Brightlingsea Harbour Commisioners, Dredging and Restoration Year 1 Works

Project Description

Dredging, hopper barge, grab dredging, mechanical dredging

The end of March brought to a close the Year 1 dredging and restoration works being carried out within Brightlingsea Creek, Essex as part of the “Using Sediment As a Resource (USAR)” programme, on behalf of the Brightlingsea Harbour Commissioners, the managing authority of the local waterways.

As Principle Designer for the works, Exo Environmental have developed a four year project that aims to dredge approximately 50,000cu.m of accumulated sediment, which is currently causing concern for the continued safe and efficient use of this busy harbour. This sediment is to be beneficially used on site (BUDM), to restore nationally and internationally recognised intertidal mudflat and saltmarsh habitats to their historic extent (1940’s) following decades of erosion.

The beneficial use of dredged material in this occasion is made possible by containing it in compartments of brushwood fascines, due to the close proximity of the navigation channels to the restoration sites. The brushwood retaining structures allow dredged sediment to be contained to form a natural gradient from the mature saltmarsh down to the intertidal mudflats. Currently the mature marsh is eroding with a 1 to 1.5 metre cliff face susceptible to wave impacts.

The design by Exo Environmental involves careful consideration of environmental conditions and impacts on archaeological assets. It incorporates a combination of natural material, including hemp matting to retain sediment whilst it consolidates.

Year 1 saw the dredging of the harbour approach, Main Channel and access routes to the commercial wharf located within the North Channel. Local dredging company Port Flair, were selected as Principal Contractors for the works, bringing with them a wealth of local knowledge, experience and tools to achieve the first year targets. A combination of water injection dredging, plough dredging and barge-mounted excavators were all utilised in order to obtain target depths and create a level bed profile in the main channels for ease of navigation and maintenance.

Grab dredging, BUDM, beneficial use of dredged material

Year 1 also saw the beginnings of the long anticipated restoration works. This involved the installation of ca.300m of brushwood fascine by Exo and Brightlingsea Harbour staff, to form four compartments in 2017. Further compartments will be created in 2018 and 2019 to realise 4ha of restored saltmarsh in the Brightlingsea Creek.  This is a traditional technique that has been in existence across northern Europe for centuries and involves the construction of a retaining wall 0.5m in height and is comprised of locally sourced, untreated timber posts and brushwood faggots secured with manila rope. The retaining structure installed created four compartments covering an area of c.3000sq.m on the south bank of Cindery West, an important site for summer breeding birds and foraging ground for overwintering species.

Once installed, dredged material excavated from the main channel was placed behind these structures as part of the restoration works. The brushwood structures successfully retained the newly placed material, whilst the sediment can now dewater, consolidate and stabilise, with the intention that biological colonisation and subsequent succession will lead to the reestablishment of saltmarsh vegetation.

Ongoing monitoring of the site, through aerial drone surveys, geotechnical testing and ongoing research with our partners the University of Essex and the University of East Anglia will continue to assess the success of the project and allow further refinement and improvements to be made if required. Early investigations however, have found high levels of biofilm production, indicating that the local biology is already taking advantage of our hard work! Long let it continue.

Brushwood, Brushwood bundles, Fascines, Polder

 Exo – Environmental have undertaken consultancy to a number of Projects ranging from a simple marina dredge to an incredibly complex European Partially funded experimental sedimentation project (USAR).

 Brightlingsea Harbour commissioners have worked with them for a number of years and continue to do so.

 The close working relationship with them has enabled us to deliver successful undertakings, safely and on budget within an extremely vigorous legislative framework.

 Sediment management requires a great deal of creative, sensitive and innovative strategy whether dealing with the material or stakeholders, be it local groups, interested parties, environmental or government agencies.

 Measuring success is a critical component of the overall delivery and the comprehensive surveying techniques employed by Exo have enabled us to develop another element of our revenue raising capacity.

 I have no hesitation in recommending the above said contractor to any organisation looking for a complete solution to any water-based challenge.

 J Thomas

Harbour Master

Brightlingsea Harbour Commisioners

Project Details

  • AuthorWilliam Coulet
  • ClientBrightlingsea Harbour Commissioners
  • DateMarch 2017
  • CatergoryDredging