Innovation in Progress: addressing coastal erosion by reusing dredged sediments

Dredged silt from the Suriname River: waste or beneficial material? The Weg naar Zee project, funded by Partners for Water, investigated whether silt dredged from the Suriname River could be used to address coastal erosion and mangrove losses along the Suriname coast. Last month, the feasibility study concluded with promising results. Below, Bob Smits from consortium partner Deltares explains the potential of dredged silt.

About 8 years ago, Nature-based Solutions Advisor Bob Smits completed his master’s thesis on mangrove restoration at the independent knowledge institute Deltares. Since then, he has developed his expertise in coastal protection and management, particularly in sediment transport. In the Weg naar Zee project, Bob serves as the technical lead and project coordinator.

The Weg naar Zee feasibility study was conducted in collaboration with Boskalis, Conservation International Suriname, InterConnect and the Anton de Kom University of Suriname.

Natural buffer

The coastal area of Weg naar Zee is an intertidal zone nearly two kilometres wide, located directly west of the Suriname River mouth. “The coastal area used to be covered with mangroves,” Bob explains, “but over the past decades, it has eroded significantly due to changing land use, leading to the disappearance of almost all mangroves.” These mangroves served as a natural buffer against erosion and flooding. “With the loss of this buffer, flooding now occurs regularly.”

However, the Suriname River is being deepened to improve navigation, releasing large amounts of silt. “Currently, this material is being released into the ocean, but it is actually a valuable resource that can be utilised,” says Bob. “With this project, we aim to investigate whether we can use this dredged material to combat further erosion.”

Silt, sand, and mangroves

“We have some interesting findings from the analysis of the historical coastal development,” Bob says. “Sand appears to play a significant role in the natural restoration of mangrove trees. This can be observed in an area west of Weg naar Zee, where mangroves have returned without active human intervention. We suspect this is due to the natural formation of sandbanks in the intertidal zone, which cause the area behind them to fill with silt, creating an ideal habitat for mangroves.” However, no sandbanks are being formed on the foreshore of Weg naar Zee. “This is most likely caused by previous sand extraction east of the Suriname River and damming upstream of the river.”

Stimulating mangrove habitat

“The potential role of sand is a significant insight that we incorporate into our recommendations,” says Bob. “We see the possibility of placing artificial sandbanks, which would allow us to fill the area behind them with the dredged silt.” This solution would improve the natural conditions for a mangrove habitat, enabling the trees to grow again and form a natural buffer. He continues, “Reusing silt from dredged material is already being done in several places, and is widely acknowledged as a promising concept. However, this combination of using dredged silt and sand for the benefit of mangrove restoration and erosion control is still new.”

Valuable collaborations

“During the research, we involved local stakeholders, such as the Ministry of Public Works and local residents,” notes Bob. “Not only are they the problem owners, but they also possess a lot of local knowledge that we can combine with our international experience. We also owe a great deal to the Dutch Embassy in Suriname, which helped us significantly in arranging meetings with the Ministry of Public Works.”

“I believe the most important aspect of collaboration is to have mutual respect and to be open to each other’s experiences and knowledge,” says Bob. “As a Dutch entity, I view challenges and solutions with my Dutch framework. To develop a solution that is adapted to the local context, it is essential to ask for input and knowledge from local parties and stakeholders and to truly work together towards a collaborative resolution.”

What’s next

“The results have been well received by the Ministry of Public Works and the local residents,” says Bob. As a follow-up to this feasibility study, the consortium would like to initiate a pilot project and is currently exploring available financing opportunities. As Bob explains, “The situation of coastal erosion and mangrove loss we have investigated is similar to the rest of the Surinamese coast and also to that of neighbouring countries Guyana and French Guiana. So if our planned pilot-project is successful, there are plenty of opportunities to scale it up.”