Flowpath Engineering Portal
FHWA HDS-5 Culvert Design and Analysis
Size road culverts with inlet/outlet control headwater, tailwater effects, water surface profiles, outlet velocity, and roadway overtopping checks.
What this tool does
Inlet and outlet control
Headwater from the governing HDS-5 control: inlet-control nomograph equations and full outlet-control energy balance with entrance, friction, and exit losses.
Circular and box culverts
Analyse single or multi-barrel circular and rectangular concrete culverts with standard headwall and wingwall inlet configurations.
Water surface profiles
Direct-step backwater and drawdown profiles through partially full barrels, with critical depth, normal depth, and flow regime classification.
Tailwater and overtopping
Fixed tailwater level or downstream channel rating, plus roadway overtopping as a broad-crested weir with flow split iteration.
Design levels and diagram
Work directly in engineering RLs for inverts, road crest, and tailwater, with a longitudinal section showing the road, culvert, headwater, and computed water surface.
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Open Culvert Hydraulic CalculatorPart of the Flowpath Engineering suite of free civil engineering tools for New Zealand.