Hydraulic Dredging Overview
What is Hydraulic Dredging?
Hydraulic dredging is the process whereby we relocate material found at the body of a body of water to somewhere else. This process shifts materials from the waterbed through suction. It moves the dredged matter from one place to another by converting rocks, dirt, and gravel to slurry.
What Problems It Solves:
Of the various problems tackled by hydraulic dredging, the majority derive from coastal and coastline areas impacted by tidal activity. The constant ebb and flow of tidal water can cause a buildup of materials, such as:
- Silt
- Sand
- Sediment
Hydraulic dredging reduces all of these from the bottom of fresh as well as seawater.
Additionally, hydraulic dredging increases water depth, facilitates the construction of dykes, dams, and bridges, and eliminates potentially harmful or pollutant material from the water. Not only that but hydraulic dredging can help ships pass through certain bodies of water by removing excess debris.
Advantages & Disadvantages of Hydraulic Dredging
Advantages:
Benefits of hydraulic dredging include:
- Reduced cost of obtaining, operating, and maintaining hydraulic dredger
- Minimal sediment suspended
- The ability to access and remove materials like sand, silt, and gold that are otherwise too fine to move
Disadvantages:
However, that’s not to say it’s a perfect system. Hydraulic dredging has several disadvantages, including:
- Longer dredging time than mechanical dredging
- Difficulty dredging large/course materials
Notably, these disadvantages are site-dependent and, depending on what needs dredging, often outweighed by the benefits.
Hydraulic Dredging Process
Process
The process of hydraulic dredging comprises various stages. These include:
1. Excavation
In the excavation stage of hydraulic dredging, the hydraulic dredger uses suction to retrieve material from the waterbed. This varies depending on the environment but frequently includes:
- Silt
- Sand
- Rocks
Crucially the dredged matter is converted to slurry to be suctioned off the waterbed. It is this that distinguishes hydraulic from mechanical dredging.
2. Removal to Dredging Vessel
Once suctioned out of the water, the dredged material gets deposited on a barge or ship reserved for dredging.
3. Transporting Dredged Material
The dredged material is then transported by boat from the excavation site to a dredging deposition location that can utilize the dredged material.
4. Placement
Once the dredging boat arrives at the placement destination, the dredged material is removed from the boat and deposited at the site. This leaves the barge free to complete further hydraulic dredging excavations.
Materials
The type of equipment required for any given dredging excavation varies depending on the kind of dredging involved. The material undergoing dredging also affects the equipment requirements.
Equipment can include:
- Trailing suction hopper dredgers
- Cutter suction dredgers
- Backhoe dredgers
- Grab dredgers
- Environmental dredgers
Other equipment may include:
- Tug or towboats
- Heavy lifting cranes
- Tenders
- Survey vessels
Different Types of Hydraulic Dredging
Depending on what needs dredging, there are different methods of hydraulic dredging. What type of hydraulic dredging you opt for is affected by:
- Site
- Size of dredged material
- The coarseness of dredged material
With that in mind, the various kinds of hydraulic dredging include:
Suction Dredging
Suction dredging works like a large and water-tolerant vacuum. In suction dredging, the suction dredge sits on a dredging barge, and from there, pumps the slurry upwards.
This kind of hydraulic dredging is popular for extracting gold. While most of the slurry moves from the waterbed to the barge, the gold remains in the suction dredge.
Cutter Suction Dredging
The equipment for cutter suction dredging is smaller and more compact than normal suction dredging. This type of hydraulic dredging utilizes a rotary piece or cutter head that facilitates breaking rock and other large matter that might otherwise be hard to shift.
This type of hydraulic dredger is highly flexible, and while the dredger remains stationary, cutter suction dredging has a wide degree of applicability. But because of the size of cutter suction dredgers, they are typically reserved for large-scale projects like deepening harbors.
Trailing Suction Hopper Dredging
Trailing suction hopper dredging is a type of hydraulic dredging that requires a ship and two suction pumps positioned on each side of the ship’s hull.
In this type of hydraulic dredging, the suctioned material goes directly into the ship’s hull and stays there until the ship can dock and move it elsewhere.
Reclamation Dredging
Reclamation dredging is the means used to unburden a trailing suction hopper of its contents. While not strictly hydraulic dredging in that it doesn’t involve water, it successfully relocates hydraulically dredged material to land.
Barge Unloading Dredgers
Barge Unloading Dredging similarly helps unburden boats of dredged cargo. Rather than transfer it directly, it first converts the cargo to slurry for ease of transport.
Alternative Solutions to Hydraulic Dredging
There are two main types of dredging, and other methods that don’t quite fit into either category. If hydraulic dredging isn’t an option, other solutions include:
- Mechanical dredging
- Amphibious dredging
The main difference between mechanical and hydraulic dredging is that while hydraulic dredging utilizes suction, mechanical dredging requires an excavator. It uses powerful machinery to retrieve, scoop and extract material quickly and efficiently from an underwater environment.
However, unlike hydraulic dredging, which can be effective for deep-water work, most mechanical dredging projects happen along the shoreline. This is because the equipment involved in mechanical dredging struggles to work as effectively at greater water depth.
Amphibious dredging, on the other hand, is a method that isn’t quite mechanical or hydraulic dredging. It can work in submerged or raised conditions, and uses buckets and shovels for dredging.
| Service vs Service | Advantages | Disadvantages |
|---|---|---|
| Hydraulic Dredging vs Mechanical Dredging | Hydraulic dredging, compared to mechanical dredging;
| Hydraulic dredging, compared to mechanical dredging;
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| Hydraulic Dredging vs Amphibious Dredging | Hydraulic dredging, compared to amphibious dredging;
| Hydraulic dredging, compared to amphibious dredging;
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Costs of Hydraulic Dredging
Just as equipment varies from hydraulic dredging project to dredging project, so does cost.
The average cost is roughly $5-15 per cubic yard.
Comparatively, mechanical dredging averages $8-30 per cubic yard, including disposal fees.
Frequently Asked Questions
The need for a permit varies depending on the kind of hydraulic dredging undertaken. Permit requirements are also affected by:
- Size of project
- Location
- Federal regulations
Hydraulically dredged material is handled differently depending on permits and available space. Throughout the dredging process, workers are careful to observe the correct protocols and dispose of the material safely.
Because hydraulic dredging happens underwater, it leaves minimal impact on the surrounding environment. Once the hydraulic dredging equipment has been removed, the ground can be treated and re-sodded, leaving little to no impact on the area.
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