I.

Introduction

Tigris (Turkish, Dicle, Arabic, Diljah), river in south-west Asia, rising in Turkey and flowing through Iraq before emptying into the Persian Gulf. The Tigris carries a greater amount of water than the Euphrates river, its historic partner in the framing of the early Mesopotamian civilizations. Its average flow is 1.25 million litres (275,000 gallons) per second. The length of the Tigris is 1,900 km (1,180 mi), and its drainage area is greater than 111,000 sq km (43,000 sq mi).

II.

Course of the Tigris

The Tigris rises in two branches in the eastern Anatolian highlands of south-eastern Turkey. One branch begins south of Lake Hazar and the other south-west of Lake Van. The branches join at Til, flowing south-east into Iraq after briefly running along the extreme south-eastern portion of the Syria-Turkey border. Major tributaries of the Tigris are the Great Zab, Little Zab, Diyālā, and the Adhaim. While all of these rivers join the Tigris inside Iraq, the waters of the Great Zab rise in Turkey, while those of the Little Zab and the Diyālā rise in Iran. At al-Qurnah in southern Iraq the Tigris joins with the Euphrates to form the Shatt Al Arab. Along its course the Tigris flows through Diyarbakır (in Turkey), Mosul, Tikrit, Samarra, and Baghdad (all in Iraq).

The Tigris is shallow in many parts and contains numerous obstructions, but is navigable by some form of craft for most of its course; small river steamers can ascend the river as far as Baghdad, which was founded on its west bank in 762 and quickly became one of the largest and most well-planned cities in the world. The main portion of the region in Iraq between the Tigris and Euphrates, now in part known as al-Jazirah, was ancient Mesopotamia. Also on the banks of the Tigris are the ruins of ancient Nineveh (opposite Mosul), Seleucia, and Ctesiphon.

III.

Human Impact

Maximum discharge from the Tigris, the result of melting winter snow in the highlands and late-winter and early-spring rains, occurs from March to May, and accounts for over half of the river's annual flow, often in the form of significant floods. Construction of the Samarra Barrage in the 1950s allowed for diversion of Tigris waters to the Tharthar Depression; this assisted in flood control, and in boosting the flow of the Euphrates, but has not provided the agricultural benefits anticipated from additional irrigation. Minimum flows are experienced from August to October. In the past the Tigris carried significant quantities of silt into the Shatt Al Arab, contributing to the extension of the delta into the Persian Gulf.

Flood control projects and the construction of dams on the major tributaries of the Tigris have decreased the silt load carried to the southern river course and the Shatt Al Arab. The expansion of irrigation in southern Iraq has resulted in a deterioration in soil quality, as rising water tables, polluted waters, and decreased silt deposits have taken their toll. As water is increasingly diverted from the Euphrates river by Turkey and Syria, Iraq's dependence on the water of the Tigris will become even more critical.