News & Media > Utility Services
23:08:2010
EA flood defence project protects Anglesey community
The £1.2m project was to create a new tidal defence system by refurbishing the tidal doors that protect Valley from coastal flooding. The scheme also included the provision of emergency features in the event of the tidal doors failing.
A study by the Environment Agency Wales showed that the tidal doors, which were first built in the 1830s but have been repaired and added to in the intervening years, needed to be improved.
The project programme was tight, and in addition to extreme weather conditions the works had to be programmed to take account of tidal influences and significant structural changes.
Despite significant challenges, the well-established site team's enforcement of good working practices, proactive planning of all operations and excellent coordination between supervisory staff and workforce, resulted in the project being completed to a high standard and on programme.
Meic Davies, Environment Agency Wales flood risk manager, said: The existing tidal doors and embankment have worked well to protect Valley from the sea for many years. This scheme will ensure that they continue to do so into the future.
The project in more detail
The works comprised:
Extension of the existing culverts to the seaward side of the embankment
Replacement of the existing timber doors with Coplastix Flap Valves
Provision of penstocks to each of the main channel and bypass culverts
Construction of cantilevered operational and viewing platforms
• Construction of RC tidal vehicle maintenance road
Construction of new masonry clad RC retaining walls
Raising the height of existing masonry walls on the crest of the embankment
Reconstruction of the coastal footpath across the embankment
Re-pointing of the existing stone revetments to the embankment
The works had to be carried on a very restricted site within the Beddmanarch-Cymryan SSSI and The Isle of Anglesey Area of Outstanding Natural Beauty and to a tight environmental calendar over the winter period.
Temporary works had to be designed to maintain flood tidal defence to the village, while also allowing the unrestricted passage of fluvial flows into the estuary.
Rock immediately below the seabed ruled out the luxury of enclosing the works within a steel sheet piled cofferdam. The solution developed by the project team was to build a cofferdam using specially adapted clay filled steel mega boxes. Although overtopped at high tides, the cofferdams significantly increased working windows and offered protection to the works from wave action.
A 5m high retaining wall supporting the embankment between the structures was found not to exist. Instead, the area had been earth filled and capped with stone and concrete, which had to be removed in order to build the new works. To ensure the embankment integrity was maintained the project team proposed mass concrete temporary works built in 1m sections, which following the maintenance road construction formed the foundations for a new masonry clad RC retaining wall.
*Footnote: Team Van Oord is a partnership between Van Oord, May Gurney and Mackley Construction which delivers projects for the Environment Agency.
