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BENEFICIAL USE OF DREDGED MATERIAL

FACT SHEET CEDA-IADC

WHAT IS BENEFICIAL USE OF DREDGEDMATERIAL?Dredging is essential for the maintenance and developmentof waterways and ports, as well as navigation, landreclamation, environmental and ecosystem improvement,drainage and flood management. Dredging removeslarge volumes of sediments that need to be appropriatelymanaged and beneficial use is the preferred way tomanage dredged material. It concerns the use of dredgedor natural sediment in applications that are beneficial andin harmony with human and natural development (CEDA2019a).

WHY IS BENEFICIAL USE OF DREDGEDMATERIAL NECESSARY?The best way to manage dredged material sustainablyis by using dredged sediments beneficially. The mostimportant principle to consider is that dredged materialis a resource instead of waste. It should not be seen interms of a material that needs to be disposed of. Instead itcreates societal, environmental and financial benefits withits reuse. Because large volumes are involved, being ableto potentially use dredged material represents a significantsustainability contribution. Nature based solutions are themost sustainable. Dredged material can be used for floodand coastal protection, which may be important to mitigatethe effects of climate change (CEDA, 2012) and landsubsidence, but also for the improvement of habitats andrelated ecosystem service functions, and as constructionmaterial.

Dredged sediments are an essential component of naturalsediment cycles and ecosystems. Therefore, the optionof retaining dredged material within the same aquaticsystem (sustainable relocation) should be considered first(CEDA 2009). Dredged material consists of sedimentarydeposits of natural materials such as clay, silt, sand, gravel,rock and organic matter. In general, dredged material canbe used beneficially immediately and without treatment.Only a small portion of sediments are contaminated to an

extent that it leads to increased costs in dredged materialmanagement. Contamination does not rule out beneficialuse. If required, treatment options are available (see CEDA2019b for further reading).

WHY IS BENEFICIAL USE NOT YET A COMMONPRACTICE?Generally the public an some National Authorities considerdredged material to be waste and is often in favour ofupland confined disposal, thinking this is to contain it.However, this type of disposal disregards its potential valuefor beneficial use, that is, as a savings on primaryresources. Moreover, this type of disposal is usually moreexpensive.

Other major constraints are the difficulty in finding suitablelocations for its use and complex and inconsistentlegislation. Because there is often no legislation specificallyfor dredging or for dredged material management,decision-makers need to deal with a patchwork of differentrules, such as regulations to protect the ocean, inlandwater, residential areas, the environment, nature and forthe handling of waste. Many different permits may berequired.

HOW CAN BENEFICIAL USE BE IMPLEMENTEDIN A DREDGING PROJECT?Matching supply and demand, taking into account quality,quantity and timing, determines the potential of dredgedmaterial for beneficial use. Therefore, beneficial use shouldbe considered in an early stage of a project together withrelevant stakeholders, particularly because communicatingof project timings and the availability of material can be adetermining factor. Legislation, but also its interpretation byregulators, can be a key driver for considering dredgedmaterial as a valuable resource, and also in facilitatingits use. Important technical criteria in the process arethe suitability of the material for use, where and howit was dredged, the opportunities available for its use,the characteristics of the proposed site for use and itsenvironmental and social acceptability (CEDA/IADC 2018).

Above: Sediment from maintenance dredging is used to restore local intertidal mudflat and saltmarsh habitats that have been subject to erosion over recent decades.

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To arrive at environmental enhancement through the use ofdredged material, an understanding of the natural system iscrucial. This will allow for an assessment of both the potential environmental benefits and risks. Environmentaland social benefits should be included in a cost-benefitanalysis.

As we underline, dredged material should be consideredfor beneficial use before disposal is considered, andpreferably it should be kept within the system (sustainablerelocation). The key factors to promote and increasesuccessful beneficial use and instances thereof are asfollows (PIANC 2009b):

• Consider the use at an early stage to allow for matchingsupply and demand;

• Engage stakeholders and partners at an early stage• Inform the regulatory process about the benefits and

potential risks) of using dredged sediments.;• Analyse comprehensively the social, environmental and

economic costs and benefits of a project, taking intoaccount the longer term;

• Make commitments to develop knowledge and furtherinnovation;

• Exchange knowledge in lessons learned from projects.

WHAT TYPES OF BENEFICIAL USES AREAVAILABLE?The two main types of beneficial use are environmentalenhancement and engineering uses. Some optionsbelong to both types.

