How does dredging offer a competitive advantage for ports?

Port dredging is fundamental to ensure the continued operation of ports and harbours, keeping them safe and maintaining the flow of goods. In the UK, ports handle 95% of the trade in goods, which equates to around 500 million tonnes of cargo every year.

Maintenance dredging is a routine – and much needed – practice in most ports, but rising costs mean that port and harbour authorities need to identify or develop ways to save money and find a competitive advantage, without cutting corners on environmental protection.

By using Haven Dredging’s hydrodynamic maintenance dredging solution, Tiamat, port authorities can adopt a cleaner, greener method of maintenance dredging, that is easy to deploy, adaptable and comes at a lower cost.

Haven Dredging is a wholly-owned subsidiary of Harwich Haven Authority (HHA) – the UK’s largest port, spanning over 150 square miles and accommodating around 40% of the country’s container traffic – which was set up to commercialise Tiamat’s offering, after its success across its trials over the last few years.

With maintenance dredging costing up to a quarter of HHA’s annual revenue, Tiamat reduces costs by around 40% and is actively helping HHA to achieve its net-zero carbon goal. Demonstrating how Tiamat reduces the overall cost of port dredging and brings substantial environmental benefits to the port authority, we recently published a compelling case study to highlight this.

At HHA, the approach channel and berths have high ongoing sedimentation with between two million and three million cubic metres of sediment on average each year requiring management. This contains around 85-90% silt and clay, with the rest being sand and gravel.

Thanks to the flexibility and effectiveness of using Tiamat as a method of port dredging at HHA, the cost of dredging with Tiamat is much lower than traditional methods, as a bespoke vessel is not required to complete the work, nor transport of the sediment to a disposal site. Its carbon footprint is lower too, reducing greenhouse gas emissions by up to 90% compared with Trailing Suction Hopper Dredging (THSD) methods.

Dredging needs are unique to each port and business, and Tiamat can be tailored to individual requirements. The most common approach to manage ongoing sedimentation in a port is maintenance dredging, with Trailer Suction Hopper Dredgers (TSHDs), Cutter Suction Dredgers (CSDs) and Backhoe dredgers (BHDs) being frequently used. Each removes the deposited sediment from the seabed and relocates it elsewhere.

Historically, sediment management at Harwich Harbour has been primarily undertaken using a TSHD.  While slowly navigating around the areas requiring dredging, the dredger lowers its draghead(s) onto the seabed and uses pumps to suck a slurry of seabed sediment and seawater into a hopper on the dredger.

A Water Injection Dredger (WID) was also discounted, as it forms a cloud of lighter material that quickly becomes reconsolidated. Another issue was that an effective density current would not be created on the deep, flat seabed.

So, without any satisfactory existing solution, HHA developed Tiamat, built by a Dutch specialist contractor, Maarten Van Oord. Four trials were undertaken in 2020 and 2021 to test the new dredging approach and extensive monitoring of sediment density, bathymetry and water quality was undertaken. This showed that the Tiamat was more efficient than traditional dredging methods.

The cost of using the Tiamat is £0.33 per cubic metre, while the cost of using the 7,500 cubic metre TSHD is about £2-£3 per cubic metre.

The trials also highlighted that predicted daily greenhouse gas emissions are just over five times larger when dredging is undertaken using a TSHD, compared to a Shoalbuster 2709 towing the Tiamat. This difference would be larger in a like-to-like comparison, as a TSHD only spends 16% of the time dredging every 24 hours, while the Tiamat is spending 50% of the time dredging every 24 hours.

Tests show that by using Hydrotreated Vegetable Oil (HVO) as fuel for the vessel towing the Tiamat and its pumps could further reduce carbon emissions by up to 90%.

In addition, the CO2 emitted during fuel combustion can be offset by absorption during the growth of the biomass which forms the biofuel. Based on these findings the actual greenhouse gas emissions associated with the use of the Tiamat could be reduced to one tonne a day, which when normalised based on production rates, would be 30 times lower than the use of a TSHD emissions.

The previous concern around the suspended sediment being deposited back into the dredged areas has been proven unfounded, as bathymetric surveys show that tidal currents transport most of the suspended sediment away from the dredged areas – thus, “Dredging with Nature”.

Tiamat offers other dredging authorities, companies, ports and harbours the opportunity to benefit from not only cost and time savings, but also reducing their impact on the environment and making a meaningful step forward towards achieving net-zero emissions by 2035.

If you want a competitive advantage in port dredging, let Haven Dredging know about your project requirements and find out how Tiamat is effective, adaptable, easy to deploy and saves money.