How to select a dredger?

Selecting the optimal dredger for a project is complex and requires understanding both project conditions and available equipment. Although choices are always site- and project-specific, general criteria include technical, project-related, environmental and economic factors. The following list outlines the main selection criteria, but other, unlisted factors may also influence the final choice.

Technical criteria

Technical criteria include the physical properties of the sediment and the transport distance to the placement site. Material type and consistency determine whether mechanical or hydraulic dredging is used and also affect transport behaviour and suitability for the receiving site.

Transport distance and routing options are also key: land sites require pipeline or road transport, with pipelines bringing large volumes of water that must be managed. For remote offshore sites, barge transport is preferred, meaning dredging operations must include hopper or barge loading.

Project-related criteria

Project-related criteria include excavation accuracy, working conditions and regulatory requirements. Mechanical dredging equipment is typically associated with higher excavation accuracy, although CSDs and TSHDs (combined mechanical/ hydraulic) can also achieve tight tolerances with appropriate operational controls and effort. Environmental conditions, such as waves and wind also influence equipment choice, as some tools perform better in harsh conditions. Legal or environmental regulations may further affect selection, sometimes requiring process adjustments or specialised equipment.

Environmental criteria

As dredging inevitably affects the environment, equipment selection should aim to minimise adverse impacts by considering conditions at both dredging and placement sites. Some marine flora is sensitive to short, high-intensity stress, while others are more affected by longer exposure at lower levels. This influences the choice between high-output dredgers that work quickly and lower-output ones operating over longer periods, requiring a careful balance of impacts.

Dredger activity can also cause social disturbance through visual impact, noise, emissions and interference with recreational or commercial traffic. However, proper information sharing and public involvement can improve understanding of the project and its benefits.

When sediments contain contaminants, specialised or modified dredgers may be needed. In many cases, standard equipment is sufficient if operated under strict procedures, potentially supported by additional mitigation measures. More detailed information on mitigation is given later in this article.

Economic criteria

Selection of the optimal dredger depends on availability; the best-suited equipment may not be accessible within the required timeframe or location or may be too costly. In such cases, the best available dredger is chosen, possibly with supporting tools. Cost is a key factor and should include not only dredging but also transport, placement, monitoring, mitigation and overall project management expenses.

Best for project selection

Dredger selection is always site- and project-specific and should be guided by experienced dredging engineers or consultants, as poor choices of these capital-intensive tools can easily lead to major cost overruns. In recent decades, environmental requirements have driven significant development, leading to continuous adaptation of traditional dredging equipment to meet new constraints.

Key developments in adapting dredging equipment include reducing suspended sediment generation to limit resuspension of both contaminated and clean material, and improving monitoring and onboard control so operators can quickly detect and correct negative effects.

Other advances include increasing the density of transported material – via pipelines or barges – to reduce final placement or treatment volumes and greater automation of manual controls to ensure continuous operation and allow crews to focus on key decisions. The optimal dredger is the one that minimises life-cycle impact, not the one with the cheapest day-rate.

Dredging and dredging equipment

Understanding what dredgers can and cannot do across project phases is key to sustainable infrastructure development. Rather than detailing equipment extensively, the focus is on selected tools and their environmental impacts, highlighting how operations can be adapted for positive outcomes and more sustainable sediment management.

Environmental Impact Mechanisms

Comparing different dredging equipment and projects with each other, on their specific merits, is a challenge as each project site is different. A framework is required to identify the most significant environmentally sensitive criteria that may be influenced by the dredging equipment and process. The following four environmental impact mechanisms provide this basis.

Sediment resuspension or turbidity

One of the main environmental impacts of dredging is the resuspension of sediment during excavation, transport, or placement. This creates turbidity – cloudiness in the water that reduces light penetration – and leads to sediment settling on the nearby seabed, causing smothering and possible later resuspension after dredging ends.

