Seen above is the Morning Glory Spillway in Napa County’s Monticello Dam. The dam creates Lake Berryessa, a 1.6 million acre-foot (about 2 million cubic meter) man-made body of water which serves as a recreational site featuring swimming, boating, fishing, hiking, and other outdoorsy activities. To make sure that the surrounding roads and area do not flood, there’s a spillway. When the water level goes over the spillway’s lip, it instead ends up flowing, rapidly, down the hole and into the drainage basin below. At the base is a hydroelectric power plant whose three generators provide electricity to the San Francisco area.
Which is nothing special. There are many spillways out there, designed to do basically the same thing the Morning Glory Spillway does. What makes the Morning Glory Spillway particularly interesting is its size. An Olympic-sized swimming pool holds roughly 88,000 cubic feet (or about 2,500 cubic meters) of water. The Morning Glory Spillway can drain that in under two seconds.
The spillway is effectively a very large funnel. Its mouth is 72 feet in diameter (seen above, dry) and runs 400 feet, tapering to a diameter of about 28 feet at the bottom opening. When it is dry, it serves a secondary purpose — as an illegal skate park for skateboarders.
The only problem? Even when the spillway itself is dry, the drainage basin typically is not, so the skateboarders need to take a raft to get there.
via Now I Know