Environmental Dredging

Small harbours, marinas and inland waterways where the bed may be contaminated are faced with an increasing demand for dredging. DEC invested in new technologies that can help to efficiently clear away these sediments.

Aim

Environmental dredging is distinct from large-scale dredging because of the approach selected. Whereas traditional dredging aims to remove sediment to a certain level for example to obtain greater depth, that is not always the case with environmental dredging. It may be necessary to clear the waterway, but where traditional equipment is too large for the project, environmental dredging can be a perfect solution. Also, the high degree of precision of environmental dredging ensures that it is possible to dredge very selectively.

The Blani, environmentally dredging in the marina of Nieuwpoort (Belgium).

Less water = less dewatering

Dredged sediment often contains too much water, so dewatering and/or stabilisation are required before the sediment can be reused.

To minimise the volume, the sediment must be returned to a relatively high level of dry matter. The greater the dry matter content, the lower the potential storage costs and the greater the guarantee that the sediment will be geotechnically suitable for reuse.

With our advanced environmental dredging techniques we achieve the necessary high concentration of sediment with low turbidity during dredging. The dredging head that our environmental dreding vessel "Blani" is equipped with for example, dredges at nearly in-situ density, limiting the dewatering process afterwards.

With its special, automated, rotating cutter head, the Blani is capable of very precise dredging without excessive water uptake.

Eye for the environment

Traditional dredging work always results in some degree of turbulence of the bottom sediment. If the sediment is contaminated, there is a heightened risk of what is known as recontamination, with the stirred up sediment repolluting the newly dredged area.

Dredging very slightly contaminated sediment can thus pose a problem because of the suspended contaminated particles. Our environmental dredging rigs do not have any problem with this and can employ an additional silt screen if necessary.

Also when sediment – even uncontaminated sediment – is located in a protected nature area, stirring up the sediment must be avoided as much as possible so as to minimise the disturbance of the aquatic environment. That is exactly what our dredging rigs are made for!

High degree of precision

Our environmental dredging rigs are equipped with advanced technological positioning and monitoring systems that provide for a high degree of precision in every dredging project. This makes it possible to dredge very selectively: relatively thin layers of sediment in a relatively small area. In this way, too, the disturbance of the aquatic environment can be kept to an absolute minimum.

Environmental dredging techniques

Hydraulic dredging techniques

The Blani is a small suction device with a closed cutter head, ideal for working in small harbours or marinas, such as those of Nieuwpoort and Blankenberge. Given that hydraulic pumping is the most efficient method for transporting sediments, this dredged material can also be pumped directly to the processing site or storage. The rotating head of the Blani limits the turbidity and adapts itself to the thickness of the layer to be dredged.

The Vlaanderen XV and the Bilba are two small dredging rigs that can be fitted with a sweeper head, which does not have rotating parts, but moves back and forth like a traditional cutter head. This means the bottom is not stirred up and turbidity is minimised.

The Pixy is a dredging rig specially developed by DEC comprised of eight pontoons and is fitted with an augur that transports the material via two screw wheels to the dredging pump inlet. The rig is positioned correctly using winches and pulled over the zone to be dredged. This "forest sprite" has proved itself in dredging two ponds contaminated with mercury in Hultsfred (Sweden).

Mechanical dredging techniques

These techniques are used primarily in places where it would be difficult to work with hydraulic dredging rigs.

The EcoDrag is a specially equipped bucket dredging mill suited to dredging up contaminated sediment. Thanks to the special design, water take-up and spillage are minimised, as is the contact of staff with the contaminated soil.

The EcoGrab is a cable crane with a specially designed bucket that works from atop a pontoon or on land. When the bucket is closed, all the openings are sealed. The bucket moves along a horizontal plane. This machine can dredge up soil layers with a thickness of less than 5 cm!

The EcoBucket is a backhoe-type dredging rig that uses a bucket with a sealing mechanism.

The Blani, environmentally dredging in Blankenberge (Belgium).

Sweep dredgers are also capable of dredging in a very controlled way with minimum disruption of the aquatic environment, because the head only moves back and forth.

The Pixy at work as part of the environmental dredging project for two ponds contaminated with mercury near Hultsfred (Sweden).

Would you like to know more?

View some projects we have completed using this technique.