Harwich Harbour scheme to protect intertidal habitats from ships’ wash

Where there is evidence that ship or boat wash is causing erosion of designated intertidal flats or saltmarsh habitat, and where other appropriate measures have been considered and applied, a further management option that may be considered is to protect the intertidal features by creating structures, such as breakwaters, bunds or mounds of sediments on the intertidal. Harwich Harbour Authority has applied this approach in Trimley Marshes on the Stour/Orwell Estuary. Such an approach to protecting marine features may also provide a beneficial use for dredged materials, however the potential impacts on local hydrodynamics and ecology, should be considered (Section 5.3.9). This should not be considered where the costs of undertaking such a scheme would greatly outweigh the potential environmental gain. Furthermore, the potential application of this approach may be limited by the need for a grant aid to fund this work and by land ownership issues.

A further method of minimising ships’ wash in the proximity of vulnerable shores might be to place moorings in the area to reduce speeds. This is a particularly useful approach where small speedboats and personal watercraft are a potential problem. Other variables which influence ships’ wash, such as propeller wake, ship design and hull form, are outside the scope and powers of any port authority and therefore cannot be changed by an SAC management plan.

In response to concern over the erosion of Trimley Marshes an intertidal recharge scheme was undertaken by Harwich Harbour Authority. 63,000 m³ of dredged sands were placed in soft groynes perpendicular to the eroding shoreline.

The benefits of the scheme were reported to be twofold. Whilst protecting the shoreline from ships’ wash, a beneficial use for dredged material was provided (Dixon 1996).

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