Dredging is a topic that has been the centre of much debate over the years. Due to EU rules about how to deal with the material recovered, some authorities have slowed the process down. But river or harbour dredging is, in many cases, absolutely necessary.
It is often a challenge when dredged material is hazardous. In such cases, using our innovative LockedIn® process ensures contaminated material is treated. This results in eliminating or reducing disposal costs.
What is dredging?
Dredging is a process that removes accumulated sediment from the bottom or the banks of rivers, lakes, streams and other bodies of water.
This is carried out for several reasons. The main aim is to increase the depth of the body of water, such as rivers, as the build up of silt can make it difficult for vessels to use it.
The dredge is either partially or totally submerged to allow sediment to be gathered. Traditionally, the material that is dredged, or dug out, is sent to a different location. Prior to new rules, recovered dredge would be dumped at sea, but this can affect marine life, such as shellfish.
If the material contains no contamination it is often reused, but there is a high cost involved in transporting and treating material off-site.
And a real problem arises when recovered material from dredging is hazardous. As a result, it may be better to treat it on-site.
Why is dredging used?
There are a number of purposes for dredging. These can include:
Maintaining waterways: This is the most important reason for dredging. It can restore the waterway to its original condition and depth and moves dead vegetation and pollutants that gather there.
Creates waterways: Harbours and ports are built or extended using dredging. For example, this was the reason for an extension we were involved with at Killybegs Harbour in Ireland. The harbour needed extending to increase docking for extra fishing trawlers. For many harbours and ports, dredging is carried out so cargo vessels of all sizes can dock without running aground.
Excavation: Removing sediment is important when preparing for large building projects, such as docks, piers and bridges. We took part in treating material that was recovered from the Wear, in Sunderland, for the construction of the Northern Spire bridge.
Reclamation: As well as excavating material for construction, such as the Northern Spire project, dredging also allows for the removal of contaminates. From sewage accumulation to chemical spills and the buildup of decayed plant life, the removal of such material is essential. In Sunderland, we helped remove 30,000 tons of contaminated material, which was the result of hundreds of years of shipbuilding on the Wear.
Increasing depth of waterways: Sediment build-up from accumulating debris means an increased risk of flooding in rivers. As a result, dredging is necessary to restore the body of water to its original depth.
What happens to the recovered material?
Material recovered from dredging is traditionally moved off-site for treatment. Fine reclaimed material, such as clay, is used for land creation or construction fill. Where there is fine dirt it is mixed with additives, including manure or compost, to create or enhance topsoil.
The real issue is when dredged material contains chemicals or hazardous waste. Many rivers around the UK and Ireland were used for industrial purposes, such as shipbuilding. As a result, oil and other contaminates builds up over time, creating a hazard.
Any material recovered cannot be reused in its untreated state. Usually, the option is to remove the material from the site for further treatment, which can be expensive and labour intensive.
But at ATG, we can use our LockedIn® process to treat the waste. Managing Director Dr Mark McKinney explains, “In Sunderland, huge amounts of oil was recovered during the bridge construction project. There was more contaminated materials recovered than was expected.
“The Environment Agency halted the works because the plans to manage the material were considered unacceptable. We were called in to assist Farrans, the construction company. We created a tailored plan to manage the hazardous dredge that met the Agency’s expectations.”
This included constructing a coffer dam and dredging and excavating within that in the river. We sent the materials by barge to our treatment facility and off loaded. The treated material was used for landfill capping.
We are now helping recover even more hazardous material further down the Wear as part of a major roadbuilding project.
We are experts at treating hazardous dredged material. Contact us for more information to ask us to design a specific plan for any dredging operation.