Wetted Perimeter Of Trapezoidal Channel Section Calculator

Formula Used:

\[ p = B + 2 \times d_f \times (\theta + \cot(\theta)) \]

Wetted Perimeter of Channel (p):

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1. What is Wetted Perimeter?

The wetted perimeter is defined as the surface of the channel bottom and sides in direct contact with the aqueous body. It is an important parameter in hydraulic engineering for calculating flow characteristics in open channels.

2. How Does the Calculator Work?

The calculator uses the formula for trapezoidal channels:

\[ p = B + 2 \times d_f \times (\theta + \cot(\theta)) \]

Where:

\( p \) — Wetted perimeter (m)
\( B \) — Width of trapezoidal channel section (m)
\( d_f \) — Depth of flow (m)
\( \theta \) — Theta angle (radians)
\( \cot(\theta) \) — Cotangent of theta angle

Explanation: The formula accounts for the channel geometry and the angle of the side slopes to determine the total length of channel surface in contact with water.

3. Importance of Wetted Perimeter Calculation

Details: Accurate wetted perimeter calculation is crucial for determining hydraulic radius, flow resistance, and discharge capacity in open channel flow calculations.

4. Using the Calculator

Tips: Enter channel width and depth in meters, and theta angle in radians. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the hydraulic radius?
A: Hydraulic radius is the cross-sectional area of flow divided by the wetted perimeter, used in flow resistance calculations.

Q2: How does side slope angle affect wetted perimeter?
A: Steeper side slopes (larger theta) result in shorter wetted perimeter for the same flow depth and bottom width.

Q3: What are typical theta values for trapezoidal channels?
A: Common theta values range from 0.5 to 1.0 radians (approximately 30-60 degrees) depending on soil stability and construction methods.

Q4: Can this calculator be used for other channel shapes?
A: No, this formula is specific to trapezoidal channels. Other shapes (rectangular, triangular, circular) have different wetted perimeter formulas.

Q5: Why is wetted perimeter important in Manning's equation?
A: Wetted perimeter is used to calculate hydraulic radius, which directly affects flow velocity and discharge in Manning's equation.