On this date in 1873 construction began on the Severn Tunnel. 10 things you might not know about the Severn Tunnel:
At 7,008 m (4.355 mi) long it’s the longest rail tunnel in the British Isles outside of the London Underground network and the Channel Tunnel. It was the longest underwater tunnel in the world until 1987.
It runs under the estuary of the River Severn.
Only 3,621 m (2.250 mi) of it is under the river. Of the remainder about half a mile is in Gloucestershire and the rest is in Monmouthshire.
It took 14 years to build, opening in 1886.
It was constructed by the Great Western Railway (GWR) between 1873 and 1886 to shorten journey times between South Wales and Western England. Before that, a train journey would have to include a ferry crossing which was dependent on the state of the tide.
In Welsh, the tunnel is called Twnnel Hafren.
As of 2012, an average of 200 trains per day use the tunnel.
In 1924, the Great Western Railway started a car shuttle train service using the tunnel, so that drivers could avoid ferry crossings or a long detour by road. This service became redundant when the Severn Bridge opened in 1966.
On average, around 50 million litres of water per day infiltrates the tunnel. This comes from a large fresh water spring which was pierced by the construction on October 16, 1879. On that day, water poured in at the rate of 6,000 gallons a minute, overwhelming the pumps. Luckily no lives were lost, but the workers did get a bit wet! Someone presumably said, “We’re going to need a bigger pump” and several large pumping engines were duly installed, and continue working to this day. The source of the water is known as “The Great Spring”.
There is a 1 in 100 gradient on the Bristol side, and 1 in 90 on the Welsh side, which makes the operation of heavy goods trains difficult.
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