Client: Cowes Harbour Commission
Contractor: Boskalis Westminster
Duration: 10 days
Date posted: 11-08-2014
MMC Divers worked with the team from Boskalis Westminster on the Cowes breakwater construction programme.
Construction of the new detached breakwater for Cowes commenced in early May 2014. The initial construction phase was completed, at which point the gravel core was laid approximately 5 metres clear of Low Water spring tides.
The first stage in the early part of the year involved the installation of an initial 1.5m layer of sand and gravel using a small trailer dredger, discharged via a 300m floating pipeline to a 30m sprayer barge anchored west/east along the line of the breakwater.
Once the initial layer was spread, the second stage was 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 drains had been installed, MMC Divers assisted in the placement of a geo-textile membrane that was laid on top of the sand and gravel layer. This process was achieved using a large barge and a multi-cat for the divers support vessel.
Once the fabric was laid and covered, MMC installed five 30 meter pipes with integrated sensors, these will be removed in a few months by our divers and the data taken off to see how much the bank has slumped.
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.