\[R_h=\frac{A}{P}\]
Variables
Rhhydraulic radius (m)
Aflow area (m²)
Pwetted perimeter (m)
Description
What is this formula?
The Hydraulic Radius is a geometric parameter used extensively in open-channel hydraulics and partially filled conduits.
It is defined as the ratio between the flow area and the wetted perimeter and represents the hydraulic efficiency of a channel section.
Larger hydraulic radii generally indicate lower frictional resistance and greater flow capacity.
When to use it
Use this formula when calculating:
- Manning Equation
- Open-channel flow
- Irrigation canals
- Stormwater channels
- River hydraulics
Example
A trapezoidal channel has:
A = 4.50 m²
P = 5.80 m
Formula:
Rh = A/P
Substitution:
Rh = 4.50/5.80
Rh = 0.776 m
Result:
Rh ≈ 0.78 m
Applications
- Manning calculations
- Channel design
- River engineering
- Drainage systems
- Flood studies
- Hydraulic modeling