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Dredging is an excavation activity in which materials are recovered from beneath the water’s surface. The purpose of dredging is generally to gather bottom sediment and either dispose of it at a different location or use these sediments in various products. For example, sand and gravel are used in concrete mixtures. There are many uses for dredges, all of which vary and require different types of dredging equipment. Below are some application examples, with some suggestions for dredge selections.
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A dredge is defined as an apparatus used for an excavation activity that is carried out at least partially or fully submerged underwater, with the purpose of gathering up bottom sediments and disposing of them at a different location.
Every dredging application is different, and every dredge operator works under unique conditions. It’s these variables that create your dredge’s own unique story. As a leader in the field of customized dredging solutions for special applications, we understand the unique characteristics of these applications, and we openly share our expertise with many industry-related organizations.
At DSC, Dreducation® describes our commitment to furthering education and training about dredges and dredging—not only for dredge owners and their crews, but also for the general advancement of the industry.
DSC specializes in hydraulic dredges. Essentially, a hydraulic dredge functions like a floating vacuum, excavating and pumping material through a pipeline to a different location using a centrifugal pump. Hydraulic dredging is the cleanest, most precise and environmentally friendly method of dredging today.
Alternatively, mechanical dredges are used for removing debris or hardened material that is tightly compacted, using buckets to dig and transport material to different locations. Mechanical dredges do not typically retain fine materials as well as hydraulic dredges.
Dredges can be used to create, maintain or improve waterways for navigational purposes. Navigational dredging is most commonly used in ports, harbors, channels as a way to maintain these waterways so that marine traffic can take place safely and efficiently. Maintenance dredging is required periodically to remove sediment and is a necessity for almost every navigable waterway and port. We recommend our Shark and Barracuda Class dredges for most navigational projects because of their compact size and their maneuverability. Our Marlin class and custom dredge designs are also used in navigation dredging when designs need to be matched for specific applications.
Similar to navigation projects, dredges are used for construction projects that require dredged material to be used as fill to construct new land, for industrial and residential zones and airports, highways, creation of trenches for pipelines and tunnels, and in the forming of foundations for structures. Construction dredging is used at the onset of a project to help create land, remove land, create channels, create harbors/marinas and for various other construction needs. Depending on the project requirements, DSC has many dredge options available to meet the rigorous demands of construction projects.
Dredges are often used to clean contaminated areas, restore land and to create or maintain aquatic recreational resources. Because of the nature of the dredging required in these applications, the dredges tend to be smaller with lower production capacities.
Environmental dredging typically involves cleaning contaminated areas to restore those areas to non-contaminated levels. Hydraulic transfer of contaminated sediments has become known as the most cost-effective and efficient way to restore contaminated sites. DSC offers a wide range of environmental dredges through our Moray and Barracuda product lines. On larger project specific environmental projects, custom designed DSC dredges can be the more efficient and practical dredge design to meet the project goals.
Dredges are often used to maintain, expand and deepen lakes that have progressively become shallow from deposits and overgrown vegetation. If lakes are not dredged periodically, they become too shallow for boats and swimmers to enjoy them. Like environmental dredging, DSC promotes our Moray and Barracuda dredges for these projects, as they are small and can be easily maneuvered in tight areas. The Barracuda and Moray dredges feature a swinging ladder configuration, so the dredge can work without external swing wires or anchors. A custom dredge design may prove to be the best alternative for the project, so DSC is a preferred choice in the overall project design process for lake projects.
Dredges are often used to restore wetlands, beaches, lakes, streams, coastlines, and for other land reclamation projects. In many coastal areas there is a shortage of land for development, therefore, dredges are used to pump material ashore and create new land or restore eroded material. Various dredge types can be used for restoration dredging depending on the project requirements. DSC’s Shark, Moray and Barracuda lend themselves well to restoration dredging projects due to their highly portable design and maneuverability. Custom dredge designs are often considered based on the specifics of the project.
