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. Deepening with a dredging-machine 

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. 

ENVIRONMENTAL 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.

Signals to be used by masters of Dredging Vessels 

Purpose of signal	Signal
Dredging master requires any vessel approaching from seaward to keep the dredger on the starboard hand of that vessel and requires any vessel proceeding seaward to keep the dredger on the port hand of that vessel	By day — a black triangle on the yardarm on the side of the dredger to be passed.  By night — a green light over a red light on the yardarm on the side of the vessel to be passed.  In fog, mist, or heavy rain — the Morse sound signal letter “A” given at intervals of not more than 2 minutes on the dredger’s bell.
Dredging master requires any vessel approaching from seaward to keep the dredger on the port hand of the vessel and requires any vessel proceeding seaward to keep the dredger on the starboard hand of that vessel	By day — a red square on the yardarm on the side of the dredger to be passed.  By night — a red light over a green light on the side of the vessel to be passed.  In fog, mist, or heavy rain — the Morse sound signal letter “N” given at intervals of not more than 2 minutes on the dredger’s bell.
Dredger is blocking channel	By day — a green cone between 2 red balls, shown vertically at the masthead.  By night — a green light between 2 red lights shown vertically at the masthead.  In fog, mist or rain — the Morse sound letter signal “S” given at intervals of not more than 2 minutes on the dredger’s bell.
Vessel may pass on either side of the dredger	By day — a white flag at the masthead.  By night — a green light on both yardarms.
Dredger is unable to move, or is out of control	By day — a red flag on the masthead.  By night — a red light on both yardarms.
Self‑propelled dredger that is under way, and is unable to manoeuvre so as to give way to or avoid other vessels	By day — one red ball over one white diamond shape over one red ball, mounted vertically.  By night — one red light over one white light over one red light, the lights being mounted vertically and so positioned as to be clearly visible at a distance of at least 2 nautical miles.

The Morse sound signals referred to in this table shall be given as follows: 

            (a)         a short ring — of 1½ seconds’ duration; and 

            (b)         a long ring — of 4 seconds’ duration; and 

               (c)         intervals between rings — of 1½ seconds’ duration.