At first glance you might mistake a bell-mouth spillway for a watery vortex into another dimension. What can only be described as a giant hole in the water is actually a method for controlling the release of flows from a dam or levee into a downstream area. These spillways help prevent floods from ‘dam’-aging or destroying a dam.
A spillway is a structure used to provide for the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed
Spillways release floods so that the water does not overtop and damage or even destroy the dam. Except during flood periods, water does not normally flow over a spillway.
In contrast, an intake is a structure used to release water on a regular basis for water supply, hydroelectricity generation, etc.
Floodgates and fuse plugs may be designed into spillways to regulate water flow and dam height.
Other uses of the term “spillway” include bypasses of dams or outlets of a channels used during highwater, and outlet channels carved through natural dams such as moraines
Some spillways are designed like an inverted bell so that water can enter all around the perimeter. These uncontrolled spillway devices are also called:morning glory, plughole, glory hole, or bell-mouth spillways.
In areas where the surface of the reservoir may freeze, bell-mouth spillways are normally fitted with ice-breaking arrangements to prevent the spillway from becoming ice-bound
LADY BOWER RESERVOIR
The images above are from the spillways located at the Ladybower Resevoir.
The Ladybower Reservoir is a large Y-shaped reservoir, the lowest of three in the Upper Derwent Valley in Derbyshire, England.
The River Ashop flows into the reservoir from the west; the River Derwent flows south, initially through Howden Reservoir, then Derwent Reservoir, and finally through Ladybower Reservoir.
Its longest dimension is just over 3 miles (5km), and at the time of construction it was the largest reservoir in Britain (1943)
The Monticello Dam is a dam in Napa County, California, United States constructed between 1953 and 1957.
It is a medium concrete-arch dam with a structural height of 304 ft (93 m) and a crest length of 1,023 ft (312 m).
It contains 326,000 cubic yards (249,000 m³) of concrete. The dam impounded Putah Creek to cover the former town of Monticello and flood Berryessa Valley to create Lake Berryessa, the second-largest lake in California.
The capacity of the reservoir is 1,602,000 acre•ft (1,976,000 dam³). Water from the reservoir is supplied mostly to the North Bay area of San Francisco.
The dam is noted for its classic, uncontrolled spillway with a rate of 48,400 cubic feet per second (1370 m³/s) and a diameter at the lip of 72 ft (22 m).