KARUN RIVER

Persian Rud-e Karun, ancient Ulai, or Eulaeus river in southwestern Iran, a tributary of the Shatt al-Arab, which it joins at Khorramshahr. It rises in the Bakhtiari Mountains west of Esfahan and follows a tortuous course trending basically southwest. The Karun's total length is 515 miles (829 km), though the direct distance from its source to the junction with the Shatt al-Arab is only 180 miles (290 km). Its catchment basin up to Ahvaz has an area of 22,069 square miles (57,059 square km), of which 7,000 square miles (18,130 square km) belong to its main tributary, the Dez. Most of the area is mountainous, forming part of the limestone Zagros ranges. The river's course divides into three parts: from the sources to Gatvand, where the river emerges from the mountains; from Gatvand to Band Qir, where it is joined by the Dez; and from Band Qir through Ahvaz southward to the Shatt al-Arab. In its upper course the Karun is a powerful stream, increasing in volume as it is successively joined by its tributaries. For long stretches it flows rapidly between high precipices. At Band Qir the river, enlarged by the Dez, is navigable to its mouth except for about 2 miles (3 km) of rapids at Ahvaz. Below Ahvaz the river is sometimes too shallow for navigation, especially during the dry season. Seasonal variation in discharge rate shows the lowest water level to be in October, and the highest, as the result of combined precipitation and meltwater, in April. Formerly the Karun had a lower course that was separated from and to the east of the Shatt al-Arab. There are three old riverbeds (apparently used successively) that branch off at the left of the Karun; they are known as Shatt al-Qadimi (Farsi: Ancient River), Shatt al-'Ameh (Farsi: Blind River), and Rudkhaneh-ye Bahmanshir. Rudkhaneh-ye Bahmanshir delimits the eastern edge of the island of Abadan. In 1765, however, the river changed to its present course through the apparently artificial Haffar Channel. According to the geographer al-Maqdisi, this channel was dug in AD 986 to facilitate water communication between Ahvaz and Basra. This change resulted in frontier disputes between the Ottoman Empire and Iran, disputes that were settled by the treaty of Erzurum (1847), giving Iran access to the eastern bank of the Shatt al-Arab and the right to use the waterway. The Karun up to Ahvaz was opened to international navigation in 1888, and boat services were later established between Ahvaz and Band Qir. Shipping on the lower course of the Karun has become increasingly important owing to oil drilling and refining in the vicinity. To increase the water supply of Esfahan, a dam and tunnel on the river were completed in 1971.