The sources for sediment resuspension differ by dredger type and dredging operation. Apart from hydrodynamic dredgers, all dredging equipment generates three main sources for sediment resuspension:

1. Disturbance of the bed by drag head, cutter, grab, buckets or otherwise;
2. Overflow when loading barges or hoppers, to obtain economic loadings, or other material removal from the barge, like screening (of gravel or aggregate) or Lean Mixture Overboard (LMOB); and
3. Leakage losses from pipes, buckets and grabs, as well as dripping and splashing.

The amount of material brought into suspension during dredging depends on factors such as sediment type, equipment characteristics, operational methods and site hydrodynamics. Dredging-induced turbidity impacts are usually quantified by means of the increase of Suspended Sediment Concentration (SSC) (in mg/l) in the near- and far-field of the dredging operations.

Seabed disturbance, spill and losses

Dredging deliberately disturbs the seabed, but not all loosened material is removed. Some is spilled and left behind in a loose state – usually limited with precise operations, but potentially significant and widespread when overflow is used or barges are loaded.

These loose sediments are easily dispersed by currents and waves, extending the impact zone and causing re-sedimentation, which can pose risks near sensitive areas such as coral reefs or aquaculture ponds.

The remaining material also differs in composition and consistency, potentially affecting existing flora and fauna, though in some cases it can create conditions for more diverse habitats. Understanding these processes can reveal new opportunities for sustainable infrastructure.

Sound and emissions

Sound from dredging is environmentally significant and occurs both above and below water. Above water (airborne) sound has long been considered, mainly for its impact on humans, with established data and guidelines, though not specific to dredging or its effects on wildlife. Underwater sound has gained attention since the early 2000s due to potential impacts on fish and marine mammals, but data on dredging-related effects remain limited. Decibel levels in air and water are not directly comparable without conversion.

Sound during dredging is strongly influenced by soil properties – the harder the soil, the higher the sound levels. Activities such as explosives or mechanical rock breaking generate much more intense underwater sound than routine dredging. Overall, dredging sound sits in the mid-range compared to other sources, with higher levels from explosions, seismic surveys and large vessels like super tankers. More information on underwater sound by dredging, and the possible environmental impact of these sounds, can be found in CEDA (2011), WODA (2013) and Jones and Martin (2016).

Dredging also increases atmospheric emissions, mainly from diesel-powered engines on vessels and land-based equipment, contributing to greenhouse gases. These emissions and discharges are increasingly regulated, with the International Maritime Organization leading efforts to reduce impacts in the maritime sector.

Area disturbance

Indirect effects from dredger presence or near sensitive sites also need consideration, with monitoring and mitigation depending on the severity of temporary or permanent impacts.

Key aspects include disturbance to marine mammals through underwater sound or vessel strikes, which can cause behavioural changes, injury, or death – particularly from moving vessels. In sensitive areas of marine fauna, crew or specialised observers are often used to report interactions that may lead to interference with marine animals.

In addition to navigation lights, dredging operations often require floodlights and other illumination at night or in poor visibility for safety. Such lighting can attract or disorient species and create artificial light pools that may increase fish – and thus predator – activity in the area. However, little data exists, so these impacts remain poorly understood.

Dredger presence further affects local communities in different ways, from concern to interest. Clear communication on project progress and planning is therefore essential to support public understanding and smooth project delivery.

The dredging toolbox

Having determined such environmental impact mechanisms at stake dredging tools can be "measured" against these mechanisms.

Dredging tools are described on basis of the functional mode of operation, here defined as

• Mechanical dredging
• Hydraulic/Mechanical dredging
• Hydrodynamic dredging

Hydraulic/mechanical dredgers

Hydraulic dredgers use centrifugal pumps to transport dredged material vertically or horizontally. Combined hydraulic/mechanical dredgers add mechanical excavation power. Two main types exist: Cutter Suction Dredgers (CSDs) and Trailing Suction Hopper Dredgers (TSHDs). Their strengths are high efficiency, integrated transport, and broad applicability, while drawbacks include turbidity generation (especially during barge or hopper loading) and relatively high energy use.

