Orontes Basin (Al Assi)

The area of Orontes basin in Syria is set-up at 21 624 km2 of which 19 907 km² of the main river stream basin and 1717 km² of the Afrin river basin. The western mountains receive precipitation ranging from 600 mm to 1 500 mm. Precipitation in the eastern parts of the basin is much lower, ranging from 400 mm to 600 mm. The Orontes River originates in Lebanon, runs through the territory of Syria from south to north and drains into the Mediterranean Sea. (The Orontes is the only river in the region, flowing to the north direction, what has given the river’s Arab name “Al Assi”).The length of the Orontes river in Lebanon is 65 km and in Syria 342 km. The Orontes River and its tributaries collect the runoff from the highlands and plateau areas situated on both sides of the rift valley. The average annual flow of the Orontes river is estimated at 2 400 million m³ equivalent to 76.1 m³/s.

The renewed surface water amount in the basin is estimated at 1110 million m³ flows into streams and valleys. There are several bid springs (Al Ghab, Al Rouj, and Al Zarka). The regulation of the Orontes river flow (in order to increase its irrigation capacity) began with the reconstruction of the ancient Quattineh dam (in 1937) and the construction of the dams at Rastan and Mhardeh on the main river stream in 1960 (the first big dams built in Syria). These reservoirs provide for control of about 12 600 km² of Orontes drainage basin upstream Mhardeh. However, the total volume of the three dam reservoirs (500 million m³) represents about 45% of the estimated average annual flow yield, from the basin area upstream the reservoirs. Until 2002 the dams built in the basin numbered 41 with total reservoir volume 741 mill.m³ or less than 40% of the total average annual runoff of the Orontes at the Darkush Village. All these dams were built on tributaries of the Orontes river and with comparatively small reservoir volumes. Among the dams with large reservoirs are the Zeita dam (80 million m3) and the Zeizun dam (71 mill.m³) which had been damaged in 2002. With the four new dams to be constructed, the total storage capacity of the dams in the basin will rise to about 1072 million m³.

The irrigation with groundwater in the basin has been expanding steadily within the last decade. The intensive groundwater use resulted in depletion of the water storage in the underground reservoirs (aquifers), lowering of the groundwater table (water table decreased 1.5-25 m in 1999), and considerable reduction of the spring yield. The discharge of 26 springs in Al Ghab valley dropped from 18.45 m³/s average annual discharge for the period 1965-1971 to 9.7 m³/s mean annual discharge in 1992/93 and steadily decline to 4.2 m³/s in 1995/96. The amount of groundwater is estimated to 1607 mill.m³, most of it flows as springs (1134 million m³) and the rest (473 million m³) is stored into aquifers and withdrawn by wells numbered 41000 wells for irrigation and water supply.

The areas irrigated increased from 155 300 ha in 1989 to 257298 ha in 2003. 129377 ha is irrigated by wells, 15641 ha is irrigated by rivers and springs, and 112280 ha is irrigated by irrigation system.

The expansion of the irrigation with groundwater has been most intensive in the Al Ghab valley and the mohafazat of Idleb. In the Al Ghab region, the areas irrigated with groundwater raised, (in the same time) the areas irrigated with surface waters were reduced (955 million m³). The amount of groundwater which is used by wells for water supply, irrigation and industry is more than 1607 million m³, while the renewed amount in aquifers is less than 473 million m³. This means 1134 million m³ of non-renewed groundwater is pumped.