Reusing Dredged Sediment: A challenging approach to sustainability
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Climate Change has prompted a rise in projects to protect sensitive habitats and develop flood defences in coastal regions around the world. Increasingly people are discovering the benefits of reusing dredged sediment as a sustainable solution to help in protecting wildlife and stemming tides.
New habitat restoration efforts have been underway at Gull Island, New Jersey, USA, and have utilised reused dredged sediment. The recently completed Gull Island Restoration Project set out with the goal to protect the abundance of wildlife found in its marsh areas.
The project is a collaboration between Philadelphia District (NAP) partnered with USACE Engineer Research and Development Center (ERDC), the State of New Jersey and The Wetlands Institute. In 2020, work was completed to raise marsh elevation to create safe areas for local salt marsh sparrows and wading birds. It also restored unvegetated interior mud flats, enhancing tidal flats, to improve habitat for fish and reduce marsh edge erosion.
While treating reused dredged sediment can be costly and there can be challenges around availability of suitable sediment and administrative burdens associated with its use, for many, the benefits still outweigh the negatives. The Gull Island team follow in the footsteps of other successful projects to protect and improve the habitat and biodiversity of marine wetlands such as the Marker Wadden restoration project. This was one of the biggest nature restoration projects in western Europe, restoring an area of up to 100 square kilometres in the Netherlands. Depositing dredged sediments in layers on marine wetlands and retreating vulnerable coastlines has also been undertaken at Horsey Island with sediment from the Harwich Channel Deepening project.
Gull Island, in Cape May County, New Jersey, supports nesting for 25% of the wading birds in New Jersey. In recent years there has been a decline in suitable habitat to support these birds at Gull Island, with remnants of previous dredging placements providing support to the only remaining suitable habitat areas. Low marsh and inland tidal flats along the southern portion of the island were selected for dredged material placement to build elevation on the marsh platform, as well as along the subtidal flats that protect the marsh edge from erosion and support wildlife.
In 2020, Philadelphia District (NAP) partnered with USACE Engineer Research and Development Center (ERDC), the State of New Jersey and The Wetlands Institute (TWI) to place dredged material from the NJ Intracoastal Waterway through the Seven Mile Island Innovation Laboratory. Success of the dredged material placements at Gull Island is still being evaluated. Field data collection in July 2021 will inform the mass balance, and stability of the marsh platform.
Innovative uses
While the Gull Project uses a traditional approach to the reuse of dredged sediment, more modern, unconventional methods are being developed to deal with the shortage of construction materials. Proposals to use dredged sediment to make bricks and roads are currently being explored.
A group of French researchers from Normandy University, the University of Lyon and Gustave Eiffel University have put forth a case study centred on reusing dredged sediments from the Usumacinta River in Mexico for the manufacture of bricks. The process requires analysing the reused dredged sediment’s particle size distribution, plasticity, chemical analyses and mineralogy to determine its suitability. It has been shown that sediments can be used as a primary raw material in the production of fired bricks, and the type of clay and sand and their ratios impact the partial or total replacement in fired brick.
The researchers claim their study has proved that producing sediment-based bricks saves primary and natural resources and can also incorporate other waste materials. The researchers also found that treatment with cement can improve the short-term and long-term mechanical performance of building materials created from reused dredged sediments. It is hoped that the study will prompt the use of reused dredged sediment in building materials for Safia harbour in Morocco, including a layer of pavement foundations.
Long Term Goals
While there are many success stories with the reuse of dredged materials there are still some challenges to overcome before it is more widely used. Effective marine plan policies need to be set up globally to help increase the use of dredged sediment and more research done to provide governments with clear benefits, costs, and legislative barriers to its use. Standard, recognised frameworks should be developed to provide industry and governments with guidance on how reusing dredged sediment can be done safely and responsibly.
However, the previous projects’ success stories speak for themselves and it is likely we can expect to see more projects reusing dredged sediment in the future with the right support from governments in place.
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