Weir

A weir /wɪər/ or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. There are many designs of weir, but commonly water flows freely over the top of the weir crest before cascading down to a lower level.

Humber Weir
A weir on the Humber River near Raymore Park in Toronto, Ontario, Canada
Culverts under yass river walkway weir
A weir on the Yass River, New South Wales, Australia directly upstream from a shared pedestrian-bicycle river crossing.
Time elapse video of a new tilting weir being installed in the Gwent levels, Wales.

Etymology

There is no single definition as to what constitutes a weir and one English dictionary simply defines a weir as a small dam, likely originating from Middle English were, Old English wer, derivative of root of werian, meaning "to defend, dam".[1][2]

Function

Thorp Gristmill Weir
A broadcrest weir at the Thorp grist mill in Thorp, Washington, USA

Weirs are commonly used to prevent flooding, measure water discharge, and help render rivers more navigable by boat. In some locations, the terms dam and weir are synonymous, but normally there is a clear distinction made between the structures. A dam is usually specifically designed to impound water behind a wall, whilst a weir is designed to alter the river flow characteristics.

A common distinction between dams and weirs is that water flows over the top (crest) of a weir or underneath it for at least some of its length. Accordingly, the crest of an overflow spillway on a large dam may therefore be referred to as a weir. Weirs can vary in size both horizontally and vertically, with the smallest being only a few inches in height whilst the largest may be hundreds of metres long and many metres tall. Some common weir purposes are outlined below.

Flow measurement

Weirs allow hydrologists and engineers a simple method of measuring the volumetric flow rate in small to medium-sized streams/rivers or in industrial discharge locations. Since the geometry of the top of the weir is known and all water flows over the weir, the depth of water behind the weir can be converted to a rate of flow. However, this can only be achieved in locations where all water flows over the top of the weir crest (as opposed to around the sides or through conduits/sluices) and at locations where the water that flows over the crest is carried away from the structure. If these conditions are not met, it can make flow measurement complicated, inaccurate or even impossible.

The discharge calculation can be summarised as:

Where:

  • Q is the volumetric flow rate of fluid (the discharge)
  • C is the flow coefficient for the structure (on average a figure of 0.62).
  • L is the width of the crest
  • H is the height of head of water over the crest
  • n varies with structure (e.g., 3/2 for horizontal weir, 5/2 for v-notch weir)

However, this calculation is a generic relationship and specific calculations are available for the many different types of weir. Flow measurement weirs must be well maintained if they are to remain accurate.[3][4]

Control of invasive species

As weirs are a physical barrier they can impede the longitudinal movement of fish and other animals up and down a river. This can have a negative effect on fish species that migrate as part of their breeding cycle (e.g., salmonids), but can also be useful as a method of preventing invasive species moving upstream. For example, weirs in the Great Lakes region have helped to prevent invasive sea lamprey from colonising further upstream.

Watermills

Mill ponds are created by a weir that impounds water that then flows over the structure. The energy created by the change in height of the water can then be used to power waterwheels and power sawmills, grinding wheels and other equipment.

Flood control and altering river conditions

Weir at Bray Lock, May 2018
The primary weir at Bray Lock on the River Thames, facing downstream. In the background is the smaller secondary 'overspill' weir. Two small boats are also visible held against the overspill weir, having been washed against it during a particularly high discharge as a result of meltwater from the 2018 winter cold wave

Weirs are commonly used to control the flow rates of rivers during periods of high discharge. Sluice gates (or in some cases the height of the weir crest) can be altered to increase or decrease the volume of water flowing downstream. Weirs for this purpose are commonly found upstream of towns and villages and can either be automated or manually operated. By slowing the rate at which water moves downstream even slightly a disproportionate effect can be had on the likelihood of flooding. On larger rivers, a weir can also alter the flow characteristics of the waterway to the point that vessels are able to navigate areas previously inaccessible due to extreme currents or eddies. Many larger weirs will have features built in that allow boats and river users to "shoot the weir" and navigate by passing up or down stream without having to exit the river. Weirs constructed for this purpose are especially common on the River Thames, and most are situated near each of the river's 45 locks.

