1795 survey map for Llangollen Canal


Plotting and building a route through the landscape.


Before a canal can be constructed, the route has to be carefully planned to work its way through the landscape. This is the job for surveyors. They need to make sure that the canal reaches industries and areas where it can support the most traffic while also staying as level as possible, through a landscape full of natural obstacles such as hills and valleys.

John Duncombe and William Turner each surveyed different routes for the canal from the River Mersey to the west and east of the River Dee at Chester, into Denbighshire and Shropshire. Both men were later employed to survey the line as the canal was being built. They ensured that the workers who built the canal followed the intended route and to report on local obstacles and difficulties they might come across.

1795 surveyor map of Llangollen Canal
This is a map of the route surveyed for the canal by John Duncombe, published in 1795. It does not show details of hills and valleys. Only a few important towns and road crossings are marked, as well as major rivers. The branch to Llangollen was not proposed until a few years later.

Following the surveyors came armies of labourers, known as navvies. They dug the cuttings, built the embankments and laid the canal bed. Behind them came masons to build bridges and aqueducts, and bricklayers to line tunnels. A permanent workforce was then formed to maintain the canal. Their work is continued today by the thousands of employees and volunteers working with the Canal & River Trust.

WRG volunteer navvies

The Waterways Recovery Group is part of the Inland Waterways Association. They are volunteers who help to preserve heritage features, take care of the environment and bring some abandoned canals back into use. Their magazine for volunteers and supporters is called ‘Navvies’ in honour of the labourers whose work they are helping to preserve.

WRG volunteer canal camps

More Information About Surveying

The Ordnance Survey was originally formed for creating military maps. It published its first public maps in 1801 but did not survey Denbighshire and Shropshire until 1840, so the canal engineers had to produce their own accurate maps of the land. This Ordnance Survey map shows the area around Pontcysyllte Aqueduct in 1872.

Ordnance Survey
Ordnance Survey : (cc-by-nc-sa/4.0)

The needle on a compass always points to magnetic north. A surveyor’s compass, an early form of the theodolite, has two or four upright sights, which the surveyor aligns, to view a point in the landscape through them. A dial around the compass gives a reading of the direction they are facing.

Compass: Science Museum Group Collection
©The Board of Trustees of the Science Museum

Keeping a canal at an even height reduced the labour of creating embankments and cuttings or for building locks which wasted water. Surveyors use instruments called levels to record rise or fall in the landscape. These are small telescopes with crosshairs through which a level rod is viewed, marked with height measurements.

Level: Science Museum Group Collection
©The Board of Trustees of the Science Museum

A theodolite combines a compass with a telescope that can move horizontally and vertically. Surveyors use it to plot the height and location of objects in a landscape. This instrument was a fairly new invention in the eighteenth century. Duncombe and Turner would have used them for surveying and engineering the canal route.

Theodolite: Science Museum Group Collection
©The Board of Trustees of the Science Museum

Surveying chains were used for measuring short distances. They were 66 feet (20.12 metres) long, divided into 100 links. In Wales and England, one mile was equivalent to eighty chains. Chains were eventually replaced by steel measuring tapes but the word chainage is still used by surveyors to mean a measurement of distance.

Chains: Science Museum Group Collection
©The Board of Trustees of the Science Museum

Longer distances were measured using a surveyor’s wheel, or waywiser. The wheel, at the end of a handle, has a measured circumference. As the surveyor walked the planned route, they wheeled the waywiser with them. The number of rotations was recorded on a counter, telling them how far they had travelled.

Measuring wheel
Measuring wheel: Science Museum Group Collection
©The Board of Trustees of the Science Museum

Heights marked on Ordnance Survey maps are shown as above or below sea level. They are marked as bench marks (BM), or spot points. Where the road runs level with the canal at Gledrid, a spot point is measured at 94 metres above sea level, or 310 feet on older maps.

Sea level
Sea level: (cc-by-nc-sa/4.0)

Spot points only show heights on maps but bench marks are chiselled into walls or buildings. The ‘bench’ for the surveyor’s instruments is placed against the top of the mark, so measurements are taken from a known height every time. This bench mark is on Rhos y Coed Bridge, over the canal at Trevor.

Bench marks
Bench marks ©Richard Law (cc-by-sa/2.0)

The huge workforce of men employed to follow the surveyors and construct the canals were called Navigators, or Navvies for short. With no machines, their work was hard but the pay was much better than for agricultural labour. Navvies had a reputation for great strength but also for rowdy behaviour and drinking.

Navvies – who were they
Navvies – who were they ©National Maritime Museum, Greenwich, London

At the height of the canal building era, the end of the eighteenth century, there were probably around 50,000 navvies in Britain. About 500 worked on the canal from Trevor to Llangollen. A gang of 25 navvies could dig about a mile of canal a year on level ground.

How much work navvies had to do
How much work navvies had to do © Y Lanfa Powysland Museum

Navvies often lived in temporary camps, close to their work. They were sometimes paid partly with tokens that could only be exchanged at ‘tommy’ or ‘truck’ shops and food canteens in the camps. These were run by the employers and this could lead to the navvies paying inflated prices.

Navvy camps and truck shops
Navvy camps and truck shops ©The Trustees of the British Museum

From the 1840s, over 200,000 navvies were employed in constructing railways. As many as thirty percent came from Ireland. Irish Bridge, and the deep cutting near Whitehouses Tunnel, is sometimes supposed to have been named after them. In fact, far fewer canal navvies were Irish. They were mainly recruited from local people.

Irish Bridge
Irish Bridge ©Roger Kidd (cc-by-sa/2.0)

Once a canal had been built, it needed regular maintenance. Canal companies employed lengthsmen, who patrolled a length of the tow path, checking water levels, cutting back vegetation and looking out for leaks or breaches. They often lived in company houses alongside the canal, such as this one at Llanddyn.

Lengthsmen ©John Haynes (cc-by-sa/2.0)

The workforce who maintained the canal included masons, blacksmiths, lengthsmen and general labourers. As well as yards, such as at Trevor and Ellesmere, they had maintenance sheds at places along the towpath, some of which are still in use. This one is beside canal workers’ cottages near Chirk Aqueduct.

Maintenance sheds
Maintenance sheds ©Humphrey Bolton (cc-by-sa/2.0)

A combination of older skills and modern technology help to maintain the canal today. Staff can access a phone app, linked to electronic monitors, to measure water levels throughout the waterway. If the technology should fail, they are still trained to take levels manually, using traditional dipsticks at designated points.

Dipping ©Andrew Deathe

The Canal & River Trust spends over £200 million a year on its work, the majority of which is to maintain the canals and navigable waterways. Today, maintenance staff and volunteers follow in the footsteps of the navvies and engineers of the past, restoring and repairing to keep the canal open for everyone.

Modern canal maintenance
Modern canal maintenance ©Canal & River Trust