A Weir Raises Water, a Dam Stops It
A weir is a barrier across a river. Water flows over it rather than being held back.
A weir is a low barrier built across a river to alter its flow. The difference from a dam is functional: water flows over the top of a weir continuously, raising the level upstream and controlling the rate downstream, while a dam is built to hold water back and store it. Weirs are used to measure flow, to make rivers navigable and to feed mill streams, and they are dangerous to swimmers because the recirculating water below them can trap a person indefinitely.
- A river barrier. *A stone weir.*
- A fish trap. *A fish weir.*
- Dam — a different structure. *A dam.*
- To weir. *Weiring a stream.*
- Old English — *wer*. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | weir | A weir. |
| Plural | weirs | Weirs. |
| Related | dam | A dam. |
| Related | sluice | A sluice. |
| Old English | wer | A weir. |
- Water poured over the weir.River.
- A dam holds water back.Contrast.
- Fish weirs are ancient.History.
Why weirs are dangerous
- Water falling over the crest creates a backward-rolling current
- That current pulls floating objects back toward the wall
- A swimmer can be recirculated and unable to escape
- The surface looks calm, which disguises the hazard
- They are sometimes called drowning machines
Old English *wer*, a dam or fish trap, from *werian*, to defend or dam.
What is the difference between a weir and a dam?
Water flows over a weir continuously to control the level; a dam is built to hold water back and store it.
Why are weirs dangerous?
Falling water creates a backward-rolling current below them that can trap and recirculate a swimmer.