Cutting the cost





Maintenance dredging is Harwich Haven Authority’s biggest single expenditure; to ensure clear access to the ports of Felixstowe, Harwich and Ipswich, it costs the authority about £7m a year to remove up to 3m cubic metres of silt from Harwich harbour and estuary every year.
However, one important change could save HHA £500,000, or more, every year. The authority is looking to move its licensed dredging disposal site five miles closer to shore, something which it says could also reduce its carbon output by 1,000 tonnes annually. “We are looking to keep our maintenance dredging sustainable, in all aspects,” says harbour engineer John Brien.
HHA carries out maintenance dredging approximately every ten weeks, with each dredge lasting between ten days and a fortnight. But because of the distance to the current disposal site at Inner Gabbard, the majority of the time is spent getting rid of the dredged material rather than actually dredging it.
The contractor’s trailer hopper dredger generally has a full load after working for 30 minutes in the harbour. But then there’s a three-and-a-half-hour round trip to Inner Gabbard to get rid of the stuff before the dredging operations can begin again.
A UK disposal site must be licensed by the Marine Management Organisation (MMO), and seeking permission for a new site is a complex process. The MMO procedure for analysing, designating and licensing new disposal sites involves a series of studies, reports and consultations; bodies such as Natural England and the Environment Agency, alongside interested groups such as fishermen, are involved in the discussions. The earliest that HHA would be likely to get the go-ahead is mid 2013.

New site 
To identify potential new sites on behalf of the authority, consultant HR Wallingford considered areas with water depth of nine metres or more; other activities were then taken into consideration, including anchorages, wind farms, gravel extraction sites, fisheries, shipping channels, habitats and marine ecology. All of these ‘no-go’ areas were overlaid onto a detailed map, and the result showed a number of ‘green’ areas from which a location could be chosen.  
At present, the dredger’s shuttling back and forth between harbour and disposal site helps generate approximately 6,000 tonnes of carbon dioxide a year – the highest CO2 output of all HHA’s operations, by a huge factor.
But quite apart from the carbon footprint, the authority’s early studies showed that for every mile the disposal site was brought closer, £100,000 a year could be saved.
“Moving closer in is logical – if the MMO doesn’t approve this [particular site], they might let us move it somewhere else which is closer to the shore,” says Mr Brien. “For us, any distance nearer is good.”
The Port of London Authority is looking to reduce maintenance dredging costs when its new mooring maintenance vessel (MMV) is delivered in 2014.
The vessel, being built by Manor Marine in Portland, will replace the Crossness and Hookness. It will be equipped with two cranes and carry out salvage, maintenance and other works within the River Thames and the estuary. “But the most important thing of all is that it will have dredging capability, enabling us to undertake maintenance dredging in-house,” says Geoff Buckby, the PLA’s marine services manager. “The plough is being built at Manor Marine alongside the MMV.”
Adding the dredging element is a very cost-effective step and was part of the business case put forward for this major investment, he adds.


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