Dredging is an efficient means to excavate sand, gravel, precious metals, coal, phosphates and various other minerals that are mined and added to materials we use every day. Most mining dredges require higher levels of throughput and must be designed for the rugged demands of the materials being dredged as well as for climatic conditions for the mining site. We recommend our Sharkuda, Marlin, and Shark Class dredges for mining applications as they are capable of digging deeper and pumping farther. Also common is a DSC custom designed dredge that incorporates specific design features required for an efficient dredge design and designed for lower operating costs. Mining and aggregate dredging lends itself to high level of automation, electric dredge designs and customized features to meet the specific site requirements.
Sometimes dredges are required for projects so specific they do not fall into any of the categories listed above. In this case, DSC engineers can work with your team to design a dredge that will incorporate your specific requirements. Whether a project calls for extreme dredging depths, high excavation forces, long discharge distances, or whatever challenges you may face, we can custom design a dredge to meet your project demands.
A
Atmospheric Pressure
Atmospheric pressure is the pressure of the air around us. An atmosphere (atm) is a unit of measurement equal to the average air pressure at sea level at a temperature of 15 degrees Celsius (59 degrees Fahrenheit). One atmosphere is 1,013 millibars, 760 millimeters, 29.92 inches of mercury, or 14.696 PSI.
B
Booster Pump
An additional pump and prime mover assembly used to increase the velocity of the material in the pipeline to enhance pumping power and pumping distance.
C
Cavitation
A phenomenon in which rapid changes of pressure in a liquid lead to the formation of small vapor-filled cavities in places where the pressure is relatively low. The dredge pump tries to discharge a greater flow than the inlet flow to the dredge pump. The formation of partial vacuums in the slurry by the passage of the impeller through it.
Concentration by Volume (CV)
The volume of solids in a liquid divided by the total volume of the solution.
Concentration by Weight (CW)
The concentration by weight reflects the percent ratio of the mass of dissolved solids to the total mass of the solution.
Cutter Hydraulic Pump Temperature
This temperature is the hydraulic pump case temperature. The temperature should not exceed 180° F for any extended time of operation.
Cutter Pressure
This is the hydraulic pressure for the cutter system. It varies as the material dredged varies and the speed of the swing. Get a base line cutter pressure with the cutter operating at full speed in water not touching any material. The base line pressure can aid the operator in determining if the cutter is clear or operating with trash caught in it. Know the stall pressure for the cutter. This is the pressure that the cutter stops, approximately 4600 psi.
D
Density
The amount of a substance contained within a specific area. In physics, density is the ratio of the mass of a substance to its volume, and it can be calculated by dividing the mass by the volume. Density is often expressed in units such as grams per cubic centimeter (g/cm3) or pounds per cubic foot (lb/ft3); on the dredge it is the specific gravity of the slurry. Specific gravity is the density of a substance divided by the density of water at 4°C (39°F). Gold has a density of 19.3 g/cm3, so its specific gravity is 19.3 g/cm3 divided by 1 g/cm3 (the density of water at 4°C), or 19.3. This means that if the displayed slurry density is 1.5 the slurry is 33 percent heavier than water at 4°C or 20 percent by weight. ((1.5-10) / (1.5)) 100 = 33%
Discharge Head
Resistance to the slurry flow in the discharge system calculated in feet of water. The discharge head consists of the discharge friction head, discharge velocity head and discharge static lift.
Discharge Pressure
The discharge pressure is displayed in pounds per square inch (PSI). It is a display of the pressure in the discharge line. The pressure changes as the discharge head changes.
Dredge Advance
To describe the dredge movement from one set of anchor positions to another.
Dredge Pump
The device that moves the slurry in the pipeline. Slurry enters the casing and is whirled by turning impellers, which force it out of the casing and into the pipeline.
Dredging
An excavation activity in which materials are recovered from beneath the water's surface. The purpose is generally to gather bottom sediment and either dispose of it at a different location or use these sediments in various products; e.g., sand and gravel that is used in concrete mixtures.
Dredging Depth
Dredging depth is the vertical distance below the surface of the water to the deposit to be dredged.
