The dam was constructed between 1953 and 1957 and is known as The Glory Hole. Monticello Dam is located west of Sacramento, California. The Hole is used when a dam is at full capacity and water needs to be drained from the reservoir.

The solid concrete-arch structure stands 93 m tall and 312 m long – it’s the largest in the world of this type of spillway, contains 249,000 m³ of concrete. This type of spillway is basically a giant cement funnel. It consumes 362,000 gallons of water per second.
The funnel’s largest diameter is 72 feet and narrows to about 28 feet. It is designed to handle a maximum of 14,400 feet ³ of water every second, which occurs when the lake level rises to 15.5 feet above the level of the funnel. For more photos click here http://fogonazos.blogspot.com/2007/02/largest-drain-hole-ever.html