Length Of Crest If Critical Depth Is Constant For Discharge Of Weir Calculator

Formula Used:

\[ \text{Length of Weir Crest} = \frac{\text{Discharge Over Broad Crested Weir}}{1.70 \times \text{Coefficient of Discharge} \times (\text{Total Head})^{3/2}} \]

Length of Weir Crest (Lw):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Length of Crest Formula?

The formula calculates the required length of a broad-crested weir crest to maintain a specific discharge, given the coefficient of discharge and total head. It's derived from the fundamental weir equation for broad-crested weirs.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ L_w = \frac{Q}{1.70 \times C_d \times H^{3/2}} \]

Where:

\( L_w \) — Length of Weir Crest (m)
\( Q \) — Discharge Over Broad Crested Weir (m³/s)
\( C_d \) — Coefficient of Discharge
\( H \) — Total Head (m)

Explanation: The formula calculates the crest length needed to achieve a specific discharge, considering the hydraulic characteristics of the weir.

3. Importance of Length Calculation

Details: Accurate calculation of weir crest length is essential for proper hydraulic design, ensuring the weir can handle the required discharge while maintaining stable flow conditions.

4. Using the Calculator

Tips: Enter discharge in m³/s, coefficient of discharge (typically between 0.6-0.7 for broad-crested weirs), and total head in meters. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What is a broad-crested weir?
A: A broad-crested weir is a hydraulic structure with a horizontal crest sufficiently long in the direction of flow to support hydrostatic pressure distribution.

Q2: What is the typical range for coefficient of discharge?
A: For broad-crested weirs, the coefficient of discharge typically ranges from 0.6 to 0.7, depending on the weir geometry and flow conditions.

Q3: How is total head measured?
A: Total head is measured from the weir crest to the upstream water surface, typically at a distance of 2-3 times the maximum head upstream of the weir.

Q4: What are the limitations of this formula?
A: The formula assumes critical flow conditions over the weir crest and may not be accurate for very low or very high heads, or for weirs with significant approach velocity.

Q5: Can this formula be used for other weir types?
A: This specific formula is designed for broad-crested weirs. Other weir types (sharp-crested, V-notch, etc.) have different discharge equations.