Evolution of Nature-Based Dredging Solutions at Harwich, UK
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
J. Spearman, T. Benson
"Harwich Harbour, in the Southeast of the UK, is the location of the Port of Felixstowe and the confluence of the highly protected Stour and Orwell Estuaries. The maintenance of the approaches to the Port of Felixstowe is carried out by the Harwich Haven Authority and entails the dredging of up to 3 Mm3 of mud by trailer suction hopper dredger, almost all of which is placed offshore. Deepening of the approach channel to the Port of Felixstowe in 1998/2000 resulted in regulatory agreements for an innovative sediment recycling strategy (or mud engine) to offset the perceived effects of the deepening. This sediment recycling involves the release of a proportion of the material dredged from the maintenance areas of the Port of Felixstowe within both estuaries to enhance the sediment supply to the intertidal areas within each estuary. The present sediment recycling methodology consists of the release into the water column of around 50,000 tonnes/year of fine sediment from small trailer suction hopper dredgers, releasing on the flood tide in a number of campaigns throughout the year. Survey evidence and detailed numerical modelling shows that this strategy is effective for improving habitat, but it is still not optimal, either environmentally or on grounds of dredging efficiency, because of the current requirement for offshore disposal of most of the dredged material from the Harbour. As a result, Harwich Haven Authority intend to develop their dredging and sediment recycling strategy further. To this end they have patented and trialled an agitation dredger which removes the need for offshore disposal, greatly reduces production of CO2 and dredging costs, and takes a leap forward in providing a more nature-based dredging solution providing the recycling of sediment within the estuarine system. "
Keywords: Dredging with nature, sustainability, agitation, sediment recycling, efficiency