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Keep Your Head Above Water

image credit: The National Archives: 2007 flooding at Waltham substation
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The danger of flooding to the electricity grid is increasing, and as we know, electricity and water do not mix well! This article covers an interesting case study of an English substation located near a river and how it is now protected against encroaching water.

National Grid’s 400kV substation at Walham, near the city of Gloucester, links the power generating stations in South Wales with the demand of central and South West England. It supplies power to half a million homes, many industries and various government establishments. It is located close to the River Severn, which is one of the UK's largest and most turbulent rivers. It's a minnow by US standards, but in a densely populated country this river flooding will easily cause havoc (see 2007 photo above).

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In 2007 water nearly overcame the existing flood defenses – only a massive effort by emergency services and the British Army managed to stop the flood surging into the substation.

There was an official inquiry and a resolve to improve existing flood defenses and resilience for critical infrastructure assets. Hydrological studies identified 38 of the National Grid’s substations with a high risk of flooding if a '100 years' storm took place with a further 79 at medium risk. In 2013 they began a program of flood defense improvements at these substations, which is planned to be finished by 2026. Walham was top of the list to be upgraded.

 

Improvements to Waltham Flood Defenses

The works, by Trant Engineering, include half a mile of integral reinforced concrete and sheet piled wall over five feet above existing ground level surmounted with an electrified fence. The new perimeter includes various access points with automated vehicular gates forming an 'airlock area' at the main entrance as well as a refuge point for rescue. Five pumping stations were installed to work in conjunction with a site-wide network of filter drains capable of removing 40 gallons of seepage water per second in a flood event. Automated electrical systems were fitted so that the site could be shut down quickly if there was water ingress. Recycled materials were used wherever possible and the 440 trees cut down during the improvements were replaced with 2000 new ones. Careful planting has made areas of the site habitable for a wide range of local plants and animals. The design also involved hydrological flood modeling, to ensure that the flow of the river was not impeded, and won five awards.

This model of substation flood defense has now become a benchmark for the UK and Trant have now performed 15 substation upgrades, with two more due for completion this year.

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