A Cutter Suction Dredger (CSD) loosens material with a rotating cutter fitted with teeth. The loosened soil is sucked through the cutterhead into a centrifugal pump on the pontoon or ladder. Material is then transported hydraulically through a pipeline – floating, land-based, or submerged – and can occasionally be pumped into barges. CSDs are mainly used for capital dredging in harder soils, with economical pipeline transport distances typically limited to 5-10 km. In environmentally sensitive areas, both the cutting and hydraulic transport processes must be carefully controlled to minimise dilution and resuspended residues.

Environmental effects of a CSD include:

Sediment resuspension – The rotating cutter can generate extra suspended sediments at the dredging site. Pipeline transport does not increase turbidity because it is a closed system, but barge loading does resuspend material. Fine grained sediments stay suspended longer, causing elevated turbidity around the dredging area for some time.

Seabed disturbance – Most CSDs do not have an optimal combination of cutting capacity and suction capacity for all types of soil. A dislodged residue layer often remains on the seabed after dredging if no special precautions are taken, but an additional pass at the same dredging depth can remove most of this layer.

Sound and emissions – CSDs use powerful engines that generate high airborne sound, though levels drop to acceptable ranges a few hundred metres away; keeping engine room doors closed helps reduce it. Underwater sound is relatively high due to the cutter and underwater engines, and additional sound comes from workboats or tugboats assisting the CSD’s anchor movements.

CSD emissions depend on energy use, which is driven by soil cutting resistance and the transport distance, whether pumping or using barges. Barge loading produces fewer CSD emissions than direct pumping ashore, but barge sailing adds its own emissions along the route. With direct pumping, all emissions occur at the CSD itself, making them easier to monitor and control.

Area disturbance – As a CSD remains within the dredging area for long periods, the chance of encountering mobile marine mammals is low, but its prolonged presence may deter species from using the area. Night time operations with sound and light can also disturb all living species, including human, especially in inhabited zones.

A Trailing Suction Hopper Dredger (TSHD) is a ship designed to dredge while sailing, using one or two suction arms that trail along the seabed. At the end of each arm is a drag head, which loosens and collects sediment, which is pumped onboard. Material fills the hopper, after which excess water – and some fine sediment – overflows, increasing turbidity but improving sand yield. The dredger then transports the load to the placement site, releasing it through bottom doors or pumping it ashore via pipeline or rainbowing. TSHDs can dredge sands, clays, and even some rock, and are widely used for capital works, sand winning, beach nourishment, island construction and maintenance dredging. Environmental control focuses on optimising suction time and limiting overflow losses, balancing ecological impact with cost and project duration.

Environmental effects of a TSHD include:

Suspended sediments and turbidity – TSHD cutting produces little turbidity because the drag head has no rotating parts but continued loading with overflow releases large amounts of suspended fines, increasing turbidity and reducing light through the full water column. Limiting or preventing overflow reduces these impacts but also reduces hopper load, lowering production and raising costs. Turbidity can be mitigated with bottom exit overflow, low turbidity (environmental) valves, airless overflow systems, or by recycling part of the overflow water (“green pipes system”).

Seabed disturbance – Because the drag head only scratches the seabed, most loosened soil is immediately sucked up, leaving little residue. Suspended sediments settle slowly – ranging from hours to a week depending on soil type – and currents can spread the turbidity plume over a wide area with decreasing concentrations. This may affect benthic life, though in dynamic areas natural dispersion keeps suspended sediment levels low.

Sound and emissions – A TSHD has powerful engines that generate notable sound, but because it works offshore and in an on off cycle, sound is less critical despite being repetitive. Measurements show that dredging does not produce louder underwater sound than the vessel’s transit, similar to a cargo ship at moderate speed. Since TSHDs regularly leave the dredging site to discharge material, sound exposure at the dredging area is limited to active dredging periods.

TSHD emissions depend on total energy use: not only the power needed for dredging – which varies with soil type and depth – but also the time required to fill the hopper and the sailing time between dredging and placement sites. Pumping ashore adds further emissions. Unlike stationary dredgers, a TSHD releases exhaust at multiple locations at working locations and along its sailing routes.

