# Channel Flow

## MANNING'S FORMULA

Q = A * 1.486/n * R^{2/3} * S^{1/2}

- 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.)

### Area of a Trapezoid

A = B * D + [(Z1+Z2)/2] * D^{2}

- A = Cross-sectional Area of Flow (sq. ft.)
- B = Bottom width (ft.)
- D = Depth of flow
- Z1 = Left side slope (z:1)
- Z2 = Right side slope (z:1)

### Wetted Perimeter of a Trapezoid

P = B + [(Z1*D)^{2} + D^{2}]^{1/2} + [(Z2*D)^{2} + D^{2}]^{1/2}

- P = Wetted perimeter (ft.)
- B = Bottom width (ft.)
- D = Depth of flow
- Z1 = Left side slope (z:1)
- Z2 = Right side slope (z:1)

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 |

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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