"...a really big drain called a spillway. And once you see it full of spiraling water, it is hard to take your eyes off it.
For the first time in a decade, January and February have brought so much rain that the lake in the Napa Valley area north of San Francisco has maxed out its water capacity. To prevent flooding, this 72-foot-wide concrete funnel is sucking down the excess.
Spillways come in many shapes and sizes. The one at Berryessa is of the “bellmouth” persuasion, which is also called a morning glory, plug hole or a glory hole....
On Tuesday, water was flowing into the hole at around two million gallons a minute, which is just a small fraction of how fast it can get.
Powerful as it looks, the spillway probably wouldn’t pull you down....It’s a lot of water, but not a lot of velocity....
In the world of spillways, bellmouths like this one are uncommon... Engineers pick them because they can spill a lot of water at one time and still maintain control...There are others spillways of this type around the world, including at the Shing Mun Reservoir in Hong Kong, Hungry Horse Dam in Montana, Nekogahora Pond in Japan and the Ladybower Reservoir in England."