E
Elevation
The angle at which a pipeline rises as it leads away from a dredge pump. Pipeline elevation can increase material’s friction and decrease its velocity, reducing efficiency. Elevation is typically the measurement from the surface of the water to the final discharge point.
G
Gear Temperature
This is an indication of trouble if one of the bearings or oil gets too hot. On premium EP oil, the peak operating temperature should be 160° F. If the temperature exceeds 160° F, the life of EP oil will be reduced. High temperature may be an indication that the level of the oil is too high or that the unit has the wrong oil in it. It can also be an indication of possible bearing failure.
H
Head
Head is another increment to measure pressure, like how distance can be measured in miles or kilometers. Head is the pressure created by the weight of 1 foot of fresh water measured at sea level at 60° F.
Hydraulic Dredging
The process of excavating and pumping underwater material through a pipeline to a different location using a centrifugal pump.
Hydraulic Oil Temperature
This is the displayed temperature of the hydraulic oil. The maximum hydraulic oil temperature should be between 160° F and 180° F. The minimum oil temperature before fully loading the hydraulic system is 70° F. Use the heating system to bring the oil up to the minimum operating temperature.
Hydraulic Pump Charge Pressure
The hydraulic charge pump is necessary to supply cool fluid to the system, to maintain positive pressure in the main system loop, to provide pressure to operate the control system and to make up for internal leakage. The normal operating pressure is between 350 psi and 380 psi, the pump control will not operate properly if the charge pressure falls below 180 psi.
M
Mechanical Dredging
The process of removing debris or hardened material that is tightly compacted, using buckets to dig and place the material in barges to transport it to different locations.
P
Porosity
Also known as void fraction which is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%.
Priming A Dredge Pump
Evacuating the dredge pump of air and starting to pump the slurry or water.
Pump Speed
The speed at which the pump’s impellers force the water and material into the pipeline. Pump speed is increased to maintain proper slurry velocity as the dredge moves farther away from the discharge point.
S
Sediment
Materials that are naturally occurring and broken down by weathering and erosion.
Service Water Pressure
The service water is displayed in pounds per square inch (PSI). The service water should never be less than the dredge discharge pressure and ideally it should be higher.
Slurry
A thin mixture of an insoluble substance, such as cement, clay, or coal, combined with a liquid, such as water or oil.
Specific Gravity
Is the ratio of the weight of a given volume of material at 73°F (23°C) to that of an equal volume of water at the same temperature.
Static Lift/Terminal Elevation
Static lift is the vertical difference between the surface of the water and the point of discharge.
Suction Head (Displayed As Vacuum Or Differential Pressure)
Suction head is the resistance to the slurry flow in the suction system calculated in feet of water. The suction head consists of the entrance head, suction friction head, suction velocity head, and suction static lift. Vacuum is actually a display of differential pressure for underwater pumps. It may be displayed as inches of mercury or pounds per square inch. The dredge pump vacuum/differential display is one of the most important dredging displays on the operator's touch screen, for this display indicates conditions in the dredge suction pipe as they occur. A submerged dredge pump relies on atmospheric pressure and the weight of the water column above the pump to push water and material into its case; the dredge suction vacuum/differential gauge indicates the effectiveness of the use of this pressure. Three suction differential readings are of importance to the operator: Indicated Differential - the differential reading directly from the gauge when dredging material. Clear Water Differential - the reading when only water is being pumped. Effective Differential - the indicated reading minus the clear water reading. The clear water reading is a measurement of the inefficiencies built into the dredge suction at a given flow rate. The clear water differential should be kept as low as possible and still allow adequate velocity for conveying material; the clear water differential can be regulated by the pump speed. The effective differential, unlike the clear water differential, is a measurement of the suction losses due to conveying material. It is therefore favorable to maintain as high an effective differential as possible without causing cavitation or pipeline plugging.
Surface Feet Per Minute
Speed of a point on a surface related to the impeller eye or outside diameter.
T
Turbulence
The product of velocity and friction within the pipeline. Turbulence keeps materials suspended so they can travel efficiently through the pipeline.
