Example preset
Choose a preset to fill the form and refresh results instantly.
Inputs
Forward (calculate V,Q)
Results
| Cross-sectional area A [m²] | — |
|---|---|
| Runbe P [m] | — |
| Diameter depth R [m] | — |
| Hydraulic average depth Dm=A/T [m] | — |
| Froude number Fr [-] | — |
| Flow situation judgment | — |
| Estimated water depth y [m] | — |
| Repetition information | — |
Cross-sectional view (outline)
Displays the cross-sectional shape according to the input value.
graph
Display a graph with valid input.
Calculation formula and procedure
R = A / P
V = (1/n) × R^(2/3) × S^(1/2)
Q = A × V
Cross-sectional type (A, P): Corresponds to rectangular, trapezoidal, and circular (partially filled) shapes. Back calculation (Q→y) is calculated using the bisection method, and back calculation (Q→S) is calculated using an analytical formula.
FAQ
What does the Froude number Fr indicate?
Fr is a measure of the ratio of inertial force to gravity. Generally, Fr<1 is a standard flow, Fr≈1 is a limit flow, and Fr>1 is a guideline for a jet flow.
What does S (slope) mean?
S in the Manning equation is the energy gradient. For learning, this tool approximates the slope to be approximately equal to the riverbed slope.
Which roughness coefficient n should I use?
The value changes depending on the waterway material, vegetation, meandering, etc. The preset values are for reference only, and please be sure to check the supporting documents for design purposes.
Can the circular cross section results be used for pressure pipes?
Cannot be used. Here, we assume a partially filled flow in an open channel with a free water surface.
What should I do first on this page?
Start with the minimum required inputs or the first action shown near the primary button. Keep optional settings at defaults for a baseline run, then change one setting at a time so you can explain what caused each output change.
How to use Open channel (Manning method) flow velocity/flow calculation effectively
What this calculator does
This page is for estimating outcomes by changing inputs in one controlled workflow. The model keeps your focus on variables, not output shape. Start with stable assumptions, then test sensitivity by changing one key input at a time to observe directional impact.
Input meaning and unit policy
Each input has an expected unit and a typical range. For reliable interpretation, check whether you are using the same unit system, period, and base assumptions across all runs. Unit mismatch is the most common source of unexpected drift in numeric results.
Use-case sequence
A practical sequence is: first run with defaults, then create a baseline log, then run one alternative scenario, and finally compare only the changed output metric. This sequence reduces cognitive load and prevents false pattern recognition in early experiments.
Common mistakes to avoid
Avoid changing too many variables at once, mixing incompatible data sources, and interpreting a one-time output without checking robustness. A single contradictory input can flip conclusions, so keep each experiment minimal and document assumptions as part of your note.
Interpretation guidance
Review both magnitude and direction. Direction tells you whether a strategy moves outcomes in the desired direction, while magnitude helps you judge practicality. If both agree, you can proceed; if not, rebuild the baseline and verify constraints before deciding.
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