Issues

Grialëces cuecenes
19th century weir of porphyry stone on a creek in the Alps. During periods of high river flow this weir would be significantly more substantial.

Ecology

Because a weir impounds water behind it and alters the flow regime of the river, it can have an effect on the local ecology. Typically the reduced river velocity upstream can lead to increased siltation (deposition of fine particles of silt and clay on the river bottom) that reduces the water oxygen content and smothers invertebrate habitat and fish spawning sites. The oxygen content typically returns to normal once water has passed over the weir crest (although it can be hyper-oxygenated), although increased river velocity can scour the river bed causing erosion and habitat loss.

Fish migration

Weirs can have a significant effect on fish migration.[5] Any weir that exceeds either the maximum height a species can jump or creates flow conditions that cannot be bypassed (e.g., due to excessive water velocity) effectively limits the maximum point upstream that fish can migrate. In some cases this can mean that huge lengths of breeding habitat are lost and over time this can have a significant impact of fish populations.

In many countries, it is now a requirement by law to build fish ladders into the design of a weir that ensures that fish can bypass the barrier and access upstream habitat. Unlike dams, weirs do not usually prevent downstream fish migration (as water flows over the top and allows fish to bypass the structure), although they can create flow conditions that injure juvenile fish. Recent studies suggest that navigation locks have also potential to provide increased access for a range of biota, including poor swimmers.[6]

Safety

Even though the water around weirs can often appear relatively calm, they can be extremely dangerous places to boat, swim, or wade, as the circulation patterns on the downstream side—typically called a hydraulic jump— can submerge a person indefinitely. This phenomenon is so well known to canoeists, kayakers, and others who spend time on rivers that they even have a rueful name for weirs: "drowning machines".[7] If caught in this situation, the Ohio DNR recommends that a victim should "tuck the chin down, draw the knees up to the chest with arms wrapped around them. Hopefully, conditions will be such that the current will push the victim along the bed of the river until swept beyond the boil line and released by the hydraulic."[8] The Pennsylvania State Police also recommends to "curl up, dive to the bottom, and swim or crawl downstream".[9] As the hydraulic entrains air, the buoyancy of the water between the dam and boil line will be reduced by upwards of 30%, and if a victim is unable to float, escape at the base of the dam may be the only option for survival.

Common types

Dorset sn weir 01
The bridge and weir mechanism at Sturminster Newton on the River Stour, Dorset, England, UK
Weir on the river wear
Two weirs on the River Wear in Durham, County Durham, England, UK. The lower weir is a compound weir that also has fish ladders to allow fish like salmon to navigate the weir.
Revin Meuse weir 20041230- 024
A manually operated needle dam-type weir near Revin on the River Meuse, France
WarkworthweirSeuilNewZealand
A broad-crest weir in Warkworth, New Zealand
Dobbsweirvdropsjan2006
A complicated series of broad-crest and V-notch weirs at Dobbs Weir in Hertfordshire, England, UK

There are many different types of weirs and they can vary from a simple stone structure that are barely noticeable, to elaborate and very large structures that require extensive management and maintenance.

Broad-crested

A broad-crested weir is a flat-crested structure, where the water passes over a crest that covers much or all of the channel width. This is one of the most common types of weir found worldwide.

Compound

A compound weir is any weir that comprises several different designs into one structure. They are commonly seen in locations where a river has multiple users who may need to bypass the structure. A common design would be one where a weir is broad-crested for much of its length, but has a section where the weir stops or is 'open' so that small boats and fish can traverse the structure.

V-notch

A notch weir is any weir where the physical barrier is significantly higher than the water level except for a specific notch (often V-shaped) cut into the panel. At times of normal flow all the water must pass through the notch, simplfiying flow volume calculations, and at times of flood the water level can rise and submerge the weir without any alterations made to the structure.

