Enter design flow, slope, and pipe material to screen standard 8- to 72-inch (200–1800 mm) RCP or HDPE storm-drain and stormwater-pipe sizes with Manning's equation and velocity guidance, in cfs or L/s.
For educational purposes only. Not a substitute for professional engineering judgment.
Manning's equation is empirical and assumes uniform, steady flow conditions
Not valid for pressurized (surcharged) pipe flow - use pressure flow equations instead
Accuracy decreases for very smooth pipes (n < 0.010) or very rough pipes (n > 0.035)
Does not account for entrance/exit losses or other minor losses
Partial flow calculations assume free surface (atmospheric pressure at water surface)
Maximum Q/Qfull occurs at approximately y/D = 0.94, not at full flow
Air entrainment effects near the pipe crown are not considered
References formatted in APA 7th Edition style.