TIGRIS RIVER

Old Persian Tigra, Greek Trigres, or Tigris, Latin Tigris, Akkadian Idiklat, biblical Hiddekel, Arabic Dijla, Turkish Dicle river in Turkey and Iraq. It originates in the Southeastern Taurus Mountains at Lake Hazar and in several conjoint streams in the tangled hill country north of Diyarbakir, Tur. It then flows generally southeastward for about 1,180 miles (1,900 km) toward the Persian Gulf, which it enters as a joint stream, the Shatt Al-'Arab, 120 miles (193 km) long, with the Euphrates River. For 280 miles (450 km), as far as Faysh Khabur, southeast of Cizre, it is a Turkish river (although before entering Iraq it forms a small, 20-mile [30-kilometre] section of the Syrian border); then for the remainder of its course it lies within Iraq. It discharges into the Shatt Al-'Arab at Al-Qurnah. The Tigris in Turkey is a typical mountain stream, flowing swiftly in a narrow, well-defined valley often slotted deeply into the surface, with gorges and rapids marking its course. Southeast of Cizre, near the Syrian and Iraqi borders, it receives the eastern Al-Khabur River. Much of the next 100 miles (160 km) of the river is impounded by a dam north of Mosul. Between Mosul and Al-Fathah the Tigris is joined on the left bank by the Great Zab and the Little Zab, two tributaries that double the river's flow during the floods of March and April. The valley walls of the Tigris recede south of the village of Tikrit (100 miles north-northwest of Baghdad), and the Tigris flows for the rest of its course over a wide, gently undulating plain with only a slight, almost imperceptible drop to sea level. Consequently, the river meanders extensively, with many loops, dead arms, and cutoffs. In order to prevent flooding and shifting of the river, embankments and diversion structures have been constructed below Samarra'. Southeast of Samarra' the river is fed by another left-bank tributary, the Al-'Uzaym, while the Diyala River adds its waters south of Baghdad. When the river reaches Al-Kut, 200 miles downstream from Baghdad, the topography becomes extremely flat. Braided channels disperse water on either side into marshland, and streams freely flow into other parts of the valley. One of the larger distributaries, the Sha tt Al-Gharraf, breaks off southward and eventually joins the Euphrates River below An-Nasiriyah. On both sides of the river lie extensive marshes, fed by distributaries, which, together with irrigation canals, seepage, and evaporation, greatly diminish the flow of the Tigris during its passage from Baghdad to Al-Qurnah. In ancient times the central Tigris was the site of urban civilizations, which were served by irrigation canals for several millennia. After the fall of the Achaemenid Empire (330 BC), this wealthy region became the political and commercial centre of Mesopotamia. Seleucia and Ctesiphon, respectively the royal cities of the Seleucid and of the Parthian and Sasanian dynasties, and Baghdad and Samarra', both 'Abbasid capitals, all lay on the Tigris. In modern times the main effort in river control has been to maintain an effective system of diversion and storage both as a precaution against inundations during the main flood period (MarchMay) and also as a means of retaining the floodwaters for distribution in the hot season after May, when rainfall ceases until late autumn and temperatures may exceed 120 F (49 C).