Polynomial

A polynomial weir[10] is a weir that has a geometry defined by a polynomial equation of any order n. Most weirs in practice are low-order polynomial weirs. The standard rectangular weir is, for example, a polynomial weir of order zero. The triangular (V-notch) and trapezoidal weirs are of order one. High-order polynomial weirs are providing wider range of Head-Discharge relationships, and hence better control of the flow at outlets of lakes, ponds, and reservoirs.

See also

References

Notes

  1. ^ "the definition of weir". Dictionary.com. Archived from the original on 2017-03-04. Retrieved 2017-03-03.
  2. ^ "Weir". www.etymonline.com. Online Etymology Dictionary. Archived from the original on 19 March 2017. Retrieved 20 May 2017.
  3. ^ "Weirs - Flow Rate Measure". www.engineeringtoolbox.com. Archived from the original on 2017-03-04. Retrieved 2017-03-03.
  4. ^ "Factors affecting weir flow measurement accuracy". openchannelflow.com. Archived from the original on 30 July 2016. Retrieved 2 May 2018.
  5. ^ Tummers, J. S., Winter, E., Silva, S., O’Brien, P., Jang, M. H., & Lucas, M. C. (2016). Evaluating the effectiveness of a Larinier super active baffle fish pass for European river lamprey Lampetra fluviatilis before and after modification with wall-mounted studded tiles. Ecological Engineering, 91, 183-194.
  6. ^ Silva, S., Lowry, M., Macaya-Solis, C., Byatt, B., & Lucas, M. C. (2017). Can navigation locks be used to help migratory fishes with poor swimming performance pass tidal barrages? A test with lampreys. Ecological Engineering, 102, 291-302.
  7. ^ Michael Robinson; Robert Houghtalen. "Dangerous dams". Rhode Island Canoe/Kayak Association. Rhode Island. Archived from the original on 2010-08-12. Retrieved 2011-06-26.
  8. ^ Boating, Ohio DNR Division of Parks and Watercraft -. "Lowhead Dam Safety". watercraft.ohiodnr.gov. Archived from the original on 30 November 2016. Retrieved 2 May 2018.
  9. ^ "Archived copy". Archived from the original on 2018-05-02. Retrieved 2017-06-15.CS1 maint: Archived copy as title (link) Escaping a low-head dam
  10. ^ Baddour, R.E. (2008). "Head-Discharge Equation for Sharp-Crested Polynomial Weir". ASCE J. Irrigation and Drainage Engineering. 134 (2): 260–262.

Works cited

  • Clemmens, Albert (2010). Water Measurement with Flumes and Weirs. ISBN 978-1887201544.
  • Akers, Peter (1978). Weirs and Flumes for Flow Measurement. ISBN 978-0471996378.

Bibliography

External links

Bob Weir

Robert Hall Weir ( WEER; born October 16, 1947) is an American musician and songwriter best known as a founding member of the rock band Grateful Dead. After the Grateful Dead disbanded in 1995, Weir performed with The Other Ones, later known as The Dead, together with other former members of the Grateful Dead. Weir also founded and played in several other bands during and after his career with the Grateful Dead, including Kingfish, the Bob Weir Band, Bobby and the Midnites, Scaring the Children, RatDog, and Furthur which he co-led with former Grateful Dead bassist Phil Lesh. In 2015, Weir, along with former Grateful Dead members Mickey Hart and Bill Kreutzmann, joined with Grammy-winning singer/guitarist John Mayer to form the band Dead & Company. The band remains active.

During his career with the Grateful Dead, Weir played mostly rhythm guitar and sang many of the band's rock-n-roll and country & western tunes. In 1994, he was inducted into The Rock and Roll Hall of Fame as a member of the Grateful Dead.

Dead Poets Society

Dead Poets Society is a 1989 American drama film directed by Peter Weir, written by Tom Schulman, and starring Robin Williams. Set in 1959 at the fictional elite conservative Vermont boarding school Welton Academy, it tells the story of an English teacher who inspires his students through his teaching of poetry.