Area disturbance – When equipment can injure or kill marine fauna, mitigation is required. Large species, such as whales or dugongs, trigger strict measures, including stopping or delaying operations when they enter a defined exclusion zone. Smaller species such as turtles can be protected with deflection devices, such as shields or chains on hopper dredger suction heads. Many projects also require trained crew or specialised observers to report any interactions that cause injury or death.

Mechanical dredgers

Mechanical dredgers use mechanical excavation to cut and lift material. The main types are the bucket ladder dredger (BLD), backhoe (BHD), and grab dredgers (GD), with the latter two most common. Their strengths are precise excavation and good process control in almost any soil, while their drawback is lower productivity due to the need for separate material transport, which also affects environmental performance. Only the BHD is discussed here. Information on other mechanical dredgers can be found on IADC’s website.

A Backhoe Dredger (BHD) is essentially a large hydraulic excavator mounted on a pontoon with a spud carriage system. As larger excavators became available, BHDs gained the power and digging depth needed for tougher dredging tasks. A rigid spud pontoon provides the reaction force required for hydraulic digging, especially in strong soils. The bucket excavates the seabed, then the arm lifts it above water to load material into a barge moored alongside.

Transport to the relocation site is usually done with barges, which discharge material through bottom doors, by pumping ashore, or by mechanical unloading. BHDs are mainly used for smaller volume projects in strong soils, where their high mechanical cutting forces are effective. Advances in monitoring and control have greatly improved their accuracy, making them suitable for precise work or for sites where other dredgers cannot operate due to physical constraints. Environmental effects of a BHD include:

Suspended sediments and turbidity – Some sediment is released during dredging. As a loaded bucket is raised, material can spill or be resuspended because it moves quickly through the water; when the empty bucket is lowered, adhering sediment may wash off. Slowing operations reduces this effect but also lowers production. Fine sediments stay suspended longer and can raise turbidity above natural levels. Closed, low spill buckets are sometimes used to limit losses.

Seabed disturbance – The cutting face of the BHD is the edge of the bucket. Almost all the soil loosened by the bucket is carried away, leaving a clean surface. A minor risk of a dislodged residue layer remains if there is excessive spillage while the material is being raised.

Sound and emissions – The BHD itself generates limited sound because it is stationary and works slowly, and well maintained engines can operate quietly. However, they require transport barges and tugboats that add to the overall sound footprint.

Emissions – Emissions come from the power needed for excavation – affected by soil hardness, excavation profile, and water depth – as well as from barge movements, which depend on transport distance and loading efficiency, plus emissions from barge unloading.

Area disturbance – A BHD is a stationary dredger, moving only very slowly within the work area, with only the excavator arm operating. The main disturbance comes from barges travelling back and forth, which can affect marine species. The prolonged presence of the dredger may discourage animals from entering or using the area and night time operations can raise similar concerns as with CSDs.

Hydrodynamic dredging

Hydrodynamic dredging lifts seabed material and releases it almost immediately into the water column, after which it is transported by currents (agitation dredging), by gravity-driven flow in water injection dredging (WID), or by mechanical pushing with an underwater plough (UWP). Because the movement of suspended or fluid mud can only be reliably predicted through detailed environmental analysis or advanced modelling, this method must be used cautiously near sensitive areas.

It is often cost effective and produces the lowest CO2 and exhaust emissions since natural forces handle transport, but its major drawback is the limited control over where the suspended material ultimately settles.

A Water Injection Dredger (WID) has a fixed array of nozzles that penetrate the seabed and inject large volumes of water, reducing the density of near surface deposits until they liquefy and rise slightly.

The fluidised material then flows naturally until a new equilibrium is reached, and even small bed gradients or currents can transport it over significant distances, where it settles in lower lying areas.

WID is mainly used in tidal basins with heavy natural sedimentation, either returning fluid mud to the main flow so it re enters natural transport processes or shifting material from inaccessible zones to areas where conventional dredgers can remove it. It is also used to help TSHDs clear shallow spots. Advances in monitoring, modelling and control have improved both performance and the predictability of fluid mud movement.

