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Assessment of Dredging Impacts and Options to Mitigate Impacts

Description:

Billions of cubic yards of material are dredged each year from waterways around the world to facilitate safe and reliable navigation. In the United States alone, the U.S. Army Corps of Engineers dredges over 400 ports and 25,000 miles of channels to ensure the efficient flow of goods to and from more than 200 deep-water harbors. Maintenance dredging of the nation’s navigation channels is crucial for commerce because more than 95 percent of U.S. international trade comes through U.S. ports, and more than 90 percent of all global trade travels by water.

However, many of the nation’s deep-water ports are ill equipped to accommodate the majority of international trade that will be shipped on post-Panamax vessels because of the depth and width limitations of the ship channels and berthing areas. By the year 2030, it is expected that post-Panamax vessels will account for 27 percent of the world’s container fleet and carry more than 62 percent of all cargo. Many of the deep-water ports in the Gulf of Mexico and the southeast United States do not currently have the capacity to support the draft requirements or dockside requirements of post-Panamax vessels or the larger New Panamax (12,000 twenty-foot equivalent unit [TEU]) vessels. Channel deepening and widening projects are being considered in the Gulf of Mexico and along the East Coast that could cost tens of billions of dollars. The demand to service larger ships will increase coastal and harbor dredging.

When managed properly, the increased dredging required to deepen U.S. navigation channels can have positive environmental benefits. For example, over the past 20 years, the U.S. Army Corps of Engineers has been using 20 to 30 percent of port and waterway dredged sediments for habitat creation and other beneficial uses.

However, dredging and development activities to support maritime uses can also:

• Result in suspended sediment.

• Re-expose buried toxic contaminants.

• Create sediment plumes.

• Impair natural habitats, such as wetlands, that help filter nutrients and protect shorelines.

• Increase saltwater intrusion into freshwater ecosystems.

• Disruption of benthic communities.

• Alter tidal circulation and transport.

Mega-dredging projects, like the planned Nicaragua canal, can connect separated waterbodies, expose long-buried contaminants, and introduce new pathways for invasive species. Such projects could have both expected and unforeseen environmental damages that must be managed and mitigated.

Channel deepening, widening, and increased dredging have environmental impacts that include:

  • Diminished water quality from resuspension of sediments and associated contaminants (including toxic substances,
  • Channel deepening can alter sediment dynamics and deposition, which can affect “downstream” habitats such as marshes that rely on sediment and their nutrients for maintaining stability

  • Increased underwater noise, and

  • Vessel collisions with federally listed species.

In addition, there are fewer and fewer viable or economic options for placement areas for the dredged materials. Research into novel or alternative uses for or products from the dredged materials may serve to lessen this burden and produce additional sustainable solutions from a life cycle perspective.

Objective:

A review of dredging-related issues and options could be a useful tool for government agencies, non-governmental groups, and port authorities to better understand the problem and potential solutions. The Review could include:

  • Impacts of channel deepening/widening on hydrodynamics and ecosystems.

  • Effects of increased suspended sediments on marine habitat and the ability of marine life to move from, into, or through affected areas.

  • Application of systems engineering concepts to analyze interdependencies and risk.

  • Indirect impacts of destroying/impairing coastal habitat that helps filter nutrients.

  • Alternative dredge disposal options for beneficial reuse (in-bay, thin-layer, etc.).

  • Methods for fine-tuning or eliminating dredge windows for certain species and geographic locations.

  • New techniques/practices for sediment management (dredging and prop wash).

  • Research into the development of new uses or products from dredged materials, such as for increased erosion protection and berms or dikes.

Benefits:

The information compiled for this study would help local, state, and federal government agencies better understand the impact and possible corrective actions that need to be taken as ports around the world deepen their channels in preparation of the arrival of larger cargo vessels

Related Research:

Environmental impact studies developed by the U.S. Army Corps of Engineers and port authorities for their dredging programs. Academic studies of impacts associated with dredging operations and possible options to mitigate these impacts.

Tasks:

Conduct a systematic and comprehensive review of the literature on the impacts of navigational dredging. Literature review should be divided up into cost and benefit categories, to allow for qualitative comparison of costs and benefits. Special attention should be paid to the value of ecosystem services and how they may be affected.

Implementation:

There should be few barriers to implementing this study as a fair amount of the data are publically available.

Relevance:

Very relevant to local, state, and federal government agencies as ports around the world and in the U.S. prepare for ever larger cargo vessels

Sponsoring Committee:AW030, Marine Environment
Research Period:12 - 24 months
Research Priority:High
RNS Developer:Richard Billings, Edward Carr, Liv Haselbach, and Bret Webb
Source Info:General literature review, to include studies academic studies as well as those implemented by the U.S. Army Corps of Engineers, National Oceanic and Atmospheric Administration, the U.S. Geological Survey, and the Bureau of Ocean Energy Management.
Date Posted:12/14/2017
Date Modified:12/22/2017
Index Terms:Dredged materials, Dredging, Ships, Water quality, Environmental impacts, Channels (Waterways),
Cosponsoring Committees: 
Subjects    
Marine Transportation
Freight Transportation
Environment

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