Tigris–Euphrates river system through the central plain and combine at Al-Qurnah to form the Shatt al-Arab and discharge into the Persian Gulf. The region has historical importance as part of the Fertile Crescent region, in which civilization is believed to have first emerged. The ecoregion is characterized by two large rivers, the Tigris and Euphrates. The rivers have several small tributaries which feed into the system from shallow freshwater lakes, swamps, and marshes, all surrounded by desert. The hydrology of these vast marshes is extremely important to the ecology of the entire upper Persian Gulf. Historically, the area is known as Mesopotamia. As
Nossob River flow about once a century. However, water does flow underground to provide life for grass and camelthorn trees growing in the river bed. The Nossob may flow briefly after large thunderstorms, causing wildlife to flock to the river. The Nossob ends at a confluence with the Molopo River some 50 km south of Twee Rivieren. The confluence at is still 890m above sea level. The Molopo is in turn a tributary of the Orange River, which it meets downstream of Augrabies Falls. Important dams in the basin, both on the Oanob River, a tributary of the Auob: Nossob River The