Center pivot irrigation in Saudi Arabia is typical of many isolated irrigation projects scattered throughout the arid and hyper-arid regions of the Earth. Nonrenewable fossil water is mined from depths as great as 1 km (3,000 ft), pumped to the surface, and distributed via large center pivot irrigation feeds. The circles of green irrigated vegetation may comprise a variety of agricultural commodities from alfalfa to wheat. Diameters of the normally circular fields range from a few hundred meters to as much as 3 km (1.9 mi).
The projects often trace out a narrow, sinuous, and seemingly random path. Actually, engineers generally seek ancient river channels now buried by the sand seas. The fossil waters mined in these projects accumulated during periods of wetter climate in the Pleistocene glacial epochs, between 10,000 and 2 million years ago, and are not being replenished under current climatic conditions. The projects, therefore, will have limited production as the reservoirs are drained.
