Clearing

Clearing or dredging of sediments

Coarse sediments, carried along by water courses and long considered to hinder the flow of flood water, are now understood to be an essential factor in the protection and restoration of the hydro-morphological and ecological balance of rivers. Transportation of the bed load is, therefore, an essential contributor to the ecological balance of water courses.

Approach

Reservoirs subject to significant sedimentation may require sediment management solutions such as dredging or actions that enable sediments to flow freely.

This type of work includes :

• operations in which sediments are simply moved on a very small scale and not lifted out of the water course's main channel,
• the removal of sediments during a large-scale maintenance operation on the water course or during maintenance work on a structure (cleaning of dam reservoirs, for example).

It is for this reason that clearing must follow strict guidelines :

• clearing only takes place when water courses are excessively clogged,
• clearing must never occur on a large scale but be organised by sectors that are restricted in size and prioritised,
• priority must be given to the clearing of the water course's main flow channels; there will be no, or limited, clearing close to the banks,
• before any clearing operation, the operator will establish whether the deposits are not attributable to the excessive breadth of the water course and whether the water course’s cross section is compatible with the hydraulic regime,
• in some cases, the sludge will not be deposited along the banks to ensure that they are not enriched or exaggerated.

Expertise

Hydrostadium manages clearing operation projects from start to finish :

• sampling strategy proposals,
• analysis of sediments upstream of works,
• detailed information on the nature and content of dossiers that have to be examined by the public department concerned,
• assistance with selecting the most appropriate dredging method,
• monitoring of the clearing operation, etc.

Fate of the sediments

If sediments cannot be used in the river, Hydrostadium helps the contractors identify possible land-based sediment management solutions: use of sediments for roadwork or landscaping projects, sale through sorting facilities, refilling of quarries, crop dusting, cement works, disposal.