The Monticello Dam, situated in Napa County, California, is famous for its unique spillway known as the “Glory Hole.” This morning-glory-type spillway represents an impressive engineering feat designed to control excess water from Lake Berryessa.
Design and Functionality
Built between 1953 and 1957, the Monticello Dam boasts a distinctive spillway structure due to the narrow canyon it occupies. The Glory Hole is a circular, funnel-shaped spillway with an outer diameter of 72 feet (22 meters) at the lake’s surface, narrowing to approximately 28 feet (8.5 meters) at the outlet. This design effectively manages overflow, channeling excess water safely downstream into Putah Creek. When Lake Berryessa reaches a reservoir elevation of 440 feet (134 meters) above sea level, water starts to flow into the Glory Hole. At full capacity, the spillway can release up to 48,400 cubic feet per second (1,370 cubic meters per second).
Operational History
The Glory Hole functions intermittently, influenced by rainfall and reservoir levels. It notably became operational in February 2017 after a drought period and again in February 2019. Most recently, the spillway was activated on February 10, 2025, following significant winter storms that raised the lake’s water level above the spillway’s edge.
Safety Considerations
Due to the strong suction and turbulence generated when the spillway is in use, swimming or boating near the Glory Hole is strictly forbidden. Safety measures, including buoys and warning signs, are implemented to avoid accidents. Despite these precautions, a tragic event occurred in 1997 when a swimmer was drawn into the spillway and drowned.
Public Interest and Accessibility
The Glory Hole has attracted considerable public attention, especially when it is active. Visitors can safely observe the spillway from designated viewpoints near the dam, particularly along Highway 128. Its striking appearance, reminiscent of a giant bathtub drain, makes it a popular subject for photography and media coverage.
Engineering Significance
The morning-glory spillway at Monticello Dam exemplifies innovative engineering, addressing the challenges posed by the dam’s geographical limitations. Its design has inspired similar structures globally, showcasing the effectiveness of such spillways in managing reservoir overflow in constrained environments.
To explore the latest innovations in water and energy technologies, and discover a wide range of products and solutions from around the world, you can visit the virtual exhibition AQUA ENERGY EXPO which featuring leading companies in water treatment, desalination, and sustainable energy through the following link:
https://aquaenergyexpo.com/
References:
1- A Massive ‘Glory Hole’ in a California Lake Has Returned After 6 Years
https://people.com/a-massive-glory-hole-in-a-california-lake-has-returned-after-6-years-11704793
2- Monticello Dam
https://en.wikipedia.org/wiki/Monticello_Dam
3- Lake Berryessa’s famed ‘glory hole’ is on full display for first time in years
https://www.sfchronicle.com/weather/article/lake-berryessa-glory-hole-20217506.php
4- Northern California’s famed ‘Glory Hole’ spillway is used for first time in years
https://www.latimes.com/california/story/2025-02-10/glory-hole-spillway-reopens-norcal-storms
5- Morning Glory Spillway
https://www.researchgate.net/publication/347869703_Morning_Glory_Spillway
