Lake Vyrnwy

Lake Vyrnwy
Welsh:Llyn Efyrnwy
View overlooking Lake Vyrnwy showing the full extent of the lake
Lake Vyrnwy
Location	Wales
Coordinates	52.78°N 3.50°W/52.78; -3.50
Lake type	Reservoir
Primary inflows	River Vyrnwyand other small streams
Primary outflows	River Vyrnwy
Managing agency	Hafren Dyfrdwy subsidiary ofSevern Trent
Built	1881–88
Max. length	7.64 kilometres (4.75 mi)
Max. width	0.80 kilometres (0.5 mi)
Surface area	4.54 square kilometres (1,121 acres)
Max. depth	26 metres (84 ft)
Water volume	59.7 gigalitres (13.125×10^9imp gal)
Shore length1	19 kilometres (12 mi)
1Shore length isnot a well-defined measure.

Lake Vyrnwy(Welsh:Llyn Efyrnwy,pronounced[ɛˈvərnʊɨ]orLlyn Llanwddyn) is areservoirinPowys,Wales, built in the 1880s forLiverpool Corporation Waterworksto supplyLiverpoolwith fresh water. It flooded the head of theVyrnwy(Welsh:Afon Efyrnwy) valley and submerged the village ofLlanwddyn.

The Lake Vyrnwy Nature Reserve and Estate that surrounds the lake is jointly managed by theRoyal Society for the Protection of Birds(RSPB) andHafren Dyfrdwyand is a popular destination for ornithologists, cyclists and hikers. The reserve is designated as anational nature reserve,aSite of Special Scientific Interest,aSpecial Protection Area,and aSpecial Area of Conservation.

Geography

Lake Vyrnwy is areservoirinPowys,Wales, created in 1888 by flooding the head of theRiver Vyrnwy(Welsh:Afon Efyrnwy) valley. The river flows from the dam intoShropshirewhere it converges with theRiver Severnnear the village ofMelverleyon the Welsh border and outflows into theBristol Channel.

When the reservoir is full, it is 26 metres (84 ft) deep, contains 59.7 gigalitres (13.125×10^⁹imp gal), and covers an area of 4.54 square kilometres (1,121 acres),the equivalent of around 600football pitches.The lake has aperimeterof 19 kilometres (12 mi) with a road that goes all the way around it. Its length is 7.64 kilometres (4.75 mi).

311 brooks, waterfalls and rivers flow into the lake and are named after the mountains or hillsides they flow from. The main ones, clockwise from the west side of the dam, are namedAfon Hirddu, Eunant, Afon Eiddew, Afon Naedroedd, Afon CedigandAfon Y Dolau Gwynionew.

On the northern edge of the lake is a small hamlet calledRhiwargorwhere the rivers Afon Eiddew and Afon Naedroedd meet. Up the valley of Afon Eiddew is a waterfall known locally as Pistyll Rhyd-y-meincau, commonly known as Rhiwargor waterfall.

Climate

Climate data for Lake Vyrnwy No 2, Elevation: 360 m (1,181 ft), 1991–2020 normals
Month	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Mean daily maximum °C (°F)	5.7 (42.3)	6.0 (42.8)	7.9 (46.2)	10.7 (51.3)	13.7 (56.7)	16.3 (61.3)	18.0 (64.4)	17.5 (63.5)	15.3 (59.5)	11.7 (53.1)	8.4 (47.1)	6.3 (43.3)	11.5 (52.6)
Daily mean °C (°F)	3.4 (38.1)	3.5 (38.3)	5.0 (41.0)	7.1 (44.8)	10.0 (50.0)	12.7 (54.9)	14.4 (57.9)	14.2 (57.6)	12.2 (54.0)	9.1 (48.4)	6.1 (43.0)	4.0 (39.2)	8.5 (47.3)
Mean daily minimum °C (°F)	1.2 (34.2)	1.0 (33.8)	2.0 (35.6)	3.6 (38.5)	6.2 (43.2)	9.0 (48.2)	10.9 (51.6)	10.9 (51.6)	9.1 (48.4)	6.6 (43.9)	3.8 (38.8)	1.7 (35.1)	5.5 (41.9)
Averageprecipitationmm (inches)	190.1 (7.48)	162.5 (6.40)	127.0 (5.00)	96.8 (3.81)	99.9 (3.93)	98.6 (3.88)	98.7 (3.89)	110.4 (4.35)	121.2 (4.77)	179.9 (7.08)	179.4 (7.06)	214.5 (8.44)	1,679 (66.09)
Average precipitation days(≥ 1.0 mm)	18.3	14.9	15.2	13.3	13.4	12.6	13.6	14.7	14.1	17.5	18.8	19.1	185.3
Source:Met Office

