Determination of Outlet Velocity

The outlet velocity, v
o
, depends on the culvert discharge (Q) and the cross-sectional area of flow at the outlet (A
o
) as shown in Equation 8-17.
EquationObject249274
Equation 8-17.
  1. Assign the variable d
    o
     as the depth with which to determine the cross-sectional area of flow at the outlet.
  2. For outlet control, set the depth, d
    o
    ,
    equal to the higher of critical depth (d
    c
    ) and tailwater depth (TW) as long as the value is not higher than the barrel rise (D) as shown in Figure 8‑13.
  3. If the conduit will flow full at the outlet, usually due to a high tailwater or a conduit capacity lower than the discharge, set d
    o
     to the barrel rise (D) so that the full cross-sectional area of the conduit is used as shown in Figure 8‑14.
Cross Sectional Area based on the Higher of Critical Depth and Tailwater (click in image to see full-size image)
Figure 8-13. Cross Sectional Area based on the Higher of Critical Depth and Tailwater
Cross Sectional Area Based on Full Flow (click in image to see full-size image)
Figure 8-14. Cross Sectional Area Based on Full Flow