II. DEFINITIONS

DREDGING:
Collecting and bringing up objects from the bed of a river, sea, etc.; bringing up, fishing up or clearing away or out (any object) from the bottom of a river, etc. (Oxford English Dictionary).
Deepening with a dredging-machine (the University English Dictionary).

MAINTENANCE DREDGING:
The activity of keeping existing watercourses, harbour basins, etc., at the required nautical and / or hydrological depth by removing siltation. The environmental effects of such an operation are in general of minor importance and limited to the effects of the dredging operation itself and the disposal operation when no beneficial use of the dredge spoil is available. Environmental issues increase in importance when the material to be dredged is polluted.

CAPITAL DREDGING:
The activity of creating new civil engineering works by means of dredging, such as harbour basins, canals, etc., and the deepening of existing waterways, approach channels. Capital dredging is carried out in virgin soil, which in general is unpolluted. The effects on the environment are limited to the actual working site(s), where the existing habitat or ecosystem is (temporarily) removed. These phenomena are beyond the scope of this book.

MINERAL DREDGING:
The activity of extracting minerals with an economic value from underwater deposits. Mineral dredging takes place to mine for instance gold, tin, so-called mineral sands (ilmenite, rutile, zircon), phosphates; but also for sand, clay and gravel. The non-valuable fractions dredged along with the mined mineral(s) are in general dumped back in the mined area. The environmental effects of mineral dredging are comparable with capital dredging, the resulting "landscape" however with e.g. deep gravel pits might cause other environmental problems, which are also beyond the scope of this book.

ENVIR0NMENTAL REMEDIAL DREDGlNG:
The activity of removing polluted sediments from rivers, harbour basins, etc. Environmental dredging therefore often will be a special type of maintenance dredging. The removal of polluted sediments just because their presence might cause a hazard to public health has created a new type of project and erosystems. Environmental aspects must be taken into account during all phases of the execution of environmental dredging works.