Dredge Basics

What you need to know about dredging.

Learn the basics to decide if dredging is right for you.

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What is dredging?

Dredging removes sediment and sludge in liquid environments, usually water. The three main types of dredges are clam shell, cutter-suction, and horizontal auger. Clam shell or bucket dredges can be small excavators, or large cranes on a barge. Cutter-suction dredges are typically large ocean going vessels, that anchor themselves with a pillar and dredge in an arch before moving to the next area.

We build horizontal auger dredges, which are the smallest of the dredge types. Our dredges are run on a cable system, or with a propulsion system. They resemble a household vacuum cleaner, with a wide cutterhead, that you push forward and pull backwards as they remove one layer of sediment per pass.

How do dredges work?

Each style of dredge works in a unique way and has it's strengths and weaknesses.

The clam shell dredges drop their bucket into the material and then extract what they collect and dump it onto a barge or land, before repeating the process. Clam shell dredges can work in almost any environment, and to any depth. It's the slowest process, from a cubic yards per hour measurement, for the size of the unit, but they can't get clogged, so they're able to operate in harsh environments, like harbors, which can have lots of debris. If you have a project requiring removing material 40' below the surface, or are worried about what's under the water, a clam shell dredge may be the best choice.

Cutter-suction dredges are generally large barges. The cutter is designed to extract compact material, and many are used near ocean shore lines to remove abrasive sand and clear erosion sedimentation. With the large size and aggressive cutting, many cutter-suction dredges use one or multiple pillars to anchor themselves into the ground before dredging in an arch in front of them. After they've cleared the arch, they move forward and clean another arch. Cutter-suction dredges are great for large projects and excel at dealing with compact material.

Auger dredges mix the sediment with water with their cutterhead, and pump the slurries to the surface of lagoons, ponds, lakes, waterways, and canals. The material is then pumped through floating and land-based pipe to a disposal/spoil site. The compact size of the unmanned dredges, and cable systems they use, mean they're ideal for dredging lagoons with linings, which would be damaged by a clam shell, or the posts and aggressive cutter of the cutter-suction dredges. We can add wheels and a cage to our auger, so the cutterhead rests on top of a liner, and won't cut into it, even if you're dredging directly on the bottom of your lagoon. 

What is a horizontal auger dredge?

Horizontal hydraulic auger dredges have a horizontally positioned cutterhead (auger) that rotates to combine sediments and water thus creating a slurry.

What are the Benefits of Horizontal Auger Dredges?

  • Ease of movement and use
  • Transportability
  • Productivity
  • Turbidity
  • Cost

Benefits of Horizontal Hydraulic dredges explained

1. Ease of movement and use

Horizonal dredges are nimble and easily maneuvered in various sized and shaped bodies of water. Operators point the dredge where they want to cut, lower the cutterhead, and move forward. This simple system can be quickly taught to an employee/operator.

2. Transportability of hydraulic dredges

Crisafulli dredges can be carried on standard step-deck or flatbed trailer. Dredges are delivered fully assembled on a truck or partially assembled when delivered in a shipping container.

3. Productivity of hydraulic dredges

Horizonal auger dredges are productive at moving liquids and solids. Productivity is measured as the percentage of solids relative to the mixture being extracted and pumped. The production of solids is measured in Cubic Yards per hour or Cubic Meters per hour. Depending on the type of materials, it is typical to extract up to a 25% or more of solids content. The rate of extraction is measured in Gallons per Minute (GPM) or Cubic Meters per Hour (m3/h) of slurry or sludge. Crisafulli dredges are matched to meet the output demands of dewatering devices such as dewatering bags, geo-tubes, drying beds, clarifiers, belt presses, filter presses, screens, centrifuges, and tanks. Depending on output demands, Crisafulli dredge output can be adjusted from 200 GPM to 2,500 GPM, which equals 45.4 m3/h to 567.8 m3/h.

4. Turbidity and hydraulic dredges

By design, horizontal auger dredges capture dredged material by sucking the dredged material into a shroud where it is directed into the pump’s suction mouth. The shrouding of material enables horizontal auger dredges to suck up dredged materials while dredging.

5. Cost of hydraulic dredges

Small horizontal auger dredges are priced for as little as $125,000 for a new unit, while the largest horizontal auger dredges are less than $600,000.

What are the basic components of hydraulic dredge?

Basic components of hydraulic dredges include a cutterhead (auger), pump, floatation system or platform, engine or motor, operational controls, and discharge.

What is the process of hydraulic dredging?

