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Both the Kara Su and the Murat Su rise northwest from Lake Van at elevations of and amsl, respectively. At the location of the Keban Dam, the two rivers, now combined into the Euphrates, have dropped to an elevation of amsl. From Keban to the Syro–Turkish border, the river drops another over a distance of less than . Once the Euphrates enters the Upper Mesopotamian plains, its grade drops significantly; within Syria the river falls while over the last stretch between Hīt and the Shatt al-Arab the river drops only .
The discharge regime of the Euphrates has changed dramatically since the construction of the first dams in the 1970s. Data on Euphrates discharge collected after 1990 show the impact of the construction of the numerous dams in the Euphrates and of the increased withdrawal of water for irrigation. Average discharge at Hīt after 1990 has dropped to per second ( per year). The seasonal variability has equally changed. The pre-1990 peak volume recorded at Hīt was per second, while after 1990 it is only per second. The minimum volume at Hīt remained relatively unchanged, rising from per second before 1990 to per second afterward.
{| class="wikitable" |- ! Name ! Length ! Watershed size ! Discharge ! Bank |- |Kara Su | | | | Confluence |- |Murat River | | | | Confluence |- |Sajur River | | | 4.1 m3/s (145 cu ft/s) | Right |- |Balikh River | | | 6 m3/s (212 cu ft/s) |Left |- |Khabur River | | | 45 m3/s (1,600 cu ft/s) |Left |}
Among the fish species in the Tigris–Euphrates basin, the family of the Cyprinidae are the most common, with 34 species out of 52 in total. Among the Cyprinids, the mangar has good sport fishing qualities, leading the British to nickname it "Tigris salmon." The Trionyx euphraticus is a soft-shelled tortoise that is limited to the Tigris–Euphrates river system. Sixteenth to nineteenth century European travellers in the Syrian Euphrates basin reported on an abundance of animals living in the area, many of which have become rare or even extinct. Species like gazelle, onager and the now-extinct Arabian ostrich lived in the steppe bordering the Euphrates valley, while the valley itself was home to the wild boar. Carnivorous species include the gray wolf, the golden jackal, the red fox, the leopard and the lion. The Syrian brown bear can be found in the mountains of Southeast Turkey. The presence of European beaver has been attested in the bone assemblage of the prehistoric site of Abu Hureyra in Syria, but the beaver has never been sighted in historical times.
With the implementation of the Southeastern Anatolia Project (Güneydoğu Anadolu Projesi, or GAP) in the 1970s, Turkey launched an ambitious plan to harness the waters of the Tigris and the Euphrates for irrigation and hydroelectricity production and provide an economic stimulus to its southeastern provinces. GAP affects a total area of and approximately 7 million people; representing about 10 percent of Turkey's total surface area and population, respectively. When completed, GAP will consist of 22 dams – including the Keban Dam – and 19 power plants and provide irrigation water to of agricultural land, which is about 20 percent of the irrigable land in Turkey. Circa of this irrigated land is located in the Euphrates basin. By far the largest dam in GAP is the Atatürk Dam, located circa northwest of Şanlıurfa. This high and long dam was completed in 1992; thereby creating a reservoir that is the third-largest lake in Turkey. With a maximum capacity of , the Atatürk Dam reservoir is large enough to hold the entire annual discharge of the Euphrates. Completion of GAP was scheduled for 2010 but has been delayed because the World Bank has withheld funding due to the lack of an official agreement on water sharing between Turkey and the downstream states on the Euphrates and the Tigris.
Apart from barrages and dams, Iraq has also created an intricate network of canals connecting the Euphrates with Lake Habbaniyah, Lake Tharthar, and Abu Dibbis reservoir; all of which can be used to store excess floodwater. Via the Shatt al-Hayy, the Euphrates is connected with the Tigris. The largest canal in this network is the Main Outfall Drain or so-called "Third River;" constructed between 1953 and 1992. This long canal is intended to drain the area between the Euphrates and the Tigris south of Baghdad to prevent soil salinization from irrigation. It also allows large freight barges to navigate up to Baghdad.
