Wikipedia
Koohrang also known as Kouhrang and Kurang is the name of a river, originating in the Zagros mountains of western Iran, which joins the Dez River to form the Karun, Iran's largest (by volume) river. A series of tunnels (Kuhrang Tunnels) have been built since the 1950s to redirect some of the Kuhrang's water toward the Zayandeh River to meet the demands of increased population in Esfahan and Yazd provinces.
The Zayandeh River basin encompasses about and is connected to the upper Karun River basin (which drains to the Persian Gulf) by the Kuhrang Dam and Tunnel 1 constructed in 1953 although first proposed in the early sixteenth century. Two additional tunnels ( Kurang 2 and Kurang 3) were constructed in late 1990s and early 2000s. A hydroelectric dam at Godar-e Langar (also known as Karun-4) would also supply piped water to Esfahan away if it is completed (Whitley and Gallagher, 1995). Dams have deleterious effects on a riverine fish and other fauna and are often stocked with exotic species. The upper Karun has not been well explored for endemic taxa. Mean annual flow of the Zayandeh River is estimated at and is used mostly for agriculture, but an increase in population and industry has necessitated dam construction ( Chadegan Reservoir, capacity ) and diversion schemes. There is also the Hana Dam on the Hana River at Semirom with a height of and a capacity of .