Delta Hydro Studio
FreemiumVerified
Browser-based hydrology and hydraulics calculators for practising engineers — no install, report-ready output.
Urban Stormwater & InfrastructureActiveRational MethodCulvert Sizing
3 tools · Topic
Rational Method Tools & Calculators
The Rational Method (Q = CiA) is still the default peak-flow estimate for small urban catchments, and nearly every drainage authority accepts it. The tools below implement it as Python packages, spreadsheets and web calculators — several with built-in IDF data and runoff-coefficient libraries, so you can go from catchment area to peak discharge in minutes.
FHWA Hydraulic Toolbox
Gov-Public
A free bundle of FHWA drainage calculators: channels, weirs, curb & gutter, riprap, detention and more.
Hydraulics & River SystemsStableOpen Channel FlowRational Method
HydroCAD
Commercial
The US land-development standard for TR-55/TR-20 hydrographs and detention pond design.
Urban Stormwater & InfrastructureActiveDetention DesignTR-55