Mechanical Dredging Overview
What is Mechanical Dredging?
Dredging is the process of removing silt and other sediments from the bottom of any body of water. This silt can clog up waterways, doing damage to natural habitats and flooding areas.
Mechanical dredging uses heavy equipment like an excavator to remove sediment from the bottoms (and sometimes the sides) of ponds, lakes, rivers, and other waterways. Often these excavators sit on top of barges. They help to maintain lagoons, marinas, and more.
Mechanical dredges remove rocks and debris by scooping debris from the bottom of a waterway and placing it onto a waiting disposal scow. Mechanical dredges work best with hard-packed materials (as opposed to goopy sludge, which is best dealt with in other ways).
What Problems It Solves:
Over time, accumulated sediment can cause a variety of problems.
An excess of sediment can make waterways more shallow, which prevents boats or ships from moving through. It can also cause water contamination that may harm aquatic plants and animals. In coastal areas, accumulated sediment can also cause erosion.
Who Needs This Service?
Many individuals and government bodies eventually require this service to maintain beaches, waterways or even to collect material for construction.
When Would You Need This Service?
Dredging can accomplish many different goals, including:
- Creating and maintaining waterways for cargo vessels
- Removing trash and other pollution
- Excavating in preparation for construction projects such as bridges and docks
- Increasing water depth to prevent floods
- Gathering materials for construction projects
- Cleaning ponds and lagoons
Advantages & Disadvantages of Mechanical Dredging
It stands to reason that mechanical dredging is only suited to certain jobs. Otherwise, a different form of dredging is necessary. Mechanical dredging is great for heavy jobs with hard-packed materials.
- It can expand ponds beyond their original contour lines
- It can be performed without water in place
- Allows for a higher degree of accuracy and precision than other methods
- Works well for removing rock and gravel
- Less time consuming than other types of dredging
Mechanical dredging is a messy process and won’t work for soft sediment.
- It may be necessary to drain the pond first
- This process can damage existing landscaping / the surrounding environment
- Dredge material may contaminate surrounding water
- Operating heavy machinery is expensive
- Requires plenty of space to operate
Mechanical Dredging Process
It’s imperative to know the process of mechanical dredging before you undertake a project. This way, you’ll understand exactly what you’re getting yourself into before you start!
- Get a Permit: You will probably need a permit before your project can begin. Consult a professional to determine what type of permit you’ll need and how long it will take to get.
- Consult With an Estimator: They’ll take measurements and give you the estimated time to completion and costs.
- Get Bids from Contractors: Marine Matcher offers free bids.
- Schedule Your Project: Availability depends upon other projects and the weather.
- Initial Excavation: Material must be loosened or dislodged from the bottom of the waterway.
- Material Removal: Once the material is dislodged, it will be lifted onto the vessel.
Material Disposal: Materials must then be relocated to another site.
There aren’t many materials that you’ll need as the contractor should supply you with everything you need, including the heavy machinery and support equipment necessary.
Different Types of Mechanical Dredging
Of course, depending on the situation and project at hand, different types of dredging will be needed.
Hydraulic dredging uses suction to remove sediment and a pipe to move it out of the location that’s under construction.
This type of dredging is preferable to mechanical dredging if you want to avoid the displacement of the water that’s over the sediment or if you need to prevent the sediment from mixing with the water above it.
Mechanical dredging is a good choice if you need to remove large amounts of rock, stones, gravel, compacted sand, or rooted vegetation.
This form of dredging works best if you don’t need to be delicate. The equipment used is bigger and heavier than hydraulic dredging, and it’s more cumbersome. This type of dredging tends to stir up sediment and, as mentioned, could cause the water to become contaminated.
There are a few different types of mechanical dredging, including:
- Grab Dredging: This type of dredging is used for deep water. It has a claw-like fixture used to lift the sediment.
- Backhoe Dredging: This form uses a bucket in a fashion similar to a backhoe to scoop up sediment, which it then empties onto the barge.
Bucket Dredging: A barge is fitted with a series of buckets and scoops up sediment. When one section is finished, the barge moves and starts again.
Alternative Solutions to Mechanical Dredging
Many circumstances call for hydraulic dredging as a better alternative to mechanical dredging. If the sediment is fine or contaminated, hydraulic dredging is often the best choice.
In some situations, biological dredging is a possibility. This term refers to the introduction of beneficial microbes that will consume accumulated sludge (even pollutants) from the bottoms of lakes and ponds.
However, this approach does not work on inorganic matter such as rock and sand.
Costs of Mechanical Dredging
The costs of mechanical dredging depend upon a number of factors, including:
- The size of the project
- Permitting and engineering costs
- How thick the sediment is
- The type of sediment
- How deep the water is
- Job site location
- Time allowed and length of workdays
- Waste disposal methods
- Water management
Just the disposal scows necessary to transport materials can cost tens of thousands of dollars to operate. The monthly cost of the dredge itself often approaches $100,000. Towing vessels cost a similar amount of money to operate.
Lastly, you must factor in wages, taxes, and insurance to your total costs.
Frequently Asked Questions
The answer to this question varies drastically according to a number of factors, including the size of the area, sediment thickness, number of scows, and water depth. The larger the area that needs to be dredged, the longer the project.
Mechanical dredging usually takes less time than other forms of dredging. The length of the project depends upon a number of factors, including the size of the project and whether or not water must be diverted or drained before the project can begin.
Weather can slow production. Foggy, icy, or rainy days can compromise visibility and worker safety, so projects may need to be delayed.
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