Apart from the changes in the discharge regime of the river, the numerous dams and irrigation projects have also had other effects on the environment. The creation of reservoirs with large surfaces in countries with high average temperatures has led to increased evaporation; thereby reducing the total amount of water that is available for human use. Annual evaporation from reservoirs has been estimated at in Turkey, in Syria and in Iraq. Water quality in the Iraqi Euphrates is low due to the fact that irrigation water tapped in Turkey and Syria flows back into the river, together with dissolved fertilizer chemicals used on the fields. The salinity of Euphrates water in Iraq has increased as a result of upstream dam construction, leading to lower suitability as drinking water. The many dams and irrigation schemes, and the associated large-scale water abstraction, have also had a detrimental effect on the ecologically already fragile Mesopotamian Marshes and on freshwater fish habitats in Iraq.
The inundation of large parts of the Euphrates valley, especially in Turkey and Syria, has led to the flooding of many archaeological sites and other places of cultural significance. Although concerted efforts have been made to record or save as much of the endangered cultural heritage as possible, many sites are probably lost forever. The combined GAP projects on the Turkish Euphrates have led to major international efforts to document the archaeological and cultural heritage of the endangered parts of the valley. Especially the flooding of Zeugma with its unique Roman mosaics by the reservoir of the Birecik Dam has generated much controversy in both the Turkish and international press. The construction of the Tabqa Dam in Syria led to a large international campaign coordinated by UNESCO to document the heritage that would disappear under the waters of Lake Assad. Archaeologists from numerous countries excavated sites ranging in date from the Natufian to the Abbasid period, and two minarets were dismantled and rebuilt outside the flood zone. Important sites that have been flooded or affected by the rising waters of Lake Assad include Mureybet, Emar and Abu Hureyra. A similar international effort was made when the Tishrin Dam was constructed, which led, among others, to the flooding of the important Pre-Pottery Neolithic B site of Jerf el-Ahmar. An archaeological survey and rescue excavations were also carried out in the area flooded by Lake Qadisiya in Iraq. Parts of the flooded area have recently become accessible again due to the drying up of the lake, resulting not only in new possibilities for archaeologists to do more research, but also providing opportunities for looting, which has been rampant elsewhere in Iraq in the wake of the 2003 invasion.
The Euphrates provided the water that led to the first flowering of civilization in Sumer, dating from about the 4th millennium BCE. Many important ancient cities were located on or near the riverside, including Mari, Sippar, Nippur, Shuruppak, Uruk, Ur and Eridu. The river valley formed the heartlands of the later empires of Babylonia and Assyria. For several centuries, the river formed the eastern limit of effective Egyptian and Roman control and western regions of the Persian Empire.
over the Euphrates, ca. 1900–1910|alt=Refer to caption]] Turkey and Syria completed their first dams on the Euphrates – the Keban Dam and the Tabqa Dam, respectively – within one year of each other and filling of the reservoirs commenced in 1975. At the same time, the area was hit by severe drought and river flow toward Iraq was reduced from in 1973 to in 1975. This led to an international crisis during which Iraq threatened to bomb the Tabqa Dam. An agreement was eventually reached between Syria and Iraq after intervention by Saudi Arabia and the Soviet Union. A similar crisis, although not escalating to the point of military threats, occurred in 1981 when the Keban Dam reservoir had to be refilled after it had been almost emptied to temporarily increase Turkey's hydroelectricity production. In 1984, Turkey unilaterally declared that it would ensure a flow of at least per second, or per year, into Syria, and in 1987 a bilateral treaty to that effect was signed between the two countries. Another bilateral agreement from 1989 between Syria and Iraq settles the amount of water flowing into Iraq at 60 percent of the amount that Syria receives from Turkey. In 2008, Turkey, Syria and Iraq instigated the Joint Trilateral Committee (JTC) on the the management of the water in the Tigris–Euphrates basin and on 3 September 2009 a further agreement was signed to this effect.
Category:Mesopotamia Category:Rivers of Iraq Category:Rivers of Syria Category:Rivers of Turkey Category:International rivers of Asia Category:Sites along the Silk Road Category:Torah places Category:Fertile Crescent
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