What is Hydraulic Dredging?

Hydraulic dredging is the process of removing solids from the bottom of a waterbody, basically underwater excavating, to enhance water vessel travel and sometimes used to clean up various contaminations, using a floating platform call a dredge, which typically contains a diesel engine powering a specialized pump and various winches and other accessories. A long front extension called a ladder with a rotating cutterhead, that can be lowered to the desired cut depth, loosens bottom sediment for travel up a pipe pulled by the pumps vacuum, through the pump which pressurizes the mixture for travel through a pipeline for discharge, which can be up to several miles away, longer distances or higher discharge locations elevations may require a booster pump in addition to the main pump on the dredge. Typically, the dredge pivots across the width of the desired “cut” or excavation by pulling on placed anchors connected to dredge winches through pulleys on the ladder end and “steps” forward with the selecting raising and lowering of “spuds” located at the rear of the dredge. (see video) Most harbors are maintained by hydraulic dredging due to the volume being moved and space available.

Advantages and Disadvantages

Some big advantages of hydraulic dredging that make its use indispensable in many situations include:

• Very efficient uptake and transport of bottom sediment over longer distances and to higher elevations.
• Capable of transporting high volumes of materiel’s relatively inexpensively compared to other methods when mobilized, typically, from a hundred up to several hundred yards per hour for larger dredges.
• Bottom excavation depth is easily accurately maintained during the dredging process.
• Materiel is only handled once from origination to a settling pond or to reestablish a beach.

Some disadvantages of hydraulic dredging include:

•  Does not dredge clay efficiently that may exist on the bottom of many waterbodies
• The transport and setting up of the dredge and pipeline (mobilization) and teardown of the dredge and pipeline (demobilization) requires extensive transport and assembly. Typically dredging in waterways connected to oceans or lakes are service by larger dredges which are rarely disassembled and use large “strings” of preassembled pipelines that are towed to the dredging location in lengths of several hundred feet and connected as needed. Smaller inland projects require high temperature “fusing” or other connection methods of typically 50’ sections of “HDPE plastic” pipe which is transported to site and subsequently cut back into 50’ sections and removed as part of the demobilization process.
• On larger water bodies, if you feel a wind on your face, typically includes the presence of waves which are not conducive to hydraulic dredging and is a variable that makes project finalization dates difficult to predict
• A “spoils” discharge site is required if not discharging on a beach or in offshore waters that includes the adequate space to construct a settling pond for the dredged materiel to be pumped with the additional capacity to allow for “settling” of the dredged materiel’s either continuously or overnight. This site must include a route to install at least one discharge pipeline as well as often a “return” pipeline to return water to the waterbody being dredged after the sediments have “settled” to the pond bottom. Settling ponds are typically comparatively large as they are typically designed to handle up to a 10-hour day of dredge discharge water volume in the range of 1,500,000 gallons for a smaller dredge. Typically, the dredge “discharge” water contains roughly 15% solids with the excess clean water returned to the waterbody being dredged.

The Process

Although Hydraulic dredging is a great solution for certain situations what is feasible and what is the process? Typically, some engineering and design work is required for even a rough quote and will also be needed for permitting as outlined below. Many public jobs have a plan done and permits issued although the plans often needs to be revised as very few engineering firms are familiar with all the elements needed for a successful dredge job.

Engineering and feasibility

• Calculate the cubic feet to be dredged by determining the length and width of area to be dredged to calculate the square footage, multiply that by the depth of the materiel to be dredged which is obtained by subtracting the current depth from the desired depth, times the square footage by materiel to be dredged depth which will provide a typically quite high number, which is divided by 27 to generate a cubic yards total to be relocated or “dredged” to a discharge site, which is critical information needed to determine the area needed for the size and depth of the settling pond. (see calculating volumes below.
• Find and secure permissions on any upland (not wetlands) parcel or parcels with enough space to construct a properly sized spoils discharge pond that also has a route available to install and remove the dredge pipelines. Dredge pipelines can be thousands of feet long and ran through lakes, culverts, be installed in creek beds, and cross roads with the appropriate safety considerations and permits and are typically under 12” in diameter.  Many farmers like the rich bottom silt spread on they’re property to enhance fertility or the spoils can be used to fill in ravines or build out land.
• Calculate a rough budget number which include “plant” mobilization including a inline booster pump if needed, projected dredging operating hours including supervision and crew, and the removal of the plant when the dredging is completed or ‘Demobilization”. Typically, the finalization of the discharge site is done by others several months later as the spoils drain in the discharge pond and become solid.
• Present the cost in the form of a dredging proposal to the client or clients.

Secure funding and apply for permits

• These types of projects require extensive planning and resources and are not inexpensive. Some private funding options we have seen include individual property owners pooling they’re money and all signing a contract for all dredging expenses with one providing a discharge ponds site, requesting a homeowner’s association or starting one to enforce association deed waterway maintenance agreements, and petitioning your local governmental unit to establish an improvement tax district which is usually not well received by that governmental unit. Individual cost has ranged from over $600K for one individual on a private Lake to as low as $10K for canal developments with a higher density of residences to share the expense.
• A State of Michigan EGLE permit, a soil erosion permits and related submittals typically including sediment sampling and testing for possible contaminants, sometimes a mussel survey, complete and extensive waterway and discharge site plans with dimensions and a completed permit application are submitted if the project is going forward. This process is often in the form of some preliminary negotiations with EGLE and waiting for EGLE to respond and issue a permit often takes up to a year.

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. In this example the settling pond for hydraulically dredging this volume of spoils should be constructed with a minimum capacity 10,000 cubic yards and ideally more to help insure no sediment enters the clean water return pipe 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.

• Michigan: Your projects often require permits from the Michigan Department of Environment, Great Lakes, and Energy (EGLE) and the U.S. Army Corps of Engineers (USACE). Recent focus includes PFAS testing requirements and specific regulations for inland lakes and streams.

We proactively manage the complexities of permitting and compliance for you, working closely with agencies like the USACE (Detroit, Buffalo, and Chicago districts for the Great Lakes region), state DNRs, and DEQs/EPAs to streamline your project’s approval process and ensure a smooth, compliant operation.

Your Trusted Partner for Hydraulic Dredging in the Great Lakes

Contractors Marine is dedicated to delivering customized dredging solutions that meet your specific needs and budget. Our 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 hydraulic dredging project in Michigan or the surrounding Great Lakes states! Let us handle the permits so you can focus on your goals.