Reducing the amount of dredged material

The amounts of material dredged in UK ports and harbours has steadily reduced over recent decades as a result of changes in dredging practice and port operations, such as technological advances, greater dredging accuracy, and increased surveying of dredged channels. However from both an economic and environmental viewpoint, it is worth ports and harbours asking the question ‘Can maintenance dredging be reduced further?’ This question is being addressed by many ports and harbours in the UK and world-wide.

There are a number of options for reducing maintenance dredging in ports and harbours (Burt & Paipai 1996), including the following examples:

  • A review of dredging practice by Tees and Hartlepool Port Authority Ltd. revealed two main improvements that would reduce the amounts of material dredged. Firstly, allowing over spill of the hopper caused materials to be deposited upstream which then needed to be dredged again later. Secondly, the estuary was being gradually deepened more than was necessary for safe navigation.
  • The Port of Rotterdam re-defined the seabed in terms of a density measurement that acknowledged the existence of fluid mud through which vessels can safely navigate, thus eliminating the need to dredge such materials.
  • In certain cases engineering solutions have been found to reduce siltation within maintained channels. For example, groynes have been constructed on the Diver’s shoal in the Thames Estuary which concentrate the flow in the navigation channel, encouraging self-scouring.
  • Work has been undertaken in the Netherlands to find engineering solutions to reducing dredging requirements in small harbours and marinas through specialised design and construction (Stichting Antislib 1997). The feasibility of such schemes are being considered in the UK (Quinn, BMIF personal communication 1998).

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