Entrance losses are computed as a function of the velocity head inside the culvert at the upstream end. The entrance loss for the culvert is computed as:
1)
\displaystyle h_{en} = k_{en} \frac{V^2_{en}}{2g}
Symbol
Description
Units
h_{en}
Energy loss due to the entrance
k_{en}
Entrance loss coefficient
V_{en}
Flow velocity inside the culvert at the entrance
g
Acceleration due to gravity
The velocity head is multiplied by the entrance loss coefficient to estimate the amount of energy lost as flow enters the culvert. A higher value for the coefficient gives a higher head loss. Entrance loss coefficients are shown in Tables 6-3, 6-4, and 6-5. These coefficients were taken from the Federal Highway Administration's "Hydraulic Design of Highway Culverts" manual (FHWA, 1985). Table 6-3 indicates that values of the entrance loss coefficient range from 0.2 to about 0.9 for pipe-arch and pipe culverts. As shown in Table 6-4, entrance losses can vary from about 0.2 to about 0.7 times the velocity head for box culverts. For a sharpedged culvert entrance with no rounding, 0.5 is recommended. For a well rounded entrance, 0.2 is appropriate. Table 6-5 list entrance loss coefficients for ConSpan culverts.
Note: Entrance loss coefficients should be calibrated whenever possible. The Tables shown in this document for entrance loss coefficients are guidelines and not absolutes.
Table 6‑3 Entrance Loss Coefficient for Pipe Culverts
Type of Structure and Design of Entrance
Coefficient, ken
Concrete Pipe Projecting from Fill (no headwall):
Socket end of pipe Square cut end of pipe
0.2 0.5
Concrete Pipe with Headwall or Headwall and Wingwalls:
Socket end of pipe (grooved end) Square cut end of pipe Rounded entrance, with rounding radius = 1/12 of diameter
0.2 0.5 0.2
Concrete Pipe:
Mitered to conform to fill slope End section conformed to fill slope Beveled edges, 33.7 or 45 degree bevels Side slope tapered inlet
0.7 0.5 0.2 0.2
Corrugated Metal Pipe or Pipe-Arch:
Projected from fill (no headwall) Headwall or headwall and wingwalls square edge Mitered to conform to fill slope End section conformed to fill slope Beveled edges, 33.7 or 45 degree bevels Side slope tapered inlet
0.9 0.5 0.7 0.5 0.2 0.2
Table 6-4 Entrance Loss Coefficient for Reinforced Concrete Box Culverts
Type of Structure and Design of Entrance
Coefficient, ken
Headwall Parallel to Embankment (no wingwalls):
Square-edged on three edges Three edges rounded to radius of 1/12 barrel dimension
0.5 0.2
Wingwalls at 30 to 75 degrees to Barrel:
Square-edge at crown Top corner rounded to radius of 1/12 barrel dimension
0.4 0.2
Wingwalls at 10 to 25 degrees to Barrel:
Square-edge at crown
0.5
Wingwalls parallel (extension of sides):
Square-edge at crown Side or slope tapered inlet
0.7 0.2
Table 6-5 Entrance Loss Coefficients For ConSpan Culverts