Environmental effects of a WID include:

Suspended sediments and turbidity – During the injection process, a layer of fluid mud is created at the dredging site, which is more sensitive to the natural erosion forces by the water currents above this layer. Most of the material, however, remains close to the riverbed and is therefore less subject to spreading over the full water column. The effect on turbidity of the upper water layers is limited.

Seabed disturbance – The actual dredging process involves the creation of a fluid mud layer that moves under natural hydrodynamic forces. The remaining seabed contains a thin layer of weakened soil; and at the drop zone an uncontrolled "blanketing" by soft sediment deposits will occur.

Sound and emissions – A WID uses propellers and pump to operate. The engines providing power generate airborne sound, while the propellers create underwater sound, with levels generally depending on the power applied. Emission of exhaust gases is directly connected to the use of power and fuel combustion which for WID is relatively low compared to many other methods.

Area disturbance – A WID, gently moving through a dredging area, will be comparable to other small work vessels in terms of view and sound.

Agitation Dredging (AD) includes any method of dredging that aims to lift the excavated material towards the overlying water layers, often just using standard equipment. This can be done either by an overboard-discharging TSHD, or by a stationary hydraulic dredger that discharges its water-sediment mixture in near surrounding waters. In fact, any method that raises sediment into the water column, such that they behave as individual particles rather than as a mass, could be termed AD. The main aim is to bring the material into suspension for further transport by the natural currents at the site. The method is not further described here.

The Underwater Plough (UWP) can be described as a frame that is pulled over the riverbed by a tugboat. The frame is equipped with a cutting device that scrapes over the riverbed cutting the bottom layers, pushing the cut material forward until reaches deeper areas, or when the cutting device is lifted at the end of the scraping track.

The UWP is mainly used for the execution of relatively small dredging tasks and for maintenance dredging in tidal basins where significant quantities of natural sedimentation accumulate. The material is either returned into the mainstream of the natural transport process; or soft soils are shifted to areas where other dredgers have access and may pick it; or a soft irregular bottom can be levelled, in order to avoid expensive levelling works by other dredgers. For some projects the technique can be an attractive alternative dredging method because of the low cost, and the fact that the dredged material remains in the natural cycle of the estuary.

The Sweep Beam (SB) is a frame, similar to an Underwater Plough, pulled over the riverbed by a tugboat to level dredged areas and remove shallow spots or ridges, typically mounted beneath an H-frame at a vessel’s stern.

Environmental effects of a UWP and SB include:

Suspended sediments – Cutting creates a cloud of suspended sediment in front of the blade, though most stays near the bed. Sometimes air is injected to agitate and move sediments with natural currents. This causes temporary re-suspension, but due to low energy, particles remain low in the water and settle quickly.

Seabed disturbance – Seabed disturbance is controlled by managing cutting depth and sweep distance. Relocated material is left untreated and becomes less compact and more easily erodible by natural forces. Modern monitoring and positioning methods allow accurate control of cutting depth and precise bed levels.

Sound and emissions – Airborne and underwater sound from UWP and SB operations mainly comes from the towing vessel’s engines and is comparable to normal shipping noise; the plough or blade adds little. Emissions are likewise governed by standard international regulations for the vessel.

Dredged material transport and placement: equipment and techniques

Transport and placement of dredged sediments strongly influence environmental impacts and are typically decided during project design, shaping the dredging methods used. Given these requirements, various transport methods are available depending on the equipment. Understanding and selecting suitable techniques helps reduce environmental effects; here, only the main systems are briefly outlined.

Pipeline transport

Pipeline transport is a widely used and generally environmentally friendly way to move dredged material. Its main drawback is the need to mix material with water, increasing volume and complicating storage or treatment, especially for contaminated fine sediments. Proper inspection and maintenance are essential to prevent leaks or bursts, and consequential environmental impacts.

