Marine aggregates

The marine aggregates are Granulat S worked out starting from materials extracted from the ground and the basement of the Mer.

Materials concerned

siliceous Materials (sand and gravels)
Materials limestones (crag, Maërl…)

Methods of extraction

The marine aggregates can be extracted by a method at fixed telephone (anchored dredger, platform), or by dredgers with systems of aspiration moving

Impacts of the extraction of the sediments

The extraction of marine sediments can have negative impacts on the environment and the other marine activities. The intensity of these impacts depends much on the choice of the extract range, and the methods of exploitation.

Environmental impacts

Erosion : The taking away of sediments in the vicinity of the coast can unbalance the sedimentary assessment locally, and involve the intensification of coastal erosion (cliff crumbling, reduction or disappearance of beaches…)

Destruction of fauna and the benthic flora : the organizations contained in the Benthos (fauna and flora) are in general destroyed during the extraction.

Increase in turbidity : the plume of sediments light put in suspension during the taking away or rejected with water of overflow can involve a big raise of turbidity, vermin to the development of the flora (photosynthesis) and thus fauna.

Other impacts

The impacts on the medium in certain hot areas (Spawning grounds, Nourriceries) can involve direct incidences on certain activities as fishing. The fine particles put in suspension can have negative consequences for other activities (Conchyliculture, bathe…)

Uses

Construction industry

The marine aggregates are used mainly in the building and public works, where they replace equivalent terrestrial materials, in particular for the demanding uses (quality, form…) like the clothes industry of the hydraulic concretes (siliceous sands).

Contrary to a spread belief, there is in this field no disadvantage to use marine materials, for little which they are treated (a simple rinsing is generally enough).

Agricultural amendment

The materials limestones can be used in agricultural amendment. It is in particular the case for the Maërl (skeletons limestones of algae with slow growth), primarily in Brittany.

In area Country of the Loire, these aggregates replaced those traditionally extracted in the bed river for the market-gardening use. Famous the Mâche Nantaise thus profits from a Protected Geographical ascription which specifies, in the elements justifying the bonds with the geographic origin, the traditional use of sand of river origin coming from the the Loire and of its estuary

Management of coastal erosion

On the coasts in erosion (natural or because of the human activities), it is possible to slow down or limit erosion while bringing sediments (sand…), which generally comes from the sea-bed (for economic reasons, but such technical: granulometry, etc).

These sediments can be poured at sea, near the eroded zones, or directly on the threatened beaches (recharging of beaches).

Other uses

The Maërl is also employed in the die of potabilisation of water, in particular as corrector of pH

Production

The main part of the aggregates used in the world are of origin terrestrial; but the share of the marine aggregates is important in certain countries (Japan, Great Britain…).

In France, only a weak share of the aggregates comes from the sea (approximately 7 million tons per annum in 2005, for an total intake of about 400 million tons per annum). It are extracted mainly in the vicinity of the estuaries from the large rivers (the Seine, the Loire, the Gironde). The surfaces directly concerned with the extractions did not exceed a few square kilometers in 2005.

Bonds

the site of the IFREMER

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