Britannica Sources used in this answer

Why have the courses of the Tigris and Euphrates rivers shifted over thousands of years?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Map showing the Tigris and Euphrates river basin and its drainage network across Turkey, Syria, and Iraq, with color shading for elevation, major dams, canals, lakes, and boundaries with neighboring countries. The green areas indicate lower elevations along the river valleys, while higher elevations are shaded in brown and orange. A small locator map in the corner shows the basin's position within the Middle East. — Tigris-Euphrates river system The Tigris and Euphrates river basin and its drainage network.

The courses of the Tigris and Euphrates rivers have shifted significantly over the millennia, particularly across the Mesopotamian alluvial plain south of Sāmarrāʾ and Al-Ramādī. These changes are driven by a combination of natural geomorphological processes and extensive human intervention.12

Natural factors include the rivers' tendency to cut into the alluvium, form tortuous meanders, and build natural levees, which can cause a river to abandon its bed for a new path. The rivers also carry massive amounts of silt—the Tigris alone carries approximately one ton per second—which settles and alters the landscape over time.13

Human activity has played a major role in these shifts for at least 7,000 years. The development of complex irrigation systems, including the construction of canals and the abandonment of cultivated tracts, has redirected water flow and influenced the formation of the landscape. Historical engineering feats, such as the Sasanian period canals that linked the two rivers, further illustrate how human efforts have intentionally and unintentionally reshaped the watercourses. Consequently, the locations of ancient tells often bear no relation to the rivers' present-day paths.12