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A large drilling rig arrives off Portsmouth today (Friday 3rd February) as part of preparations to accommodate the Navy's huge new aircraft carriers.
The rig Deep Diver will spend up to six weeks sampling the sea bed in the harbour approaches and within the harbour itself.
Twenty-seven bore holes will be sunk to a depth of 32m along various parts of the route which will be dredged to make it wider and deeper during 2014-15.
The Ministry Of Defence is undertaking the sampling to better understand the geology of the area to be dredged.
The first of the two 'super carriers' - HMS Queen Elizabeth - is due to arrive in Portsmouth in 2016.
Captain Iain Greenlees, who is in charge of the transformation project to prepare for the arrival of the aircraft carriers, said: "The carriers will use the existing channel to approach the harbour but because of their size, the channel needs to be both deeper and widened by removing the edges of the banks at the eastern end of Spithead anchorage, allowing a more direct approach to the entrance.
"We will also be deepening the pockets at the berth and ensuring that there is a suitable turning circle at the top end of the harbour."
He added: "Work so far has identified this to be the route which balances best navigational safety, lowest environmental impact and cost. The analysis of these final boreholes will complete our detailed understanding of the work that will be required and allow us to apply for final approvals and run a competition for the work."
He said the first constructive work would be the replacement of telephone cables from Southsea to the Isle of Wight in 2013-14.
"We expect to be moving around 3.5 millions tonnes of the seabed in 2014-15. It is important that we understand its structure to ensure any material that can be reused or contains contaminants for separate disposal is localised."
The rig will be brightly-lit and will work 24 hours a day. Specifically designed for use near built-up areas, it has a noise suppression system to keep disturbance to a minimum.
Portsmouth Queen's Harbour Master, Commander Nigel Hare, said five samples needed to be taken in the harbour entrance which was likely to cause minor delays to vessels while the rig was working there.
"Every effort will be made to keep delays to a minimum and the rig will not be working at the harbour entrance at weekends," he said.
"This is clearly important work in the run-up to the new carriers arriving in Portsmouth and it is hoped that harbour users and local residents will understand the relatively short-term inconvenience of the rig, set against the much longer-term benefit of the project to the harbour and the city."
Letters to approximately 50 residents at Spice Island warning them of the works will be sent this week.
Preparations for the dredging of the harbour began in 2004 with detailed environmental analysis of the harbour and its approaches. More recently, the bridge simulator at HMS Collingwood, Fareham, has been adapted to the new route to prove the carriers can access and leave the base safely in a range of tidal and weather conditions. So far more than 180 successful run-throughs have been completed.