Noise from Agitation Dredging Safe for Marine Mammals and Fish

In the first study conducted into agitation dredging noise in harbors, Haven Dredging’s Tiamat Hydrodynamic dredger has been confirmed to be below the safe levels for marine mammals and fish.

Tiamat, launched last year, is a hydrodynamic dredging solution that the study by environmental hydraulics consultancy, HR Wallingford, was found to be significantly quieter than a small trailing suction hopper dredger (TSHD).

When being pulled by a small workboat, the noise level of Tiamat was around 170 decibels (dB), while a 3,500 cubic meter TSHD – was around 185dB.

The US-based, National Oceanic and Atmospheric Administration suggests approximate sound pressure level (SPL) thresholds are 180dB for whales and 190dB for seals.

Jake Storey, Executive Director of Haven Dredging, said: “We are committed to working with nature, for nature and to sustain nature. The results of this study are testament to the years of research and field testing that has been put in to creating Tiamat.

“Tiamat aims to not only build awareness around environmental issues from traditional dredging methods in the port and dredging community, but also to provide businesses with the opportunity to choose a more responsible, sustainable and economical method of dredging.”

As well as being quieter, he says Tiamat provides a cleaner and greener method of maintenance dredging that is easy to deploy, adaptable and at a lower cost.

Dr. Thomas Benson from HR Wallingford – who completed the noise study – adds, “Measuring underwater dredger noise within a busy harbor environment presents considerable challenges because of all the other noise generating activities taking place, but the results of this study are clear in that the Tiamat makes a lot less noise compared to more traditional trailer dredgers. This adds to the other benefits of the Tiamat such as having a low-carbon footprint and being cheaper to run.”

The 43-page report compared SPLs of Tiamat and the 3,500 cubic metre TSHD. The tests were conducted at Harwich Harbour, in Essex, UK, in April and May 2023.

Tiamat is designed to be mounted on a small workboat or multi-cat. It features three pumps; two to inject water into the sediment overlying the harbor bed and a third pump to extract diluted silt, pump it up and release it back into the water column.

Tiamat encourages self-replenishment of the sediment through the natural re-suspension in the marine environment. And by harnessing the power of the tide and currents, and only needing a small workboat, Tiamat can reduce the costs associated with maintenance dredging by up to 67% compared to traditional maintenance dredging methods. The technology is adaptable and easy to deploy, making it suitable for port authorities and harbor engineers around the world.

Haven Dredging, the commercial arm and wholly owned subsidiary of Harwich Haven Authority, was launched in April 2023.

Harwich Haven Authority has included Tiamat in its dredging strategy and thereby reduced costs by two-thirds and greenhouse gas emissions from maintenance dredging by up to 35%.