What is dredging?
Dredging is the removal of a layer of mud, sand or silt (dredge) from the water bottom, of a watercourse (ditch) or a body of water (for example, a lake). Dredge consists primarily of dead aquatic plants, leaves from trees along the banks, and soil particles (sediment) that wash into the ditch through the drainage of agricultural land and banks. Soil material that enters the water via wind due to subsidence and/or crumbling of the riparian zone (calving) and soil material from surrounding plots is also specified as dredge. The creation of dredge is a natural process. Each year the layer of dredge grows one to three centimeters.
Why dredge?
By dredging, we ensure that the watercourses remain sufficiently deep and maintain the correct water quality. If the watercourse is no longer sufficiently deep because dredging is not done on time, there is a chance that when there is too much water it cannot be drained sufficiently. Or that when there is a water shortage it cannot be replenished sufficiently. As a result (more than the national standards require) flooding or drought damage may occur.
In waterways of a shipping route, dredging is necessary to maintain sufficient navigational depth, for example, for cargo ships.
Also, because of the decomposition processes, a thick dredge layer leads to a decrease in oxygen in the water, especially if the water is shallow. Shallow water also involves more extreme temperature fluctuations (higher maximum temperature and lower minimum temperature). This can be extra detrimental to underwater life.
Dredging aims to:
- ensure supply and drainage of water;
- keeping waterways navigable;
- maintain water quality and life in and around water and improve it where possible.
How to dredge?
Usually excavators from the land dig the dredge out of the ditches and spread it on the strip of land where they drive.
This often works well in rural areas, but not usually in built-up areas. There is often no place for an excavator or dredge along the ditch because there are houses or gardens. Then the dredge is pushed by a push boat to a place where an excavator loads it into a truck or tippers behind a tractor. These then take the dredge to an off-site destination, such as a maturation depot (dredging depot).
In wide or deep water such as canals and storage basins, dredged material is sometimes removed by an excavator on a pontoon (large raft). This fills hopper barges (cargo vessels without engines), and tows them to a further destination, such as a deep pool along a river. Another technique used in wide or deep water is a cutter suction dredger. This vessel loosens the dredge layer with a cutter head while simultaneously suctioning the surrounding water with dredge. The released dredge flows into the suction mouth and goes through a discharge pipeline to a further temporary depot.
Preconditions for dredging
The regulations for natural values impose requirements on how and when dredging may take place. For example, if the water temperature is too high or there is a layer of ice, dredging is not allowed. In addition, in principle no dredging is allowed during the breeding season. The direction of dredging also has rules. Fish must be able to escape, so dredging must not be done in the direction of a dead-end ditch. Environmental legislation also imposes requirements on dredging, such as quality requirements for dredged material to be spread on land and dredged material to be reused after maturation. There are also various other regulations, for example vessel certification, but there are too many to mention here. More regulations can be found on the Dredging by Yourself page.
