The Cornish harbour town of Padstow has attracted explorers and sea traders from across the world for centuries. Once home to famous Elizabethan explorer Sir Walter Raleigh, today Padstow is famous for its strong maritime history.
Towards the end of the 1990’s, sections of Padstow’s 16th century Grade II Listed harbour wall started to collapse underneath the flood defence wall that the Environment Agency had built on top of it. This damage led to remedial measures comprising the construction of gabion baskets, against the face of the outer harbour wall. However, the ancient wall continued to deteriorate and, in 2005, the Environment Agency, in partnership with Padstow Harbour Commissioners, engaged Royal HaskoningDHV and Carillion Civil Engineering to prepare a business case and design for a permanent repair.
Working closely with the local planning authority, county archaeologists and English Heritage, consent to build a new harbour wall was granted and work on site began in September 2006. Royal HaskoningDHV’s Paul Winfield, explained why the construction of the new wall was so important, and why the team decided to allow tidal influence within the harbour while undertaking the work.
“The section of the harbour wall supports a vital flood defence. Failure to act would have resulted in the loss of the inner harbour, causing severe flooding. To minimise the risk of the harbour wall collapsing and to work safely, we had to revert to the harbour’s original tidal status. This decision reduced the need for temporary works, improved safety and saved time and cost.”
In advance of starting work, the team constructed trial panels with local slate to give planners a realistic representation of how the finished wall would look. Additionally, this enabled the team to develop, test and refine construction techniques. The team also held a series of workshops, bringing together the permanent and temporary design work teams to agree the most appropriate design solution.
“The chosen approach was to dismantle the gabion baskets, while ensuring the safety of the existing quay wall,” Paul continued. “The team adopted a concrete culverts system instead of the traditional encasement, which would have taken longer to construct than the short tidal working window allowed. This created a safer working environment, reducing time and cost.”
Another example of innovative teamwork was the value engineering workshops undertaken during the design review. A number of the designs required temporary works which would have led to significant costs to the project. The project team developed a design solution that incorporated the temporary works within the permanent design. Carillion suggested the use of precast concrete pipes as a permanent formwork while Royal HaskoningDHV designed reinforcement cages which could be lowered through the pcc pipes, removing the need for personnel to work at the base of an unstable seawall.
Royal HaskoningDHV then produced a specification for an underwater self compacting concrete which again minimised the need for personnel to work at the base of the existing seawall and minimised the amount of over pumping required.
During the project, the team encountered two key challenges which meant reverting back to the drawing board. These involved site access and timing. “One of the busiest resort towns in Cornwall, access through Padstow is mainly via narrow pedestrianised streets. Therefore, the transportation of materials to the site was one of our main challenges,” Paul explained. “Challenge number two had everything to do with timing. Starting any coastal project in the autumn can be difficult, particularly when you know that delays are unacceptable. As the town centre is far too busy to accommodate a construction project after the May Bank Holidays, work had to start in September, when there is still some tourist activity.”
To address both these issues, the Environment Agency appointed a liaison officer and the team maintained communication with local businesses.
“To avoid disruption to businesses that rely on tourism, we scheduled delivery times to avoid busy trading hours and revised our design to reduce the delivery of materials. In addition, we operated an on site ‘open door policy’ to deal with enquiries and inform visitors. The project was completed without a single complaint.”
Paul concluded, “By managing risks and reducing the volume of works, the duration of the programme was reduced by almost a third. The project completed on time, without accident, and significantly under budget.” The project was awarded an ICE Small Project Merit Award in 2008.”