Berm

A berm is a level space, shelf, or raised barrier separating two areas. Berm is a loanword from Dutch.

Embankment dam with two berms

History

In medieval military engineering, a berm (or berme) was a level space between a parapet or defensive wall and an adjacent steep-walled ditch or moat. It was intended to reduce soil pressure on the walls of the excavated part to prevent its collapse. It also meant that debris dislodged from fortifications would not fall into (and fill) a ditch or moat.

In the trench warfare of World War I, the name was applied to a similar feature at the lip of a trench, which served mainly as an elbow-rest for riflemen.

Modern usage

In modern military engineering, berm has come to mean the earthen or sod wall or parapet itself. The term especially refers to a low earthern wall adjacent to a ditch. The digging of the ditch (often by a bulldozer or combat engineering vehicle) can provide the soil from which the berm is constructed. Walls constructed in this manner are an effective obstacle to vehicles, including most armoured fighting vehicles, but are easily crossed by infantry. Because of the ease of construction, such walls can be made hundreds or thousands of kilometres long.

Berms are also used to control erosion and sedimentation by reducing the rate of surface runoff. The berms either reduce the velocity of the water, or direct water to areas that are not susceptible to erosion, thereby reducing the adverse effects of running water on exposed topsoil. Following the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, the construction of berms designed to prevent oil from reaching the fragile Louisiana wetlands (which would result in massive erosion) was proposed early on, and was officially approved by the federal government in mid-June, 2010, after numerous failures to stop and contain the oil leak with more advanced technologies.

Uses in other applications

• In modern highway construction, a berm is a noise barrier constructed of earth, often landscaped, running along a highway to protect adjacent land users from noise pollution.
• In the natural building movement, berming refers to piling earth against an exterior wall to create thermal mass or reduce the visible footprint of an earth-sheltered home.
• In archaeology, a berm is a narrow space, such as that between banks and ditches. It can also refer to a raised linear bank separating two areas.
• In corners on Motocross tracks. A 30 centimetre (1 ft) high wall of soil around the outside of the corner allows riders to enter faster and exit with a slingshot-like effect, which results in maintaining higher speeds.
• In Pennsylvania, Ohio, Indiana, and West Virginia the word "berm" refers to the shoulder of a highway.
• In some regions a berm refers to a strip of grass that is located between a sidewalk and the curb of a street, also known as a tree lawn, verge, or parkway.
• In Bicycle Motocross (BMX) bicycle racing mountain biking (MTB) Supercross and Motocross, a berm refers to a banked turn made from dirt with a relatively tight radius.
• In Snowboard Cross, a berm is a wall of snow built up in a corner.
• In coastal systems, a berm is a raised ridge of pebbles or sand found at high tide or storm tide marks on a beach.
• In snow removal, a berm or windrow refers to the linear accumulation of snow cast aside by a plow.
• In open-pit mining, a berm refers to dirt and rock piled alongside a haulage road or along the edge of a dump point. Intended as a safety measure, they are commonly required by government organizations to be at least one-half as tall as the wheel of the largest mining machine on-site.
• At some sports stadiums (mainly baseball, in the US), the berm is a grass area along the fence in foul and fair territory where spectators may sit and view games. Grassy berms are mainly found at smaller ballparks, such as for spring training, minor league teams, or college baseball. Admission prices are typically quite low and help attract fans. One such example is Bright House Field in Clearwater, Florida, where the Philadelphia Phillies train and the minor league Clearwater Threshers play.
• Disneyland Park in Anaheim, California is surrounded by a berm that was implemented to maintain the illusion of the park being a magical place removed from the real world. In many locations, the train that travels around the park rests upon or next to this berm. Some attractions, such as the Haunted Mansion and Pirates of the Caribbean, are too large to fit entirely within the park, and thus are partly constructed outside the berm. Also, Mickey's Toontown was added to the park in 1993, and the lack of space necessitated that it lay almost entirely outside the berm.
• Fabric products designed to provide secondary containment against leaks and spills are also known as berms. Placed under or around equipment, it acts as a barrier between machinery or fueling operations and serves to protect the environment beneath. One such example is the Insta-Berm.
• Physical security systems employ berms to exclude hostile vehicles and slow attackers on foot (similar to the military application without the trench). Security berms are common around military and nuclear facilities. An example is the berm proposed for Vermont Yankee nuclear power plant in Vermont.
• Plans to build multiple berms off the wetlands of Louisiana to protect the fragile ecosystem from the Deepwater Horizon oil spill were announced in June 2010, first by local authorities and eventually by President Barack Obama. It is unclear whether these berms will provide any benefit by keeping oil offshore; that is, the benefits may be purely psychological. Experts seem to disagree on this; further input on the merits (or lack thereof) of this project are needed, especially as the announcement of this project is a recent development, and nothing on this scale, in this type of situation, has ever been attempted. Louisiana Governor Bobby Jindal has been a staunch advocate for the building of these berms; in the case of protecting wetlands with relatively narrow channels into the gulf of mexico, berms may theoretically be more effective than in relatively open water, but the truth - as it has never been attempted - is that nobody really knows what effect they will have.

See also

• Earthworks (engineering)
• Moroccan Wall