Gully
From Wikipedia, the free encyclopedia
- This article refers to the landform. For other uses, see Gully (disambiguation).
A gully is a landform created by running water eroding sharply into soil, typically on a hillside. Gullies resemble large ditches or small valleys, but are metres to tens of metres in depth and width. When the gully formation is in process, the water flow rate can be substantial, which causes the significant deep cutting action into soil.
Gullying, or gully erosion, is the process by which gullies are formed. Hillsides are more prone to gullying when they are cleared of vegetation, through deforestation, over-grazing or other means. The eroded soil is easily carried by the flowing water after being dislodged from the ground, normally when rainfall falls during short, intense storms such as during thunderstorms. Gullies reduce the productivity of farmland where they incise into the land, and produce sediment that may clog downstream waterbodies. Because of this, much effort is invested into the study of gullies within the scope of geomorphology, in the prevention of gully erosion, and in restoration of gullied landscapes. The total soil loss from gully formation and subsequent downstream river sedimentation can be sizable.
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[edit] Hydraulic mining
Artificial gullies are formed during hydraulic mining when jets or steams of water are projected onto soft alluvial deposits to extract gold or tin ore. The remains of such mining methods are very visible landform features in old goldfields such as in California and northern Spain. The badlands at Las Medulas for example, were created during the Roman period by hushing or hydraulic mining of the the gold-rich alluvium with water supplied by numerous aqueducts tapping nearby rivers. Each aqueduct produced large gullies below by erosion of the soft deposits. The effluvium was carefully washed with smaller streams of water to extract the nuggets and gold dust.
[edit] Etymology
The earliest usage of the term is from 1657. It originates from the French word goulet, a diminutive form of goule which means throat. It is possible that the term was derived from a type of knife at the time, a gully-knife, because hills that have gullies look as if they are cut open with a sharp knife.
[edit] See also
[edit] References
- Oxford English Dictionary
