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280 Chapter Eight
Aquifer is in a deficit situation with outflows greater and best-management farming practices including,
than inflows. In the southern and central regions, ultimately, a shift from irrigated agriculture to dry-
outflows are about twice the inflows. Prior to irriga- land farming with its attendant far-reaching implica-
tion development, precipitation recharged the aquifer tions for the local economy.
at an average rate of 15 mm a −1 and small quantit- Although the High Plains Aquifer presents a case
ies of water discharged to the springs and rivers. of non-sustainable development of groundwater,
Irrigation represents a largely consumptive use of in practice there is no fundamental reason why the
water and since development, groundwater abstrac- temporary over-exploitation of aquifer storage for
tion has removed about 7% of the original total water a given benefit should not be allowed as part of a log-
volume from the aquifer. The water budget indicates ical water resources management strategy as long
that the decrease in storage would have been worse if as the groundwater system is sufficiently well under-
30–40% of the water pumped for irrigation had not stood to evaluate impacts. An example of the deliber-
infiltrated to the aquifer as irrigation return flows ate mining of groundwater resources for the benefit
each year. Declining groundwater levels are a direct of a national economy is the Great Man-made River
threat to the current way of life of the area, and project (GMRP) in Libya (Box 8.1). The GMRP
Dennehy et al. (2002) detail attempts that are being involves the abstraction of fossil groundwater
made to introduce more water-efficient irrigation recharged during a pluvial period of the last ice age
BO X
The Great Man-made River Project, Libya
8.1
2
6
Libya covers an area of some 1.8 × 10 km bounded in the north by fields at Sarir and Tazerbo (Fig. 1) are situated 381 km and 667 km
the Mediterranean coastline of approximately 1600 km in length south of Ajdabiya in the Sirt and Kufra Basins, respectively. The Sirt
(Fig. 1). The climate varies from Mediterranean along the coast with Basin contains a post-Eocene thickness of 1600 m of continental
winter rainfall totals of about 270 mm in Tripoli and Benghazi to a sands with increasing amounts of limestone found northwards. The
desert climate in the south where rain seldom falls. Rainfall is important aquifer sediments of the Kufra Basin are Lower Devonian
−1
higher at about 400 mm a in the mountainous areas to the south well-sorted, uncemented sand and sandstone. Regional groundwa-
of Tripoli and east of Benghazi. A total of 80% of Libya’s population ter contours indicate a small natural groundwater flow from south
of about 4.7 million is concentrated in the coastal area with approx- to north which is believed to be fed mainly from degradation of a
imately 2.5 million residents in the major towns and cities of Tripoli mound of fossil groundwater located below the northern flank of
and Benghazi. The majority (80%) of Libya’s agricultural production the Tibisti mountains. This palaeogroundwater was recharged dur-
is centred on the coastal plains and adjacent uplands but arable ing a major pluvial period at the time of the last ice age between
crops are only viable with irrigation. Importation of cereals, sheep 14,000 and 38,000 years ago. Present recharge from rainfall is
meat and other food stuffs are costly in terms of foreign exchange effectively zero in the central part of the Sirt Basin and Kufra Basin.
and has given impetus to improving the productivity of the land Therefore, the eastern region well-field developments are depen-
through irrigation and creating employment opportunities in agri- dent on groundwater mining with only a minor contribution from
culture. However, the relatively shallow aquifers in the coastal areas interception of throughflow (Pim & Binsariti 1994).
and the pressure of competing municipal and industrial demands The Sarir well-field contains 136 production wells drilled at
−1
for water pose a limitation on further agricultural development. 450 m depth, each able to deliver 92 L s . Pumping tests indicated
−1
2
2
During the 1960s, exploratory drilling for oil in the Libyan desert that transmissivity ranges from 400 m day −1 to 6000 m day .
−1
established the presence of extensive groundwater reserves in three The pumped water quality ranges from 530 mg L to 1367 mg L −1
−1
to four major basins but an unwillingness of people to move to the of total dissolved solids with an average of 815 mg L . At Tazerbo,
Libyan desert to utilize this resource for irrigation gave rise to the 118 production wells are drilled at depths varying between 380
−1
State decision to initiate the Great Man-made River Project (GMRP), and 600 m depth, with each borehole able to deliver 102 L s .
one of the world’s major groundwater developments. The total Modelled drawdowns for the Tazerbo well-field are 95 m after 50
3
capacity of the major basins, which is estimated to be 35,000 km , years with the greatest contribution (86%) to abstraction from ver-
is immense and the only technical constraints on development are tical leakage (Pim & Binsariti 1994). Assuming an average annual
3
considered to be local ones of water quality and aquifer hydraulics. demand of 10,000 m ha −1 for irrigation water, the limit for irrig-
The principal features of the GMRP are described by McKenzie ated agriculture for the Phase I supply is about 70,000 ha.
and Elsaleh (1994) and include well-fields and conveyance systems Phases II and III well-field developments in the western region are
comprising long lengths of very large diameter (4 m) pipelines planned on a similar scale in the Hammadah Al Hamra and Murzuq
required for the transfer of water to coastal districts. Phase I well- Basins which lie north and south of the Gargaf uplift, respectively