ENVIRONMENTAL ENHANCEMENTSustainable relocationSustainable relocation of dredged material is theintroduction of dredged material into aquatic systems tomaintain and/or supplement sediment supply. It is placedthere to sustain natural processes. A number of situationsexist where regular removal of sediment by dredging fromthe aquatic system may cause physical problems suchas erosion and unacceptable impact to the environmentand ecosystems. In these cases, recycling the sedimentwithin the natural sediment transport system may provide asolution.

Habitat creation and improvementDredged material can be used in various ways to createor maintain marine wildlife habitats. These include thefollowing types: intertidal mudflats, salt marshes andwetlands. These habitats can be for birds (upland habitatsand nesting islands) and aquatic habitats can be forfish and benthic organisms including aqua culture. It isimportant to note that mudflat nourishment and marshrecharge may also contribute to flood protection. Extensive

shallow fore-shores are created by placing fine-graineddredged material in intertidal areas to restore or extendestuarine mudflats. This technology has been mostextensively developed in the USA. In Europe, mainlysmall-scale projects are being undertaken, including in theUK and the Netherlands. It should be noted that thecreation of any new habitat means replacing an existingone. A full environmental cost-benefit study is alwaysnecessary before making a decision and any scheme willinevitably mean some losses as well as gains.

AgricultureDredged material from mainly rivers and inland waterwayshas been used in agriculture, horticulture and forestry. Itsprimary drawbacks are possible contaminants includingsalt (in the case of marine sediments), and regulatoryconstraints.

RecreationThis involves the creation of amenities, for example hikingtrails, through marshlands, or access to constructed orexisting waterways. It should be noted that habitat creationand enhancement areas as well as beach nourishment forflood protection could also create significant recreationalbenefits which may not have been their primary purpose.

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Creating coastal wetland habitats for wildlife diversity using sediment from maintenance dredging.

De-watered sediment from inland waters is used as agricultural soil.

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Amenity in this context means the improvement or provisionof facilities that are designed for recreation. It includes theregeneration of derelict land, landfill, landscaping and thecreation of recreation areas.

Rehabilitation of borrow pitsArtificial depressions, such as borrow pits from theextraction of sand and gravel, in and near river, estuarineand marine systems, are potentially very useful locations toplace dredged materials. Filling pits can offer opportunitiesfor environmental improvement. Many pits are quite deepwhich leads to the development of a stagnant, anoxic zonewith negative effects for the ecosystem. Dredged materialcan be used to make the pits shallower and thus eliminateanoxia and improve ecological conditions.

ENGINEERING USESFlood and coastal protectionThere are several ways in which dredged material can beused in flood and coastal protection schemes. Examples areas follows:• Beach nourishment and the direct replacement of eroded

beach material. This is now an accepted form of ‘soft’coastal defence. In the past, it was usually required thatthe beach be nourished with similar material to what haderoded. Research has led to the creation nowadays of amore stable beach with a different profile.

• Development of unenforced coastlines (managedretreat). This approach is suitable for muddy coastsbacked with low-value land. The objective is to createa buffer zone by setting back the defence works andbreaching the existing wall.

• Mudflat nourishment and marsh recharge. By placingfine dredged material in intertidal areas for restoration orto extend estuarine mudflats, the extensive shallow foreshores also contribute to flood protection.

• The formation of offshore berms designed to modify thewave climate. These berms may be hard (rock) designedto withstand wave energy, or soft (sand) designed toabsorb wave energy. It is also possible to form sacrificialfeeder berms supplying the sediment intended to moveonshore.

• The placement of dredged material on the banks ofwaterways and upland. To gain elevation and use ofdredged material for dyke, dam or dune construction forflood protection.

ConstructionIn the construction industry, dredged material may be usedfor the following purposes:• Construction material and reclamation. Dredged

material such as sand, clay and gravel can be used asan alternative for some primary resources. These may beused as construction material for many applications suchas land or mine reclamation, replacement fill, land-fillcover, road foundations and noise barriers.

• Land reclamation. Dredged material may be used toconstruct islands and other man-made land. In the caseof traditional land reclamation, the material is excavatedspecifically for this purpose.

• Land development. Dredged material may be used todevelop commercial sites (e.g., rehabilitating ofbrownfield sites, agriculture land and recreational sites).

