Open Channel Flow Calculator
Calculate water flow velocity and discharge rate using Manning's equation for open channels
Calculate Open Channel Flow
Surface roughness affects flow resistance
Percentage slope (rise/run × 100)
Vertical distance from channel bottom to water surface
Custom Channel Dimensions
Flow Calculation Results
Channel Properties
Flow Results
Manning's Equation: V = (1/n) × R^(2/3) × S^(1/2)
Flow Rate: Q = V × A
Design Type: Custom dimensions
Flow Analysis
Example Calculation
Concrete Rectangular Channel
Given:
• Cross section: Rectangular
• Design: Most efficient (width = 2 × depth)
• Water depth: 2.0 m
• Manning coefficient: 0.012 (concrete)
• Channel slope: 0.5%
Results
• Area: A = 2 × 2² = 8.0 m²
• Wetted perimeter: P = 2 + 2(2) = 6.0 m
• Hydraulic radius: R = 8/6 = 1.33 m
• Velocity: V = (1/0.012) × 1.33^(2/3) × 0.005^(1/2)
• V = 6.64 m/s, Q = 53.1 m³/s
Units
Manning's Coefficients
Efficient Channel Shapes
Semi-circular
Most efficient (minimum wetted perimeter)
Trapezoidal
Practical efficient design
Rectangular
Easy to construct
Triangular
Good for small flows
Understanding Open Channel Flow
What is Open Channel Flow?
Open channel flow occurs when water flows under the influence of gravity with a free surface exposed to atmospheric pressure. Unlike closed pipe flow, open channels like rivers, canals, and irrigation ditches have this characteristic free surface.
Key Characteristics
- •Free surface exposed to atmosphere
- •Flow driven by gravity and channel slope
- •Pressure at free surface equals atmospheric pressure
- •Flow depth varies with flow rate and channel geometry
Manning's Equation
Velocity Formula:
V = (1/n) × R^(2/3) × S^(1/2)
Flow Rate:
Q = V × A
Hydraulic Radius:
R = A / P
V: Average flow velocity (m/s)
n: Manning's roughness coefficient
R: Hydraulic radius (m)
S: Channel slope (m/m)
A: Cross-sectional area (m²)
P: Wetted perimeter (m)
Factors Affecting Flow
Channel Roughness (n)
Surface material affects friction and flow resistance
Channel Slope (S)
Steeper slopes provide more gravitational driving force
Cross-sectional Shape
Geometry affects hydraulic efficiency
Flow Depth
Determines cross-sectional area and wetted perimeter
Applications
Natural Rivers
Flood analysis and river engineering
Irrigation Canals
Agricultural water distribution systems
Storm Drainage
Urban stormwater management
Hydropower
Water conveyance for power generation