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Dredging waterways: Turning muddy muck into something sustainable

Dredging and beneficial material reuse—it’s not merely possible but should be best practice

A barge-mounted excavator mechanically dredges a canal.

By Matthew Starr, Southeast Coastal Team Leader (Naples, Florida)

Florida has more than 11,000 miles of rivers, streams, and waterways, and 2,200 miles of coastal/tidal shoreline. That means dredging projects are commonplace and are typically initiated to aid in navigation or for water quality improvement projects.

During the 1950s and 1960s, there was a statewide construction boom to create manmade residential canals for waterfront homes. In the past 60 years, these canals have had minimal maintenance and have accumulated layers of fine-grained sediments with mud and decaying organic material—with some areas containing depositions of mud that are 15 feet thick!

The sediment and mud must be removed to maintain boating access and ensure compliance with state water quality standards. So, what’s the risk? The sediment and mud could possibly contain contaminants—including many of the priority pollutant materials designated in the Environmental Protection Agency’s Resource Conservation and Recovery Act (RCRA) like arsenic and copper, which are commonly found in pressure-treated pilings for docks/boat lifts and anti-fouling paint used on the bottom of boats.

Related item: Community Development: Bringing community to life

A hydraulic dredge removes sediments within a residential canal.

What should you expect from your coastal engineering consultant when dealing with dredge material that possibly contains contaminants? Here’s the approach my team takes on a typical dredging project:

  1. Detailed data collection early on to identify exactly what’s in the sediment.
  2. If the sediment is free of contaminants, we investigate beneficial reuse solutions and consider the dredge material as a commodity, with both economic and structural value including being used for:
    ∙   Fill for bank erosion or shoreline stabilization
    ∙   Living shoreline and habitat island creation
    ∙   Top soil spread on local agriculture and farm pastures
    ∙   A daily cover at local landfills
    ∙   Stockpile material for future project needs
  3. Initiate interdepartmental and local communication to identify other public needs for fill material. Finding beneficial reuse for the dredge material saves our clients future dollars by limiting the need to purchase fill for other construction projects.
  4. Develop disposal options for potentially contaminated materials if the dredged material is unable to be reused. Typically, the dredge material can be dried and mixed with clean fill to create environmentally-compliant material. If the material can’t be brought below soil cleanup target levels, then it’s disposed of at a lined landfill, which may be a more expensive option.
  5. Obtain proper state and federal permit authorizations by conducting professional bathymetric and topographic surveys, ecological resources investigations, pre-application permit meetings, and performing dredge template engineering design based on the collected data.
  6. Upon receiving executed permits, we help guide their client through the complex construction bidding and contractor procurement process. The most important part of the project is selecting a highly qualified and experienced marine contractor that has the knowledge and capacity to complete the dredging project. This is where the “rubber meets the road,” or in this case, the water!

A hydraulic dredge pipeline discharges sediment into dewatering basin.

What benefits does dredging provide? The removal of the mud and fine-grained sediment provides environmental restoration, allows for increased boating access and recreation, increases water quality, spurs economic development along underutilized corridors, increases livability and property values along the waterways, and may even increase jobs depending upon location. The possible economic, social, and environmental benefits to dredging are numerous—and one of the reasons I’m passionate about my career.

Our approach to dredging and dredged material management works, and we’ve got a successful track record with local/state municipalities, private developers, water management districts, the US Fish and Wildlife Service, and the Natural Resources Conservation Service to prove it.

Related item: Freshwater & Marine

Matthew is the Southeast Coastal Team Leader and Project Manager in the Water division of Stantec. He’s based in Naples, Florida, along the Gulf of Mexico.

A successful dredging project requires an experienced team of coastal engineers and scientists.

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