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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
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