Culvert Design

Course Name: Basic Civil Engineering – Culvert Design (1 hour)


Gravity Flow Gravity flow through pipes not under pressure is usually determined using the Manning formula developed by Robert Manning. Robert Manning was an engineer born in Wicklow, Ireland. He had a long career in Dublin and Belfast during the latter half of the 1800’s. He is famous for hydraulic engineering and in textbooks for the “Manning Coefficient”, still in use to describe water flow in open channels.
The most commonly used empirical equation to determine open channel flow is Manning’s Equation:

v=K/n R2/3S1/2(English Units) [SI units]

    v = Fluid Velocity (ft/s) or [m/s]
    K = 1.486 (English); K = 1.00 [SI]
    R = Hydraulic Radius (ft) or [m] = A/Pw
    A = Cross-Sectional Area of Flow (ft2) or [m2]
    Pw = Wetted Perimeter (ft) or [m]
    S = Channel Slope
    n = Manning’s Roughness Coefficient

The cross-sectional area to flow and wetted perimeter are related to the depth.

Pressure Flow Flow through pipes under p