The film received critical acclaim and was a box office success. It won the BAFTA Award for Best Film, and César Award and David di Donatello Award for Best Foreign Film. Schulman received an Academy Award for Best Original Screenplay for his work.

Grateful Dead

The Grateful Dead was an American rock band formed in 1965 in Palo Alto, California. The band is known for its eclectic style, which fused elements of rock, folk, country, bluegrass, blues, gospel, and psychedelic rock for live performances of lengthy instrumental jams, and for their devoted fan base, known as "Deadheads". "Their music", writes Lenny Kaye, "touches on ground that most other groups don't even know exists". These various influences were distilled into a diverse and psychedelic whole that made the Grateful Dead "the pioneering Godfathers of the jam band world". The band was ranked 57th by Rolling Stone magazine in its The Greatest Artists of All Time issue. The band was inducted into the Rock and Roll Hall of Fame in 1994 and a recording of their May 8, 1977, performance at Cornell University's Barton Hall was added to the National Recording Registry of the Library of Congress in 2012. The Grateful Dead have sold more than 35 million albums worldwide.

The Grateful Dead was founded in the San Francisco Bay Area amid the rise of the counterculture of the 1960s. The founding members were Jerry Garcia (lead guitar, vocals), Bob Weir (rhythm guitar, vocals), Ron "Pigpen" McKernan (keyboards, harmonica, vocals), Phil Lesh (bass, vocals), and Bill Kreutzmann (drums). Members of the Grateful Dead had played together in various San Francisco bands, including Mother McCree's Uptown Jug Champions and the Warlocks. Lesh was the last member to join the Warlocks before they became the Grateful Dead; he replaced Dana Morgan Jr., who had played bass for a few gigs. Drummer Mickey Hart and non-performing lyricist Robert Hunter joined in 1967. With the exception of McKernan, who died in 1973, and Hart, who took time off from 1971 to 1974, the core of the band stayed together for its entire 30-year history. The other official members of the band are Tom Constanten (keyboards; 1968–1970), John Perry Barlow (nonperforming lyricist; 1971–1995), Keith Godchaux (keyboards; 1971–1979), Donna Godchaux (vocals; 1972–1979), Brent Mydland (keyboards, vocals; 1979–1990), and Vince Welnick (keyboards, vocals; 1990–1995). Bruce Hornsby (accordion, piano, vocals) was a touring member from 1990 to 1992, as well as a guest with the band on occasion before and after the tours.

After the death of Garcia in 1995, former members of the band, along with other musicians, toured as the Other Ones in 1998, 2000, and 2002, and the Dead in 2003, 2004, and 2009. In 2015, the four surviving core members marked the band's 50th anniversary in a series of concerts that were billed as their last performances together. There have also been several spin-offs featuring one or more core members, such as Dead & Company, Furthur, the Rhythm Devils, Phil Lesh and Friends, RatDog, and Billy & the Kids.

Indianapolis International Airport

Indianapolis International Airport (IATA: IND, ICAO: KIND, FAA LID: IND) is an international airport located seven miles (11 km) southwest of downtown Indianapolis in Marion County, Indiana, United States. It is owned and operated by the Indianapolis Airport Authority. The Federal Aviation Administration (FAA) National Plan of Integrated Airport Systems for 2017–2021 categorized it as a medium hub primary commercial service facility.Opened as Indianapolis Municipal Airport in 1931 and later known as Weir Cook Municipal Airport, Indianapolis International occupies about 7,700 acres (3,116 ha) in Wayne and Decatur townships in Marion County and Guilford Township in Hendricks County. It is the 45th busiest U.S. airport in terms of passenger traffic, serving 8.5 million passengers annually. As home to the second largest FedEx Express hub in the world, IND ranked as the seventh busiest U.S. airport in terms of air cargo throughput in 2015.A $1.1 billion midfield passenger terminal opened in 2008 as one of the first designed and built in the U.S. following the September 11 attacks. The Colonel Harvey Weir Cook Terminal contains two concourses and 40 gates, connecting to 51 nonstop domestic and international destinations and averaging 145 daily departures.

