What is dredging? 

Dredging is the removal of sediment from the bottom of waterways, including coastal harbors.  Sand and silt move over time due to natural physical processes, filling in channels and harbors – a process known as sedimentation. Dredging removes the built-up sediment to maintain and improve navigation, anchorages, and berthing areas for safe operation of vessels. Environmental dredging, another form of dredging, is utilized to prevent the spread of contaminants and limit exposure to marine life and humans through the removal of contaminated sediment.1 

In the United States, dredging and disposal activities requires extensive review and permitting before the removal of sediment can occur. Permitting is required by the U.S. Army Corps of Engineers (USACE) in coordination with the Environmental Protection Agency (EPA), and also by several other local, state, and federal agencies focused on assessing impacts of dredging to endangered species, wetlands and fish habitats, and other coastal issues, depending on project-specific factors. 

Why do coastal communities dredge? 

Because dredging is essential to navigation, it plays a critical role in national and local coastal economies. In many locations, without dredging, the flow of goods, commercial services, and recreational uses would be greatly reduced or could stop entirely. It is no surprise, then, that dredging is a hot topic when developing harbor management plans.  

In most coastal communities in Massachusetts, the need for dredging is specific to maintaining navigation of waterways used for recreational and commercial boating. This includes maintaining appropriate depth in channels and within public and private marinas and mooring areas.  

Massachusetts is home to several deep-water ports such as the Port of Boston and the Port of New Bedford. These harbors require intensive dredging to support access and movement of commercial vessels, including cargo for ships, commercial fishing boats, cruise ships, and ferries.  

Additionally, many harbors along the coast of Massachusetts, are relatively enclosed and protected. These embayment‘s, have little exposure to wave energy, (making them ideal harbors). However, issues can arise when the transport of sediment is slow, due to a lack of currents and waves. The process of natural sedimentation is made worse by human activities like coastal development, artificial barriers, and the construction of in-water infrastructure (e.g., piers). 

Nutrient pollution from wastewater and surface water runoff can also impact the depths of waterways. Excess nitrogen can result in the overgrowth of algae. The decomposing algae matter can build up bottom sediment over time. 

What dredging concerns arise during the harbor planning process? 

Managing the dredge spoils 

Municipalities have to determine what can be done with the dredged material once removed from the waterways. There are several methods for disposing of dredged spoils, all of which require the material to undergo sampling and testing protocols before a permit can be issued. One of the most common (and easiest and most cost-effective) methods is using dredged material for beach nourishment, which helps provide sand for beach sites that need regular replenishment due to sediment loss from erosion. However, for this method to be viable, the dredged spoils must be clean of contaminants and similar in grain size to the disposal site.  

If the material is not suitable for beach nourishment, alternative disposal methods include offshore disposal or creating upland stockpiles (allowing dredged material to dry) for disposal. These alternative methods come with additional testing to ensure that materials are managed in an environmentally responsible manner. Furthermore, transporting the material to an appropriate upland site can increase project costs and extend the timeline.  

The permitting process 

When applying for dredge permits, applicants must meet several requirements that can complicate and extend the process, particularly for projects that involve dredging in new areas. Some permitting reviews can even take five years or more.  

 Key considerations for permitting include: 

  • Sediment Analysis: The physical grain size of the sediment to be dredged must be analyzed, and additional testing for chemical contaminants may be required upon outcome of analysis.  
  • Boundary Evaluation: The proposed dredged area boundaries need to be assessed for coastal wetland resources and sensitive habitats to minimize the environmental impact of dredging activities. 
  • Coordination with Regulatory Agencies: If dredging is planned in critical resource areas or sensitive habitats, further coordination may be required with: 
    • Mass Wildlife’s Natural Heritage and Endangered Species Program 
    • MA Division of Marine Fisheries 
    • NOAA National Marine Fisheries Service  
  • Environmental Review: Projects proposing to dredge above the mean high tide line must also undergo review by the Massachusetts Environmental Policy Act Office. 

Balancing uses of waterways with environmental impacts 

While dredging can be a tool for improving water circulation or removing contaminants from waterways, it also has the potential to negatively impact the marine ecosystem. Potential impacts include a short-term increase in suspended sediments that can block sunlight, and damage to bottom habitat, including such as fish spawning grounds and eelgrass habitat.   

For many coastal communities, dredging is essential for creating and maintaining navigable waters; however, when expanding navigation channels or deepening naturally shallow waterways, it is crucial to consider the potential environmental impacts of altering the ecosystem.