 The penstocks are a pair of tunnels , 260 metres ( 850 ft ) long and inclined at 56 ° from the horizontal with a 5 @.@ 3 metres ( 17 ft ) diameter , which then bifurcate into four steel lined 190 metres ( 620 ft ) long , 2 @.@ 5 metres ( 8 ft 2 in ) diameter shafts . The penstocks underwent a major inspection and refurbishment in 2003 . 