Isabella of France

Isabella of France (1295 – 22 August 1358), sometimes described as the She-Wolf of France, was Queen of England as the wife of Edward II, and regent of England from 1327 until 1330. She was the youngest surviving child and only surviving daughter of Philip IV of France and Joan I of Navarre. Isabella was notable in her lifetime for her diplomatic skills, intelligence, and beauty. She became a "femme fatale" figure in plays and literature over the years, usually portrayed as a beautiful but cruel and manipulative figure.

Isabella arrived in England at the age of 12 during a period of growing conflict between the king and the powerful baronial factions. Her new husband was notorious for the patronage he lavished on his favourite, Piers Gaveston, but the queen supported Edward during these early years, forming a working relationship with Piers and using her relationship with the French monarchy to bolster her own authority and power. After the death of Gaveston at the hands of the barons in 1312, however, Edward later turned to a new favourite, Hugh Despenser the Younger, and attempted to take revenge on the barons, resulting in the Despenser War and a period of internal repression across England. Isabella could not tolerate Hugh Despenser and by 1325 her marriage to Edward was at a breaking point.

Travelling to France on a diplomatic mission, Isabella may have begun an affair with Roger Mortimer, and the two may possibly have agreed at this point to depose Edward and oust the Despenser family. The Queen returned to England with a small mercenary army in 1326, moving rapidly across England. The King's forces deserted him. Isabella deposed Edward, becoming regent on behalf of her son, Edward III. Some believe that Isabella then arranged the murder of Edward II. Isabella and Mortimer's regime began to crumble, partly because of her lavish spending, but also because the Queen successfully, but unpopularly, resolved long-running problems such as the wars with Scotland.

In 1330, Isabella's son Edward III deposed Mortimer in turn, taking back his authority and executing Mortimer. The Queen was not punished, however, and lived for many years in considerable style—although not at Edward III's court, though she often visited to dote on her grandchildren and was marginally involved in peace talks—until her death in 1358.

Johnny Weir

John Garvin Weir (born July 2, 1984) is an American figure skater, fashion designer, and television commentator. He is a two-time Olympian, the 2008 World bronze medalist, a two-time Grand Prix Final bronze medalist, the 2001 World Junior Champion, and a three-time U.S. national champion (2004–2006). He is also known for his sports commentary with Tara Lipinski, as well as his work in LGBTQ activism.

Mary, Queen of Scots

Mary, Queen of Scots (8 December 1542 – 8 February 1587), also known as Mary Stuart or Mary I of Scotland, reigned over Scotland from 14 December 1542 to 24 July 1567.

Mary, the only surviving legitimate child of King James V of Scotland, was six days old when her father died and she acceded to the throne. She spent most of her childhood in France while Scotland was ruled by regents, and in 1558, she married the Dauphin of France, Francis. Mary was queen consort of France from his accession in 1559 until his death in December 1560. Widowed, Mary returned to Scotland, arriving in Leith on 19 August 1561. Four years later, she married her half-cousin, Henry Stuart, Lord Darnley, and in June 1566 they had a son, James.

In February 1567, Darnley's residence was destroyed by an explosion, and he was found murdered in the garden. James Hepburn, 4th Earl of Bothwell, was generally believed to have orchestrated Darnley's death, but he was acquitted of the charge in April 1567, and the following month he married Mary. Following an uprising against the couple, Mary was imprisoned in Loch Leven Castle. On 24 July 1567, she was forced to abdicate in favour of her one-year-old son. After an unsuccessful attempt to regain the throne, she fled southward seeking the protection of her first cousin once removed, Queen Elizabeth I of England. Mary had once claimed Elizabeth's throne as her own and was considered the legitimate sovereign of England by many English Catholics, including participants in a rebellion known as the Rising of the North. Perceiving Mary as a threat, Elizabeth had her confined in various castles and manor houses in the interior of England. After eighteen and a half years in custody, Mary was found guilty of plotting to assassinate Elizabeth in 1586, and was beheaded the following year at Fotheringhay Castle.

