Definitions

roller gate

Roller dam

A Roller dam is a type of hydro control device which is specially designed to mitigate erosion. They are most often used to divert water for irrigation but the largest and most outstanding examples are employed to ease river navigation.

Use

Roller dams are a type of weir, or a dam that is designed to allow water to constantly spill over the top. They are used on rivers or other such moving bodies of water where erosion damage is undesirable, yet likely to occur. A short wall, lip, or parabolic channel is constructed on the downstream side of the dam parallel to the dam face. As the water pouring over the dam hits this baffle, it is reflected back toward the dam face creating a continual "rolling" action at the foot of the dam; hence the name "Roller Dam". The purpose of this rolling is to dissipate the energy gained by the water when it falls from the top of the dam. Otherwise this energy would be exerted downstream causing large amounts of bank and river bed erosion.

Type

Roller dams can be either fixed (non-moving) or active. Fixed roller dams are generally made from reinforced concrete or masonry. Active roller dams are made out of large metal cylinders that can be lifted out of the water using a system of powerful hydraulic rams or cables and motors. This is also known as a roller gate, though its name has nothing to do with the rolling action of the water. The largest of these active dams in the world is Locks and Dam 15 which spans the Mississippi River between Rock Island, Illinois and Davenport, Iowa.

Active roller dams are a German invention stolen by the U.S. during World War I. The U.S. later paid the Germans for the patent after being sued.

Hazards

Roller dams of any type pose an extreme drowning hazard. Anyone that goes over the top of the dam will be caught in the rolling action at its base and may not be ejected from the cycle for days or possibly weeks. Even very buoyant objects such as inflatable balls, inner tubes, and life vests can often be seen resurfacing near the downstream face every few seconds for several hours before escaping the so called "washing machine of death".

Because of the hazards, dam opponents have called for the removal of roller dams. A roller dam on the Fox River near Yorkville, Illinois has killed 16 people since its construction in 1960; most recently, three in a single incident on May 28, 2006. Similar dams have already been removed on the Fox River at Aurora, Illinois and near Batavia, Illinois, but Yorkville residents successfully petitioned to keep the dam because of tradition.

Sources

Army Corps of Civil Engineers

Western Colorado Civil Engineers Society

References

External links

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