On the other hand, where the bottom consists of clay, rock or other hard substances, dredging must, in the first instance at any rate, be employed to deepen and widen the channel which it is sought to improve. In rivers and estuaries where the bottom is composed of light soils, and where the scour of the tide can be governed by training walls and other works constructed at reasonable expense, so as to keep the channel clear without dredging, it is manifest that dredging machinery with its large cost for working expenses and for annual upkeep should be as far as possible avoided. The employment of dredging plant and the selection of special appliances to be used in different localities and in varying circumstances require the exercise of sound judgment on the part of the engineer. It has long been useful in works of marine and hydraulic engineering, and has been brought in modern times to a state of high perfection. In the following account the operations of dredging in this sense are discussed (1) as involved in hydraulic engineering, (2) in connexion with the work of the naturalist in marine biology.ĭredging is the name given by engineers to the process of excavating materials under water, raising them to the surface and depositing them in barges, or delivering them through a shoot, a longitudinal conveyor, or pipes, to the place where it is desired to deposit them. (2) Connected with “drag,” or at least derived from the same root, dredge or dredger is a mechanical appliance for collecting together and drawing to the surface (“dredging”) objects and material from the beds of rivers or the bottom of the sea. dragée), and in mining is applied to ore of a mixed value. “Dredge” is also a local term for a mixed crop of oats and barley sown together (“maslin” or “meslin,” cf. The word in this sense is obsolete, but survives in “dredger,” a box with a perforated top used for sprinkling such a sugar-mixture, flour or other powdered substance.
τραγήματα, sweetmeats, it means a confection of sugar formed with seeds, bits of spice or medicinal agents.
0 kommentar(er)
