What is end contraction of a sharp crested weir?

End contraction refers to the phenomenon where the nappe flowing over a sharp-crested weir tends to contract at the ends of the weir. This contraction is caused by the surface tension of the water, which pulls the nappe inward towards the center of the weir.

The amount of end contraction depends on several factors, including the height of the weir, the width of the weir, and the surface tension of the water. Generally, the higher the weir and the narrower the weir, the greater the amount of end contraction.

End contraction can be significant and can affect the accuracy of flow measurements made using a sharp-crested weir. To compensate for end contraction, the effective width of the weir must be reduced by an amount equal to twice the amount of end contraction.

The following equation can be used to calculate the end contraction for a sharp-crested weir:

```

C_e = 0.1 + \frac{0.154H}{W}

```

where:

* \(C_e\) is the coefficient of end contraction

* \(H\) is the height of the weir

* \(W\) is the width of the weir

For example, consider a sharp-crested weir with a height of 1 meter and a width of 2 meters. The coefficient of end contraction for this weir would be:

```

C_e = 0.1 + \frac{0.154(1)}{2} = 0.177

```

This means that the effective width of the weir would need to be reduced by 2 * 0.177 = 0.354 meters to account for end contraction.