Dredging

How It Works

The primary economic reason dredging is needed is to maintain maritime industries. Due to a variety of processes including natural erosion, fine particulates in the form of silt gradually wash downstream. Over periods of time, the silt gradually fills bodies of water, causing the bodies to eventually become shallower or even creating small islands in the waterway.

It is widely acknowledged that without precaution, dredging can be greatly environmentally damaging. For this reason, disposal of dredged materials is highly regulated by the U.S. Environmental Protection Agency (EPA). The EPA lays out three key criteria that must be met before dredging material may be disposed of: (1) the party must demonstrate a concrete need for dredging, (2) there must be a comprehensive analysis of all reasonable dredging methods and disposal sites for the dredged material, and (3) testing must be performed to ensure that dredged material to be placed will not harm the environment of the dump site.

While there may be a great variety of equipment and highly specialized techniques, all dredging can be put into one of two categories: hydraulic and mechanical. Neither type is more efficient or safer in every context. Hydraulic dredge systems use pumps and are typically mounted on a barge. Once the dredged material is pulled into the system by the pump, it is moved via a pipeline to either the barge or a nearby disposal area. Mechanical techniques remove dredged materials from the body of water in question by using machinery. This is typically done with a clamshell bucket (also known as a grab dredger), but bucket ladder dredgers are also commonly used. Mechanical techniques may be [Page 445]preferred when there is risk of airborne emissions from the dredged material, such as when said material is particularly toxic or volatile.

Environmental Impacts

As mentioned, dredging may have either positive or negative environmental impacts. Unfortunately, the net impact of dredging is likely more negative than positive. Environmentally positive dredging may be used to reduce exposure of natural and human contaminants that have been brought into a body of water by vessels using it; this type of dredging is called “environmental dredging.”

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