head through partial gate openings. In these cases, a special valve or sluice gate is required to pass the
flow safely without equipment damage.
Turbine Pulsing. TVA began providing minimum flows via turbine pulsing below 8 dams
(Appalachia, Boone, Cherokee, Douglas, Fontana, Fort Patrick Henry, Ocoee 1, and Wilbur) in 1991.
Minimum flows provided are typically in the range from 0.5 to 1.5 the natural summertime 7Q10 at the
Small Turbine Units. TVA has small units at Tims Ford, Nottely, and Blue Ridge dams,
completed 1986 and 1993. The small unit at Tims Ford is attached to the powerhouse exterior. The
91.44 cm (36 inch) diameter mini-penstock is tapped into the sluice way adjacent to the powerhouse.
The small unit provides 2.12 m3/s (75 cfs) to the downstream channel and generates 500 kW. The
turbine is a salvaged pump from a nuclear plant application. Installing the pump backwards allows it to
act like a turbine and generate electricity.
The small unit at Nottely is located on the right bank, about 45.8 m (50 yards) downstream of
the powerhouse. The 36-inch diameter mini-penstock is flanged to the housing where an old regulating
sleeve valve used to be. The small unit provides 1.42 m3/s (50 cfs) to the tailwater reach and generates
400 kW. The hydropower machinery is also a backward-running pump obtained from a nuclear plant
The small unit at Blue Ridge uses a 121.9 cm (48-inch) diameter mini-penstock was attached to
the surge tank of the main unit and routed 45.8 m (50 yards) downstream to the small unit turbine. The
small unit provides 3.26 m3/s (115 cfs) to the tailwater reach and generates 600 kW.
Reregulation Weirs . TVA has been developing, testing, designing, and constructing
innovative weirs to provide minimum flows since 1983. The first TVA weir was a unique experimental
flow reregulation weir in the Clinch river below Norris Dam. The original weir was constructed of
galvanized steel gabion baskets. It was 1.52 m (5 ft) high, 6.4 m (21 ft) in upstream to downstream
dimension, and 128.9 m (423 ft) long, and had 54 30.48 cm (12-inch) diameter steel pipes passing
through it for discharge control (Shane, 1985). The weir deck had to be paved with concrete in March
1987 because of excessive deterioration of the gabion baskets. This modification resulted in the
emergence of a recirculating flow pattern in the tailwater of the weir when only one turbine at
Norris was discharging. The recirculation was eliminated by addition of a rock filled wood crib
structure to the downstream end of the weir, which allowed water to flow through the structure as it did
before the deck was paved. The through flow eliminated any recirculation (Loiseau, 1987).
The experimental weir structure was replaced with a permanent timber crib design in 1995.
The new weir is a stepped timber crib filled with loose rock resting on a concrete pad and lined with