The Probert Encyclopaedia of General Information

DREDGING

Dredging is a term applied to the operation of removing mud, silt, and other deposits from the bottom of harbours, canals, rivers, docks, etc. The most simple dredging apparatus is the spoon apparatus, which consists of a strong iron ring or hoop, properly formed for making an impression upon the soft matter at the bottom, so as to scoop it into a large bag attached to the ring and perforated with a number of small holes. The means for working it is a long handle, a suspending rope, and a crane or sweep-pole planted in a boat.

Much more effective was the steam dredging-machine that became common during the 19th century. It had a succession of strong iron buckets on an endless chain, which traversed on a frame whose lower end was vertically adjustable so as to regulate the depth at which it worked. It was worked by steam, and the buckets tore up the matter at the bottom, raised it, and discharge it into punts or hoppers close to the dredging vessel. Various forms of steam - pump dredgers, in which suction-pipes were the chief features, were also used.

The river Clyde, from being a shallow stream, was converted, mainly by dredging, into a waterway carrying large vessels up to Glasgow.

Dredging rivers for gold has been largely carried on since the 19th century; and the gold-dredge may even be floated in water artificially supplied.

Dredging is also the operation of dragging the bottom of the sea for molluscs, plants, and other objects, it may be for scientific observation. The oyster-dredge is a light iron frame with a scraper like a narrow hoe on one side, and a bag attached to receive the oysters. The dredges used by naturalists are mostly modifications of or somewhat similar to the oyster-dredge. Scientific dredging assumed a high importance at the end of the 19th century for research into the life of deep-sea areas, before the invention of deep-sea diving equipment and cameras.
Research Dredging