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Thirlmere Reservoir and Dam
Lake Thirlmere, 8km south of Keswick, Cumbria, UK
Thirlmere Reservoir and Dam
associated engineer
George Henry Hill
date  1890 - 1894
era  Victorian  |  category  Dam/Reservoir  |  reference  NY308189
ICE reference number  HEW 607
photo  ICE R&D Fund
Twin lakes in the Cumbrian hills have been subsumed into Thirlmere Reservoir, the solid masonry/concrete gravity dam for which was completed in 1894.
The reservoir covers 320 hectares and impounds some 36,900 million litres of water, gathered from a catchment area of 4,450 hectares. The dam's overflow cill raises the water level some 16m above the average level of the two original lakes. The water is taken to Manchester, 160 kilometres away, through a draw-off well at the southern end and a tunnel under Dunmail Rise.
The dam is 261m long and has a maximum height of 20.1m, though its foundations are as much as 17.7m below the present toe level. It is 5.5m wide at the crest, where a 5m-wide road runs the length of the dam between stone parapet walls. There are commemorative plaques located on a raised section of the outer wall at the centre.
The dam is made of mass concrete and masonry. Behind the masonry faces — Annan sandstone on the downstream face and Longridge stone on the upstream face — the core of the dam consists of large rocks (‘plums’) embedded in concrete.
Unusually for solid dams of this period, the overflow is not an integral part of the dam's structure. Overflow water passes through a hole located at the west end.
Dam construction: Morrison & Mason, Glasgow
Research: PD and AJD
"The Thirlmere Works for the water supply of Manchester" by G.H. Hill, Minutes of the Proceedings of Institution of Civil Engineers, Vol 126, 1896
"Thirlmere Water — a hundred miles, a hundred years" by N. Hoyle and K. Sankey, Centrwrite, Bury, 1994
reference sources   CEH North

Thirlmere Reservoir and Dam