Broad Crested Weir Flow Rate Calculator

Formula

The formula to calculate the Broad Crested Weir Flow Rate (Q) is:

\[ \text{Q} = \text{D} \times h2^2 \times b \times \sqrt{2 \times g \times (h1 - h2)} \]

Where:

\( \text{Q} \) is the flow rate (ft³/s)
\( \text{D} \) is the discharge coefficient
\( h2 \) is the head from mid-weir to the bottom of the weir (ft)
\( b \) is the width of the weir (ft)
\( h1 \) is the head from the top to mid-weir (ft)
\( g \) is the acceleration due to gravity (32.174 ft/s²)

What is a Broad Crested Weir?

A broad-crested weir is a hydraulic structure commonly used in civil engineering and water management to control water flow in rivers, canals, and reservoirs. Broad-crested weirs are crucial for regulating water levels, ensuring a controlled and stable water flow downstream. By adjusting the height of the weir crest, engineers can manage the quantity of water passing through the structure. This control helps prevent both excessive flooding and inadequate water supply, protecting communities and ecosystems alike.

Example Calculation

Let's assume the following values:

Discharge Coefficient (D) = 0.6
Head from mid-weir to bottom (h2) = 2 ft
Width of the weir (b) = 10 ft
Head from top to mid-weir (h1) = 3 ft

Using the formula to calculate the Flow Rate:

\[ \text{Q} = 0.6 \times 2^2 \times 10 \times \sqrt{2 \times 32.174 \times (3 - 2)} \]

\[ \text{Q} = 0.6 \times 4 \times 10 \times \sqrt{64.348} \]

\[ \text{Q} = 24 \times 8.02 \approx 192.48 \text{ ft}^3\text{/s} \]

The Flow Rate is approximately 192.48 ft³/s.