Posted on February 2, 2026
By Andrew Ekwueme
Dredged sediment from Harwich harbour is being reused in the Blackwater Estuary to strengthen natural defences and protect habitats, showing how routine dredging can support coastal resilience through collaboration.
Along the Essex coast, communities in the Blackwater Estuary are facing increasing pressure from erosion, flooding, and habitat loss, particularly around low-lying areas such as West Mersea, Tollesbury and Salcott.
The extent and quality of Essex Saltmarshes have been declining due to development, rising sea levels, and increased storm frequency in recent years. A study on erosion rates found that after 25 years, 1000 ha had been lost. Saltmarshes provide ecosystem services such as reducing flood risks and the effects of storm surges, as well as acting as a carbon sink. These key habitats also provide important feeding grounds and refuges for nationally scarce plants and insects, juvenile fish species such as Bass and Gobies, and internationally important numbers of birds, such as Shoveler and Dark-bellied Brent Geese.
Alongside these challenges, ports must continue routine dredging to maintain safe navigation. While dredging is not a driver of saltmarsh loss within estuaries, it does generate sediment that has historically been managed separately from wider coastal processes. In the Harwich Haven, the entrance to the Stour and Orwell estuaries, rather than viewing dredged material as waste, a collaborative £2.5 million scheme run by the RSPB, Essex Wildlife Trust and Harwich Haven Authority is reinforcing natural coastal defences and creating intertidal habitats at sites including West Mersea, Tollesbury, and Salcott. The two-year project, funded by the Environment Agency Natural Flood Management budget, the Harwich Haven Authority, and the Endangered Landscapes Programme through the Transforming the Thames project, brings together a wide range of dredging and port expertise and environmental management to address multiple challenges through a single, coordinated effort.
The dredged material will be used to reinforce flood defences, defending 25km (16 miles) of coastal flood defences, 406 hectares of coastal flood plain grazing marsh and 240 hectares of coastal saltmarsh.
Engagement Map (Photo credit: Jim Pullen Surveys)
Why sediment matters
In estuarine systems such as the Blackwater, sediment plays a central role in maintaining shoreline stability and habitat health. Saltmarshes depend on sufficient sediment supply to build elevation over time, allowing them to keep pace with sea-level rise and recover following storm events. Where sediment inputs are limited, erosion can outstrip natural regeneration.
In the Blackwater Estuary, long-term coastal processes including tidal reworking, wave-driven erosion and rising sea levels have contributed to a gradual sediment deficit, leaving saltmarshes increasingly vulnerable. As these habitats sit close to their tolerance limits, reduced elevation can accelerate degradation, diminishing their ability to dissipate wave energy and buffer nearby communities from flooding.
Understanding sediment dynamics is therefore critical for harbour authorities and coastal managers. The key issue is not dredging activity within the estuary, but how sediment sourced from maintenance dredging elsewhere can be managed to support estuarine systems experiencing material shortfall.
From dredging to beneficial reuse
Rather than being removed from an estuarine system, the sediment used in the Essex scheme is sourced from routine maintenance dredging in the Harwich deep-water harbour and approach channel, some distance offshore. The material is recovered using a small trailing suction hopper dredger (TSHD) and transported for reuse within the Blackwater Estuary.
The approach focuses on importing sediment in a way that aligns with existing estuarine processes. Placement locations are selected to support saltmarsh elevation and stability, helping habitats better withstand erosion and storm impacts over time. Speaking to CEDA Industry News, James Dunn, Senior Project Manager at the Royal Society for the Protection of Birds (RSPB), explained “You can’t just put sediment anywhere, it has to be the right material, in the right place.” The sediment being reused consists of a mix of sand and gravel, assessed as suitable for placement at the selected intertidal sites.
placement methods vary depending on site conditions within the estuary. Material is either rainbowed from the vessel or pumped ashore via pipeline, depending on access constraints and the presence of sensitive features such as oyster beds.
By planning sediment movements in parallel with environmental requirements, the scheme demonstrates how dredging undertaken outside an estuary can be used strategically to support habitat resilience elsewhere, without compromising navigational or operational needs.
Old Hall Point (Photo credit: Jim Pullen Surveys)
Making collaboration work
Delivering beneficial sediment reuse at scale requires more than environmental intent. It depends on close coordination between port operations, dredging programmes, and environmental objectives, particularly in a busy estuarine setting, where navigation, consent, and timing must all align.
For Harwich Haven, this means integrating sediment reuse into routine maintenance planning rather than treating it as a separate activity. Dredging schedules, material characteristics, and placement locations are coordinated in advance, enabling sediment movement to support both operational requirements and habitat objectives.
Speaking to CEDA Industry News, Jim Warner, Harbour Engineer at Harwich Haven Authority, said early alignment is critical to making schemes like this workable. He explained that close coordination between marine operations, dredging teams, and environmental partners helps reduce risk, avoid delays, and ensures material is available when and where it is needed, rather than becoming a constraint later in the process.
Mr Warner also noted that dredging programmes already operate within tight operational and regulatory windows. Adding reuse into the mix, he said, only works when volumes, material quality, and placement requirements are clearly understood in advance, giving contractors and harbour operators the certainty they need to deliver safely and efficiently.
That collaboration also extends into monitoring and management. Sediment placement is informed by survey data and environmental oversight, with adjustments made as conditions change. This adaptive approach allows the project to respond to estuarine dynamics while maintaining safe access for shipping throughout the dredging programme.
Rather than adding complexity, collaboration can simplify delivery when embedded from the outset. By bringing operational and environmental considerations together early, ports can incorporate beneficial reuse into ongoing dredging activity as part of routine delivery.
Terns (Photo credit: Paul Davis/RSPB)
Looking ahead
As pressure on estuarine coastlines continues to grow, dredging can be more closely aligned with broader coastal management objectives. By strategically placing sediment sourced from maintenance dredging into estuarine environments experiencing erosion, harbour authorities have a practical alternative to traditional disposal-led approaches.
Crucially, beneficial reuse does not happen by default. It depends on early planning, a clear understanding of material characteristics, and close coordination between port operators, dredging teams and environmental partners. Where those elements are in place, routine maintenance activity can support both navigational access and long-term coastal resilience.
For harbour authorities operating in similar estuarine environments, the lesson is not that every scheme can be replicated directly, but that sediment management can be reconsidered within a broader system. Integrating dredging, environmental objectives, and operational planning from the outset offers a more joined-up approach to managing sediment as coastal conditions continue to change.
