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Challenges presented by ongoing dredging have led to innovative solutions.  Dredging activities in coastal waterways are routinely required to maintain safe navigation for both commercial and recreational boating.  Regional dredging needs assessments indicate that millions of cubic yards of dredge material are generated annually within the New England area alone.  While much of this dredged sediment is suitable for reuse as beach replenishment because of its sandy nature, significant quantities of dredged sediment are too fine-grained for beach nourishment, and must be placed elsewhere.   

Historically, the presence of fine-grained sediments (fines) has dramatically increased the cost of dredging projects.  Today, the use of innovative management practices in one or more phases of dredging can help to reduce construction costs and provide a beneficial environmental resource using the fine-grained dredged material. 

The Centerville River dredging project located in the Town of Barnstable on Cape Cod, Massachusetts exemplifies the use of innovative management practices for fine-grained dredge sediments.  The Woods Hole Group worked with the Town of Barnstable to design, permit, and implement a dredging project that involved the removal of a mixed sand and fine-grained substrata from the Centerville River.  The primary objective was to reduce costs by maximizing the separation of fines from the sand-sized sediments.  Sandy dredged sediments were planned for onsite beach nourishment, which saved cost by reducing the volume to be trucked offsite.  The finer-grained sediments were trucked offsite for upland beneficial reuse.  A secondary objective was to use the Barnstable County hydraulic dredge, which offers its services at substantial cost savings. 

To accomplish these objectives, the project team utilized an innovative and low-cost approach to separate and dewater sediments in the dredged slurry.  Two in-situ dewatering basins were constructed at the nearby public Craigville Beach, and used to hydraulically sort sands from the fine-grained sediments.  The combination of dewatering basin design and coordinated dredging operations resulted in successful completion of the project. 

  

At the Craigville Beach project, environmental benefits also were maximized through beach nourishment and upland beneficial reuse, while project costs were minimized through innovative and effective management of the fine-grained dredge material.  By separating the fine material from the beach-compatible sand, approximately 6,000 extra cubic yards of sand were available for beach nourishment.  The volume of sediment to be trucked offsite also was reduced proportionally, resulting in a cost savings of approximately $50,000 or 10% of the construction costs for the project.

 

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Woods Hole Group