Home
Back
Manning Equation:
| From: | To: |
Manning's equation is an empirical formula that calculates the average velocity of water flowing in an open channel. It's widely used in hydraulic engineering for designing and analyzing channels, pipes, and natural waterways.
The calculator uses Manning's equation:
Where:
Explanation: The equation relates flow velocity to channel characteristics, where roughness coefficient represents channel surface friction, hydraulic radius describes channel efficiency, and slope represents energy gradient.
Details: Accurate velocity calculation is crucial for designing efficient drainage systems, predicting flood behavior, sediment transport analysis, and ensuring proper water conveyance in irrigation and municipal systems.
Tips: Enter Manning's roughness coefficient (typical values: 0.012-0.015 for concrete, 0.025-0.035 for natural streams), hydraulic radius (cross-sectional area divided by wetted perimeter), and channel slope. All values must be positive.
Q1: What are typical Manning's n values?
A: Smooth concrete: 0.012-0.013; Earth channels: 0.022-0.025; Natural streams: 0.030-0.040; Dense vegetation: 0.050-0.150.
Q2: How is hydraulic radius calculated?
A: Hydraulic radius = Cross-sectional area ÷ Wetted perimeter. For full circular pipes: R = D/4.
Q3: What units should be used?
A: The equation requires consistent units: ft for length, ft/s for velocity, and ft/ft for slope.
Q4: When is Manning's equation not applicable?
A: Not suitable for pressurized flow, very steep slopes, or non-uniform flow conditions. Use with caution for rapidly varied flow.
Q5: How accurate is Manning's equation?
A: Generally accurate for steady, uniform flow in open channels. Accuracy depends on proper selection of roughness coefficient.