Construction

The dam under construction,c. 1885

The dam looking east, showing compensation water being released from the reservoir

Water flowing over the crest of the dam

Rhiwargor Falls on the Lake Vyrnwy Estate

In 1879,George Deaconwas instructed to prepare the parliamentary plans for the Vyrnwy Dam. The valley was chosen because of its size, favourable geology and its source, theRiver Vyrnwy,having a largewater catchmentarea.

Thomas Hawksleywas appointed as engineer-in-chief and prepared the design for a stone dam.Dam construction with great blocks ofWelsh slatestarted in 1881 and was completed in 1888. Hawksley resigned in 1885 because of a conflict with George Deacon who was appointed as joint engineer.The dam was the first large stone-built dam in theUnited Kingdomand cost £620,000 (equivalent to £70 million in 2019).Earlier dams in Britain had been built using great earth embankments to hold back the water.In 1889, shortly after completion, the lake was stocked with 400,000Loch Leventrout.

Between 1881 and 1892 the aqueducts carrying water to Liverpool were constructed.

Construction of the dam flooded the village ofLlanwddyn.The residents of the village were not consulted about the proposal for a dam and opposed the plan. Their relocation involved the demolition of a church, two chapels, three inns, ten farmhouses, and 37 houses. A new settlement to house them was built lower down the valley by Liverpool Corporation.

Description

The Vyrnwy dam is 44 metres (144 ft) high from the bottom of the valley, and 39 metres (128 ft) thick at the base; it is 358 metres (1,175 ft) long and has a road bridge running along the top. It is decorated with 31 arches each spanning 7.3 metres (24 ft) and two small towers each with four corner turrets rising 4.3 metres (14 ft) above the road surface. The dam was the first to be constructed with drainage tunnels designed to prevent a build up of pressure beneath the base. It is listed as aGrade I historic buildingbyCadw.

The dam was the first to carry water over its crest instead of in a channel at the side. At the bottom of the dam is a body of water known as astilling basinnecessary to absorb the energy when the water flows over the crest and into the valley, and to stop the water eroding the foundations of the dam.

A power house located under the west tower contains an electrical generator driven by water leaving the reservoir. Beforemains electricityarrived in the 1960s this was the area's only source of power.

About 1,200 metres (0.75 mi) from the dam is the reservoir'sstraining tower.Standing only 30 metres (98 ft) from the shore, its purpose is to filter or strain out material in the water with a fine metal mesh, before the water flows along theaqueductto Liverpool. Its architecture representsGothic revival,built at the same time as the dam. The tower as a whole is 47 metres (154 ft) tall, 32 metres (104 ft) of which is above top water level, and is topped with a pointed copper-clad roof, coloured light green.

The west and east towers release compensation water into the River Vyrnwy through huge valves; the river would dry up unless a minimum flow was maintained. Depending on the levels downstream, the reservoir can release from 25 to 45 Ml (5 to 10 million imp gal) of compensation water daily. The flow is measured byNatural Resources Walesat a weir a few hundred metres downstream.

Water supply

A sideview of the dam (2009)

TheGothic revivalstraining tower

19th century

The water from Lake Vyrnwy is carried 109 kilometres (68 mi) in theVyrnwy Large Diameter Trunk Main(LDTM) aqueduct which originally consisted of two pipelines, made largely ofcast iron.To help maintenance work on the 2.7 metres (9 ft) diameter cast-iron tunnel which took the aqueduct under theMersey,riveted steel piping was also used, which was to become the norm for trunk water-main piping.

