Unlike traditional spillways--essentially chutes or channels allowing the controlled release of water from a dam--the Monticello Dam at Lake Berryessa has what is known as a glory hole spillway (also called morning glory or bell mouth after its shape). At the height of the drought, this spillway looked like a concrete donut on a tongue of land sticking into the lake (see photo here). Now it brings to mind a massive bathtub drain--and it acts essentially the same way. Water rushes down a 275 ft. concrete pipe and exits on the far side of Monticello Dam into Putah Creek.
The statistics are truly impressive: The glory hole is 275 ft. deep and 72 ft. wide and can release more than 300,000 gallons of water per second. In fact, the suction is so strung that it creates wind that you can feel as you stand by the side of the road.