The Owyhee Dam has a unique spillway known as "The Glory Hole" located partway up the dam that utilizes a 60-foot (18 m) in diameter tunnel to send excess water to the river below.  This spillway acts like a sink drain during high-water periods.

Check out the links below to watch some aerial videos of the spillway in action courtesy of The Idaho Statesman & The Bureau of Reclamation.

https://www.youtube.com/watch?v=DtHvG_5RWRA

https://www.idahostatesman.com/news/northwest/idaho/article142848289.html

Ring Gate during construction 1928-1932

Ring Gate during construction 1928-1932

High water period with water spilling through "Glory Hole"

Water spilling into the river from the "Glory Hole"

Owyhee Dam "Glory Hole"

Visit the Bureau of Reclamation Site for more Project Details:

https://www.usbr.gov