Manning Formula for Gravity Flow

Manning equation for calculating gravity flow in open channels

Manning's equation can be used to calculate cross-sectional average velocity flow in open channels

v = k_n/n R^2/3 S^1/2 (1)

where

v = cross-sectional average velocity (ft/s, m/s)

k_n = 1.486 for English units and k_n = 1.0 for SI units

A = cross sectional area of flow (ft², m²)

n = Manning coefficient of roughness

R = hydraulic radius (ft, m)

S = slope of pipe (ft/ft, m/m)

The volume flow in the channel can be calculated as

q = A v = A k_n/n R^2/3 S^1/2 (2)

where

q = volume flow (ft³/s, m³/s)

A = cross-sectional area of flow (ft², m²)

Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Web The Engineering ToolBox