Culvert Entrance Loss Coefficients (Ke) — HDS-5
Entrance loss under outlet control: he = Ke·V²/(2g), with V the barrel velocity. Ke depends on inlet geometry and barrel material. Values are from FHWA HDS-5, Table 12 (Hydraulic Design of Highway Culverts).
Concrete Pipe
| Inlet configuration | Ke |
|---|---|
| Projecting from fill, socket (groove) end | 0.2 |
| Projecting from fill, square-cut end | 0.5 |
| Headwall / headwall & wingwalls, socket end | 0.2 |
| Headwall / headwall & wingwalls, square edge | 0.5 |
| Headwall, rounded edge (radius ≈ 1/12 D) | 0.2 |
| Beveled edges (33.7° or 45° bevels) | 0.2 |
| Side- or slope-tapered inlet | 0.2 |
Corrugated Metal Pipe (CMP)
| Inlet configuration | Ke |
|---|---|
| Projecting from fill (no headwall) | 0.9 |
| Mitered to conform to fill slope | 0.7 |
| Headwall or headwall & wingwalls, square edge | 0.5 |
| End section conforming to fill slope | 0.5 |
| Beveled edges (33.7° or 45° bevels) | 0.25 |
| Side- or slope-tapered inlet | 0.2 |
Box Culvert (Reinforced Concrete)
| Inlet configuration | Ke |
|---|---|
| Wingwalls 30°–75° to barrel, square edge at crown | 0.4 |
| Wingwalls 30°–75°, crown edge rounded (r ≈ 1/12 D) | 0.2 |
| Wingwalls 90° & 15° to barrel, square edge | 0.5 |
| Wingwalls parallel (extension of sides), square edge | 0.7 |
| Beveled edges on 3 sides | 0.2 |
Outlet-control headwater.
HW = TW + H − L·So, H = (1 + Ke + 29n²L/R1.33)·V²/(2g)
where H is total head loss (entrance + friction + exit), TW is tailwater depth, L barrel length, So barrel slope,
R hydraulic radius. The "1" is the exit (velocity-head) loss. Design HW is the larger of the inlet-control and
outlet-control results.
Source: FHWA, Hydraulic Design of Highway Culverts (HDS-5, Publication FHWA-HIF-12-026), Table 12. Inlet-control headwater uses the nomographs / polynomial coefficients of HDS-5 Appendix A, not Ke.
Sizing a crossing? Open the culvert calculator →
· Need the design flow first? NRCS runoff or Rational Method.
Related cheat sheets and tools
Pair Ke with the culvert hydraulics tool and a barrel Manning's n. Get the design discharge from NRCS runoff or the Rational Method, and see the full inlet-vs-outlet worked example. For routing a crossing within a whole watershed model, see HydroComplete.