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News - 02/04/14

2014 Cowes breakwater construction programme

Construction of the new detached breakwater for Cowes is set to commence in early May. The initial construction phase will be completed this autumn, at which point the gravel core will be visible approximately 5 metres clear of Low Water spring tides. Following a settlement period, contractors Boskalis Westminster will return in spring 2015 to level up the core and complete the project. 

The first stage this year involves the installation of an initial 1.5m layer of sand and gravel using a small trailer dredger, discharging via a 300m floating pipeline to a 30m sprayer barge anchored west/east along the line of the breakwater. 

Once the initial layer is sufficiently progressed, the second stage will see the installation of a series of wick drains using a stitcher sited on a large barge. The purpose of these drains is to draw the water from the seabed up to the surface, which in turn will increase the ground bearing capacity of the seabed. 

Once the drain installation has been finalised, a geotextile membrane will be laid on top of the sand and gravel layer. This process will be achieved using a large barge and a multicat.

The next stage involves the installation of the gravel pre-load up to approximately 5.0m above chart datum using the same trailer hopper dredger, floating pipeline and spraying barge as was used for the sand layer.

When the crest levels reach around Mean High Water, the spraying pontoon will be utilised spraying gravel against the slopes of the breakwater. Excavators will be utilised to shape the breakwater and retrieve gravel outside of the intended profile.

A nine month consolidation process will then follow over the autumn and winter of 2014-2015, to allow for settlement of the gravel core.

It must be emphasised that the breakwater will resemble a gravel spit during the winter of 2014/15 and will only begin to take its final finished appearance during the 2015 works.

For all the latest news, safety and navigational information regarding the construction of the detached breakwater in Cowes, please check the latest Local Notices to Mariners and the Cowes Breakwater Project section.