 Before water from Lake Mead reaches the turbines , it enters the intake towers and then four gradually narrowing <unk> which funnel the water down towards the powerhouse . The <unk> provide a maximum hydraulic head ( water pressure ) of 590 ft ( 180 m ) as the water reaches a speed of about 85 mph ( 140 km / h ) . The entire flow of the Colorado River passes through the turbines . The spillways and outlet works ( jet @-@ flow gates ) are rarely used . The jet @-@ flow gates , located in concrete structures 180 feet ( 55 m ) above the river , and also at the outlets of the inner diversion tunnels at river level , may be used to divert water around the dam in emergency or flood conditions , but have never done so , and in practice are only used to drain water from the <unk> for maintenance . Following an <unk> project from 1986 to 1993 , the total gross power rating for the plant , including two 2 @.@ 4 <unk> <unk> turbine @-@ generators that power Hoover Dam 's own operations is a maximum capacity of <unk> megawatts . The annual generation of Hoover Dam varies . The maximum net generation was 10 @.@ 348 TWh in 1984 , and the minimum since 1940 was 2 @.@ 648 TWh in 1956 . The average power generated was 4 @.@ 2 TWh / year for 1947 @-@ 2008 . In 2015 , the dam generated 3 @.@ 6 TWh . To lower the minimum power pool elevation from 1 @,@ 050 to 950 feet ( 320 to 290 m ) , five wide @-@ head turbines , designed to work efficiently with less flow , will be online by 2017 . Due to lack of water , the dam mostly provides power only during periods of peak demand . 