• The production of aggregates and mudcrete (mudstabilised with cement). The sand and gravel componentof dredged material arising from capital dredging andthe maintenance of a certain site may be used to makeconcrete. Logistics and economics are the biggest issues.

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Clean dredged sediment is used to cover and landscape the upland CDF of dredged harbour silts (Hamburg, Germany).

Cliffe Pools, UK: a win-win for river dredging and nature.

Using dredged sediment for coastal defence and habitat restoration, Horsey Island 2009 (Jim Pullen UAV Surveys, April 2017).

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• Filling geotextile containers. These include sandbags,geotextile tubes and geotextile containers. Existingand possible uses for geotextile containers includedyke construction, groynes, breakwaters, sand dunestabilisation, stabilisation of banks of waterways andwetland stabilisation.

• The manufacture of synthetic building materials.Several methods have been developed to re-usedredged sediments to manufacture synthetic buildingmaterials such as bricks and artificial gravel. Economicfeasibility is a major constraint for these uses.

SEDIMENT MANAGEMENT TECHNIQUESThis is a different category that does not directly deal withthe use of dredged material but with the management ofon-site sediments. The aim is to create benefits such asreducing the volumes to be dredged using engineeringtechniques. Another example is landscaping the sea- orriverbed to restore the ecology of the underwater landscapesand and gravel have been extracted.

The analyses of numerous case studies in CEDA 2019a and CEDA 2019b demonstrate that there is significant technical knowledge on and experience with the beneficial use of sediment. The case studies can be found on the CEDA website.

IS THE FUTURE OF USING DREDGED MATERIALBENEFICIALLY?Global and regional conventions on dredged materialmanagement have recently led to the publication of recentlypublished guidelines that acknowledge the origin andspecific properties of dredged material and activelypromote beneficial use of dredged material (LC/LP, 2013;OSPAR 2014), stating:

‘Sediment is an essential component of fresh water,estuarine and marine ecosystems. Sediment processesplay important roles in determining the structures andfunctions of aquatic systems. Therefore, managementprocesses applied to sediment, in relation to humanactivities, should recognise that sediment is an importantnatural resource.’

In addition, in many countries disposal is becomingincreasingly difficult owing to the lack of space and toenvironmental concerns. Because of this, there is a growinginterest the potential of dredged material as a resource.

Good communication is essential to gain support fromthe public, regulators and other stakeholders. Goodcommunication is needed for dredged material to be viewedas a valuable resource and prevent it being stigmatised aswaste.

Several international programs and initiatives centred onthe sustainable and nature-based development of hydraulicand civil infrastructures seek to support the sustainabledevelopment of infrastructure through a better alignmentof engineering and natural systems and their integration.The beneficial use of sediment is a key, constant themeacross these programmes.

WHAT IS RELEVANT LITERATURE?The various management options are discussed in-depth inthe publications below.

Aarninkhof, Stefan, Laboyrie, Polite & van Koningsveld,Mark, 2018. Dredging for Sustainable Infrastructure.(CEDA/IADC).

CEDA, 2010. ‘Dredged Material as a Resource: Optionsand Restraints’. A CEDA information paper.

CEDA.-- 2012. ‘Climate Change Adaptation as it Affects theDredging Community’. A CEDA position paper.

CEDA 2019a. Sustainable Management of the Beneficialuse of sediments. A CEDA information paper.

CEDA 2019b. ‘Assessing the Benefits of UsingContaminated Sediments’. A CEDA position paper.

IADC, 2009. ‘Facts about Dredged Material as a Resource’.An IADC technical report.

LC/LP, 2013. Revised Guidelines for Assessment ofDredged Material.

OSPAR, 2014. OSPAR Guidelines for the Management ofDredged Material at Sea.

PIANC, 2009a. ‘Dredging Management Practices for theEnvironment: A Structured Selection Approach’. PIANCEnviCom: Report 100, a technical report.

PIANC, 2009b. ‘Dredged Material as a Resource’. PIANCEnviCom: Report 104, a technical report.

Geotubes for bank stabilisation.

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The book Dredging for Sustainable Infrastructure gives state-of-the-art guidance on how to design, implement and manage a water infrastructure project with a dredging component to project owners, regulators, consultants, designers and contractors.

More information:IADC CEDA +31 (0)70 352 33 34 +31 (0)15 2682575 info@iadc-dredging.com ceda@dredging.org

THIS FACT SHEET IS BASED ON THE BOOK DREDGING FOR SUSTAINABLE INFRASTRUCTURE

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