Editing Ladybower Reservoir (section)

==Design and construction==
[[File:Ladybower Reservoir viaducts - April 2021.jpg|thumb|left|alt=Ladybower Reservoir, showing two viaducts carrying roads over the water|The Ashopton Viaduct (left) carries the [[Snake Pass]] [[A57 road]] and the Ladybower Viaduct carries the A6013 to [[Bamford]] over the reservoir.]]
Ladybower was built between 1935 and 1943 by the [[Derwent Valley Water Board]] to supplement the other two reservoirs in supplying the water needs of the [[East Midlands]]. It took a further two years to fill, which was done by 1945. The dam differs from the Howden Reservoir and Derwent Reservoir in that it is a clay-cored earth embankment and not a solid masonry dam. Below the dam is a cut-off trench {{cvt|180|ft}} deep and {{cvt|6|ft}} wide filled with concrete, stretching {{cvt|500|ft}} into the hills each side, to stop water leaking around the dam. The dam wall was built by Richard Baillie and Sons, a Scottish company. The two viaducts, Ashopton and Ladybower, needed to carry the [[trunk road]]s over the reservoir, were built by the London firm of Holloways, using a steel frame clad in concrete. The project was delayed when the Second World War broke out in 1939, making labour and raw materials scarce, but construction was continued due to the strategic importance of maintaining supplies. [[George VI|King George VI]], accompanied by his wife, [[Queen Elizabeth The Queen Mother|Queen Elizabeth]], formally opened the reservoir on 25 September 1945.

During the 1990s, the wall was raised and strengthened to reduce the risk of over-topping in a major flood. The original dam wall contains 100,000 tons of concrete, over one million tons of earth, and 100,000 tons of [[clay]] for the core. The upstream face is stone-faced. Materials were brought to the site on the Derwent Valley Water Board's own branch line and their sidings off the mainline in the [[Hope Valley, Derbyshire|Hope Valley]].
[[File:Ladybower Reservoir.jpg|thumb|left|The reservoir]]
The dam's design is unusual{{efn|Although there are not many dams of this design, examples include [[Pontsticill Reservoir]] in Wales and [[Monticello Dam]] in California.<ref name=BBC19/>}} in having two totally enclosed [[Spillway#Bell-mouth spillways|bellmouth spillway]] overflows (locally named the "plugholes") at the side of the wall. These are stone and of {{cvt|78|ft}} diameter with a drop of {{cvt|66|ft}}. The plugholes regulate water levels in the reservoir by draining away excess water when they overflow. The water is then carried to the River Derwent through tunnels.<ref name=BBC19/> The overflows originally had walkways around them,<ref>{{Cite web |title=Ladybower Reservoir, c 1945 |url=https://picturethepast.org.uk/image-library/image-details/poster/ptpd300443/posterid/ptpd300443.html |access-date=28 October 2019 |website=Picture the Past |language=en}}</ref> but they were dismantled many years ago. The plugholes typically overflow in winter months if there has been wet or snowy weather in the nearby hills. According to [[Severn Trent]], the reservoir’s operating company, the overflowing plug holes attract many visitors each year.<ref>{{cite news|access-date=2022-01-15|first=Amy|last=Woodfield|title=Ladybower Reservoir's overflowing 'plug holes' attract photographers|url=https://www.bbc.com/news/uk-england-derbyshire-59966942|publisher=BBC News|date=14 January 2022}}</ref>