How the Clyde Was Deepened

The most audacious thing Glasgow ever did was not to build a great port, but to rebuild a river. In the middle of the eighteenth century the Clyde at Glasgow was a shallow, braided salmon stream that a man could wade across at low tide; a century and a half later it was a deep-water channel down which the largest ships in the world were launched and sailed. No natural harbour made Glasgow a maritime city. Engineering did — jetty by jetty, dyke by dyke, and dredger-load by dredger-load.

This page tells the story of that transformation: the shallow river that throttled a trading city, the elegant idea that set the water to dig its own channel, the training walls and the fleet of dredgers that carried the work on for a century, and the deep, sheltered channel that — almost as a by-product — became the greatest shipbuilding river on earth.

A river you could walk across

For all that Glasgow grew rich on Atlantic trade, the river on which the city stood could not carry the ships that trade required. Above Dumbarton the Clyde spread out wide and shallow, dropping its sand and silt across a shifting bed that was, in places, only a foot or two deep at low water. A laden ocean ship drawing fifteen feet had no hope of reaching the city’s quay at the Broomielaw, where the first wharf had been built in 1688. The tobacco and sugar fleets of the Tobacco Lords had to unload far down the firth, at Greenock or at Port Glasgow — the deep-water harbour the city’s merchants had built for themselves down the coast in the 1660s — and their cargoes came the last miles up to Glasgow by lighter, cart and packhorse.

For a city whose whole ambition was trade, this was an intolerable bottleneck, and building harbours downstream only ever moved the problem rather than solving it. What Glasgow needed was to bring the ocean to its own doorstep — to make the shallow Clyde deep.

The first surveys

The first serious attempt to understand the problem came in 1755, when the great English engineer John Smeaton surveyed the river. Three years later, in 1758, an Act of Parliament gave the Town Council the power to cleanse, straighten and deepen the channel. Smeaton’s own proposal — a lock and weir to hold back a navigable depth of water — was sound enough, but it was cumbersome and expensive, and it was never built. The answer, when it came, was cleverer and cheaper, and it worked with the river rather than against it.

Golborne’s elegant idea

In 1768 the council brought in John Golborne, an engineer from Chester, and his idea was elegantly simple: make the river dig its own channel. A wide, sluggish river drops its sediment; a narrow, fast one carries it away. Golborne proposed building pairs of rubble jetties — low walls of stone reaching out from each bank — to squeeze the tidal flow into a single narrower course, so that the quickened current would scour the sand and mud from the bottom and carry it off to sea. Where the river would not scour itself, a dredging plough — an iron blade dragged across the bed between two floating platforms — would break the bottom up.

Golborne was confident enough to sign a contract guaranteeing a depth of seven feet, and the river delivered. A survey in 1775 found that his jetties had won a depth of seven feet in just five years, and a grateful city presented him with a silver cup. It was one of the earliest triumphs of a whole new science of river engineering — and it set the method that would deepen the Clyde for the next century and more.

Watt’s report & the Lang Dyke

The most stubborn obstacle was the Dumbuck shoal near Dumbarton, where an island split the river into two shallow channels and defeated the scour. In 1769 a young Glasgow engineer surveyed the problem and reported on it — James Watt, a few years before the separate condenser made his name — and a jetty was thrown out at Longhaugh Point to try to block the southern channel. When that proved not enough, Golborne answered with his single most famous work.

The Lang Dyke, built in 1773, was a long, low training wall run out along the Dumbuck shoal to close the southern channel for good and force the whole river down one deepened course. It was a formidable piece of work: the building stone was floated out on barges and laid on submerged timber foundations to keep it from sinking into the mud, and in a matter of months some 800 yards of wall had been built. Two and a half centuries later the Lang Dyke is still there, breaking the surface at low tide — the oldest of the works that made the modern Clyde.

Rennie, Telford & the dredgers

Golborne had proved the principle; the engineers who followed applied it on an ever greater scale. From 1799 John Rennie multiplied and standardised the jetties, raising their number from around fifty to more than five hundred and joining the ends of some with rubble walls. From 1806, on the advice of Thomas Telford, the jetties were tied together into continuous parallel walls that held the river to a uniform width, so that it ran as a single trained channel rather than a comb of separate groynes. Telford, who had seen what steam dredgers could do on the Caledonian Canal, helped bring them to the Clyde around 1824, and from then on the deepening never really stopped.

Through the nineteenth century a fleet of steam bucket-dredgers worked the channel the year round, biting silt and gravel from the bottom and loading it into hopper barges to be dumped out in the firth. Between the trained walls and the tireless dredgers, the river was driven steadily deeper: from about six feet at low water in Golborne’s day to some seventeen feet by 1840, and deeper still as the century wore on and the ships grew ever larger.

Elderslie Rock

Sand and silt would yield to a dredger; solid rock would not. In 1854 the transatlantic steamer Glasgow, coming up the river from New York at what was thought a safe draught, ran hard aground near Renfrew on a hidden ridge of whinstone — Elderslie Rock, a bar of hard trap-rock lying just eight feet below low water and stretching more than 900 feet across the bed. It was the single greatest obstacle left in the river, and removing it became one of the hardest tasks the Clyde Trustees ever faced.

The work of drilling and blasting away the rock underwater went on, on and off, for half a century, and it cost lives among the men who did it. Not until 1907 was Elderslie Rock finally cut down to some twenty-eight feet below low water and the hazard removed for good — by which time the deepened Clyde could float the greatest liners in the world.

The river that built the ships

The work was directed, from 1858, by the Clyde Navigation Trust, which drew together the city’s merchants, shipbuilders and magistrates to manage the river and its trade and consolidated a century of piecemeal Acts of Parliament. Under its engineers the Broomielaw grew into a great harbour of quays and docks, and Glasgow became one of the busiest ports of the empire without ever standing on the sea.

And the deepening did something its authors had never set out to do: it created the perfect conditions for shipbuilding. A deep, sheltered, controlled channel, lined with flat bankside land and running through the middle of a city full of iron, coal and skilled labour, was the ideal place to build and launch big ships — and the yards of Govan, Partick, Clydebank and Scotstoun rose along the very banks the engineers had trained. It is worth pausing on how strange the achievement is. Other cities built docks; Glasgow rebuilt a river. There is an old saying that the Clyde made Glasgow — but Glaswegians know the truer version is that Glasgow made the Clyde. Every liner and warship that ever slid into the water at Govan or Clydebank floated out on a river that engineering, not nature, had put there.

The deepening in numbers