Broad Crested Weir Calculator

Broad Crested Weir Equation:

\[ Q = C L H^{3/2} \]

Flow Rate (Q):

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1. What is Broad Crested Weir Flow?

The broad crested weir is a flow measurement device used in open channels. It consists of a raised, horizontal crest over which water flows. The flow rate is determined by measuring the head (water height) upstream of the weir.

2. How Does the Calculator Work?

The calculator uses the broad crested weir equation:

\[ Q = C L H^{3/2} \]

Where:

\( Q \) — Flow rate (m³/s)
\( C \) — Discharge coefficient (m^1/2/s)
\( L \) — Length of the weir crest (m)
\( H \) — Head over the weir crest (m)

Explanation: The equation relates the flow rate to the head over the weir, with the coefficient accounting for energy losses and flow conditions.

3. Importance of Flow Rate Calculation

Details: Accurate flow measurement is crucial for water resource management, irrigation systems, and hydraulic engineering projects.

4. Using the Calculator

Tips: Enter the discharge coefficient (typically between 1.6-2.2 m^1/2/s), weir length in meters, and head in meters. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical value for coefficient C?
A: For broad crested weirs, C typically ranges from 1.6 to 2.2 m^1/2/s, depending on weir geometry and flow conditions.

Q2: How accurate is this calculation?
A: Accuracy depends on proper weir construction and head measurement. Under ideal conditions, accuracy within ±5% can be achieved.

Q3: What are the limitations of broad crested weirs?
A: They require significant head loss, have limited rangeability, and need careful installation to ensure accurate measurements.

Q4: How should the head (H) be measured?
A: Measure upstream of the weir at a distance of 3-4 times the maximum head, in a straight section with uniform flow.

Q5: When is a broad crested weir preferred?
A: They're ideal for medium to large flows where minimal maintenance and good accuracy are required.