Water Injection Dredging provides a hydrodynamic dredging technique that is both cost-effective and environmentally sound.

THE PROBLEM

Ports, harbours, navigation channels and marinas are continually confronted with siltation, which reduces access. Consequently, dredging works can quickly account for a large proportion of port authorities’ budgets and the pressure to reduce these ongoing costs is increasing. Therefore, maintenance dredging is a necessity for companies operating in these waterways to ensure safe navigation depths in these locations. Planning this dredging work can be complex and daunting without access to the right expertise.

THE SOLUTION

As a company, we own and operate several marinas giving us first hand experience and an in-depth understanding of the requirements of dredging operations. As part of our service we can offer advice and support throughout a dredging project. Our dredgers and team of highly qualified marine engineers, offer water injection dredging which provides a cost effective, environmentally sound dredging method.  Given the varied nature of the locations our fleet of dredgers can work in, we price each project individually to offer a competitive quote to meet your individual requirements.

THE METHOD

Water injection dredging is one of a number of hydrodynamic dredging techniques, where the basic principle is to remobilise the sediments, using the action of natural currents. Water injection dredging uses water pumps connected to a series of nozzles on a horizontal jet bar. The nozzles inject large volumes of water at low pressure directly onto the sediment build up. This process fluidises the sediment build up, turning it into a density current which remains close to the water bed. The sediments are then picked up by this current and able to flow horizontally out of the channel or port. This process eliminates the need for traditional excavation dredging methods and the subsequent transportation of the dredged material. Nature takes care of the sediment transport, making water injection dredging a cost-effective dredging technique with less impact on the environment.

water injection dredging THE BENEFITS

• Cost effective method of dredging
• No disposal licence required
• Vessel is fully road transportable
• Quick mobilisation/demobilisation times
• No need to move pontoons or infrastructure
• Shorter timeframes for carrying out work
• Vessel has great manoeuvrability
• Able to reach hard to reach areas close to embankments and quay walls
• Environmentally sound solution
• Creates a considerably lower CO2 footprint compared with conventional dredging

Water injection dredging is often combined with other dredging technologies which can then operate with increased efficiency. The process can therefore provide either a stand-alone dredging solution or complement traditional dredging methods.

Applications

Water injection dredging is a popular and effective method for maintenance dredging as it involves variable quantities of material, from thin to thicker layers. With maintenance dredging in navigation channels and harbours, the sediments to be dredged are the most recent layers which have formed. This process is a regular activity, within a dynamic environment, where sedimentation and erosion are on-going occurrences even as dredging is taking place.

As the process does not dig into or excavate as traditional dredger do, water injection dredgers can operate in places where other types of equipment cannot reach including:

• Marinas
• Underneath jetties and moored vessels
• Alongside quay walls
• In locks
• Inland waterways/canals
• Culverts
• Access channels
• Flood prevention
• Increasing depths for ship berthing
• Wind farm installations
• Levelling the water bed for pipelines and tunnel sections
• Increasing the depth of pipelines and cables

environmental considerations

For water injection dredging to be effective, it is essential that the environmental and ground conditions on-site are clearly understood. Site specific bathymetry and geometry plays an important part in the effectiveness of water injection dredging.

Factors influencing the dredging production rates include:

• The water depth
• The dredge template
• The bathymetric features
• The site geometry of the sediment deposition areas
• The characteristics of the transport path of the density current

When required, we can assist with carrying out the necessary surveys and trials prior to dredging commencing.

Environmental impact

The process of transporting dredged material horizontally along the water bed, compared to traditional dredging techniques, results in the following specific circumstances which reduces the impact of the process on the environment:

• An increased quantity of sediment goes into the lower layers of the water column
• The rate of sediment input in the natural systems at the dredged area is increased
• The sediment is transported by natural phenomena to the final destination through the density current
• The rate of sedimentation in the deposition areas may vary if the natural conditions vary
• Dredged sediments remain within the ecosystem

Special attention should always be given to areas nearby the dredging location to determine if there are sensitive habitats such as shellfish beds or spawning habitats. In addition, in most cases, if the soil is contaminated water injection dredging is not a suitable method. We can offer advice in organising environmental studies and the types of permissions that are likely to be required prior to dredging.