Energy

The energy equation, Equation 6-6, applies to conduit flow, too. Additionally, the following concepts apply to conduit flow.
  • For pressure flow, the depth, d, represents the distance from the flowline to the hydraulic grade line.
  • For pressure flow, the slope of the energy grade line and hydraulic grade line through the conduit are parallel and are represented by the friction slope.
  • Compute friction losses, h
    f
    , as the product of friction slope and length of conduit.
  • Consider the kinetic energy coefficient (α) equal to unity.
  • Other losses include entrance losses, exit losses, and junction losses.
Refer to
Chapter 8
for directions to accommodate such losses for culvert design and
Chapter 10
for storm drain design.
Compute the velocity head at any location in a conduit using Equation 6-20.
where:
EquationObject214235
Equation 6-20.
where:
  • v
     = flow velocity in culvert (ft./s or m/s).
  • g
     = the gravitational acceleration = 32.2 ft/ s
    2
     or 9.81 m/s
    2
    .
The friction slope represents the slope of the energy grade line and is based upon Manning's Equation, rearranged as follows:
EquationObject215236
Equation 6-21.
where:
  • S
    f
    = friction slope (ft./ft. or m/m)
  • z
    = 1.486 for English measurements and 1.0 for metric.