Marine Dredging (Hydraulic Suction)

As we covered in another article discussing "Marine Dredging (Conventional)", the primary objective of a marine (maintenance or infrastructure) dredging project is usually quite similar from one project to another because the "end-game" is usually the same: to remove material from a target area down to a predetermined grade.

That being said, how this objective is achieved is the true project maker (or breaker). The methodology chosen to achieve project objectives can vary greatly due to multiple factors, including the type of material to be dredged (silt, sand, gravel, cobbles, etc.), the approved disposal method, the level of contamination (if any) and so on. As such, geotechnical data and lab analysis of samples are crucial to properly identify the "how"; this is especially true when dredging areas that have never been dredged before (as is often the case for new infrastructure projects).

"I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." - Abraham Maslow

Thankfully, the dredging industry has multiple tools from which to choose; not just the proverbial hammer!

There are numerous articles available online discussing in great detail the various methodologies applied to dredging, the benefits of dredging, etc. Some of the industry authorities in the matter are WEDA and IADC, and I highly recommend taking some time to review their articles, knowledge bases and FAQ's. However, in this article, I want to focus on...

Hydraulic Suction Dredging:

There are several types of dredges that perform hydraulic suction dredging, but all of them harness the power of fluids (hydraulics) to displace the material - i.e.: the material is displaced hydraulically through a pipeline in slurry form (mix of water and solids). The centrifugal pumps that form part of the dredging apparatus produce sufficient flow to lift the solids from the bottom (ocean floor / watercourse / pond bed) and displace the slurry via a network of pipes, be it floating and/or land-based.

From our experience, the most popular models seem to be Auger Dredgers, Cutter Suction Dredgers (CSDs), and Trailing Suction Hopper Dredgers (TSHDs), although there are also some Suction Dredgers and Water Injection Dredgers working on projects throughout the world.

In my previous article, I briefly touched on the fact that our fleet of amphibious excavators can perform conventional dredging using an excavation bucket, but all our dredgers can also be transformed into Horizontal Cutter Suction Dredgers in a matter of a few hours, allowing for quick onsite adaptation should a switch in methodology be required - as evidenced in the image below.

Our hydraulic suction configuration allows us to loosen compacted soil using our proprietary horizontal auger-type cutter and pump the material in slurry form at a high solids content to a designated disposal area. When the disposal area is located at a great distance or at a significant elevation differential, booster pumps can be mobilized to site to supplement the dredger's pumping capacity and maintain dredging efficiency.

The bulk of our work in terms of marine dredging calls for hydraulic suction rather than conventional dredging, and is often referred to as maintenance dredging. On these projects our crews are deployed to clear navigation channels and wharves in order to ensure safe passage for fishermen. The video below was taken during a navigation channel project in PEI (Canada).

Of course, on projects where we are dealing with contaminated materials, the Disposal at Sea (DAS) permit will not allow for an open discharge into the environment (as is being done in video above). In order to separate and isolate contaminated material for proper disposal, dewatering solutions will usually be deployed to treat the slurry, separating solids from water which will eventually allow for the dewatered material to be disposed of in an approved location. Popular dewatering methods include centrifuge, filter press, geotextile bags and temporary (or sometimes, permanent) containment cells. I will elaborate a bit more on the subject of dewatering and contaminated material in future articles.

As with any project, accurate and timely data for reporting is key to avoid any unpleasant surprises. To this end, we need to be able to keep track of our progress and provide our clients with accurate and reliable data to demonstrate our progress on a daily basis. In order to provide accurate and meaningful data, we use a combination of GPS coordinates (logged by our operators at every position they clear), layered with satellite imagery, pre-dredging sounding results and CAD files for spatial reference. We also provide a daily compilation of our manual soundings to validate that finale grade has been achieved, but also to track total volumes to keep a close eye on project budget.

This combination of reports provides a thorough daily accounting of our progress in comparison to project objectives, keeping everyone involved with the project informed of up-to-date progress with just a quick glance. Below is an example of a visual report we produce for our projects, showing progress in terms of completed area.

Once a project is completed, a post-dredging survey will be conducted by the end-client or a 3rd party contractor to validate project objectives have been met and confirm quantities for payment.

Have a potential requirement for hydraulic dredging? Get in touch with me! join my network, DM me, comment on the article - I would be happy to discuss the subject matter further. Cheers!

Note: The above is only meant as a high-level summary and is in no way intended to represent an in-depth review of the subject matter.

About us:

ECO Technologies Ltd. is a dredging and environmental services provider located in New Brunswick (Canada), with project management and development offices in Belo Horizonte (MG - Brazil) and Santiago (Chile). Learn more about ECO Technologies on our website: www.ecotec.ca