Engineering Like No Other – Gairlochy Lock Gate Replacement

irene-patsalou-project-managerWith over 4,100 major engineering structures in over 140 linear miles of waterway, Scottish Canals is home to some of the greatest engineering assets in the country. This financial year, we look to replace the largest lock gates on the network at Gairlochy, undertaking a project of engineering like no other.

Project Manager Irene Patsalou explains how and why we chose to replace these gates, and the benefits and impact the replacement will bring:

At Scottish Canals, our improvement and upgrading works are assessed and prioritised according to our Asset Management Strategy 2018-30. This details each asset throughout the canal network, ranked based on risk of failure and the risk to safety of our staff and the public.

Gairlochy top lock gates at Lock 17 were identified as a priority for replacement due to their age, condition and risk. At 10.4 metres high, the gates are not only the largest on the canal, but the largest in Scotland. Importantly, they form part of the flood defence mechanism separating Loch Lochy from the canal infrastructure.

In this respect, the gates, which are around 2.5 double decker buses high, also act as a functioning dam separating Loch Lochy from the canal infrastructure and communities to the west of this point. The Loch Lochy levels can vary greatly throughout the year and its storage capacity can reach 46.3 billion litres with a surface area of 17.5 km².  That’s about the equivalent of an area 2.5 times the size of the island of Gibraltar holding back over 20,000 Olympic swimming pools of water!

The existing gates were installed in the late 1980s and have undergone multiple repairs over the last eight years. These include emergency repairs undertaken to the north gate heel post in 2012, emergency repairs to the cill in 2016 and most recently emergency repairs due to defects found on all structural members across the lower joint line.

As a first phase towards their replacement, diver surveys were undertaken in 2019/20 to collect the exact measurements and assess the condition of all structural elements. This allowed us to identify the most beneficial design solution for the new lock gates. By using divers, we were able to minimise disruption on the canal rather than dewater the area to undertake our inspection.

Within the 2020/21 financial year, we will progress with the fabrication of the new lock gates, remove the existing lock gates and install the new gates before the high boating season commences in spring. We have appointed contractor AmcoGiffen, who have a proven track record working with waterways, to undertake the lock gate replacement.

The new lock gates have been chosen based on their effectiveness and resilience – the steel gates have a life expectancy of over 40 years, and will require minimum maintenance in comparison to older gate styles. When replacing the gates, we retain the timber elements for future use, as they may provide functional spares for other lock gates on the network.

In addition to installing new gates at Lock 17, works will also be undertaken to upgrade the surrounding elements of the lock chamber which support the gates. These upgrades include installation of new stainless steel quoin liners, which will ensure the historic quoins are protected from further deterioration. Choosing stainless steel for this will eliminate the requirement of interventions to the historic structure in the future, as well provide watertight seal around the gates which will result in reduced losses of water resources.

This major investment in the canal at Gairlochy will not only help water users enjoy our canal for years to come, it will also help safeguard the area from flood damage, protecting local residents and ensuring the canal can continue to contribute to the local economy in the Highlands.

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