One of the most formidable challenges facing canal engineers was how to deal with the inevitable elevations and descents required when traversing the countryside. As the network grew, routes encountered hills that needed climbing and valleys that required crossing. Engineers approached the challenge with gusto – experimenting with increasingly innovative designs. Some techniques are still widespread today; others remain only in the archives. Let’s take a look at five most interesting strategies to negotiate the ups and downs of the British landscape…
In the mid-18th century, James Brindley changed the world of canal construction forever, armed with a large round of Cheshire cheese. Faced with the challenge of crossing the River Irwell in Lancashire, he knew he had to convince Parliament that his new structure was the way forward. Apparently, Brindley demonstrated the unconventional idea of carrying one body of water above another by dividing the cheese into two equal halves, to represent the semicircular arches, and then laying a rectangular object over the top to show how the the river would flow below the aqueduct and the canal would flow above (as told in Memoir of James Brindley, John Weale, 1844). Although dismissed by many for his proposed ‘castle in the sky’, Brindley won them around and the Barton Aqueduct (opened 17 July 1761) went on to become the first navigable aqueduct in the country, and remained a pioneering structure until the use of cast iron allowed more ambitious projects to be built. In 1805, Thomas Telford completed the 307-metre Pontcysyllte Aqueduct on the Llangollen Canal, which is today the longest navigable aqueduct in the UK. At 38 metres, it’s also the highest in the world. The construction of the ‘Ponty’ included some unorthodox methods: oxblood was mixed into the mortar (it was believed to strengthen a building) and supposedly the cast iron joints were caulked with flannel dipped in boiling sugar, before being sealed with lead.
An inclined plane consisted of two caissons (watertight chambers) connected by a piece of wire rope that was wound by a steam powered winch, simultaneously raising one caisson and lowering the other. Offering significant water efficiency over locks, a number were built around the country – with notable examples on the Bude and Shropshire canals. Sadly, there are no operational inclined planes left in the UK, however you can see the remains of one of the finest at Foxton on the Leicester Line of the Grand Union Canal. The existing flight of locks took 45 minutes to navigate and used 25,000 gallons of water per trip, resulting in queues that could last for several hours. The inclined plane, constructed in the late 19th century, made the journey possible in just 12 minutes. This meant that around 6,000 tonnes of cargo could pass through the mechanism in a 12-hour period. However, a lack of traffic and the demands of the steam engine (which needed to be powered even when boats weren’t making their way up the incline) made it uneconomic, so it was dismantled in 1911 and the machinery sold for scrap.
Vertical boat lift
A number of lifts were built on canals around the UK to provide a water efficient method of linking waterways, but most were replaced with locks or inclined planes due to operational problems. Today, the Anderton Boat Lift, navigating the 15.2 metres between the Trent & Mersey Canal and the River Weaver, is the only working vertical boat lift in the UK. Constructed in 1875 to facilitate distribution of salt being extracted in Cheshire, it operated for over 100 years before corrosion caused it to close in the early 1980s. In the original design, a pair of hydraulic rams were used to lift or lower the two counterbalanced caissons. However, a number of incidents – including a burst hydraulic cylinder that caused the caisson, which held a boat at the time, to rapidly descend – led to the mechanism being switched to electrical set-up that used a series of overhead pulleys and wires. When the lift was restored and re-opened in 2002, the decision was made to return to a hydraulic operation, but retain the overhead structure for historical reference. The weights used as counterbalances were kept and now form part of a maze in the grounds.
The Falkirk Wheel
Just as people mocked James Brindley for his ‘castle in the sky’, many thought the idea of a rotating boat lift was equally unrealistic. Instead of a block of cheese, architect Tony Kettle used his daughter’s Lego set to model aspects of the ambitious design for his clients and funders. Originally linked by a series of 11 locks, the journey between the Forth and Clyde and Union Canals took almost a day and required 3,500 tonnes of water per run. The locks were disassembled in 1933 and it wasn’t until 1994 that plans for a new way to connect these waterways commenced and a team was assembled, led by Kettle. Construction began in 1998, and the 1,200 tonnes of steel manufactured in Derbyshire was reassembled on site using 15,000 hand-tightened bolts. The Falkirk Wheel opened in in 2002 and today it takes around four minutes to turn, lifting and lowering boats a distance of 24 metres. The design is surprisingly energy-efficient, taking just 1.5kWh of electricity to make the half turn (the same amount as boiling eight electric kettles), and it remains the only rotating boat lift in the world.
Locks are a familiar sight on our canals but ‘guillotine locks’ are now relatively uncommon. Surprisingly, these locks managed the flow of water over level stretches, rather than helping boats to move up and down elevations. As the name suggests, they had vertically rising gates that lift to allow boats to pass underneath. Due to the higher maintenance costs, only a few remain today. One of the finest is the Kings Norton Stop Lock (last used in 1959) – a Grade II listed structure on the Stratford-upon-Avon Canal near its junction with the Worcester & Birmingham Canal. At the time, water was a precious and keenly conserved commodity and this lock was constructed to stop the flow between the two waterways, which were owned by different companies. A beautiful cast iron girder frame holds the gate, which was raised and lowered by chains and balanced by a counterweight built into the side of the lock. The gates are now left open as, since the nationalisation of canals in 1948, there is no need to be concerned about the flow of water from one stretch to another.