The weird hole at the centre of a reservoir

The Glory Hole spillway at Monticello Dam in operation, February 19, 2017.
The Glory Hole spillway at Monticello Dam in operation, February 19, 2017. Wikipedia
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There is a weird hole at the centre of Lake Berryessa reservoir at the top of Monticello Dam in Napa County, California, United States. When the water rises too high in the dam, it seems to fall into what looks like a hole constructed on the surface of the lake. The locals have given it the moniker ‘Glory Hole’.

Monticello Dam was constructed between 1953 and 1957 and engineers at the time also wanted to construct a spillway to control the flow of water out of the dam. Usually, such a spillway is a side chute but the Vaca mountains, where the dam is situated, have narrow cliffs, making it difficult for water to flow out of a side chute. So, the engineers built one that went downwards like a bathtub drain. They expected it to be used once every five decades, however, it has already been utilised three times since the start of this century, because of more frequent and intense rains due to a changing climate.

Just peeking over the top of the glory hole naturally for the first time in over a decade, February 16, 2017.

Just peeking over the top of the glory hole naturally for the first time in over a decade, February 16, 2017. Wikipedia

 

Such types of spillways are known as bell-mouth and they have been used to control the water level of various other dams around the world. The Glory Hole is 72 feet or 22 m in diameter at lake level and narrows down to about 28 feet or 8.5 m at the exit. During peak level, the spillway can drain 48,400 cubic feet per second (1,370 m3/s). This occurs when the lake level rises to 15.5 feet (4.7 m) above the level of the funnel.

Glory Hole spillway on October 10, 2009, when the water was 32.24 feet (9.83 m) below the crest.

Glory Hole spillway on October 10, 2009, when the water was 32.24 feet (9.83 m) below the crest. Wikipedia

 

And this gives us a very weird but spectacular man-made site to behold. It has now become quite the tourist attraction, with hundreds of people visiting to see it in action during particularly wet seasons. The last time the reservoir naturally spilled through the glory hole was on the afternoon of February 26, 2019.

Previously, when a number of storms caused the lake level to rise 35.5 inches since January 1, 2017, and the reservoir was almost brimming over, a number of local boaters wanted to see the event. They generated enough wake to cause it to spill on February 13, 2017 for a brief period. Eventually, the reservour did fill up and water drained down Glory Hole for the first time in over a decade on February 16, 2017.

Swimming or boating near the Glory Hole is prohibited and the whole reservoir is roped off. Plus the speed at which the water flows into the hole is not much and most people could easily swim against it. The only known case of death from the drain occurred in 1997, when Emily Schwalek of Davis died after being caught in the current while swimming near the Glory Hole and being swept down the pipe. She held on to the rim for about 20 minutes but could not hang out long enough for rescue to arrive. 

There was however the incident of the intrepid cormorant, which swam into the hole and apparently survived.

Definitely worth a visit.

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I am a Chartered Environmentalist from the Royal Society for the Environment, UK and co-owner of DoLocal Digital Marketing Agency Ltd, with a Master of Environmental Management from Yale University, an MBA in Finance, and a Bachelor of Science in Physics and Mathematics. I am passionate about science, history and environment and love to create content on these topics.