Pushing water uphill: the genius of John Rennie

In the era of ‘Canal Mania’, this pioneering Scottish civil engineer created a wealth of iconic canals, bridges, pumps and lock flights, still used and admired today. Join us as we explore and celebrate his life and works, 200 years after he passed away.

A painting of of a victorian man with a green background John Rennie 1761-1821, by Henry Raeburn. Portrait courtesy of Institution of Civil Engineers.

John Rennie was instrumental in shaping our canals and waterways. Take a stroll along the Lancaster Canal to the Lune Aqueduct or make the thrilling ascent of Caen Hill lock flight on the Kennet & Avon, and you’ll witness Rennie’s magnificent feats of engineering in action.

Born in Phantassie, East Lothian in 1761, Rennie’s early interest in mechanics led him to work with millwright Andrew Meikle then on to Edinburgh University. In 1784, the steam engine makers Boulton & Watt gave Rennie his first commission, at Albion Mills in Blackfriars, London. He soon demonstrated his ingenuity, pioneering the use of cast-iron instead of wood for the gears, shafting and framing of the machinery.

Rennie’s reputation grew and in 1791 he started his own business in London, expanding into civil engineering. It was the dawn of ‘Canal Mania’, a prolific period of canal-building driven by speculators and investors. Rennie was in the right place at the right time. Over the next 30 years, he designed many of the iconic canals, bridges, pumps and lock flights still working on our network today.

One of Rennie’s first canals, the Rochdale, begun in 1791, traverses the Pennines via an impressive series of locks; the Grade 1 listed Lune Aqueduct, which he designed in 1794, carries the Lancaster Canal in style, and Staffordshire’s tranquil Rudyard Lake was created in 1797, to feed the Caldon Canal.

An engraving of a boat travelling down the Kennet & Avon Canal An early engraving of the Rennie’s Kennet & Avon Canal passing a Mill Town © The Waterways Archive

However, it was on the Kennet & Avon Canal that Rennie really made his mark, defining its route and building three major structures between 1794 and 1810. The first of these, Dundas Aqueduct in Somerset, was designed in 1797. Constructed of local Bath stone, the daring width of its central arch became a signature feature of his later designs, taken to extremes in his bridges across the Thames.

Rennie’s iconic lock flight at Caen Hill near Devizes is one of the “Seven Wonders of the Waterways”. Upon completion in 1810, it was described as “a most curious and striking instance of the wonderful perfection to which the art of engineering has been carried in this country.”

Navigating this series of 29 locks is a real rite of passage. Boaters who take up the challenge will rise an incredible 237 feet over just 2 miles, thanks to Rennie’s ambitious design.

An engraving of a canal boat passing over Dundas Aqueduct Dundas Aqueduct by A. Ashley after J.F. Burrell, for the British Gazeteer © The Board of Trustees of the Science Museum, London

Both Dundas Aqueduct and Caen Hill have been designated as Scheduled Ancient Monuments, on par with Stonehenge for heritage protection. However, the Kennet & Avon Canal would not have been navigable without Crofton Pumping Station and several others along the route, which literally push water uphill.

Crofton was Rennie’s clever solution to the problem of low water levels at the summit. Its two steam-powered beam engines, built in 1812 and 1845, are amongst the world’s oldest still in operation. In 2009, they even stepped in when the electric pumps at Crofton failed. These pieces of living history are well worth a visit.

Rennie’s illustrious career led to worldwide fame, particularly for his bridges. Opened in 1819, Southwark Bridge featured cast-iron arches “the largest of the kind ever constructed” and was lauded by Robert Stephenson.

The Italian sculptor Canova declared Waterloo Bridge to be “the noblest bridge in the world”. On a smaller scale the elegant Wellington Bridge in Leeds still spans the Aire & Calder navigation today.

Leisurecraft passing under London Bridge in Arizona Rennie’s London Bridge, rebuilt in Arizona. © Iris Donovan under creative commons licence

Rennie’s work continued through his sons George and John, who oversaw the posthumous completion of New London Bridge in 1831. Incredibly, by 1968 it was sold and its façade reassembled in Lake Havasu City, Arizona.

Despite his success, Rennie remained a man of integrity. His biographer Samuel Smiles described him as “calm, serene, and solid, like one of his own structures”. John Rennie died on 4th October 1821 and was buried in St Paul’s Cathedral, a fitting honour for one of the greatest engineers of his age.

Last date edited: 19 November 2021

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