Hopper or barge transport

Hopper or barge transport is widely used in dredging, where material is loaded hydraulically (TSHD, CSD) or mechanically (BLD, BHD, GD). It is relatively environmentally friendly compared to road transport, with low noise, emissions and no road congestion. Its main advantage over pipelines is that no transport water is required, allowing material to be moved at near- original density if maintained during disintegration.

Regular inspection and maintenance of barges and hoppers is essential to ensure proper closure of bottom doors. Automatic monitoring systems further improve environmental performance by enabling full surveillance during transport and disposal.

Road transport

Although pipelines and barges are most commonly used in dredging, alternative transport such as road haulage should be considered when further transport is needed after unloading or when no nearby waterway is available.

Truck transport allows flexible delivery to multiple destinations and can handle material at any density. However, many trucks are not watertight and may cause spillage, while large numbers are needed to match dredger output, leading to road congestion and disruption to public areas.

Conveyor belt transport

A fourth, less common option for large-scale transport of dredged material is conveyor belts. These are rarely used in dredging due to high installation costs. However, when combined with barges between the unloading quay and reuse or relocation sites, conveyor systems can be attractive because they can transport high-density material with minimal environmental risk.

Combined transport cycles

Transport of dredged material is increasingly complex and often involves bi- or even tri-modal systems, where two or three transport modes are combined to reach the final destination. Examples include barge transport followed by pipeline transfer, barge unloading with conveyor or truck transport, trailing suction hopper dredger sailing with subsequent pumping ashore and pipeline discharge to an intermediate facility followed by truck, barge, or conveyor transport.

Selecting the optimal transport cycle requires careful planning, as multi-modal systems combine both the advantages and disadvantages of each method. The dredging, transport and treatment or relocation phases must therefore be considered in an integrated way.

Placement techniques

The placement of dredged material can have significant environmental effects, making the selection of an appropriate site and its infrastructure crucial during project design. The choice of equipment and techniques also influences both the placement site and overall environmental impact. Various placement options are briefly outlined below. In the context of sustainable infrastructure, beneficial reuse of dredged material is promoted and will be discussed in the next issue of the magazine.

Land placement involves pumping dredged material via pipelines to confined or semi-open areas for reclamation, storage or beach nourishment, or discharging it directly onto land using jet nozzles (“rainbowing”). Key environmental effects include burial of sensitive surfaces, sediment dispersion from open sites, changes in topography, and the risk of transport water leaking into subsoil layers.

Underwater (or aquatic) placement, usually following hopper or barge transport, involves releasing sediment that falls through the water column, creating a dense cloud and temporarily increasing turbidity. The impact depends on the local ecosystem, with more sensitive environments being more affected (e.g. in a mudflat area the effect will be far lower compared to a coral reef environment). An additional effect is the burial of the natural sea-, lake- or river bottom, by the large volumes of deposited material.

Similar conditions occur when hydraulic dredgers pump material directly to an underwater site. Compared to bottom door placement, disposal takes longer, leading to lower peak turbidity and suspended sediment levels, but has a significantly longer impact.

Environmental effects can be reduced by adapting equipment, such as discharging through a vertical pipeline to the seabed to limit dispersion and fine losses, with further improvement achieved by using an underwater diffuser at the end of the discharge outlet. Controlled placement of dredged material is often required to ensure thin-layer deposition that prevents instability in soft soils, limits dispersion in open water, or enables sand capping of contaminated material.

Mitigation and optimisation strategies

Environmental mitigation measures can be included from the start of project planning or applied through an adaptive management approach. While early design is still required, implementation may be adjusted during the project based on ongoing environmental monitoring. For more information see the CEDA Position Paper on adaptive management (CEDA, 2015).

Mitigation through selecting equipment and tools for sustainable dredging

Careful project design, including an Environmental Impact Assessment (EIA), and selecting appropriate dredging and placement equipment are key to reducing environmental impacts. Potential effects, such as increased turbidity, habitat disturbance or burial, impacts on fisheries, and coral smothering, must be assessed and mitigated to acceptable levels through targeted measures.

