Boskalis and the Final Phase of Cowes Breakwater

2015 is set to be a landmark year for Cowes Harbor with the final stages of works on the new detached breakwater commencing in June and construction due to be completed by October.

Following a successful winter settlement period of the breakwater’s gravel core, Cowes Harbor Commission (CHC) announced that contractors Boskalis Westminster will soon return as scheduled to carry out the final re-shaping and placement of rock armor layers.

Boskalis Westminster’s Head of Capital and Coastal Projects Paul Datson, said: “We are conducting regular surveys and cone penetration tests on the breakwater and after detailed evaluation of the settlement process we are confident that gravel settlement and bearing capacity of the seabed meets our design predictions. We can therefore proceed as planned with the 2015 construction program and final phase of this 18-month project.

Captain Stuart McIntosh, Cowes Harbor Master, said: “2015 is going to be an exciting year on the development front for Cowes Harbor. Completion on the new Cowes Breakwater will realize the Commission’s long-term goal of transforming Cowes into a true sheltered harbor.

Cowes Breakwater 2015 construction program

Boskalis Westminster will mobilize in June to commence the reshaping of the Breakwater’s gravel core, bringing sections into profile before applying layers of smaller rock of up to 60kg that act as a filter to prevent the gravel migrating out of the core structure. Following this, a rock armor layer consisting of 300-1000kg rocks will be installed to provide long-term weather and wave protection.

A total of around 45,000 tonnes of rock will be brought from Cherbourg in France and transported by barge to Cowes.

The rock barge will be offloaded by excavators and shovels on the western end and northern side of the breakwater where there is sufficient water depth to accept the barges. Excavators located on the breakwater will position the rocks working anti-clockwise, starting on the southern face working to the east and then back along the northern face to the west, bringing the breakwater to its final profile and finished appearance.

Finally, permanent navigation aids, fixed beacons and buoys will be put in place before a monitoring and handover period in autumn 2015. The 50-year design life height of the breakwater is 5.5 meters above chart datum, but at the moment of handover the height will be approximately 5.9 meters to allow for long-term settlement.

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