Tuat, or Touat, is a natural region of desert in central Algeria that contains a string of small oases. In the past, the oases were important for caravans crossing the Sahara. Geography Tuat lies to the south of the Grand Erg Occidental, to the east of the Erg Chech and to the south west of the Tademaït Plateau. It contains a string of small oases strung out along the eastern edge of the Wadi Messaoud, a continuation of the Wadi Saoura. The oases extend over a distance of 160 km from the district of Bouda in the north to Reggane in the south. The largest town in the region is Adrar, 20 km south east of Bouda. Adrar was established by the French after their conquest in 1900 and had a population of 43,903 in 2002. Associated with each oasis are small walled villages called ksour (singular ksar or gsar). There are also some forts (kasbahs), most of which have been abandoned. There is almost no rainfall in the region and the agriculture depends on groundwater from the Continental Intercalary, an enormous aquifer that extends for over 600,000 km2, an area that includes parts of Algeria, Libya and Tunisia. The Continental Intercalary is a layer of porous sandstone deposited between the Moscovian and the Cenomanian periods. It forms the deeper of the two aquifers of the North Western Sahara Aquifer System (NWSAS). Tuat is situated at the south western boundary of the Continental Intercalary where the aquifer lies only 2–6 m below the surface. The oases contain 700,000-800,000 date palms (Phoenix dactylifera) in an area of 4,500 hectare. The palm groves are irrigated by a system of foggaras. These are traditional gravity catchment systems which consist of a tunnel constructed with a gentle uphill gradient from the low ground near the wadi into the aquifer lying under the nearby higher ground. Vertical access holes every 10–20 m along the tunnel provide ventilation and facilitate the construction and maintenance. Many of the foggaras are over a kilometre in length. They typically provide flow rates of between 2 L/s and 3 L/s. In 1963 the region of Tuat contained 531 foggaras of which only 358 were functioning. The total combined flow rate was approximately 2000 L/s. Foggaras are expensive to construct and to maintain. As they collapse they are often not repaired. Instead, water is obtained using vertical wells and electric pumps