Mannings Formula
MANNING'S FORMULA
Q = A *1.486/n * R2/3 * S1/2
- Q = Discharge (cu. ft./sec.)
- A = Cross-sectional Area of Flow (sq. ft.)
- n = Coefficient of Roughness
- R = Hydraulic Radius (ft.)
- S = Slope of Pipe (ft./ft.)
Hydraulic Radius
R = A / P
- R = Hydraulic Radius (ft.)
- A = Cross-sectional Area of Flow (sq. ft.)
- P = Wetted perimeter (ft.)
Material | Manning's n |
---|---|
Metals | |
Brass | 0.011 |
Cast Iron | 0.013 |
Smooth Steel | 0.012 |
Corrugated Metal | 0.022 |
Non-Metals | |
Glass | 0.010 |
Clay Tile | 0.014 |
Brickwork | 0.015 |
Asphalt | 0.016 |
Masonry | 0.025 |
Finished Concrete | 0.012 |
Unfinished Concrete | 0.014 |
Gravel | 0.029 |
Earth | 0.025 |
Planed Wood | 0.012 |
Unplaned Wood | 0.013 |
Corrugated Polyethylene (PE) with smooth inner walls | 0.009-0.015 |
Corrugated Polyethylene (PE) with corrugated inner walls | 0.018-0.025 |
Polyvinyl Chloride (PVC) with smooth inner walls | 0.009-0.011 |
Excavated Earth Channels | |
Clean | 0.022 |
Gravelly | 0.025 |
Weedy | 0.030 |
Stony, Cobbles | 0.035 tr |
Natural Streams | |
Clean and Straight | 0.030 |
Major Rivers | 0.035 |
Sluggish with Deep Pools | 0.040 |
Floodplains | |
Pasture, Farmland | 0.035 |
Light Brush | 0.050 |
Heavy Brush | 0.075 |
Trees | 0.15 |
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