Increasing capacity at Penwhirn dam

Penwhirn Dam Reservoir

An £8.3 million scheme to increase the capacity of a water treatment works in Stranraer is currently taking place.

The project – titled Improvement to Supply and Demand Balance for Auchneel, Barclye, Palnure, Penwhirn Water Resource Zone – will see the Penwhirn Reservoir dam increased by 1.5 metres. With the height of the dam increased the water treatment works capacity will also increase by 1.2MLD to reach a total of 17.2MLD. In addition, process losses will be reduced by approximately 2%.

The work – which is being implemented by Scottish Water – is taking place adjacent to the Penwhirn Reservoir, where the dam is situated. Penwhirn Reservoir is popular with the fishing community and with the local community as a beauty spot and walking/hiking location.

Penwhirn is the main water treatment works in the zone and supplies the bulk of Wigtownshire in Dumfries and Galloway. Once work on the project reaches completion the scheme will address a resource yield deficit and upgrade the works for increased output, which in turn will improve the supply/demand balance.

Work began on the project in August 2012 and is currently on programme to reach completion in February 2014. Funding for the scheme has been provided via central investment funding to address supply and demand requirements laid out by Scottish Water’s regulators.

Black & Veatch is the main contractor and architect on the project.

The main material being used throughout the construction work is concrete, whilst steel is being used for the construction of the dam. The project is being delivered using NEC3 Option C – Target Cost Contract.

Penwhirn Dam Reservoir

Commenting on the project, Ian Morton, Project Manager, Scottish Water, said:

“The Reservoir raising phase of the work involves the construction of a new labyrinth weir at the reservoir spillway, the refurbishment of the reservoir spillway and the increase in height of the valve tower. In addition, a new access bridge to the valve tower is being constructed, we are increasing the crest height using approximately 290 meters of precast wave wall sections and we are installing new access roads and paths.

“As for the water treatment works (WTW); we are building an extension to the WTW which will accommodate a new dissolved air flotation (DAF) stream. We are also installing new recycle pumps and saturators, upgrading raw water booster pumps, modifying pipeworks and chemical dosing units and improving washwater handling and supernatant return systems.”

Ian added:

“This project offers security of water supply in times of low rainfall or drought. While this risk can never be fully eliminated this project will reduce the risk significantly. It is essential for security of water supply in the area.”

Work on the improvement scheme in Stranraer is currently on schedule and within budget. To date, the original weir has been demolished and a new base slab has been constructed for the labyrinth weir. The initial wall pours to labyrinth have also been completed, along with excavation and bank stabilisations for the WTW building extension.

Associated landscaping works is being kept to a minimal, although the scheme does incorporate some works to accommodate water voles and otters.

Scottish Water is a publicly owned company providing 1.3 billion litres of drinking water per day to residents of Scotland. In addition, the company takes away 840 million litres of waste water on a daily basis.

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