Lady Bower Bellmouth (plug hole)

A great place to visit if your running between Manchester and Sheffield on the "Snake Pass" is Ladybower Reservoir, this 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.
As well as being a nice place to walk around, there is always a burger van on the main road layby or you can use the cafe sat at the top of where Howden & Lady Bower reservoirs meet. But be careful when driving here plenty of police with hand held and unmarked speed camera vans

Lady Bowers design is unusual in having two totally enclosed bellmouth overflows (think of a big plug hole) at the side of the main retaining wall. Its called a bellmouth as it is designed like an inverted bell so that water can enter all around the perimeter. The two on Lady Bower are made of stone and of 80 feet (24 m) diameter with outlets of 15 feet (4.6 m) diameter that each discharges via its own valve house at the base of the dam. The overflows originally had walkways around them but they were dismantled many years ago. The bell mouths are often completely out of the water and only rarely submerged, often after heavy rainfall or flooding.

The water is used for river control and to compensate for the water retained by all three dams, along with supply into the drinking water system and hydroelectricity generation.

Drinking water is pumped to the Bamford water treatment works and treated water flows down the 28 miles (45 km) long Derwent Valley Aqueduct to a covered service reservoir at Ambergate to supply clean water to the cities of Derby and Leicester. The aqueduct passes through the park of Chatsworth House on its way south. The path of the aqueduct is marked by a series of distinctive valve houses built of stone & domed steel access chambers. A tunnel carries some of the water from the Derwent Valley eastwards through the hill and into the lower of the two Rivelin Dams in order to supply Sheffield.

Lady Bowers main claim to fame is being the training place for 617 Squadron "The Dam Busters"