Groundwater resources of Eastern Libya (Cyrenaica)

Abstract

Cyrenaica, excluding the Jebel Akhdar, forms part of the Libyan Sahara. It is a true desert with a mean annual rainfall generally less than 20 mm, and a land surface of sand, gravel or rock, largely devoid of vegetation (Plate 1). Yet a few thousand years ago, the Libyan Sahara, as elsewhere in North Africa, enjoyed an abundant rainfall and supported a varied flora and fauna as can be seen from pre-historic rock paintings. The abundant rainfall filled huge subterranean reservoirs which since then have been slowly draining to the Mediterranean Sea or low lying sabkhats and inland lakes. In consequence of the moderate relief of the Sahara and the wide regional extent and uniform structure of the sedimentary basins which form the reservoirs, the groundwater bodies occur in huge flow systems which may extend over several hundreds of miles. The reservoirs' thicknesses vary but the two most important series, the Continental Intercalaire or Nubian, and the Continental Terminal of mid-Tertiary to recent age, frequently exceed 3000 feet. Two major flow systems occur in Cyrenaica, in the Sirte and Kufra basins (Fig.1).Until oil was discovered in the late nineteen fifties, groundwater development in Cyrenaica was mainly concentrated in coastal areas where the prevailing rainfall is sufficient to permit some recharge, and in a few interior scattered oases — Giarabub, Jalo-Augila, Kufra and Tazerbo, where the ground surface lies close to the upper phreatic (water table) surface of regional groundwater systems.Oil exploration requires fairly large supplies of water for the main drilling operations. During exploration in the Sirte basin it was discovered that water of variable quality could be found virtually anywhere at moderate depths between 100 and 500 feet below ground level. Oil company practice to obtain temporary water supplies is to drill two or three simply constructed water wells to a few hundred feet below the water table, and to pump by air lift. The wells are subsequently capped, when no longer required.