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Underwater excavation is called dredging. A dredge is a machine that scoops or suctions sediment from the bottom of the waterways or is used to mine materials underwater. While the instrumentation of modern dredges is computer assisted, the basic excavation methods of dredges have remained the same since the late 1800s. The two main types of dredges Local 25 members work aboard are mechanical dredges and hydrhydraulic dredges.

Mechanical dredges remove material by scooping it from the bottom and then placing it onto a waiting barge or a disposal area. The two most common types of mechanical dredges are dipper dredges and clamshell dredges. These names refer to the type of scooping buckets they employ. The dredge is mounted on a large barge and is usually towed to the dredge site and secured in by anchors or anchor pilings, called spuds. Disposal barges, called dump scows, are used in conjunction with the mechanical dredge.

Hydraulic dredges work by sucking a mixture of dredged material and water from the channel bottom. The amount of water sucked up with the material is controlled to make the best mixture. Pipeline and hopper dredges are the two main types of hydraulic dredges.

Pipeline dredges suck dredged material through one end and push it out the discharge pipeline directly into the disposal site. Most pipeline dredges have a cutterhead on the suction end. A cutterhead is a mechanical device that has rotating blades or teeth to break up or loosen the bottom material so that it can be sucked through the dredge. Pipeline dredges are mounted to barges and usually not self-powered, but are towed to the dredging site and secured in place by anchor piling, called spuds.

Hopper dredges are ships with large hoppers, or containment areas, inside. The dredge suctions dredged material from the channel bottom through long intake pipes and stores it in the hoppers. When the hoppers are full, the dredged material is either pumped off through a pipeline or the ship travels to an in-water disposal site, where the dredged material is discharged through the bottom of the ship.

Disposal site selection for dredged material is one of the most important and challenging parts of planning a dredging project. The most common disposal methods are beach renourishment, ocean placement and confined disposal facilities.

Beach renourishment is the placement of dredged material on or near the beach through a pipeline, usually to replenish an eroding beach or protect an eroding wetland. This is the most visible dredging project to the public. The dredged material is generally sand coming from inlets, coastal entrance bars, or main offshore waterways. Both hopper dredges and pipeline dredges can use beach renourishment sites. Once the dredged material is on the beach, heavy equipment operators help control the placement and direction of the sand.

What’s the Difference Between a Suction Hose and a Discharge Hose?

A suction hose does just that, it’s a pump, pulls, vacuums, or sucks the material or liquid through the hose. They can also be referred to as Delivery Hoses. Typically, suction hoses can be used for both suction and discharge. Each hose is different, double-check with Atlanta Rubber & Hydraulics if you are unsure or if you are considering a specialty hose.

Suction hoses are constructed to maintain their round shape and not collapse when used under the hose’s normal use. Note that using a hose other than its unintended use will damage the hose.

There is also no such thing as a hose that a vehicle can run over. No matter what, a vehicle driving over a hose will destroy it.

What is a Discharge Hose?

A discharge hose is also referred to as a lay-flat hose. Most discharge hoses are made to handle water and mild chemicals.

Only use discharge hoses with the flow of gravity. Discharge hoses are not meant to discharge liquid against gravity. (Yes, this must be stated and we won’t further elaborate.)

Discharge hoses take up less space than suction hoses, hence the name lay flat. They can be made from different materials and take up less space.