Anchorsholme Outfall Cofferdam

Blackpool is famous for its iconic Tower, Pleasure Beach and Illuminations, and has been the destination of choices for British holiday-makers for generations. In order to cope with this demand United Utilities, are undertaking a large scale upgrade of the water facilities in the town. This includes the construction of a new water storage tank, and outfall pipe to ensure untreated stormwater isn’t discharged during the stormy weather that often hits the west coast of Great Britain, and the coastal waters can be kept clean for many generations to come.

WJ have a long history of working in and around Blackpool, having completed the Anchorsholme Park Storage Phase 1 and Phase 2 works for Ward and Burke and the Lennox Gate project for Ward and Burke and JN Bentley, both during 2016 and 2017.

Working with the CH2M HILL – VolkerStevin joint venture, C₂V⁺, the next phase of these works was to aid the construction of a new 6m by 20m cofferdam in the Irish Sea, directly off the coast from the Anchorsholme Park Storage site. The particularly challenging aspect of this project was the offshore location of the cofferdam, fortunately WJ are experts in projects of this nature, having undertaken several similar projects in Ipswich and Dover.

The dewatering system comprised eight 9.5m deep deepwells installed around the internal perimeter of the cofferdam, installed using a rotary drilling rig, in to interbedded sand and clay deposits during February 2018.

The first technical challenge on this project was the installation of the wells themselves. It was only possible for works to take place during the two 6-hr low tide windows each day, as during high tides the cofferdam would be flooded. During each of these windows it was necessary to pump out the cofferdam, crane the drilling rig in to position, drill, seal off the works so they wouldn’t flood when the tide came back in, and remove the rig from the cofferdam. Fortunately due to the meticulous planning of the works by the WJ Project Engineer, Michael Cummiskey, the wells were all successfully installed during the planned installation period.

The second technical challenge was also a result of the offshore location. As the cofferdam would be flooded during high tides it was necessary for the WJ control cabin and generators to be located onshore on an existing revetment, above the maximum tide level, with cables running between the cofferdam and the cabins along the beach and existing sea defences.

Despite the best efforts of the Irish Sea the target drawdown was successfully achieved.

You can read more about the Anchorsholme project as it progresses on United Utilities website.

• LOCATION: Anchorsholme, Blackpool

• CLIENT: United Utilities

• MAIN CONTRACTOR: C₂V⁺,