V
Vacuum
Vacuum is a unit of pressure measurement represented or measured by inches of mercury. Vacuum is a pressure less than atmospheric pressure; Negative pressure. Since there is only roughly 14.7 PSI of atmospheric pressure, vacuum gauges only measure up to 30 inches or Mercury (Hg). The vacuum display is a display of the suction head.
Velocity
Velocity is a measure of speed. The velocity displayed is measured in feet per second (FPS). Normally the dredge discharge slurry velocity is the velocity measured. The discharge velocity is contingent on the discharge head. This includes the pump speed, the slurry density, and the type of solids in the discharge, the discharge line length, discharge static lift, and the horse power available to the pump. The velocity must be kept in a range that will maintain the flow of the desired discharge slurry. The velocity that is most productive and is the best utilization of the energy, and equipment costs is what is desirable.
W
Water Hammer
An increase in pressure due to a fluid in motion has a sudden change in momentum (sudden change in direction).
Winch Hydraulic Pump Temperature
This temperature is the hydraulic pump case temperature. The temperature should not exceed 180°F for any extended time of operation.
C
Construction Dredging
The process in which dredges are used during construction projects that require the creation of trenches for pipelines and tunnels and for the forming of structural foundations.
E
Environmental Dredging
A dredging process used to remove contaminated materials from a body of water in order to restore the water to non-contaminated levels.
M
Mining Dredging
The process used to excavate sand, gravel, precious metals, coal, phosphates and various other minerals from bodies of water.
N
Navigational Dredging
A process used to deepen channels and waterways as a means to improve navigation. Navigational dredging is most commonly used in ports, harbors and shipping channels as a way to maintain these waterways so that large ships, oil tankers, container ships, barges and naval vessels can pass.
R
Recreational Dredging
A dredging process is used to maintain, expand and deepen lakes that have progressively become shallow from deposits and overgrown vegetation. If lakes are not dredged periodically, they become too shallow for boats and swimmers to enjoy them.
Restoration Dredging
A process used to restore wetlands, beaches, lakes, streams, coastlines and other land reclamation projects by removing material from one area and placing it in the area that requires restoration.
S
Specialty Dredging
Unique projects so specialized in nature that they cannot be categorized.
C
Cutterhead
The rotating excavation device attached to the end of the dredge ladder or boom. The cutterhead is typically equipped with cutting teeth to help agitate and break up densely-packed sediment for feeding the pump.
D
Dredge Ladder
The boom that is lowered below the water to reach the material to be dredged.
Dredge Pump
A horizontal centrifugal pump designed to handle abrasive granular materials and solids of limited size in suspension. Quite distinct from water and slurry pumps which carry liquid and homogeneous mixtures respectively.
I
Instrumentation
Digital instruments used as display meters or process meters.
L
Ladder
The framework or boom that extends from the front of the dredge. The ladder is lowered below the water to reach the bottom to excavate the material to be dredged. The ladder is outfitted with a suction pipe and a cutting/digging device.
P
PLC (Programmable Logic Controller)
Ruggedized computer used for pump control. The PLC receives information from connected sensors or input devices installed on the pump, processes the data, and triggers outputs based on pre-programmed parameters.
S
Spuds
Long stakes that are driven into the floor of the water body and used to hold the dredge in place. Winches with wire cables swing the dredge around one spud in an arc, as it removes material. A second spud can then be lowered to move the dredge to a different position.
U
Underwater Pump
Ladder pump or submerged pumps are typically mounted on the dredge leader or lowered from a boom. Underwater pumps typically allow for higher concentrations of solids to be pumped.
W
Winch
A mechanical device used to wind in or wind out a wire cable. The wire cable winds around a powered drum, which turns to create the winding action. Winches may be used to position a dredge in the water, as well as to raise and lower the ladder.
We design and build custom dredges that boost efficiency and lower operating costs. Our team works with you to understand every aspect of your unique story. Your customized dredge solution will be designed and built to boost your efficiency and lower your costs.
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