Severn Tunnel - The Great Western's longest railway tunnel

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In the 1860's the Welsh coal-mining industry expanded rapidly. With new pits opening it became essential to find an economic method of moving the coal from the pits to the docks and main industrial areas of the UK.

The obstacle to this was the River Severn. A broad river, prone to high and variable tides, severe flooding and the tidal surge known as the Severn Bore, it was wide and unpredictable. With the second highest tides in the world to contend with, as well as ships and docks to avoid, it was not going to be simple to overcome.

A railway link had to be established to move the coal. Bridges were considered, but the supports across the estuary would create a hazard for shipping, particularly in morning or evening mists.

Tunnels were considered a risk, especially since the only engineer with experience of long railway tunnels and underwater tunnelling was no longer available. Isambard Kingdom Brunel died in 1859, but his influence lived on.

Charles Richardson, who had worked with the Little Giant on the Thames Tunnel and Box Tunnel projects, proposed a plan for a railway tunnel under the river. It was greeted with some scepticism, and it was only due to another of Brunel's associates that the scheme progressed. Daniel Gooch had been the chief locomotive engineer for the Great Western Railway, and was now its chairman. He reviewed the scheme and cautiously agreed to it. John Hawkshaw, another distinguished tunnel engineer, also reviewed the scheme and believed it practical.

With their support permission for the tunnel was passed in 1872 and construction began.

Severn Tunnel Flooded
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Not surprisingly, the greatest problem faced by the tunnel was water. When the initial shaft was dug the workers enountered a spring which had to be damed and diverted. Then they began to dig out, under the river.

Although the tunnel was through solid sound rock, rather than the sandy clay that had given so many problems with the Thames tunnel, cracks and fissures in the stone allowed water to enter, sometimes in great quantities. This could result in flooding, but progress was being made.

Surprisingly it was not the Severn that lead to the disatrous flooding in 1879. Instead as they dug forward the workers encountered an underground body of water of such size that it flooded the tunnel. Work halted abruptly with the entire tunnel flooded.

Sir John Hawkshaw was appointed to take over the project. With the aid of two large steam engines he reduced the water pressure so that divers could go down and begin to seal the tunnel with Portland cement - a new compound whose underwater properties made it ideal. The water they had tapped was named "The Great Spring."

Finally in 1881, the last door was closed, the brickwork complete and "The Great Spring" was isolated. Work on the tunnel could begin again in earnest.

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By 1883 the tunnel was almost complete. The men were understandably nervous of flooding and flase alarms slowed the work. It was towards the end of the year that there was another setback, when the diverted Great Spring once again broke through into the tunnel. This was barely under control when a gale sweeping in in October drove a tidal wave over the tunnel entrance, flooding it and the workers' cottages on the land above. Once again the remainder of the year was spent sealing the tunnel and removing the water.

The tunnel was finaly completed in 1885, and in September of that year Sir Daniel Gooch inspected the tunnel on a Great Western train. However further pressure problems with the great spring resulted in a new pumping house being added to permanently remove the springwater that threatened to flood the tunnel. In 1886, the tunnel was finally opened for traffic.