Channel Flow

Channel flow travel time is computed by dividing the channel distance by the flow rate obtained from Manning’s equation. This can be written as:
EquationObject3042
Equation 4-19.
Where:
  • t
    ch
     = channel flow time (hr.)
  • L
    ch
     = channel flow length (ft)
  • S
    ch
     = channel flow slope (ft/ft)
  • n
     = Manning’s roughness coefficient
  • R
     = channel hydraulic radius (ft), and is equal to InlineEquation1343, where: a = cross sectional area (ft
    2
    ) and p
    w
    = wetted perimeter (ft), consider the uniform flow velocity based on bank-full flow conditions. That is, the main channel is flowing full without flow in the overbanks. This assumption avoids the significant iteration associated with other methods that employ rainfall intensity or discharges (because rainfall intensity and discharge are dependent on time of concentration).