Harwich Maintenance Dredging
| Client | Harwich Haven Authority | Value | £13m |
| Location | Harwich, Essex | Quantity | 1,200,000m3 approx per year |
| Date | 2011 – 2013 Campaign |
Project Information
The Maintenance Dredging in Harwich has been a WDC project for many decades. In 2008 Harwich Haven Authority went out for tender once again to renew their Maintenance Dredging Contract which was awarded to a Joint Venture set up between WDC and Van Oord UK. The initial contract was for a 2 year period which started 1st January 2009 and runs till 31st December 2010 . Harwich Haven Authority decided to extend this to a further two year period starting January 2011.
The works under the JV contract is split in two parts with WDC as the lead company :
A) The major works :
The maintenance dredging in the approaches and berth pockets to Felixstowe and Harwich and disposal at sea of the dredged material at the Inner Gabbard disposal ground . The volume to be dredged each year is approx. 2,000,000 m³ which has to be done in 4 or 5 dredge campaigns spread over the year. Each campaign takes approx 3 weeks from start to finish while the presence on site for the THSD during the campaign is approx. 10 – 11 days. The preferred THSD is a vessel with a carrying capacity between 8000 and 12000 m³. A plough vessel is used to bring material from the berth faces in to the reach of the dredger but also to assist in maintaining Harwich International, Harwich Navyard , Mistley and other port users channels and jetties.
B) The minor works :
These form the Beneficial Sediment Replacement Scheme which controls disposal of dredged material and is intended to feed mobile sediments back into the estuary and river regimes. The material is generally dredged from the Felixstowe berths and some of the approaches and disposal takes place at 2 locations at the River Stour and 2 locations at the River Orwell . This has to be done over 3 campaigns of 40,000 m³ each with a minimum of 6 weeks in between campaigns , the works are done over the winter period ( November – April ) to minimize disturbance to wildlife . The works require a shallow draft THSD .
Disposal of the dredged cargo is done on the flood tide and by sailing over a predetermined track at a speed of 4 knots while discharging the cargo at the water surface using the dredge pump . The major works are shared 50/50 between WDC and Van Oord while the minor works are 100 percent WDC.
Surveying during the dredging campaigns has so far been done by WDC and is a very intensive exercise . The size of the main dredge area is approx. 1,500,000 m² which is surveyed every day and the survey information update is supplied to the dredger, plough vessel and the Harbour Engineer every afternoon and area’s other than the main area also require survey updates.