Hydraulics and sanitation
Gravity flow in circular pipe (Manning)
Formulas
θ = 2 arccos(1 − 2y/D)
A = D²/8 (θ − sin θ) ; P = D θ / 2 ; Rh = A/P
V = (1/n) Rh^(2/3) I^(1/2) (K = 1/n, Strickler)
Q = V × A
Assumptions
- Steady uniform open-channel flow; n = 0.013 is typical for concrete/PVC in service (K ≈ 77).
- Check minimum (self-cleansing) and maximum velocities against the owner’s specification.
Gravity flow in circular pipe (Manning)
Fill in the inputs and run the calculation: results and every intermediate step will appear here.
These tools provide estimates and calculation aids. They are neither design calculations nor an engineering approval: any design or safety decision must be checked by a qualified professional against the applicable standards.