What minimum pipe slope is needed for self-cleaning?

Minimum velocity 0.6 m/s (2 ft/s) for self-cleaning. For 300mm pipe (Manning n=0.013): slope = V²n²/(R^(4/3)) = 0.0005 minimum. Most designs use 0.001-0.005 (0.1%-0.5%).

How do I select pipe size for storm drain?

Calculate design flow Q (Rational method). Find pipe flowing full: Q_full = A·V_full (Manning). Select smallest pipe diameter where Q_full ≥ Q_design. Check velocity adequate (> 0.6 m/s) and headwater acceptable.

What return period for storm drain design?

Minor (enclosed) storm drain system: 10-year return period typical. Major (surface overflow) system: 100-year. ASCE/FHWA recommends minor for residential 2-10 year; commercial/arterial 10-25 year; freeway 10-50 year.

Storm Drain Sizing Calculator

Size storm drain pipes using Manning equation for full pipe flow and Rational method for peak flow. Q = A·i·C. Pipe diameter, slope, and velocity calculations. Minimum self-cleaning velocity 0.6-0.9 m/s.

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How It Works

Each component has a specific meaning:

Manning equation — The manning equation recorded for the patient or scenario being assessed.

Note: Interpret the storm drain result against the clinical thresholds and context described above.

How to Use

Enter the Manning equation for the patient or scenario you are assessing. Size storm drain pipes using Manning equation for full pipe flow and Rational method for peak flow. Q = A·i·C. Pipe diameter, slope, and velocity calculations. Minimum self-cleaning velocity 0.6-0.9 m/s. Use the storm drain result to inform your clinical assessment.

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Frequently Asked Questions

What minimum pipe slope is needed for self-cleaning?

How do I select pipe size for storm drain?

What return period for storm drain design?