What determines whether a culvert is in inlet or outlet control?

Inlet control: flow is controlled by the culvert entrance; discharge depends only on headwater depth and culvert size. Outlet control: full pipe flow; discharge depends on both headwater and tailwater. The actual control is whichever gives the higher required headwater. Per FHWA Hydraulic Design Series No. 5 (HDS-5).

What are typical culvert design headwater ratios?

FHWA HDS-5 recommends headwater-to-diameter (HW/D) ratios of 1.0–1.5 for minimum impact, and up to 2.0 for acceptable backwater. For corrugated metal pipe: n = 0.024; concrete pipe: n = 0.012; HDPE pipe: n = 0.009–0.011 per FHWA HDS-5 Table 3-1.

Culvert Capacity Calculator

Calculate culvert flow capacity for circular and box culverts under inlet and outlet control conditions per FHWA HDS-5 design guidelines.

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How to Use

Enter the values for the patient or scenario you are assessing. Calculate culvert flow capacity for circular and box culverts under inlet and outlet control conditions per FHWA HDS-5 design guidelines. Use the culvert capacity result to inform your clinical assessment.

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Frequently Asked Questions

What determines whether a culvert is in inlet or outlet control?

What are typical culvert design headwater ratios?