I. HYDROGEOLOGY OF ARID REGIONS
23
Utilization of this water, however, is not a simple matter. A general restriction will always be the fact that water drawn from the aquifer will not
be replenished by modern recharge. Replenishment must be through lateral
migration of water from distant parts of the aquifer that are not developed
as yet. A specific restriction in many areas is the fact that the aquifer is
not very permeable. Yields of wells are sufficient only for small garden
plots and a few homes but generally lower than desired for efficient irrigation. Initial yields of wells in the New Valley Project of the United Arab
Republic were generally from 100 to 200 liters/second with pressures of
more than 7 kg/cm
2
(Harshbarger, 1968). Like most deep artesian
aquifers, pressures, and hence yields, have decreased rapidly after development of irrigation wells. In order to produce large quantities of water,
either large numbers of wells must be drilled or the water levels in wells
must be pumped down to a low level in order to create a steep hydraulic
gradient toward the well. Both methods of obtaining large yields are costly.
The quality of water also is a limiting factor, particularly in the northern
half of the United Arab Republic. The accumulation of salt in irrigated
regions must be prevented by using excessive amounts of water for leaching
the salts into drainage systems. Again, this increases the cost of irrigation
projects.
B. GREAT ARTESIAN BASIN OF AUSTRALIA
The Great Artesian Basin of Australia is probably the largest unified
hydrogeologic system in the world. It covers a large part of the eastern
half of Australia (Fig. 12). Much of the basin is arid and semiarid. The
basin is also noted for its deep wells which are probably some of the deepest water wells in the world. A few exceed 2000 meters in depth. Water
from some of the deepest wells reaches the surface with temperatures
slightly greater than 100°C.
The primary use of deep artesian wells in eastcentral Australia has
been to provide water for stock. Some wells supply domestic, municipal,
and minor irrigation needs, although the chemical quality of the water
is commonly marginal for these uses (see Table I, sample 11).
The deep artesian aquifers are Mesozoic continental sandstones, largely
Jurassic, which are covered in much of the basin with thick Cretaceous
clays. Two main water-bearing zones are generally present, the upper
"Blythesdale Series" and the lower "Marburg and Bundamba Series." Each
of the water-bearing "series" contains numerous individual aquifers that
have only limited lateral continuity. Despite local faciès changes, the
water-bearing zones appear to behave in a regional sense as an integrated
unit.
23
Utilization of this water, however, is not a simple matter. A general restriction will always be the fact that water drawn from the aquifer will not
be replenished by modern recharge. Replenishment must be through lateral
migration of water from distant parts of the aquifer that are not developed
as yet. A specific restriction in many areas is the fact that the aquifer is
not very permeable. Yields of wells are sufficient only for small garden
plots and a few homes but generally lower than desired for efficient irrigation. Initial yields of wells in the New Valley Project of the United Arab
Republic were generally from 100 to 200 liters/second with pressures of
more than 7 kg/cm
2
(Harshbarger, 1968). Like most deep artesian
aquifers, pressures, and hence yields, have decreased rapidly after development of irrigation wells. In order to produce large quantities of water,
either large numbers of wells must be drilled or the water levels in wells
must be pumped down to a low level in order to create a steep hydraulic
gradient toward the well. Both methods of obtaining large yields are costly.
The quality of water also is a limiting factor, particularly in the northern
half of the United Arab Republic. The accumulation of salt in irrigated
regions must be prevented by using excessive amounts of water for leaching
the salts into drainage systems. Again, this increases the cost of irrigation
projects.
B. GREAT ARTESIAN BASIN OF AUSTRALIA
The Great Artesian Basin of Australia is probably the largest unified
hydrogeologic system in the world. It covers a large part of the eastern
half of Australia (Fig. 12). Much of the basin is arid and semiarid. The
basin is also noted for its deep wells which are probably some of the deepest water wells in the world. A few exceed 2000 meters in depth. Water
from some of the deepest wells reaches the surface with temperatures
slightly greater than 100°C.
The primary use of deep artesian wells in eastcentral Australia has
been to provide water for stock. Some wells supply domestic, municipal,
and minor irrigation needs, although the chemical quality of the water
is commonly marginal for these uses (see Table I, sample 11).
The deep artesian aquifers are Mesozoic continental sandstones, largely
Jurassic, which are covered in much of the basin with thick Cretaceous
clays. Two main water-bearing zones are generally present, the upper
"Blythesdale Series" and the lower "Marburg and Bundamba Series." Each
of the water-bearing "series" contains numerous individual aquifers that
have only limited lateral continuity. Despite local faciès changes, the
water-bearing zones appear to behave in a regional sense as an integrated
unit.