Beneficial Uses of Dredged Sediment

Description:

The Fehmarnbelt Tunnel is an 18-kilometer immersed tunnel currently under construction beneath the Baltic Sea, connecting Rødbyhavn on the Danish island of Lolland to Puttgarden on the German island of Fehmarn (Femern n.d.). The massive scale seabed excavation has created a trench 90 m wide and 16 m deep. This excavation has necessitated a major ecological restoration and land reclamation plan. Rather than disposing of the excavated soil, project planners realized the dredged material provided a "win-win" opportunity to establish new coastal wetlands, beaches, and reefs to offset historical ecological degradation and the localized impacts of construction (DHI n.d.).

The overall footprint of this effort will yield approximately 19 million cubic meters of dredged sediment. The Fehmarnbelt area is highly valuable ecologically, serving as a critical migration corridor between the North Sea and the Baltic Sea for marine mammals, fish, and birds, and containing several Natura 2000 protected habitats (BFN 2026). The comprehensive restoration plan focuses on using the excavated seabed to build artificial peninsulas that extend about 500 meters into the sea on both the Danish and German coasts. This includes creating over 300 hectares of new coastal wetlands, lagoons, and dune landscapes, as well as establishing 42 hectares of new marine reefs (BFN 2026).

The project's official treaty was signed in 2008, with actual offshore construction and early dredging works commenced in June 2020. The total project cost is estimated at over €7 billion (approximately $8.2 billion USD), primarily financed by the Danish state-owned company Femern A/S, with additional funding for hinterland connections (Geoengineer 2025). To excavate the 19 million cubic meters of required sediment, the contractors (Fehmarn Belt Contractors, a joint venture of Boskalis and Van Oord) are utilizing mechanical dredging (using specialized backhoe and grab dredgers) for the shallower trenches and to carefully extract hard "upper till" clay without destroying its structural integrity, alongside hydraulic dredging (using Trailing Suction Hopper Dredgers, or TSHDs) for the deeper, silty sections (DHI n.d.).

The Baltic Sea and the specific Fehmarnbelt project area host sensitive wildlife, including harbor porpoises—a strictly protected cetacean highly vulnerable to underwater construction noise and eutrophication (BFN 2026). The area is also a vital flyway for migratory birds and supports various benthic flora and fauna. To date, the project is considered a massive engineering and environmental success, though it is still actively ongoing (scheduled for completion around 2029–2031). The beneficial reuse of the sediment is proceeding precisely as modeled, with strict sediment spill budgets enforced through advanced recirculation systems on the dredgers (Femern n.d.). In 2024, newly created compensation habitats, such as the Lungholm Lake area, were already seeing an influx of diverse bird species and protected plants, proving the viability of the "Working with Nature" design philosophy (Femern n.d.).

Published Articles & Case Studies:

• Iversen, C., van der Weck, A., & van der Klis, P. (2022). The Fehmarnbelt tunnel trench dredging project. Terra et Aqua, 168, 16–27.

Website Links Discussing the Project:

• Femern A/S. (n.d.). Fehmarnbelt Tunnel. Accessed October 5, 2026.
• European Commission. (n.d.). EU Transport Flagships - Fehmarnbelt. EU Funding & Tenders Portal. Accessed October 5, 2026.
• DredgeWire. (2023, February 13). "The Fehmarnbelt Tunnel Trench Dredging Project."

References:

• Femern A/S. (n.d.). Fehmarnbelt Tunnel: Northern Europe's largest infrastructure project and the world's longest immersed tunnel.. Accessed October 5, 2026.
• DHI. (n.d.). An Environmental Portal for the Fehmarnbelt Tunnel Project. Accessed October 5, 2026.
• German Federal Agency for Nature Conservation (BfN). (n.d.). Fehmarn Belt Nature Conservation Area (NCA). Accessed October 5, 2026.
• Geoengineer. (2025). Fehmarn Belt Tunnel: World's Longest Immersed Tunnel Faces Delays. Accessed October 14, 2026.
• DredgeWire. (2023 February 13). The Fehmarnbelt tunnel trench dredging project. Accessed October 14, 2026.