Harwich Haven Authority’s multifaceted dredging toolkit  

As the home of the UK’s busiest container port, Felixstowe sees over 2,000 container ships annually – which equates to 40% of the country’s container traffic – leading to the accumulation of up to three million cubic metres of sediment each year. Managing this buildup is essential in order to keep the global supply chain moving, however traditional dredging methods are both expensive and environmentally demanding.

Harwich Haven Authority (HHA) – the Authority managing and preserving the Port of Felixstowe, as part of its 150 square miles of the UK – recognised the pressing need for innovation to help enhance its operational efficiency, whilst driving change to mitigate the environmental impact of its operations.

Its primary dredging challenge is the significant sediment buildup in the Port of Felixstowe’s channels and berths. Made up of 85-90% silt and clay, this poses a risk to vessels trying to safely navigate the waters and often impacts dredging costs, which for HHA, equates to 20-25% of its annual revenue. Additionally, the carbon footprint associated with frequent trips to offshore disposal sites by Trailing Suction Hopper Dredgers (TSHDs) necessitated a re-evaluation of dredging practices, especially in light of HHA’s commitment of achieving “net-zero” by 2035.

A new approach

Following years of development, Tiamat was officially launched in April 2023, as part of a new and improved, integrated dredging toolkit for HHA, which sees Tiamat deployed throughout the year to relieve some of the workload previously managed by TSHD campaigns. The new programme also includes increased surveying of navigable mud with Stema Systems’ Rheotune, supported by the use of a plough to finalise the campaign.

Today, HHA’s toolkit includes:

1. Utilisation of TSHD: The dredging campaign begins with several days of dredging using a TSHD to manage large sediment volumes effectively. The TSHD handles the initial dredging of particularly heavy sand sediments.
2. Transition to Tiamat: Following the conclusion of the TSHD operations, Tiamat is deployed. The innovative hydrodynamic technology in Tiamat is designed to remove the sediment from the seabed and naturally redispose it into the water column at the appropriate depth, minimising the need for offshore disposal – significantly reducing GHG emissions.
3. Survey with Rheotune: RheoTune is deployed to provide an assessment of both density and yield stress profiles of the fluid mud. This enables swift and accurate data acquisition, to assess the performance of the dredging and understand the navigable properties of the mud in the port.
4. Finishing with a plough: Assuming the combined dredging processes have performed to the expected standard, the process concludes with a few days of using a plough to redistribute any remaining sediment, allowing for easy access for further TSHD operations. Tiamat’s activity can be carried out from the same workboat which hosts the plough, optimising logistics and reducing mobilisation costs.

The results

Tiamat achieved such great success in Harwich, showing an average production rate of 9,800 tonnes of dry solids per day, while significantly reducing operational costs to around £1 per cubic meter, compared to £3-4 per cubic metre for a TSHD campaign. As a result, HHA has now reduced its TSHD campaigns from six per year to just three, supplemented by three Tiamat campaigns.

Tiamat also reduces GHG emissions, with estimates suggesting a reduction to just one tonne per day when using eco-friendly fuels like Hydrotreated Vegetable Oil (HVO), offering an impressive potential for reducing emissions by up to 90% compared to traditional diesel fuels.

To evaluate such an innovative strategy, HHA measured the success of the new integrated toolkit against several factors including the impact on cost, operational efficiency and the local environment.

The great news is that incorporating both proven dredging techniques and innovation through Tiamat, HHA has not only tackled its sediment management challenges, it also achieved substantial cost and emissions reductions. Today, it saves The Authority up to £3 million per year!

This comprehensive approach deployed by HHA sets a valuable example for other port authorities facing similar issues. With a continued focus on monitoring and refining its methods, it is more than possible for every port to enhance dredging efficiency, lower capital costs and deliver lasting environmental benefits by embracing dredging innovation.