Dam Raising and “Piano Key” Weir Improve Water Supply Security for Scottish Water Customers
Occasional periods of dry weather in Scotland have highlighted the importance of ensuring reservoirs have the storage required to meet the demands of customers and businesses. In July 2010, following a prolonged dry spell across the Dumfries and Galloway region in Scotland, the Black Esk Reservoir, which supplies drinking water to a population of 36,000 in surrounding villages, was estimated to have a supply deficit of 10 million litres a day.
In the short term, Scottish Water worked locally on contingency measures to maintain supplies. For the long term, an ambitious capital project was developed to boost water supply resilience by raising the height of the impounding dam at Black Esk.
“Our Black Esk Reservoir has the world’s only circular piano key weir in the middle of a reservoir. Black & Veatch’s design is ingenious.”
Ian Skilling, Water Operations Manager, Scottish Water
Black & Veatch, as the designer and contractor, raised the dam by 2.5 metres, increasing the storage potential and capacity of the reservoir by 40 percent, or nearly 1 billion litres. A major project challenge was that the inlet for the reservoir was required to be raised by 2.5 metres along with the dam. This presented a significant engineering hurdle because the spillway is located within the reservoir and permanently surrounded by water.
Black & Veatch incorporated two separate innovative solutions: a radical design of a bellmouth overflow weir in the form of a circular “piano key,” and an earthworks solution that allowed most of the construction to be on the downstream side of the embankment.
The circular weir is constructed of 24 blocks of precast concrete, each weighing 17 tonnes.