Measures may include physical actions on or around the dredger to limit sediment spillage and reduce turbidity, as well as organisational measures such as environmental windows (EWs) (e.g. tidal, seasonal or monitoring controlled operations) to minimise ecological disturbance at dredging or relocation sites.

For more information on how to decide when and how EWs might help in achieving sustainability targets, see Guide for a risk-based approach to environmental windows for dredging and navigation infrastructure works (PIANC WG 227). Various onboard measures can reduce dredging impacts, mainly by limiting turbidity and increasing transport density in hydraulic operations. Precise control of dredging depth and water intake is key to optimising production and minimising losses, spillage and seabed disturbance, supported by advanced monitoring and automated control systems.

When dredging in environmentally sensitive areas, contractors should include operational environmental measures in their quality control system. This may form part of an Environmental Management Plan or similar documentation, as required by the client.

Mitigation at the project site through monitoring and process adjustment

Mitigation can also be applied directly at the project site. Besides careful planning and control of dredging, physical barriers can be used to limit the spread of suspended sediment and underwater noise. Sediment dispersal can be reduced by installing silt screens or turbidity barriers near the dredging site, provided wave and current conditions are suitable.

The effectiveness of silt curtains varies widely depending on local oceanographic conditions. In ideal conditions (no currents, waves, or tides), retention can reach 80-90%, but this decreases significantly as conditions worsen. Currents above 0.5 m/s, waves above 1 m, or tidal ranges above 3 m reduce retention to about 25-40%, and crosscurrents can even cause negative retention. Installing silt screens is also complex and requires skilled execution to prevent leakage through the curtain.

As an alternative to silt screens, bubble curtains can be used. These consist of a perforated pipe laid on the seabed that continuously releases air, creating rising bubbles that help block fine sediment from crossing the line. Bubble curtains are most effective on flat seabed and in low-velocity, calm conditions. They require large air compressors and therefore high energy input but allow for vessels to carefully pass the barrier.

Mitigating underwater noise from dredging is limited mainly to improving equipment sound sources. Operational timing can also help, such as avoiding sensitive periods like breeding or calving seasons for marine life through environmental windows set in project specifications. In some cases, observers may monitor high- risk areas before operations begin. Bubble curtains, also used for turbidity control, can reduce peak sound levels in special situations but do not significantly lower overall sound levels.

Energy efficiency improvement options

Improving energy efficiency in dredging is driven both by economic benefits and by the need to reduce fuel emissions under international regulations. Emissions can be reduced by cleaning or filtering exhaust gases or by using cleaner alternative fuels. Over time, newer, larger and more efficient vessels have already improved energy performance. More recently, systems that remove harmful substances from exhaust gases have further enhanced the environmental performance of modern dredgers.

Several modern dredgers can operate on cleaner fuels, such as LNG and biofuels, with successful applications reported. Electricity is also used for smaller vessels and land-based equipment, shifting emissions away from the site or reducing them significantly. Other alternatives include non-combustion power sources, such as fuel cells, nuclear energy or shore-side power supply.

Reducing energy demand through operational adjustments is highly effective in lowering total emissions. Advanced modelling of dredging operations and logistics can identify more energy- efficient and lower-emission construction methods, including considerations such as availability, mobilisation emissions and combined operations. These models may also cover not only the dredging plant itself, but also reclamation works, surveying, monitoring and transport activities.

Execution matters, as much as design

Sustainable infrastructure begins with project initiation but is ultimately determined by the ability to construct infrastructure in an environmentally, socially and economically responsible way. Selecting the most suitable construction methods, tools and equipment is essential. The best dredger may not be the cheapest, but the one offering multiple capabilities and highest life-cycle value.

Understanding of the environmental performance of dredging equipment has shifted from merely mitigating impacts during execution to proactively aligning dredger capabilities with value-adding, sustainable outcomes. The industry recognises its responsibility and continues to invest in improving sustainable production methods. Dredging companies can play a key role in collaborating with developers and designers to achieve sustainable infrastructure goals. Promoting mutual understanding of each other’s options and limitations is essential.