Once sediments are dredged from the waterway, they are referred to as "dredged material." Therefore, they require underwater excavation or "dredging." After the initial excavation establishes a channel, periodic or "maintenance" dredging must be done to keep that channel clear and safe for navigation. However, few rivers or harbors are naturally deep. The rocks deposited behind the dredge (by the stacker) are called "tailing piles." The holes in the screen were intended to screen out rocks (e.g., 3/4 inch holes in the screen sent anything larger than 3/4 inch to the stacker).With their increased size, ships need improved navigation channels to enter and leave ports efficiently, quickly, and safely. The material that is washed or sorted away is called tailings. The cylinder has many holes in it to allow undersized material (including gold) to fall into a sluice box. On large gold dredges, the buckets dump the material into a steel rotating cylinder (a specific type of trommel called "the screen") that is sloped downward toward a rubber belt (the stacker) that carries away oversize material (rocks) and dumps the rocks behind the dredge. The material is then sorted/sifted using water. Small suction machines are currently marketed as "gold dredges" to individuals seeking gold: just offshore from the beach of Nome, Alaska, for instance.Ī large gold dredge uses a mechanical method to excavate material (sand, gravel, dirt, etc.) using steel "buckets" on a circular, continuous "bucketline" at the front end of the dredge. The original gold dredges were large, multi-story machines built in the first half of the 1900s. Machine to mine stream beds for gold Gold Dredge, Klondike River, Canada, 1915 The Yankee Fork dredge near Bonanza City, Idaho, which operated into the 1950s.
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