Tainter Gates are specialized gates installed across the top of the dam spillway. Each Tainter Gate is a huge semi-circular steel prefabricated unit-24 feet high and 45 feet wide. Four of the Tainter Gates span the 210-foot gated section at the top of the concrete portion of the dam. Regular flow of water will pass through the 8 sluice gates, which can each pass more than 100 cubic feet of water per second. The tainter gates are used for excess runoff from the reservoir. After the tainter gates were installed, the 18-foot-wide service road was constructed across the top of the dam.
The dam is designed for a flood peak flow of 151,000 cubic feet per second. Prior to construction, maximum flow recorded at the site of the dam was 60,500 cubic feet a second in March, 1956, a year of record floods. There is enough concrete in the spillway section of the dam to build a 300- mile, two-lane highway. The earth and rock portion of the dam represents 300,000 trips to the site by 20-ton trucks.
How the dam works...
The Seneca Power Plant, a pumped-storage hydroelectric plant, contains five major elements: a water intake structure behind the dam; two 15-foot diameter steel pipes from the intake structure, through the dam, to the powerhouse; the powerhouse, housing two reversible pump-turbines, each rated at about 175,000 kilowatts of generating capacity, and one non-reversible turbine of about 30,000 kilowatts capacity; a 22-foot diameter, steel and concrete lined tunnel extending into the mountain for a half-mile; and an upper reservoir for water storage.
Water behind the dam provides the lower pool for the power plant. This water is drawn into the powerhouse through two 15-foot diameter pipes extending through the dam from the intake structure on the upriver side. The pumped-storage reservoir covers some 100 acres to a depth of 64 feet. It is located atop a mountain 800 feet above and a half-mile from the power plant.
Essentially, with the huge water reservoir uphill from the dam, this facility stores the ability to generate large quantities of electricity for later use. The plant installed two 175,000 kilowatt reversible pump- turbines, which were a relatively new development at the time, for both pumping water and generating electricity. During low power demand periods, electricity drives the reversible turbines as pumps lift the water from the reservoir up 800 feet to the upper reservoir.
When peaks in power demand occur, water stored in the upper reservoir can be released, generating electricity as it falls through the same turbines which pump it up hill. Instead of flowing downriver after generating power, as is the usual case, most of the water is sent back into the Allegheny Reservoir behind the dam from which it came. In addition, the Kinzua plant installed a 30,000 kilowatt conventional hydroelectric turbine, to operate from water in the upper reservoir to generate additional electricity. The non-reversible turbine operates only during periods of water discharge.
During the generating operation, one of the reversible turbines returns all discharged water only to the reservoir behind the dam. The other reversible unit discharges either behind the dam or downriver, in keeping with the Army Corps of Engineers river flow requirements. The non-reversible unit only discharges downriver.
What is distinctive in this variable discharge feature of the Seneca Power Plant is that much of the water will be used over and over to generate power. When the Allegheny Reservoir storage must be conserved, the power plant returns all water, except a minimum specified release, to the Allegheny Reservoir storage. When a large downriver discharge is desired, the power plant discharges a large amount of water downstream. The Corps of Engineers reports that there is no significant temperature variation, which could be harmful to fish life and the Allegheny River.
Kinzua Dam Pump Station Reservoir