Publication Abstract

Dredged material from port developments: a case study of options for effective environmental management

H.L. Rees, L.A .Murray, R. Waldock, S.G. Bolam, D S Limpenny and C. Mason

The disposal of dredged material arising from port expansion to accommodate larger vessel sizes or increased trade can pose significant environmental challenges, because of the large amounts that may be generated over a relatively short space of time. The conventional management option has been that of sea disposal, for which licences are issued by the Department for Environment, Food and Rural Affairs under the Food and Environment Protection (FEP) Act, 1985, following a satisfactory outcome to a risk assessment of the environmental consequences.

This Act also requires consideration of alternative uses and, while sea disposal continues to account for the bulk of dredged material in the UK, an increasing quantity has been directed elsewhere to serve a variety of purposes. In this paper, we reflect this trend by reference to activities associated with recent dredging of the approach channel and port facility at Harwich, on the SE English coast. Dredged material has been employed in a variety of schemes, designed to counter the effects of net erosional regimes in the adjacent Stour and Orwell estuaries, and to replace intertidal habitat as a result of port development. The outcome of ongoing evaluations of the success of these schemes, both by the industry and regulatory interests, will be briefly reviewed.

The majority of the dredged material (29 million t wet wt) arising from the Harwich development was licensed for sea disposal at 'Roughs Tower', a nearby deposit ground in the outer Thames estuary, UK. Located in shallow water of 10 – 20m, the site is characterised by relatively strong tidal currents (>1m.sec^-1 on springs) and periodic exposure to the influence of wave action at the sea bed. The site has been in use for many years as a recipient for maintenance dredgings and (until 1996) sewage sludge, as well as periodically for large capital arisings from earlier port developments.

In view of increasing concerns over the dispersive capacity of the local environment in response to such large quantities of material, and the development of a nearby crustacean fishery, the 1999 deposit was accompanied by effective closure of the site. The disposal operation was conducted in such a way as to promote containment of the material within the licensed boundary, and a final sprinkling of gravel was intended to create a habitat suitable for commercial shellfish.

We report on the outcome of surveys of the sediments and the benthic fauna in the vicinity of the disposal ground before and after the event of cessation. These were conducted as part of a wider programme of monitoring at sites around the England and Wales coastline, in order to provide an independent check that licence conditions are being met, and to provide information relevant to the future decision-making process under the FEP Act. Finally, we explore the view that, when properly managed, the conventional sea disposal route may itself be considered as an enlightened use of dredged material.

Reference:

H.L. Rees, L.A .Murray, R. Waldock, S.G. Bolam, D S Limpenny and C. Mason. 2004. Dredged material from port developments: a case study of options for effective environmental management. Proc 28th International Coastal Engineering Conference.