What Is the Manning's Equation Open Channel Flow Calculator?
Manning’s equation was developed by Robert Manning in 1889 for uniform gravity-driven water flow in open channels.
How Does the Manning's Equation Open Channel Flow Calculator Work?
Gravitational driving force along channel slope is balanced by viscous boundary wall friction along the wetted perimeter.
Manning's Equation Open Channel Flow Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Q = \frac{1}{n} A R_h^{2/3} S^{1/2}, \quad v = \frac{1}{n} R_h^{2/3} S^{1/2}, \quad Fr = \frac{v}{\sqrt{g y}}
Discharge Q equals flow area A times velocity, where velocity depends on hydraulic radius Rh and slope S.
How to Use the Manning's Equation Open Channel Flow Calculator
- Enter channel base width and water depth.
- Input longitudinal channel bed slope S.
- Specify Manning roughness coefficient n.
Step-by-Step Example Calculation
Concrete Storm Canal
Input Values:
channelWidth:2.0
flowDepth:0.8
channelSlope:0.002
manningN:0.013
Worked Steps: In a 2m wide channel with 0.8m depth, flow velocity is 1.90 m/s delivering 3.04 m³/s discharge in tranquil subcritical flow (Fr = 0.678).
Understanding Your Result
Discharge Flow Rate (Q): Total volume flowing per second.
Velocity: Average cross-sectional fluid speed.
Regime: Froude number classification.
Factors That Affect the Result
- Channel roughness, bottom bed slope, and hydraulic radius.
When Should You Use This Calculator?
- Stormwater flume sizing, irrigation canal design, river flood routing, and road culvert capacity evaluation.
Assumptions & Limitations
- Assumes steady, uniform, prismatic rectangular open channel flow.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard open channel hydraulic formulation with exact arithmetic.