1944 90mw Norfork Dam on North Fork River near Salesville, AR

(Satellite)

USACE, Little Rock District
Here’s video of the Norfork Dam Syphon Tube on Aug. 8, 2023. The syphon tube was installed as part of the White River Minimum Flows Project. Releases from the syphon are intended to increase the downstream wetted perimeter below Norfork Dam.
Brad Bates: It appears to be aerating the flow.
Josh Draper: What's the flow rate on that?
Tyler Nickle: Josh Draper 185 cubic feet/second.

They need to use the syphon because none of the turbines are running because of "multiple data issues." [swl-wc]

USACE

"The length of the dam is 2,624 feet. The spillway gross crest length is 568 feet, and there are twelve spillway gates. Elevation to the top of the dam is 590 feet. At a normal lake level of 552 feet mean sea level (msl), the lake covers 22,000 acres and has a shoreline of 380 miles. The lake’s level at the top of the flood pool is 580 feet msl, covers 30,700 acres with a shoreline of 510 miles, and contains 732,000 acre-feet of water....Approximately 1.5 million cubic yards of concrete were required, and the dam was said to be the fifth-largest concrete dam in the country at the time." It was one of the oldest USACE multi-purpose concrete structures. It was built with four 18' penstocks, but two of them are plugged with concrete. [EncylopediaOfArkansas]

This source calls it the country's sixth largest concrete dam.

 

USACE Facebook, Jun 9, 2020
"Each gate is open a half of a foot. The total spillway and hydropower release is just above 10,000 cubic feet per second. This is a non-damaging release. The peak rainfall runoff from Tropical Storm Cristobal poured into the reservoir around 32,000 c.f.s. Without the dam, flows downstream would be roughly 3 times higher."

OzarksHistory, 1 of several construction photos

HydroReview, photo courtesy Voith Hydro
The two turbine-generator units are being upgraded from 31.3mw to 46.5mw. And "the water quality below the dam will be improved thanks to Voith Hydro’s dissolved oxygen enhancement technology."

tklo
A single turbine releases 2,900cfs.

This view provides an overview of the downstream part of the syphon.

Brandon Lawrence, May 2020

Improving the aerationof the river explains the design of this nozzle.

garverusa
The 42" [1.1m] pipe has the inlet far enough below the surface of the lake that it draws cooler water out of the reservoir. A steady stream of aeriated, cool water helps support "the area’s world-class fishery."