The aqueducts cross the valley floor nearPenybontfawrand then runs north ofLlanrhaeadr-ym-Mochnantand Efail-rhyd on the north-east of theTanat Valley.The aqueducts are largely underground although there are some visible surface features including air valves, the Cileos valve house, the Parc-uchaf balancing reservoirs, and a deep cutting to the west ofLlanrhaeadr-ym-Mochnant.

Brick and concrete-lined tunnels carried pipes atHirnant,CynynionandLlanforda,and a fourth was later added at Aber, so that the Hirnant tunnel could be made accessible for maintenance.

20th century

From 1926 to 1938 the first section of a third pipeline was laid using bituminous-coated steel.in 1946, a fourth pipeline was added south ofOswestryto increase capacity to 227 million litres per day.

In 1978–81, the pipe crossings beneath theMerseyand theManchester Ship Canalwere reorganised. After privatisation of the water companies, responsibility for the Vyrnwy Dam and associated structures fell toSevern Trent Water,and since 2018 to its subsidiary companyHafren Dyfrdwy. The rights to the water abstraction are withUnited Utilitiesfor drinking water supply toLiverpool.

21st century

In 2013,United Utilitiescommenced a major refurbishment of the entire 240 km (150 mi) of theLDTMaqueduct, which was scheduled for completion in 2020. As of 2014 water provision relied on three parallel, 80 km long gravity pipelines, 1.1 metres (42 in) in diameter delivering up to 230,000 cubic metres (50×10^⁶imp gal) per day into reservoirs atPrescot,east of Liverpool, which supplied customers in Cheshire and Merseyside.

Nature reserve and conservation

Lake Vyrnwy is a designatedNature Reserve.TheRSPBhas severalbird hidesaround the lake, where a number of rare species of birds are known to be breeding, including theperegrine falcon,thepied flycatcher,thecommon redstart,theEurasian siskinand thewood warbler.Every spring they host adawn chorustour.

Around 90 species of bird have been recorded as breeding on the reserve, and six species of bat, including thepipistrelleand brown long-eared bat.Butterflyspecies include purple hairstreaks, commas and peacocks.Dragonfliesinclude golden ringed, common hawker and four spotted chaser.

Managing the moorland helps improve the habitat forred grouseand theshort-eared owl. Heathermoorlandwhich grows on the mountains around the lake is nowbeing restored. In the past, heather was burnt, cut and the seeds collected to be sowed where the heather has gone. Burning at the Lake Vyrnwy moorland is no longer carried out, as the burning can have negative consequences for water management, namely water colouration.

Sheep, cattle and ponies also graze on the heather, managed by tenant farmers who farm the moorland in accordance with organic agriculture.

Broadleaf trees are being planted to replaceconiferoustrees, and man-made features such ashedgerowsanddry-stonewalls are also being restored, and wildflower areas are being restored to help insects, birds and other wildlife.

Tourism

Wood sculpture

Llanwddyn has had since 1995 a sculpture park in the valley below the dam, containing many wooden carved works. There are large wooden picnic benches in the shape of leaves and trees on the west side of the lake at Llechwedd Ddu. Near the old village on the beach is a sculpture of dolphins which, when the lake rises in a flood, appear to be jumping out of the water. Severaltotemsare carved into standing trees and re-erected fallen trunks.

Recreation

Activities in the area include sailing, hiking onGlyndŵr's Way,rock climbing, cycling, walking and horse riding.TheLake Vyrnwy Half Marathonis conducted annually. TheRSPBhave laid out sevenwaymarkedtrails ranging from 2 to 9 kilometres (1 to 5.5 mi) in a range of habitats.

Tallest tree

The site was once home to the tallest tree in the UK, aDouglas Fir63.79 metres (209.3 ft) high. This was damaged in stormy weather duringthe winter of 2010-2011and had to be felled at 124 years old in March 2011. A 15.2 metres (50 ft) stump was left intact, which in autumn 2011 had its top carved into a 2 metres (6.6 ft) tall giant outstretched hand.A nearby Douglas Fir is now, at 60.62 metres (198.9 ft), the tallest tree in Wales.

External links

• Lake Vyrnwy Nature Reserve
• Lake Vyrnwy on the Powys Digital History Project
• Abandoned communities: Llanwddyn
• Lake Vyrnwy Cycle Route
• "Vyrnwy Waterworks".Graces Guide.