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A trench is a type of excavation or depression in the ground. Trenches are generally defined by being deeper than they are wide (as opposed to a wider gully or ditch), and by being narrow compared to their length (as opposed to a simple hole).^[1]

Contents 1 Usage 1.1 Agriculture 1.2 Archeology 1.3 Geology 1.4 Infrastructure 1.5 Military usage 1.6 Other uses 2 See also 3 References 4 External links

A number of areas exist in which trenches play a significant role:

Trenches have long been used to carry water to or away from areas. Trenches can be used for draining purposes, leading water away from a swamp that is to be dried out, likewise they can be used for irrigation purposes, directing water into dry fields. Both uses generally require a slope for the water to flow down.

Archeologists may use the 'trench method', pioneered by Dame Kathleen Kenyon in Israel, for searching and excavating ancient ruins or to dig into strata of sedimented material to get a sideways (layered) view of the deposits - with a hope of being able to place found objects or materials in a chronological order. The advantage of this method is that it destroys only a small part of the site (those areas where the trenches, often arranged in a grid pattern, are located). However, this method also has the disadvantage of only revealing small slices of the whole volume, and modern archeological digs usually employ combination methods.^[2]

Trenches are a natural feature in many landscapes. Some are created by rivers in flow (which may have long since fallen dry), others are features created by geological movement, such as oceanic trenches. The later form is relatively deep, linear and narrow, and is formed by plate subduction.^[3]

In the civil engineering field of construction or maintenance of infrastructure, trenches play a major role. They may be created to search for pipes and other infrastructure that is known to be underground in some general location, but whose exact location has been lost ('search trench' or 'search slit'). They are also used to put easily damaged and obstrusive infrastructure or utilities (such as gas mains, water mains or telephone lines underground. A similar use of higher bulk is pipeline transport. Finally, they may be created as the first step of creating a foundation wall.

Main article: Trench warfare

While trenches have often been dug as defensive measures, in the pre-firearm eras, they were mainly a type of hindrance for an attacker of a fortified location, such as the moat around a castle (this is technically called a ditch). Only with the advent of accurate firearms, and the tactics that evolved in World War I, did the use of trenches as positions for the defender of a fortification become common (though the Māori of New Zealand were known to have used it earlier in their Pā fortifications in the late 19th Century). The usage of trenches evolved very quickly in the First World War, until whole systems of extensive main trenches, backup trenches (in case the first lines were overrun) and communication trenches had been developed, often stretching dozens of kilometres along a front without interruption, and some kilometres further back from the opponents lines.

• Trenches are often used for mass graves, sometimes even dug by prisoners about to be executed, as described in the World War II novel Night.
• Sunken trenches may be combined with a wall on one of their sides to form a rare type of hidden fence, a ha-ha.

• Ditch
• Gully
• Trench coat
• Trench foot

1. ^ Code of Federal Regulations, Title 29, Volume 8, Page 374 (Code revised as of July 1, 2003, via Compliance Magazine's website)
2. ^ Archaeology - Restore! Magazine, Winter 1998
3. ^ Ocean trench (glossary from Student Resource Center website, Houghton Mifflin college division)

• Trenching and Excavation (a NIOSH Safety and Health Topic, Centers for Disease Control and Prevention)
• Trench Safety Awareness (a NIOSH Publication, Centers for Disease Control and Prevention)