What is mechanical dredging?

Mechanical dredging is just as the name implies, moving solids off the bottom of a waterway mechanically, like using a giant shovel although these shovels are diesel power in the form of a hydraulic excavator or some form of a cable crane with a bucket.

Advantages, mechanical dredging offers a great and often an only solution in many situations such as:

When excavating from shore and depositing the “spoils” on land where it’s typically spread by a bulldozer when drained or loaded into trucks for transport to an offsite location.
In restricted places, like a marina that needs slips dredged between docks.
When potentially harmful contaminants are identified at a certain depth/layer and area/plumes originating from the pollutant discharge point, which can be quite precisely excavated with specialized flat closing clamshell bucket’s and equipment installed software which indicates the bucket’s depth and location to accurately remove the contaminants with as least possible adjoining or covering uncontaminated spoils be excavated greatly reducing the amount of spoils to be treated or transported to a landfill or specially constructed “CDF’, or confined disposal facility.

Disadvantages:

Lots of floating equipment if not working from shore! Typically, “deck” barges are needed to be moved to the dredging site via a tug or “pushboat” with the excavating equipment secured on the flat deck, and moved often due the limited “reach’ of the excavating equipment as the excavation/dredging progresses. Typically, these deck barges have large upright steel “spuds” that can be lowered or “spudded down” into the bottom to hold the deck barge in place as the excavation commences until relocated to the next position to continue dredging. The excavating equipment takes a bucketful of spoils, raises it above the water and rotates to dump the spoils into a floating container “scow” or another deck barge with sides, ideally several such scows are available so dredging can be as continuous as possible process. When loaded the scow is towed or pushed by a tug or pushboat to a hopefully nearby dock and ties off where it is unloaded by another excavator or crane and stockpiled for drainage. When the spoils are drained enough for truck transport they are loaded once again into a truck and transport to a final destination where they are spread by excavation equipment. This process as described above, to achieve maximum production, would be using a deck barge with spuds, 2 excavator’s or cranes, at least 2 scows, and ideally two push boats as well as 2 crane operators, 2 push boat captains, several deckhands, and ideally a engineer to supervise maintenance including greasing, lubricating oils and fuel supply, and a project manager to coordinate all the moving parts. There are a lot of options and variables that may not be included in the above description.

The process

Very similar to the process for hydraulic dredging, (please see “the process” under hydraulic dredging), although with more moving parts and production rates much harder to predict, the weather must be somewhat calm to control excavation depths and other maritime traffic must be navigated through or around. The time it takes to scoop a bucket and dump it and return to the same point of action, or “cycle time” can vary from 1 minute to up to 15 minutes depending on the equipment being used and bucket cubic yard capacity, transport scow cycle times can vary greatly depending on the scow cubic yard capacity, travel distance and many other variable’s, it’s somewhat a educated guess based on the situation and all the involved elements. Typically, proposals are based on worst case scenarios or defined parameters with allowances for faster or slower production rates differences from projections.

Calculating spoils cubic yards to be dredged

A 500’ long x 60’ wide channel equals 30,000 square feet, X a 8’ thick layer of spoils to be removed equals 240,000 cubic feet, which divided by 27 equals approximately 8.889 yards A cubic yard is a cube 3’X 3’ X 3’ containing 27 cubic feet, a typical 3 axle dump truck hauls roughly 12 yards per load.

Your Trusted Partner for Mechanical Dredging in the Great Lakes

Contractors Marine is dedicated to delivering customized mechanical dredging solutions that meet your specific needs and budget. Our extensive experience and regional focus ensure your project is completed correctly, on time, and in full compliance with all regulations, including the crucial task of permit acquisition.

Contact us today for a site evaluation and to discuss your mechanical dredging project in Michigan or the surrounding Great Lakes states! Let us handle the permits so you can focus on your goals.