51°27′18″N 2°35′28″W / 51.455°N 2.591°W / 51.455; -2.591

Northern Stormwater Interceptor outlet, River Avon.

The Northern Storm Water Interceptor (NSWI), is a large stormwater tunnel that acts as a flood prevention measure for Bristol, England.

Building of the storm drain started in 1951 to relieve flooding over many parts of Bristol, and was completed in 1962.[1] It is some 4–5 metres (13–16 ft) in diameter and runs from the River Frome at Eastville to the Black Rocks Quarry in the Avon Gorge[2][3] - some 3 miles. There are however over 7 miles of tunnels in total. Originally proposed by the County Surveyors Frederick Ashmead and Col T H Yabbicom in the 1890s, due to the Great War, the Depression and the Second World War, construction was postponed until 1951. The scheme was reborn after the floods in Bristol 1947. The Tunnel was designed by Bristol City Engineers including Peter Steele and Bernard Smission from 1947. The tunnel was blasted through limestone, Dolimitic conglomerate and Keuper marl and lined with a 375 mm (14.8 in) thick concrete lining. At its deepest the tunnel is 90 metres (300 ft) deep. It was constructed by A.E.Farr Limited.

Smission invented the Energy Dissipating Vortex Drop Pipe System of which two were constructed along the tunnel. The technology has since been used in Chicago, New York and closer to home in Plymouth.[4]

Plaque
Plaque near the outfall of the Northern Storm Water Interceptor - June 2020

There is a plaque commemorating the building of the tunnel just across the Portway road from the outfall. This says:

This is the outfall of the Northern Stormwater Interceptor constructed to relieve flooding in the central North and East of Bristol. Started in 1951 the project consists of 7 1/2 miles of tunnel.

The main tunnel is 16 feet in diameter and over 3 miles long, begins at the flood water intake on the River Frome at Eastville and discharges into the River Avon at this point.

The works were inaugurated by Dr. the Rt. Hon. Charles Hill, M.P. Minister of Housing and Local Government on the 4th April 1962

The future management of flooding risk in the Eastville area is under consideration.[5]

References

  1. ↑ "Northern Storm-water Interceptor". Nettleden. Retrieved 29 October 2016.
  2. ↑ Begun, Selina; Stive, Marcel J.F. (2007). Flood Risk Management in Europe: Innovation in Policy and Practice. Springer Science & Business Media. pp. 216–219. ISBN 9781402042003.
  3. ↑ "Bristol Floating Harbour Recreational Water Profile". Bristol City Council. Retrieved 29 October 2016.
  4. ↑ "Bristol City Council: Pollution control – water: Bristol Living Rivers Project – Waterways Monitoring". www.bristol.gov.uk. Retrieved 26 May 2009.
  5. ↑ "Bristol Frome Flood Management Strategy" (PDF). Atkins. Archived from the original (PDF) on 30 October 2016. Retrieved 23 November 2018.
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