Publication Abstract

Large scale use of muddy dredged material for sustainable flood defences and habitat management

M. Dearnaley, C. Fletcher, S.Bolam*, A. Kenny*, M. Schratzberger

Muddy dredged material has been used over the past decades in England and Wales for flood defence and habitat management. Use has generally been at small scales (up to a few thousand cubic metres per scheme) and often in a site-specific fashion. Options for use include: direct placement onto intertidal areas (confined or unconfined); sediment recycling and trickle charge; and placement into managed realignment sites to build up bed levels prior to, or immediately following breaching. Only a very small percentage of the muddy material dredged on a routine basis has been used beneficially, most of it is placed at licensed offshore disposal sites.

In January 2003 Defra commissioned research to improve knowledge and understanding of the key processes governing the success or failure of beneficial use schemes which utilised the large scale placement of muddy dredged material (a few hundred thousand cubic metres per scheme). This research built upon previous and ongoing work looking at smaller scale uses of muddy dredged material.

The main emphasis of the research was to undertake detailed physical and biological monitoring of a beneficial use scheme at Shotley in the Orwell Estuary in Essex. The study included measurements of the physical processes at the site, ecological monitoring of the recovery and evolution of the site and, through the application of hydraulic and ecological modelling techniques, an assessment of the factors influencing the ecological recovery. The monitored scheme included different methods for containing the muddy material on the intertidal area and the exposure of the different areas to wave action and tidal currents also varied. The monitored scheme thus provides a useful basis for considering the likely outcome of beneficial use schemes in other locations.

This paper presents the results of the four year project completed in December 2006. It will summarise the key findings of the research and review the current status and potential for large-scale use of muddy dredged material in the UK.

Reference

M. Dearnaley, C. Fletcher, S.Bolam*, A. Kenny*, M. Schratzberger (2007) Large scale use of muddy dredged material for sustainable flood defences and habitat management. Defra Flood and Coastal Defence Conference, University of York, July 2007.