Seen from Steel Fell at the southern end of the lake
|Location||Lake District National Park, Cumbria, England|
|Primary inflows||Launchy Gill, Dob Gill, Wyth Burn, Birkside Gill|
Thirlmere Aqueduct (engineered off-take);St John's Beck (natural)
|Max. length||6.05 km (3.76 mi)|
|Max. width||0.178 km (0.111 mi)|
|Surface area||3.25 km2 (1.25 sq mi)|
|Max. depth||40 metres (131 ft)|
|Shore length1||15 km (9.3 mi)|
|Surface elevation||178 m (584 ft)|
|1 Shore length is not a well-defined measure.|
Thirlmere is a reservoir in the Borough of Allerdale in Cumbria and the English Lake District. It runs roughly south to north and is bordered on the eastern side by the A591 road and on the western side by a minor road. It occupies the site of two former natural lakes (or - on a different analysis - a single lake with a narrow fordable waist). In the 19th century Manchester Corporation constructed a dam at the northern end, raising the water level, flooding the valley bottom, and creating a reservoir to provide the growing industrial city of Manchester with water supplies via the 96 mile-long Thirlmere Aqueduct. The reservoir and the aqueduct still provide water to the Manchester area.
Before the construction of the reservoir there was a smaller natural lake, known by various names including Leathes Water, Wythburn Water Thirle Water, and Thirlmere. The Ordnance Survey six-inch map of 1862 shows a single lake (Thirlmere) with its narrowest point at Wath Bridge roughly level with Armboth; at this point "The water is shallow and crossed by a bridge, so that piers are easily built and connected with little wooden bridges, and that difficult problem in engineering - crossing a lake - accomplished" and the map shows both a bridge and a ford between the west and east banks. ('Wath' = 'ford' in Cumbrian placenames: the 'Bridge' itself can be seen in a photograph of the pre-reservoir valley: it was repeatedly carried away by floods (eg in November 1861.)) Because of this constriction there were "practically at low water two lakes, the river connecting them being crossed at the Narrows by a little wood and stone bridge", and the natural lake is sometimes characterised as two lakes.
In 1863, a pamphlet urged that Thirlmere and Haweswater should be made reservoirs, and their water conveyed (via Ullswater (used as a distributing reservoir)) 240 miles to London to supply it with two hundred million gallons a day of clean water; the cost of the project was put at ten million pounds. By 1876, the scheme had grown to include a branch feeder from Bala Lake; the cost had risen accordingly to £m 13.5. Nothing came of this, but both Manchester and Liverpool were becoming concerned that their existing water supplies would be rendered inadequate by their growth, and seeking supplies from further afield. In 1875 John Frederick Bateman suggested that Manchester and Liverpool should supply themselves with water from Haweswater and Ullswater (made reservoirs) as a joint undertaking. This was rejected by Manchester Corporation who felt the interests of the city required its water supply to be independent of that of any other city: in 1877 they proposed instead to supply Manchester with water from a Thirlmere reservoir.
There was strong local opposition to the construction of the lake and the Thirlmere Defence Association (TDA) was formed to oppose the parliamentary act which was required before work could begin. The TDA opposed on the basis that raising the water level by 50 feet would submerge the dramatic cliffs which then surrounded the lake and a receding shoreline in summer would expose the smelly and unsightly lake bed. The organisation managed to stall the Bill in Parliament in 1878, but the Act was passed in 1879.
The water level in the valley was raised by construction of a dam by Manchester Corporation Waterworks at the northern end of Thirlmere, in 1890–1894. The reservoir supplied water to Manchester via the Thirlmere Aqueduct which is 95.9-mile (154.3 km). John Frederick Bateman was advisor to the corporation for both projects.
The creation of the reservoir flooded the village of Wythburn and the hamlet of Armboth, with the loss of a school, vicarage, inns, farms and houses. Only the hamlet of Steel End (at the south end of the present Thirlmere) and Wythburn Church (above the reservoir on the east) remained. New housing was created at Fisher End and Stanah. east of the northern end of the reservoir.
" ...Leathes-Water' called also 'Thirlmere' or 'Wythburn-water' 1769...Probably 'the lake with/at the narrowing' from OE þyrel 'aperture', pierced hole' plus OE mere 'lake'. The lake had an especially narrow 'waist', spanned by a causeway and bridges", before the dam was built. (OE = Old English.)
- Ritvo, Harriet. The Dawn of Green: Manchester, Thirlmere, and Modern Environmentalism. Chicago: The University of Chicago Press, 2009, ISBN 978-0-226-72082-1.
|Wikimedia Commons has media related to Thirlmere.|
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