Beneficial reuse and dredging go hand in hand in Harwich

Harwich Haven Authority (HHA) recently announced the start of a massive dredging scheme, the €140 million worth Harwich Haven Channel deepening project.

Royal Boskalis Westminster and Van Oord are the joint venture contractors of the project, which is scheduled to be completed over the next two years.

The dredging project entails the deepening of the approach channel and inner harbor from minus 14.5 to minus 16 meters to allow unimpeded access of the latest generation container vessels to Harwich Haven and the Port of Felixstowe.

During the works, approximately 15 million cubic meters of silt, sand and clay will be dredged by jumbo trailing suction hopper dredgers and a large backhoe dredger.

According to HHA, the dredging contractor Boskalis/Van Oord mobilised the first vessel to Harwich in early October to commence dredging of the main channel.

“Over the next few weeks, trailer suction hopper dredger (TSHD) Sospan Dau will be busy dredging the area of the main channel known as area C2 covering the whole width of the main channel and running from about 250m east of the Platters / Pitching Ground buoys to about 1,000m west of the same buoys,” HHA announced.

They also added that dredged material will be disposed of to two beneficial disposal schemes, one on the northern end of Horsey Island (Hamford Water) and to four separate sites in Mersea Harbour (at Cobmarsh Island, Old Hall Marsh, Tollesbury Wick and Packing Marsh Island).

Horsey Island is a private island in the north of Essex, it was first recharged in the 1990’s using sand and shingle from a previous deepening operation conducted by Harwich Haven Authority. More recently it has evolved into the most important little tern colony in Essex. Its unique offshore location means that it is relatively free of disturbance from people and mammalian predators this has allowed little terns to thrive and develop a productive colony.
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However, over time the beach has moved westward and landwards and gradually flattened out. This has meant the beach is increasingly vulnerable to high tide events especially over the breeding season. In order to secure the future of the little tern colony, the area needed to be recharged.

This is done by dredging sand and shingle then transporting it to the island. The material is deposited either via blowing it out over the bow or connecting a pipe and pumping it directly on to the foreshore. This is then moved around by the wind and tides until it settles on the existing beach raising the beach. This type of scheme is also known as a beneficial reuse scheme.

Another important feature of this project is the fact that the consortium of Van Oord and Boskalis will reduce its CO2 emissions significantly on this project by using a sustainable biofuel. This allows a substantial carbon reduction of up to 90%, which contributes to the reduction of carbon footprint.

Since the launch of their biofuel programmes, both companies have successfully used various biofuel blends on both dredging and offshore installation vessels and on dry earthmoving equipment as an alternative to fossil fuels.