During hydraulic dredging, the engine (diesel or electric powered), transfers power to the cutterhead and pump by means of hydraulic motors and high-pressure hoses. Then the cutterhead creates a slurry from the sediment. The centrifugal pump (mounted directly behind the cutterhead) draws the slurry into a discharge piping system. From there, the pump pushes the slurry through a floating discharge pipe to the surface and then to the discharge/spoil site.

What size dredge do I need?

To determine the best dredge to fulfil project requirements, consider these questions:

  • 1. What are the dimensions of dredging area (L, W, D)?
  • 2. What is amount of material to be extracted?
  • 3. What is depth of the material to be extracted?
  • 4. Is the material compacted or not?
  • 5. Is the material free flowing?
  • 6. What is the specific gravity (weight relative to size) of the material?
  • 7. What is the maximum distance from dredge to the discharge/spoil site?
  • 8. What is the vertical lift from the dredge to the discharge site (elevation change)?
  • 9. What is the particle size in the material to be dredged?
  • 10. Are there any flow requirements?

Who is SRS Crisafulli?

SRS Crisafulli, Inc. is a Montana USA-based manufacturing and engineering company founded in 1966 with customers throughout the United States and around the world. SRS Crisafulli, Inc. manufactures hydraulic auger dredges, power take off (PTO) powered trailer pumps, smaller submersible pumps, power units, floating pumps, and floating platforms. See Crisafulli pumps and dredges.

What dredges does SRS Crisafulli manufacture?

Crisafulli manufactures standard and custom hydraulic dredges. Crisafulli dredges are available in manned Rotomite or unmanned FLUMP with electric motor or diesel engine models. Four models of Rotomite (manned) dredges and many configurations of FLUMP (unmanned) dredges are available. SRS Crisafulli customizes standard dredges to meet customer’s specifications.

Rotomite manned dredges

Rotomite dredges are nimble, self-propelled, and steerable with superior maneuverability. Rotomite dredges are easy to operate and provide maximum versatility for a wide range of applications. Operators can dredge various sizes and/or shaped ponds, lagoons, or lakes without external support vessels or draglines. The Rotomite can also be operated with a cabling system.

The Rotomite 6000’s 275 HP engine, coupled with a Crisafulli sludge pump is capable of extracting up to 2,500 gal/min (567.8 m3/h) of mixture. The fuel tanks are sized to provide up to 10 hours of continuous operation. The hydraulically powered propulsion and steering system provide both thrust and steering which is unique in the dredging world. The system provides adequate force to enable the horizontal auger on the cutterhead to engage, cut, and dislodge settled solids.

The standard models are diesel and hydraulically powered. Electric configurations are available by special order. Four Rotomite models are available: Rotomite 6000CD, Rotomite 6000, Rotomite 4000, and Rotomite SD-110.

FLUMP unmanned dredges

Dredge operators control FLUMP dredges remotely which reduces their exposure to potentially hazardous materials. FLUMP dredges are designed and built for dependable service in harsh environments. FLUMP unmanned dredges are portable, cabled, and remote controlled with an optional Pivoting Traverse System available.

FLUMP stands for “Floating Lagoon Pumper”. FLUMP dredges are popular with customers for cleaning settling ponds and extracting sludge, sediment, biosolids or residuals from lagoons.  FLUMPS are compact and work in small ponds and/or lagoons where other conventional dredges are too large. Its structural steel framework and lightweight construction make it durable and easy to transport.

There are many configurations for the standard FLUMP. Various models available depending customer’s requirements.

How can dredging productivity be increased and reduce dredging time?

Every pass is a productive forward pass with the Pivoting Traverse System, available on new FLUMPS. With the Pivoting Traverse System, operators dredge forward then rotate the dredge at 180 degrees and dredge forward again. The Pivoting Traverse System makes dredging faster.  

Dredge Rentals

Many domestic and Canadian customers rent Crisafulli dredges and then buy them. Click here to see available rental dredges.


What is a Gantry Dredge?

A gantry dredge is on a dredge built atop a bridge like structure. Crisafulli gantry dredges are hydraulic dredges mounted on a rail system above a rectangular basin. Gantry Dredges operate on a X, Y and Z axis and effectively remove sediments and wastes. Gantry Dredges tend to be integrated into a permanent system. Gantry Dredges are placed where conventional dredges are unsuitable. Each Crisafulli Gantry Dredge is custom built to meet customer specifications.

What is sludge lagoon removal also called lagoon sludge removal?

Sludge lagoon removal is removing sludge (thick mixture of solids and liquids) from ponds, basins, and lagoons.

What is wastewater lagoon sludge removal?

Wastewater lagoon sludge removal is removing sewage sludge and biosolids from a wastewater treatment lagoon.

Why is sludge removal necessary?

