Canal Lock Bypasses Explained

The next topic in our Explainer series is the mysterious Lock Bypass. Hidden below ground, subject to impenetrable equations, and largely unknown to those walking along Scotland’s canals – and yet, they are crucial to water stewardship and play a role in mitigating the effects of climate change. Intrigued? Let’s get into the nitty-gritty… 

What is a lock bypass? 

A lock bypass is a structure consisting of various elements. Simply put, it is a concrete inlet structure and a concrete outlet structure which are connected by a large pipe that passes water around a canal lock using gravity.  

Much like a road bypass diverts traffic around a town or village, a lock bypass diverts water around the lock gates/chamber and allows for a constant feed of water downstream. It ensures that the canal remains adequately supplied with water, and that locks further downstream have enough water to operate. 

On the diagram below, you can see that water is diverted from the canal via the inlet chamber, before progressing through a large pipe to the stilling chamber. From here, the water passes through two pre-cast concrete culverts and into the canal channel.  

Why do we need it? 

A canal bypass brings two key advantages:  

• Sustainability and cost efficiency: A bypass reduces the need for diesel-fuelled over-pumping during maintenance works, which helps manage the canal’s carbon footprint. It also makes the environment cleaner for residents, and cuts running costs during maintenance works.  
• Better control: A bypass offers greater capacity for managing water levels and the flow of large volumes of water when our water control teams identify potential issues with the level of a canal. There is also the potential to introduce automated water controls at lock bypasses. 

What’s the link to climate change? 

There is nothing new about lock bypasses, but Scottish Canals is installing new bypasses along the Forth & Clyde Canal to enable better control over water flows as part of the canal’s evolution into a Smart Canal.  

This means that ahead of heavy rainfall, the Forth & Clyde Canal can lower its water level automatically (by four inches over 20 miles of canal) to take in surface-water run-off from new housing developments in the North of Glasgow.  

With this additional drainage available for adjacent land, the Smart Canal unlocks derelict sites for housing too (3,500 houses are in plan in Glasgow as a direct result). 

As climate change makes extreme weather events more common and severe across Scotland, our canals can play an important role in mitigating the effects. New bypasses, like those being installed at locks 20 and 16 on the Forth & Clyde Canal, provide improved control over the flow of water passing downstream, which will be needed as water management becomes more challenging. 

Case Study: Lock 20 Bypass (Wyndford Road, Banknock) 

The first phase of the bypass installation was carried out over a period of approximately 5 months (between November 2024 and April 2025) with a final phase set to begin in November this year.  

This project involved: 

• Installation of sheet piles to form a cofferdam at the inlet chamber and a limpet (or temporary) dam near the stilling chamber. 
• Excavation of the site of the stilling chamber, inlet chamber, flow meter chamber, culverts and pipes (with some puddle clay used to reduce leakage between the dams and excavations).  
• Installation of pre-cast concrete culverts near the stilling chamber as well as steel reinforcement work and multiple concrete pours for the chamber bases and walls. 
• Laying of pipework to connect the chambers. 
• Backfilling around the concrete chambers and excavated areas. 
• Installing trash screens, flooring panels and handrails. 
• Landscaping and resurfacing of nearby pathways and roads. 

Related projects

• Lock 16 (Camelon) Bypass Installation, Forth & Clyde Canal
• Lock 20 (Wyndford Road) Bypass Installation, Forth & Clyde Canal