit the lower aquifer (Ebraheem et al. 2004). The transmissivity is on
average 950.4 m
2 /day and the hydraulic conductivity 5.3 m/day (Bakhbakhi 2002).
The depth of groundwater throughout the Dakhla Oasis area will not hit the current
economic level of 65 m in the next 100 years, even if the current rate of extraction
is higher than expected (1.71x10
6 m
3 /day). The economic level gives an idea of the
drilling costs associated with the pumping speed. Because of the high drilling and
pumping costs, e.g. from electricity prices, the pumping rate limit in the Dakhla
Oasis is estimated to be 65 m before it is irrigated economically. In the middle of
the oasis, the aquifer’s permeability and thickness are strongly affected by a NorthSouth fault and an anticline bounding from East and West respectively. New well
fields should therefore be established in the western part of the oasis (Ebraheem et al.
2004). It is understood that a long-term increase in groundwater extraction is feasible
at the Dakhla Oasis. Nevertheless, Ebraheem et al. models predict multiple places
to dewater the first aquifer in Dakhla Oasis before the year 2100. Therefore, wells
reaching the first aquifer will be dried up (Ebraheem et al. 2004). In Dakhla Oasis,
the groundwater quality is generally good and below the safety levels of national and
international standards except for enhanced Pb occurrence. The concentration levels
of Pb in groundwater samples ranged from 0.06 to 0.17 mg L
−1 relative to acceptable
values (0.01–0.05 mg L
−1 ). The water is slightly acidic (pH 6.09–6.71), whereas the
soil is somewhat alkaline (pH 7.95–8.27). When used for medicinal purposes (as per
national and international standards), Pb can cause some problems. Consequently,
water quality can cause problems with the wells as drinking water sources (Soltan
1997).
There are huge areas appropriate for agriculture the western sector represents
about three-quarters of the area grown in the oasis, many wells, and land reclamation
has spread to the western region of West Mawhub. A lot of villages are scattered in
the western region. There are much less developed areas in the eastern sector than
the western sector and the number of wells. Dakhla is one of the richest oasis with
freshwater resources. In the far east of Dakhla, there are three sites with arable fields