Sludge needs to be removed from a body of water such as pond, basin or lagoon when it reaches its full holding capacity and/or when the water depth decreases to a point where it interferes with its proper functionality.

What is the most common and cost-effective method of wastewater lagoon sludge removal?

Lagoon dredging is the most common and cost- effective form of wastewater lagoon sludge removal. The biggest advantage of hydraulic dredging is that ponds and lagoons can be dredged without draining or taking them out of service. Lagoons can be taken offline and dried out then removed with an excavator, but that can take months or years, and is only an option at the end of the lagoons life.

How to remove sludge and extend the service life of wastewater lagoons?

Dredging can extend the service life of a wastewater lagoon. Wastewater lagoons can effectively operate for an extended number of service years if sludge accumulation is properly managed. Wastewater systems that are clogged with excessive sludge, could be out of compliance with EPA regulations, create a nuisance for the general population living nearby and become a liability for the owners of the wastewater lagoon.

Four Options available for removing sludge from wastewater lagoons

  • Floating dredging equipment in the pond and then pumping solids to drying beds, belt press or land application.
  • Pulling the lagoon offline, draining the lagoon, drying the sludge in place, and then scraping the dry solids for removal and disposal.
  • Removing the lagoon from service, draining the water cap off and then pumping the sludge to drying beds.
  • Bio Stimulation/ Bio augmentation.

Sedimentation and hydraulic horizontal dredging

Sedimentation is a gradual accumulation of sediments usually resulting from soil erosion. Sedimentation can decrease water storage capacities for community drinking water, industrial water supplies, and irrigation. It can also reduce flood protection, impede recreational activities, slow water flow, obstruct navigation and contribute to poor water quality. Accumulated sediments periodically need to be removed from ponds, lagoons, reservoirs, lakes, streams, rivers, marinas, and waterways. Hydraulic horizontal dredging is ideal for sedimentation remediation in water up to 20 feet deep.

WTP’s and hydraulic horizontal dredging

Municipal water plants use Crisafulli Rotomite and FLUMP dredges for the removal of sediments from their settling ponds. Municipal water plants utilize settling ponds in the process of producing clean drinking water. The settling ponds eventually reach a saturation point and dredging of the ponds becomes a necessity for the water plant to continue operating.

WTP- Water plant settling pond full of sediment


Pond hydraulic dredging

Many golf courses, communities, estates, and ranches use Crisafulli dredges to maintain their ponds. Over time, ponds tend to lose their holding capacity because of sediment accumulation, usually a result of erosion. In this case, one must consider hydraulic dredging.

Lake hydraulic dredging reduces blue-green algae blooms and improves water quality

Lakes are hydraulically dredged to improve water quality, maintain property and recreational value, as well as protect aquatic and wildlife. Hydraulic dredging can remove sediments with excessive nutrients and as a result reduces the risk of blue-green algae blooms.

Community of Powers Lake, North Dakota uses a Rotomite 6000 to improve water quality in 1,1616-acre lake

Marina hydraulic dredging

Dredging ensures that boat and yacht owners may freely move into and out of boat slips and the marina. Regular dredging of sediments out of marinas is essential for marina operations. The Rotomite hydraulic dredge is the smart choice for marina maintenance because of its maneuverability, unlike a typical swing ladder dredge.

Mine tailings and hydraulic dredging

The safe dredging of tailing ponds ensures that they are performing adequately. Dredging also allows for the recycling of the tailings to produce additional minerals. The Crisafulli liner protection system enables operators to dredge lined lagoons without fear of damaging the geomembrane liner.

Mine resource recovery with hydraulic dredging

Waste streams and tailing ponds are becoming more valuable due to increasing prices of various precious metals. From Clays to Gold, Crisafulli dredges help improve profitability. Most tailings ponds contain very fine solids with potentially valuable materials trapped within the sediment. The cutterhead effectively slurries the solids to be re-processed. This process enables the mining industry to recover more of the valuable and historically lost minerals. The dredging process enables mines to keep their ponds in service, while eliminating the need for dry ponds.

Mine Environmental Remediation with Hydraulic Dredging

As waste material accumulates in retention ponds, the available storage space declines. This creates the potential for hazardous waste spills. To prevent spills during high water events, operators need to clean their ponds and maintain containment capacity. Crisafulli dredges work well in a corrosive environment without any disruption of the mine operation.

Mine Retention Pond Waste Removal

Both active and abandoned mine sites are potentially hazardous as waste products can leach or spill into the environment. Hazardous pollutants are usually held in a lined lagoon. Crisafulli dredges effectively remove, for proper disposal, these contaminated substrates, without damaging the geomembrane liner.