| Tunstall Reservoir | |
|---|---|
| Tunstall Reservoir, showing the dam and, on the left, the now-disused water treratment works | |
| Location | County Durham, England |
| Lake type | reservoir |
| Catchment area | 23.6 sq km [1] |
| Managing agency | Northumbrian Water |
| Average depth | 16.9 m [1] |
| Max. depth | 22.6m [1] |
| Surface elevation | 220 m asl |
Tunstall Reservoir lies 3.5 km north of the village of Wolsingham, in Weardale, County Durham.
The reservoir was constructed on behalf of the Weardale and Shildon District Waterworks Company between 1887 and 1879.[2][3] It was created by erecting an earth embankment dam across the valley of Waskerley Beck. The dam, 1020 feet long and 82 feet high, was constructed with a puddle clay core. Puddle clay was also used in the cut-off trench into the hillside but when this was found to leak, the supervising engineer, Thomas Hawksley, adopted the then novel technique of pouring cement grout into holes bored along the trench. Tunstall was one of the first two dams on which the grouting technique was used, the other being at Cowm Reservoir in Lancashire, for which Hawksley was also responsible.[2]
As a result of amalgamations, Tunstall reservoir passed to the Weardale and Consett Water Company in 1902 and to the Durham County Water Board in 1920.[2] Following nationalisation and subsequent privatisation, it is now owned and operated by Northumbrian Water.
Until 2004, the reservoir supplied a water treatment works located immediately below the dam wall, but, with the opening of a new treatment works adjacent to Burnhope Reservoir at Wearhead, the Tunstall works was abandoned. The reservoir is now used solely to maintain minimum regulatory flows on the River Wear, in support of raw water abstractions further downstream, at Chester-le-Street.[4]
The reservoir borders the Backstone Bank and Baal Hill Woods Site of Special Scientific Interest. At the northern end of the reservoir, there is a small marshy area where the nationally scare Thread rush, Juncus filiformis, occurs; to protect this, Northumbrian Water has designated the marsh as a private nature reserve. The rest of the reservoir is used for boating and angling.[3]