One big duct!

Lab outing to the biggest duct of all – the glory hole spillway at Lake Berryessa west of Davis – a once in a rare-rainfall lifetime chance to see overtopping. This sucker is big – 22 meters diameter at the inlet behind us!! Yet, eerily quiet…..

From Wikipedia: Near the dam on the southeast side of the reservoir is an open bell-mouth spillway, 72 feet (22 m) in diameter, which is known as the Glory Hole. The pipe has a straight drop of 200 feet (61 m),[3] and the diameter shrinks down to about 28 feet (8.5 m). The spillway has a maximum capacity of 48,000 cfs (1360 m³/s). The spillway operates when there is excess water in the reservoir; in 2017 after heavy rains it started flowing, for the first time since 2006.[4] In 1997 a woman was killed after being pulled inside the spillway.[3]