The 2000-MW Karun III hydroelectric project in Iran is now complete. Impounding started on November 2004 and the reservoir reached full supply level in May 2006. The project, one of the largest in the world to be constructed at this time, includes a 205-m high double curvature arch dam; spill facilities comprising a two bay chute spillway, two orifice spillways and a crest spillway; a 400-m long concrete lined plunge pool; a 50-m high mass concrete tailpond dam and a huge underground powerhouse complex. This complex comprises two 12.6-m diameter intake tunnels bifurcating into four 9.5-m diameter power tunnels and S-shafts which in turn bifurcate into eight 5.5-m diameter tunnels which feed water via steel lined penstocks to eight 250-MW generating units each protected by a 5-m diameter butterfly inlet valve. Water is discharged from the units via draft tube tunnels, four each through a manifold to each of two 14-m diameter tailrace tunnels. Major underground facilities include an intake gate gallery, inlet valve gallery, powerhouse cavern and transformer cavern; each of these is accessed through underground tunnels.