Length Of Crest For Discharge Through Drowned Portion Calculator

Formula Used:

\[ L_w = \frac{Q_2}{C_d \cdot h_2 \cdot \sqrt{2 \cdot g \cdot (H_{\text{Upstream}} - h_2) + v_{su}^2}} \]

Discharge through Drowned Portion (Q₂):

m³/s

Coefficient of Discharge (C_d):

Head on Downstream of Weir (h₂):

Acceleration due to Gravity (g):

m/s²

Head on Upstream of Weir (H_Upstream):

Velocity over Submerged Weir (v_su):

m/s

Length of Weir Crest (L_w):

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1. What is the Length of Crest for Discharge through Drowned Portion?

The Length of Crest for Discharge through Drowned Portion is a hydraulic engineering parameter that determines the required length of a weir crest to accommodate a specific discharge flow when the weir is submerged or drowned. This calculation is essential for proper weir design in various water management systems.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ L_w = \frac{Q_2}{C_d \cdot h_2 \cdot \sqrt{2 \cdot g \cdot (H_{\text{Upstream}} - h_2) + v_{su}^2}} \]

Where:

\( L_w \) — Length of Weir Crest (m)
\( Q_2 \) — Discharge through Drowned Portion (m³/s)
\( C_d \) — Coefficient of Discharge
\( h_2 \) — Head on Downstream of Weir (m)
\( g \) — Acceleration due to Gravity (m/s²)
\( H_{\text{Upstream}} \) — Head on Upstream of Weir (m)
\( v_{su} \) — Velocity over Submerged Weir (m/s)

Explanation: This formula calculates the required crest length for a weir to handle a specific discharge when the weir is submerged, taking into account various hydraulic parameters including head differences and flow velocity.

3. Importance of Length of Weir Crest Calculation

Details: Accurate calculation of weir crest length is crucial for proper hydraulic structure design, ensuring adequate water flow capacity, preventing overflow issues, and maintaining structural integrity in dams, spillways, and other water control systems.

4. Using the Calculator

Tips: Enter all required parameters with appropriate units. Ensure that Head on Upstream of Weir is greater than Head on Downstream of Weir for valid calculation. Use standard values for Coefficient of Discharge (typically 0.6-0.8 for sharp-crested weirs).

5. Frequently Asked Questions (FAQ)

Q1: What is a drowned or submerged weir?
A: A drowned weir occurs when the downstream water level is above the weir crest, affecting the discharge characteristics and requiring different calculation methods than free-flowing weirs.

Q2: How does the coefficient of discharge vary?
A: The coefficient of discharge depends on weir shape, crest characteristics, and flow conditions, typically ranging from 0.6 to 0.8 for sharp-crested weirs.

Q3: What are typical values for acceleration due to gravity?
A: Standard gravity is 9.8 m/s², though slight variations occur based on geographical location and altitude.

Q4: When is this calculation most applicable?
A: This calculation is particularly important for weir design in situations where submergence is expected, such as in tidal areas or during flood conditions.

Q5: What units should be used for input values?
A: All length measurements should be in meters, discharge in cubic meters per second, and velocity in meters per second for consistent results.