Plug hole

[The spillway at Monticello Dam in operation, February 19, 2017. Snapped by Jeremy Brooks, the name of at least two photographers]

This being prompted by a bit of news from the Daily Mirror, via Microsoft News. Although news is a bit of a misnomer, as this plug hole is well over fifty years old. About 22m in diameter at the top, 9m at the bottom. Maybe 70m deep. Most of the time the concrete rim of the plug hole is visible above the water.

We have one of these plug holes in Derbyshire, as reported by the BBC at reference 3, although it is not as big as the Californian one. On the other hand, there are two of them, one on each side of the dam. An entirely respectable way to keep dammed waters down, although I think open spillways are a lot more common.

And I have learned from reference 4 that the Dartmoor spillway noticed at reference 5 is an example of a labyrinth spillway. I think the idea is to break the force of the water as it flows out of the reservoir.

References

Reference 1: https://en.wikipedia.org/wiki/Monticello_Dam. More information.

Reference 2: https://daviswiki.org/Morning_Glory_Spillway. Still more.

Reference 3: https://www.bbc.co.uk/news/uk-england-derbyshire-50157693.

Reference 4: https://en.wikipedia.org/wiki/Spillway. The science of spillways is non-trivial.

Reference 5: https://psmv4.blogspot.com/2021/05/round-pond.html. The spillway at Venford Reservoir.