Roller dam
Encyclopedia
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
is a type of hydro
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...
-control device specially designed to mitigate erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
. They are most often used to divert water for irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
but the largest and most notable examples are used to ease river navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
.
Use
Weir
A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...
, or a dam that is designed to allow water to flow over the top in continuous action. 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 the rolling is to dissipate the energy gained by the water as it falls from the top of the dam. Otherwise the energy would be exerted downstream, causing significant bank and river bed erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
.
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 from large metal cylinders, which can be lifted out of the water using a system of powerful hydraulic rams or cables and motors. This type is also known as a roller gate. The largest of the active dams in the world is Locks and Dam 15
Lock and Dam No. 15
Lock and Dam No. 15 is a lock and dam located on the Upper Mississippi River. It spans the river between Rock Island, Illinois and Davenport, Iowa. Lock and Dam 15 is the largest roller dam in the world, its dam is long and consists of nine non-submersible, non-overflow roller gates and two ...
, which spans the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
between Rock Island, Illinois
Rock Island, Illinois
Rock Island is the county seat of Rock Island County, Illinois, United States. The population was 40,884 at the 2010 census. Located on the Mississippi River, it is one of the Quad Cities, along with neighboring Moline, East Moline, and the Iowa cities of Davenport and Bettendorf. The Quad Cities...
and Davenport, Iowa
Davenport, Iowa
Davenport is a city located along the Mississippi River in Scott County, Iowa, United States. Davenport is the county seat of and largest city in Scott County. Davenport was founded on May 14, 1836 by Antoine LeClaire and was named for his friend, George Davenport, a colonel during the Black Hawk...
.
Hazards
Roller dams of any type pose an extreme drowningDrowning
Drowning is death from asphyxia due to suffocation caused by water entering the lungs and preventing the absorption of oxygen leading to cerebral hypoxia....
hazard. Any person going 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. Sixteen people have died by drowning at the roller dam on the Fox River
Fox River (Illinois River tributary)
The Fox River is a tributary of the Illinois River in the states of Wisconsin and Illinois in the United States. There are two other "Fox Rivers" in southern Illinois: the Fox River and a smaller "Fox River" that joins the Wabash River near New Harmony, Indiana.-Wisconsin:The Fox River rises near...
near Yorkville, Illinois
Yorkville, Illinois
Yorkville is a city located in Kendall County, Illinois, United States. The population was 6,189 at the 2000 United States Census and is estimated to be 16,505, . It is the county seat of Kendall County...
since its construction in 1960. Most recently in a single accident on May 28, 2006, three persons died. Similar dams have already been removed on the Fox River at Aurora, Illinois
Aurora, Illinois
Aurora is the second most populous city in the U.S. state of Illinois, and the 112th largest city in the United States. A suburb of Chicago, located west of the Loop, its population in 2010 was 197,899. Originally founded within Kane County, Aurora's city limits have expanded greatly over the past...
and near Batavia, Illinois
Batavia, Illinois
Batavia was founded in 1833, and is the oldest city in Kane County, Illinois, with a small portion in DuPage County. During the Industrial Revolution, Batavia became known as ‘The Windmill City’ for being the largest windmill producer of the time...
, but Yorkville residents successfully petitioned to maintain the roller dam near their town because of tradition. In July 2009, a man died at a roller dam on the Cedar River in Cedar Rapids, Iowa
Cedar Rapids, Iowa
Cedar Rapids is the second largest city in Iowa and is the county seat of Linn County. The city lies on both banks of the Cedar River, north of Iowa City and east of Des Moines, the state's capital and largest city...
. His death was notable because he was wearing an approved personal flotation device, intended to help bring a person quickly to the surface of the water.
Sources
Army Corps of Civil Engineers - need specificsWestern Colorado Civil Engineers Society