# How do you find the flow of a rectangular weir?

## How do you find the flow of a rectangular weir?

The equation recommended by the Bureau of Reclamation in their Water Measurement Manual, for use with a suppressed rectangular weir is: Q = 3.33 B H3/2, where Q is the water flow rate in ft3/sec, B is the length of the weir (and the channel width) in ft, and H is the head over the weir in ft.

### How do you measure flow in a weir?

Weirs to Measure Flow It works by raising the water level upstream of the weir, and then forcing the water to spill over. The more water is flowing over the weir, the deeper the water will be upstream of the weir. So measuring flow rate (CFS) can be done by simply measuring the depth of the water upstream.

**What is rectangular weir?**

[rek′taŋ·gyə·lər ′wer] (civil engineering) A weir with a rectangular notch at top for measurement of water flow in open channels; it is simple, easy to make, accurate, and popular.

**What is the coefficient of discharge for a rectangular weir?**

In the study for rectangular weir, for flat level, the coefficient of discharge is 0.571503 while for 1:2400 slope, the coefficient of discharge is 0.52528.

## How to calculate contracted rectangular weir flow in Excel?

The first page of the Excel template for contracted rectangular weir flow calculations is shown at the left and a second page is shown at the right. For a contracted rectangular weir, L < B, so in addition to the three input values needed for the suppressed rectangular weir (P, B, and H), a value for the weir length, L, must be entered.

### What are the dimensions of a rectangular weir?

USBR (1997) provides equations for a “standard” fully contracted rectangular weir and a “standard” suppressed weir. The U.S. Bureau of Reclamation has conducted many weir tests over several decades using weirs with particular dimensions – usually b’s in 1 ft. increments up to about 10 ft.

**How is the flow rate of a weir determined?**

The flow rate measurement in a rectangular weir is based on the Bernoulli Equation principles and can be expressed as: c d must be determined by analysis and calibration tests. For standard weirs – c d – is well defined or constant for measuring within specified head ranges.

**How is the notch width of a weir determined?**

A suppressed weir’s notch width (b) is equal to the channel width (B); thus, there really isn’t a notch – the weir is flat all the way along the top. For a weir to be fully contracted, (B-b) must be greater than 4hmax, where hmaxis the maximum expected head on the weir (USBR, 1997). A partially contracted weir has B-b between 0 and 4hmax.