Weir facts for kids

A weir is a special kind of barrier built across a river or stream. It's a bit like a small dam, but it doesn't usually block the whole river. Instead, a weir changes how the water flows. Sometimes, weirs can make it hard for fish to swim upstream, but many new designs help fish get past them easily.

What is a Weir?

A weir is a structure that stretches across a river. It's usually made of strong materials like concrete, stone, or wood. Weirs are built to control the water's movement. They can raise the water level upstream, slow down the flow, or even help measure how much water is in the river.

How Weirs Work

When water flows over a weir, it creates a small waterfall or a smooth, controlled drop. This drop helps to manage the river's energy. Imagine a river flowing very fast; a weir can slow it down and make it calmer. This can be useful for many reasons, like preventing erosion or making the river safer for boats.

Different Types of Weirs

Weirs come in many shapes and sizes, each designed for a specific job. Some are wide and flat, called "broad-crested weirs," while others might have a V-shape or a sharp edge, known as "V-notch" or "sharp-crested weirs." The design depends on what people want the weir to do, whether it's to measure water accurately or to create a calm pool.

Why Do We Build Weirs?

People build weirs for several important reasons. They have been used for hundreds of years to help manage rivers and use their power.

Controlling Water Levels

One main reason for building a weir is to control the water level in a river. By raising the water level upstream, weirs can create deeper areas that are good for boats or for drawing water for farms and towns. This also helps keep a steady water supply for industries or for drinking.

Measuring Water Flow

Some weirs are designed specifically to measure how much water is flowing in a river. By observing how high the water is as it flows over the weir, engineers can calculate the exact volume of water passing by. This information is very important for managing water resources, especially during droughts or floods.

Creating Water Features

Weirs can also create beautiful water features. They can form calm pools for recreation, like swimming or fishing, or create small waterfalls that add to the scenery. In some places, weirs are part of a system to create canals for boats to travel on.

Helping with Flood Control

While weirs are not dams, they can play a small role in flood control. By slowing down the river's flow, they can sometimes help reduce the speed of floodwaters, giving communities more time to prepare. However, large-scale flood control usually requires much bigger structures like dams.

Weirs and Fish

One challenge with weirs is that they can sometimes block the path of fish that need to swim upstream to lay their eggs. This is a big problem for fish like salmon that travel long distances.

Fish Ladders and Passes

To help fish, engineers have developed special designs called "fish ladders" or "fish passes." These are like staircases or gentle ramps made of water that allow fish to swim around or over the weir. They have small pools where fish can rest before continuing their journey. These designs are very important for keeping rivers healthy and protecting fish populations.

Modern Weir Designs

Today, when new weirs are built, or old ones are updated, designers often include features that are friendly to fish and other river animals. This shows how people are working to balance human needs with the needs of nature.

Images for kids

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  A weir in Mende, France

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  Many fish have the capability to jump over weirs. This shows a salmon

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  This kind of weir is difficult for fish to climb

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  Weir designed to make it easy for fish to climb

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  A weir on the Humber River near Raymore Park in Toronto, Ontario, Canada

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

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  A sluice gate-based weir at Bray Lock on the River Thames, facing downstream.

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  During periods of high river flow, this nineteenth century weir of porphyry stone on a creek in the Alps would have significantly more water flowing over it.

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  The bridge and weir mechanism at Sturminster Newton on the River Stour, Dorset, England, UK

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  A manually operated needle dam-type weir near Revin on the River Meuse, France

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  A complicated series of broad-crest and V-notch weirs at Dobbs Weir in Hertfordshire, England, UK

See also

In Spanish: Vertedero hidráulico para niños