5 Interesting Facts about Dredging

Muck is formed from rotted algae, grass clippings and silt from stormwater runoff. Because of low oxygen levels, nothing other than mostly bacteria lives in the organic muck along canal bottoms.

If you’ve ever taken a boat out onto a lake, river, or canal, you know you have to be careful to navigate around the amount of much in the water body. Much is comprised of sediments at the bottom of a body of water. The more muck the water has, the greater impact it will have on the quality of the water and the recreational activities that take place there. Dredging is used when the sediments begin to affect water quality and inconvenience to recreational activities.

Depending on the channel, maintenance might be the responsibility of federal, regional or local governments; some are the responsibility of the adjacent private property owners.

What benefits does dredge pump rentals provide?

Removing mud and fine-grained sediment provides environmental restoration, allows for increased boating access and recreation, increases water quality, spurs economic development along underutilized corridors, increases livability and property values along the waterways, and may even increase jobs depending upon location

Cutter Dredge Pump Features

• Low operating costs

• Environmental compatibility in terms of dust and noise

• Minimum weight and dimensions

• Ease to operate and good mobility

• Flexibility in the dredging different types of sediments

• Reduced times for cleaning between operations on different types of materials;

The long-term benefits of canal dredging include maintaining the ability of the canal to efficiently convey storm water flows to the ocean to reduce the risk of flooding and to improve aesthetics and use of the canal for recreational users.

The direct effect of dredging is the removal of sediment and its associated contaminant mass. Experience at a variety of sites has shown that dredging is effective at removing contaminant mass. Where sediments are subject to scour by storm or other high-flow events, buried contaminated sediment may be the source of future exposure and risk. In such cases, mass removal may result in risk reduction because the future

Dredging is also often undertaken in order to:

• Create underwater foundations;

• Facilitate the emplacement of pipelines or immersed tunnel

elements;

• Construct flood control structures such as dams, dikes or levees;

• Ensure flood defences (by improving or maintaining the

discharge capacity of watercourses);

• Create or maintain storage capacity in water supply reservoirs.

Dredging for the environment

Dredging can be undertaken to benefit the environment in several ways. Dredged materials are frequently used to create or restore habitats. Recent decades have also seen the increasing use of dredged materials for beach replenishment. These schemes are designed to prevent – or reduce the likelihood of – erosion or flooding. Such beach nourishment or recharge is achieved by placing dredged sand or gravel on eroding beaches. This represents a “soft-engineering” solution, an important alternative to – often more costly – structural solutions such as rock armour or concrete walls.

Another environmental use of dredging has been in initiatives designed to remove contaminated sediments, thus improving water quality and restoring the health of aquatic ecosystems. This so-called “remediation” or “clean-up” dredging is used in waterways, lakes, ports and harbours in highly industrialised or urbanised areas. The removed material may be treated and used afterwards, or disposed of under strict environmental controls. Under proper conditions a viable alternative to removal is in-situ isolation, i.e. the placement of a covering or a cap of clean material over the contaminated deposit.

THE DREDGING PROCESS

Capital (or new) dredging projects can be both extensive and expensive. Maintenance dredging is often a regular, perhaps annual ongoing, long-term activity. In either case, what are the key elements of dredging? The dredging process consists of the following three elements:

• Excavation: this process involves the dislodgement and removal of sediments (soils) and/or rocks from the bed of the water body. A special machine – the dredger – is used to excavate the material either mechanically, hydraulically or by combined action. The main types of dredgers are described below. • Transport of excavated material: transporting materials from the dredging area to the site of utilisation, disposal or intermediate treatment, is generally achieved by one of the following methods:

(a) in self-contained hoppers of the dredgers; (b) in barges;

(c) pumping through pipelines; and (d) using natural forces such as waves and currents.

Other, rarely used transport methods are truck and conveyor belt transport. The method of transport is generally linked to the type of dredger being used.

• Utilisation or disposal of dredged material: in construction projects, dredging is driven by the demand for dredged material. In navigation and remediation dredging, the project is driven by the objective of removing the material from its original place. Thus, the question of “what to do with the removed material?” arises. As a result of growing environmental pressure, finding an answer to this question has become increasingly difficult, especially when the material is contaminated. The main alternatives for the management of the dredged material are described later in this document.

Hydraulic dredgers

Three main sub-groups of hydraulic dredger are:

• stationary suction dredgers;

• cutter suction dredgers; and

• trailing suction hopper dredgers.

These dredgers use hydraulic centrifugal pumps to provide the dislodging and lifting force and remove the material in a liquid slurry form. They usually work well in loose, “unconsolidated” silts, sands, gravels and soft clays. In more cohesive materials teeth or waterjets may be applied for breaking up the material. Cutter suction dredgers are equipped with a cutting device to increase the dislodging force. These “cutter” dredgers are suitable for use in high strength materials such as clays, packed or compacted sands and rocks.

Transport methods associated with hydraulic dredgers are pipeline and hopper transport. In some cases, hydraulic dredgers may pump the materials into barges for transport. Hydraulic dredging and transport methods “slurry the sediment”, that is, they add large amounts of process water and thus change the original structure of sediments.