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News - 23/07/14

Construction of breakwater advances into third stage

Work on the construction of a new breakwater structure at the mouth of Cowes Harbour, which will transform the port into a true sheltered harbourage, has successfully moved into the third stage of this vital 18-month coastal protection project. 

Cowes Harbour Commission’s appointed contractors Boskalis Westminster, world leaders in the design and construction of breakwaters, have completed the installation of an initial 1.5 metre layer of sand and gravel along the breakwater footprint (350m x 50m) and inserted a total of 11,000 wick drains to draw out water, thereby improving the ground bearing capacity of the seabed. 

Cross section of Cowes breakwater - courtesy of Boskalis Westminster
Cross section of Cowes breakwater – courtesy of Boskalis Westminster

Capt. Stuart McIntosh, Harbour Master at Cowes, said: “We are very pleased to report that construction on Cowes’ new detached breakwater is progressing extremely well and we have now commenced stage three of the 2014 works programme which is the placing of a geotextile membrane on top of the sand and gravel layer. This phase of the operation, carried out during daylight hours by a large barge and multi-cat, will run up to the start of August and Aberdeen Asset Management Cowes Week as planned.”

The Exclusion Zone that is in place around the submerged breakwater and construction area will remain in place during the Cowes Week regatta; all harbour users and competitors are strongly advised to take careful note of the Cowes Local Notices to Mariners for the most up-to-date information on the extent and shape of the Exclusion Zone, which is shown by lit buoys and cardinal marks. A 300 metre long floating orange and black pipeline, also lit, is anchored parallel to the breakwater on its northern side, and a 60 metre barge may be positioned anywhere along the breakwater footprint. For their safety, all vessels must ensure they stay outside of this Exclusion Zone and enter or depart Cowes Harbour via the fairway or Small Craft Channel.

Following a recent agreement between Cowes Harbour Commission and Boskalis Westminster, the fourth stage of construction on the breakwater is now set to start after Aberdeen Asset Management Cowes Week and will see the installation of the breakwater’s gravel core up to between 4 and 5 metres above chart datum using a trailing suction hopper dredger, floating pipeline and spraying pontoon. When the crest of the breakwater is visible above the water surface, the spraying pontoon will then be utilised to spray gravel against the slopes of the breakwater. The gravel will be left to consolidate for one month prior to being raised up to 5 metres above chart datum along the whole length of the breakwater.

By this September, and during a nine month period over the autumn and winter to allow for settlement of the gravel core, the breakwater will resemble a gravel spit and will only begin to take its final finished appearance during the 2015 works.

Cowes Harbour Commissioners are very grateful for the continued co-operation of local residents and assistance from all relevant parties during the construction of the breakwater, which will, once completed, protect the harbour and deliver a range of long-term benefits to the local economy.

The Cowes breakwater at Low Water in September 2014
The Cowes breakwater at Low Water in September 2014. CHC/ Boskalis Westminster

The Cowes breakwater at High Water in September 2014
The Cowes breakwater at High Water in September 2014. CHC/ Boskalis Westminster