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Two islands agree to rubble mound survey

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THE States of Guernsey has agreed to split costs with Alderney to carry out a sonar survey of the rubble mound on which Alderney breakwater sits.

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The mound has not been surveyed for some years. If it has moved substantially, it could compromise the stability of the superstructure.

Environment & Infrastructure looks after the breakwater and initially refused to pay for a sonar survey, saying that it did not have the funds.

However, when Alderney’s General Services Committee offered to commission the survey boat to examine the seabed around the sewage outfall at Platte Saline, in preparation for potentially lengthening it, E&I agreed to pay for a hydrographic survey of the mound. The two islands will split the logistical costs of getting the boat to Alderney and accommodation for surveyors.

Work to repair storm damage to the breakwater was carried out earlier this year.

Graeme Falla, States of Guernsey project service manager, said: ‘There’s a concern that over time the mound will get worn down in places, and this is especially concerning if it has started dropping at the furthest end where there’s a 30 metre depth of water.

‘Knowing what is happening won’t stop anything, but it will help with planning. If it’s dropping we can extrapolate when it would drop to a level that would affect the superstructure.’

The survey work is not limited to summer months as the boat has sophisticated positioning equipment.

Norma Paris, chairman of the General Services Committee, said: ‘Although our breakwater is the responsibility of the States of Guernsey, Environment & Infrastructure and the Alderney General Services Committee have been working together closely over the last two years.

‘When it became clear that Guernsey funding was not available to do an urgent sonar survey on the breakwater, the GSC offered to fund the survey with other work we wish to have done so that the opportunity was not lost this year. Funding from Guernsey has now been found and we expect the survey to be carried out as soon as we can.’

She said that the exact cost of the project had not been confirmed.

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