Mike Weir

Michael Richard Weir, (born May 12, 1970) is a Canadian professional golfer who plays on the PGA Tour. He spent over 110 weeks in the top-10 of the Official World Golf Ranking between 2001 and 2005. He plays golf left-handed and is best known for winning the Masters in 2003.

Peter Weir

Peter Lindsay Weir, AM ( WEER; born 21 August 1944) is an Australian film director.

He was a leading figure in the Australian New Wave cinema movement (1970–1990), with films such as the mystery drama Picnic at Hanging Rock (1975), the supernatural thriller The Last Wave (1977) and the historical drama Gallipoli (1981). The climax of Weir's early career was the $6 million multi-national production The Year of Living Dangerously (1983).

After the success of The Year of Living Dangerously, Weir directed a diverse group of American and international films covering most genres—many of them major box office hits—including Academy Award-nominated films such as the thriller Witness (1985), the drama Dead Poets Society (1989), the romantic comedy Green Card (1990), the social science fiction comedy-drama The Truman Show (1998) and the epic historical drama Master and Commander: The Far Side of the World (2003). For his work on these five films, Weir personally accrued six Academy Award nominations as either a director, writer or producer.

Since 2003, Weir's productivity has declined, having directed only one subsequent feature, the critically acclaimed but financial flop The Way Back (2010).

RatDog

RatDog is an American rock band. The group began in 1995 as a side project for Grateful Dead guitarist and singer Bob Weir. After the Dead disbanded later that year, RatDog became Weir's primary band. They performed some Grateful Dead songs, a mixture of covers (including Bob Dylan and Chuck Berry tunes), and some originals. RatDog's repertoire consisted of more than 150 songs. They released two albums – Evening Moods (2000) and Live at Roseland (2001). RatDog has not toured since July 2014.

The lineup of RatDog evolved over time. Musicians who were members of the band at different times include Rob Wasserman and Robin Sylvester on bass, Jay Lane on drums, Matthew Kelly, Mark Karan, and Steve Kimock on guitar, and Vince Welnick, Johnny Johnson and Jeff Chimenti on keyboards.

The Truman Show

The Truman Show is a 1998 American satirical science fiction film directed by Peter Weir, produced by Scott Rudin, Andrew Niccol, Edward S. Feldman, and Adam Schroeder, and written by Niccol. The film stars Jim Carrey as Truman Burbank, adopted and raised by a corporation inside a simulated television show revolving around his life, until he discovers it and decides to escape. Additional roles are performed by Laura Linney, Noah Emmerich, Natascha McElhone, Holland Taylor, Ed Harris, and Brian Delate.

The Truman Show was originally a spec script by Niccol, inspired by an episode of The Twilight Zone called "Special Service". Unlike the finished product, it was more of a science-fiction thriller, with the story set in New York City. Scott Rudin purchased the script, and set up production at Paramount Pictures. Brian De Palma was to direct before Weir signed as director, making the film for $60 million—$20 million less than the original estimate. Niccol rewrote the script while the crew was waiting for Carrey to sign. The majority of filming took place at Seaside, Florida, a master-planned community located in the Florida Panhandle.

The film was a financial success, debuting to critical acclaim, and earned numerous nominations at the 71st Academy Awards, 56th Golden Globe Awards, 52nd British Academy Film Awards and The Saturn Awards. The Truman Show has been analyzed as a thesis on Christianity, metaphilosophy, simulated reality, existentialism, and reality television.

Weir Group

The Weir Group plc is an engineering company headquartered in Glasgow, Scotland. It is listed on the London Stock Exchange and is a constituent of the FTSE 250 Index. The company operates in over 70 countries employing approximately 14,000 people focused on mining, oil and gas and power markets.

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