WALHAM 400 KV SUBSTATION, FLOOD DEFENCE SCHEME

Our Role:

This multi-award winning EPC Project involved the survey, design, construction and commissioning of flood defences to ensure the continuing operation of the Walham Substation. Presenting one of the project’s five awards, the RICS judges commented: ‘Preventing an incalculable loss to the local community if the facility failed, the scheme is good value for money and a worthy winner’. Key to our success was the extensive use of Ground Penetrating Radar surveys pre-empting issues with the myriad of underground services, through innovative design solutions, including RC gravity retaining walls and optimised pile lengths.

The Site

The National Grid Substation at Walham is of strategic national importance. It links the power generating stations in South Wales with the demand of central and South West England. It is vitally important that it continues to operate at all times. With the substation having suffered severe flooding in 2007, Trant were engaged to design and build a flood defence scheme, whilst also taking the opportunity to upgrade security to the Centre for the Protection of National Infrastructure (CPNI) standards.

The Project

The flood defence scheme consisted of the design and build of over 1Km of reinforced concrete and sheet piled wall, between 1.6-1.9m above existing ground level, providing protection against a 1 in 1000 year flood event. To enhance security, an electrified palisade fence was mounted on top of the wall and flood gates. Earthworks were also completed to mitigate impact on local flooding. Mechanical and electrical works encompassed 5 pumping stations and a control philosophy to protect the environment in the event of a flood. Highlights of the Project include:

Project completed on time, on budget
Over 130,000 working hours without a reportable incident
Health & safety score of 100% in Achilles UVDB audit
First use of Movax Vibro-Piler, coupled with electronic sensor motion limiters and remote shut-off facility, to ensure avoidance of contact with adjacent structures and electrical equipment, whilst enhancing productivity
Extensive use of Ground Penetrating Radar (GPR) surveys to map underground services
Temporary defences maintained in a constant state of readiness to respond to flood threats, including a temporary boat slipway
Sustainability measures included:
- Engagement with local community via liaison officer
- Flood modelling to ensure upstream and downstream behaviours not adversely affected, but actually improved
- 2,200 trees planted, replacing 440 removed
- Recycled materials used where possible, including recycled plastic draw-pit chambers
- Habitats enhanced with log piles and hibernacula