Work to increase the capacity of a reservoir which serves communities in Annadale and Eskdale has been completed by Scottish Water.

A total of £3.4m has been spent at Black Esk Reservoir to ensure the secure supply of drinking water for the future. The project has included increasing the height of the reservoir by 2.5m, while the height of the overflow weir has also been increased through the use of a 'piano key weir' extension – the first of its kind in the UK. As a result, capacity of the reservoir has increased by around 40%.

Project Manager Jim Tudhope explained: "This project will significantly improve the security of the water supply from the Black Esk Reservoir. This will further enhance our ability to deliver water to customers, such as in the event of prolonged dry weather.

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"We have raised the crest of the dam by 2.5m, using clay that already existed on site, helping to minimise costs and traffic in and out of the site. The project has also involved raising the existing spillway weir, which sits inside the body of the reservoir and to the casual observer has the appearance of a large plughole.

"To do this we have installed a circular 'piano key' extension to the weir which consists of 24 pieces of cast concrete, each the size of a portacabin. This is believed to be one of the first times such an approach has ever been undertaken anywhere in the world. The weir design adds to the operational efficiency of the reservoir, and also enhanced safety for the construction team.

"We have demolished part of the existing structure and recycling the steel and concrete. The concrete will be used as a sub-base for improvements we are making to the Forestry Commission road nearby. The steel will be taken off-site.

"We have also raised the height of the valve tower and replacing the bridge to the tower, a forestry road diversion, landscaping works and installing new valves."

Bill Elliot, Community Team Manager, added: "The Black Esk water treatment works is a key asset for Scottish Water in Dumfries and Galloway. The facility serves a population of around 36,000 customers, and has already seen substantial investment and improvements by Scottish Water in the last few years."

The design and construction for the scheme was carried out by Black & Veatch.

(JP/IT)