Edinburgh sewers

Year:1864

Duration:112 years

Cost:£20m (£132m today)

Country: Edinburgh, UK

What did this project achieve?

Provide a sewer system for Edinburgh to improve public health

By the mid-18th century the Scottish capital of Edinburgh was a growing, increasingly prosperous city. It was also one of Europe's most densely populated, overcrowded and unsanitary urban areas.

Over 50,000 people were crammed behind the city walls in narrow, winding streets. Many of the poorer inhabitants lived in tenement buildings up to 14 storeys high with no sanitation. Waterborne diseases such as cholera were common in some areas.

Although wealthy residents had running water in their homes, sanitation for the poorer locals – particularly in the north and west of the city – was inadequate.

The Water of Leith scheme aimed to create a better sewer system for Edinburgh. Starting in 1864, the project built an interceptor sewer to connect to earlier systems and carry waste to the river Forth.

In 1889 Engineers built another deeper sewer. This extended the network inland to the city suburb of Balerno, 8 miles south west of the centre. The Balerno project created an effective purification scheme for the river.

Although there were many other developments Edinburgh had to wait until the mid-1970s for its first major sewage treatment works.

Engineers constructed the long-awaited plant at Seafield in the north east of the city on the banks of the river Forth. The scheme included an 11 mile interceptor sewer.

Difference the sewer improvements have made

The Water of Leith and Balerno schemes improved sanitation in Edinburgh. Public health improved with cholera and other water-borne diseases significantly reduced.

Improved sanitation made Edinburgh more attractive to business and investors. Although it didn't become as industrialised as other UK cities in the 19th century, new companies including rubber and engineering firms moved in - helping boost the local economy.

Apart from improving the city's capacity to process sewage effectively, the 1976 Seafield scheme improved the environment on the Forth estuary with benefits to local wildlife.

How the work was done

Engineers working on the Water of Leith sewer built the structure in an egg-shape. This made water flow faster and the tunnel self-cleaning. Many earlier sewers were the shape of an arch with a flat bottom.

Workers on the project lined the structure with bricks. The brickwork was sealed using Portland cement and rope yarn.

The system was ventilated by sinking shafts every 90m. Ventilators in streets came up under manhole-sized metal gratings. Ventilators in public parks were set under bushes or shrubs.

The 1976 Seafield project saw engineers excavate an 11 mile (17.7km) long interceptor sewer. The structure was up to 10ft (3m) in diameter.

Digging the sewer tunnels was a major challenge due to the wide range of ground conditions. Explosives were sometimes used in areas of rock or granite if there were no homes nearby.

Engineers also used the 'cut and cover' method in softer ground. This meant workers dug a D-shaped trench and then roofed it over with earth.

The project team used ground freezing where soil was unstable. The method saw workers running pipes into the ground and pumping liquid nitrogen into the earth. This made excavation work safer – frozen earth can be as hard as concrete.

"​‌

I believe that in no city in the world, so many people have so little room.

Daniel Defoe

Author of 'Robinson Crusoe' after a visit to Edinburgh in 1706. At the time Defoe was a spy for the English authorities.

Fascinating facts

Before they had proper sanitation people living in Edinburgh's tenement buildings used buckets or chamber pots for toilets. Residents on the upper floors would empty their waste into the street below with the warning shout 'Gardez l'eau!' meaning 'watch the water.' The phrase later became corrupted to 'Gardyloo!'.

The Nastiness Act was passed in 1749 to stop people in the streets being drenched from above. The new law decreed waste could only be thrown out between 10pm and 7am the next morning.

The Nastiness Act has never been repealed. Technically, it's still legal to chuck your waste matter out of a window in Edinburgh – if you do it at night.

People who made it happen

  • Client: Edinburgh city council
  • Consulting engineers for Water of Leith: John Cooper, D&T Stevenson
  • Consulting engineers for Balerno: D&T Stevenson, Leslie and Reid

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