Dredging & Marine Construction

CEDA & IADC Publish New Book, “Dredging for Sustainable Infrastructure”

Dredging is more than simply lifting sediment out of the water and moving it to somewhere else. This was once again obvious on November 19 and 20 in Amsterdam, the Netherlands, when a conference was held with the theme, “Dredging for Sustainable Infrastructure.” The conference marked the launch of the book of the same name, the latest joint publication effort of the Central Dredging Association (CEDA) and the International Association of Dredging Companies (IADC).

Both the conference and the new book confront the complexities of dredging in the 21st century where, more and more, sustainability

Decision tree for implementing a Dredge Management Plan in line with environmental objectives.

has become a prerequisite. After five years of researching, organizing,

writing and editing, an editorial board comprised of CEDA and IADC members has issued this reference work. It captures the dredging industry’s views, advice and specific techniques on how to dredge in a sustainable way. In this time of climate change, where the fragility of the earth becomes more apparent daily, the book is philosophically based, but not with its head in the clouds. It is embedded in mud and sand, a hands-on guide to the practical implementation of environmentally sound dredging methods.

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The new publication is the successor to the co-operative venture of an earlier book, “Environmental Aspects of Dredging” (2008), which focuses on the responsible approach to dredging and disposing of contaminated materials. The new book’s focus is the issue of sustainability, which nowadays is in the forefront of environmental struggles, and not only for the dredging industry.

As stated in the preface of the book, the “leading principle for writing” this highly technical and comprehensive work, “is to achieve dredging projects that fulfill their primary functional requirement, while adding value to the (natural and socio-economic) system based on thorough understanding of the natural system and proactive engagement of stakeholders throughout. This book provides guidance to make this possible.”

Given the often contentious atmosphere in which dredging projects take place, the book also aims to reassure stakeholders that the industry has the best interests of the public in mind. Dredging projects should be viewed as tools to support economic development while simultaneously bettering the environment. That is the basis of “sustainability.”

A horizontal closing grab

Dredging traditionally has been seen as an agent of economic activity. Deepening harbors for increased marine traffic and such. But times change and the focus of dredging as well. Projects should also be informed by the “three pillars” of sustainability: economy is one, but society and environment are equally important.

Cable Arm environmental clamshell.

 One key way to create added value is to consider dredged material as a valuable resource to be used, instead of a waste material that has to be disposed. Another important aspect in implementation is stakeholder-inclusiveness, as early as possible, before the project is set in stone.


Environmental Impact Assessments

The premise of the book is that dredging and sustainability are compatible. One step proposed to integrate dredging and sustainable development is through the use of Environmental Impact Assessments (EIAs). This is not as simple as it sounds. The authors distinguish several stages of EIAs, starting with:

  • “Screening” to confirm an EIA is necessary and, when deemed necessary.
  • “Scoping” then sets parameters for the EIA. This is followed by “baseline data gathering” to set baseline conditions against which impacts can be measured;
  • “An objective environmental assessment” then identifies significant potential negative and positive effects and “mitigation” identifies management tools to avoid or reduce the significant negative effects.
  • “Residual impacts” are evaluated which determine overall impacts of the proposed project and establish monitoring requirements.
    The silt curtain used at Vuosaari Harbour, Helsinki, Finland for tributyltin (TBT) decontamination dredging. Total area dredged: 11 hectares; mean depth 5 meters; total dredged volume, 500,000 cubic meters.
  • “Cumulative impacts” are ascertained for other projects in the entire area.
  • And finally “an evaluation of effectiveness” determines the success of implemented management measures.

Corps Environmental Operating Principles (EOP)

A good example of this complex path to achieving “the application of sustainability” is delineated in the Environmental Operating Principles (EOP) of the U.S. Army Corps of Engineers.

“The Corps dredges (including permits for dredging issued through its regulatory program) approximately 250 million cubic meters [almost 327 million cubic yards] of sediment annually. This level of dredging supports a network of nearly 40,000 kilometers [25,000 miles] of navigation channel and the associated ports, in addition to good risk management and ecosystem restoration projects.”

The EOP was published in 2002 and updated in 2012 and “demonstrates the Corps’ commitment to responsible stewardship of air, water and land resources, while protecting and improving the environment. These principles have been communicated within the Corps … so that each of the more than 30,000 employees of the agency understand his or her responsibility to proactively implement the EOP as a key to the Corps mission.”

Ultimately the EOP recognizes “the importance of considering the long-term, life cycle implications of agency actions, and the essential need to openly engage the stakeholders and interests affected by its projects and programs.”

Equipment, Methods and Data

A chapter is devoted to the comprehensive explanation of dredge equipment and methods of dredging. While most people working in the field will recognize most equipment, there are some good explanations and diagrams that give those less familiar with equipment added information.

For certain methods, such as “environmental mitigation” never enough can be said about what actions can be taken to “minimize or negate potential negative consequences” around the execution of dredging works: options such as “selecting the right equipment, possibly with modifications; for process control and process adjustment; and pro-active actions that can turn negative effects into positive opportunities.” Tools such as silt

Part of the calibration of the numerical model, where blue indicates the simulated sediment flux out of the work zone and red indicates the measured sediment flux out of the work zone.

screens to protect surrounding waters during dredging of contaminated areas are explained. An extensive table provides an overview, per type of dredging equipment, of the most prominent causes for sediment release, and their control methods.

 One aspect of dredging projects, often times not fully discussed, is the importance of reliable data collection and monitoring. And significantly, monitoring is not a one size fits all action. For instance, “adaptive” monitoring is the type of surveillance monitoring, which is associated with adaptive management of the dredging project. The focus of adaptive monitoring is the effective management/control of the dredging works to ensure that any negative environmental impacts remain consistent with (or less than) prediction. Adaptive management uses trigger thresholds for the implementation of pre-agreed management actions.

“Compliance” monitoring on the other hand is conducted during and after dredging to demonstrate whether dredging complies with the requirements of environmental protection mechanisms including legislation, agreements with regulators, licenses or permissions and contract conditions.

Expert Authors

Part of the value of this new book lies in the broad base of the contributors. For each chapter, different authors were recruited to share their expertise. These include private industry consultants such as Witteveen + Bos, Hakstege Consultancy, Royal Haskoning DHV, Danish Hydraulics Institute,

Deltares, Harris Holden Ltd. and HR Wallingford (United Kingdom) as well as academics from Technical University Delft, Wageningen University & Research / Wageningen Marine Research, all in the Netherlands, University of New South Wales, Australia, and the Russian State Hydrometerological University.

A combination of modelling and measurements significantly reduced the cost of monitoring on a relatively small dredging job for an access channel at Storestrommen, Denmark


Dredging industry professionals who contributed come from Royal Boskalis Westminster; Dredging, Environmental & Marine Engineering (DEME); Jan De Nul; Van Oord; Rohde-Nielsen; and the U.S. Army Corps of Engineers, as well as the Port of Lisbon Authority, Dragages Ports (GIE), and the Port of Rotterdam.