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How It Works
This calculator handles two key open-channel parameters. The hydraulic radius (Rh = A/Pw) measures channel efficiency by dividing the flow area by the wetted perimeter. The Froude number (Fr = v/√(ghm)) classifies flow as subcritical (Fr < 1), critical, or supercritical (Fr > 1).
Example Problem
A rectangular channel is 3 m wide with a flow depth of 1 m. What is the hydraulic radius?
- Area: A = 3 × 1 = 3 m²
- Wetted perimeter: Pw = 3 + 2(1) = 5 m
- Rh = 3 / 5 = 0.6 m
Frequently Asked Questions
What is hydraulic radius and why does it matter?
Hydraulic radius is the flow area divided by the wetted perimeter. It appears in Manning's and Chezy's equations and measures how efficiently a channel shape conveys water. A semicircular channel has the highest Rh for a given area.
What does the Froude number tell you?
It classifies open-channel flow regime. Fr < 1 is subcritical (slow, deep); Fr > 1 is supercritical (fast, shallow). At Fr = 1, a hydraulic jump can form, which is important for spillway and stilling basin design.
What is the hydraulic radius of a full circular pipe?
For a pipe of diameter D flowing full, Rh = D/4. A 200 mm pipe has Rh = 0.05 m.
Related Calculators
- Manning Equation Calculator — uses Rh to compute open-channel flow velocity.
- Chezy Equation Calculator — another open-channel formula that uses hydraulic radius.
- Continuity Equation Calculator — relate flow area, velocity, and discharge.
- Darcy-Weisbach Calculator — use hydraulic diameter (4Rh) for pipe friction calculations.
- Gutter Design Calculator — applies hydraulic radius to triangular gutter flow.
- Length Unit Converter — convert between feet, meters, and other length units for channel dimensions.