Verified Drainage Calculations with Full Methodology
Every result includes step-by-step calculation breakdowns with KaTeX-rendered equations and citations to published standards. Use these tools for preliminary design, checking hand calcs, or quick screening analyses.
What Makes This Different
Methodology Transparency
Every calculator shows the equations used, with step-by-step breakdowns you can follow. No black boxes. Read how we build and verify each tool.
Standard Citations
Results cite the specific standard, manual, or publication used. Know exactly where the method comes from.
Verified Against Examples
Calculations are verified against published textbook examples and standard reference solutions.
Advanced Analysis Tools
These tools go beyond basic sizing into detailed hydrologic and hydraulic analysis.
Flood Frequency Analysis Calculator
Enter annual peak flows to estimate return-period magnitudes with Log-Pearson Type III following USGS Bulletin 17C, optionally alongside a separate Gumbel analysis.
Open CalculatorUSGS Regional Regression Calculator
Enter drainage area and applicable basin characteristics to get an educational, screening-level peak-flow estimate from generalized regional equations; use state-specific USGS publications or StreamStats for design.
Open CalculatorHydrograph Convolution Calculator
Calculate runoff hydrographs using unit hydrograph convolution.
Open CalculatorLevel Pool Routing Calculator
Enter an inflow hydrograph plus stage-storage and stage-discharge data to route a level pool with the Modified Puls method and return the outflow hydrograph, peak attenuation, maximum stage, and storage.
Open CalculatorMuskingum Routing Calculator
Enter an inflow hydrograph, time step, and Muskingum K and X parameters to calculate the routed outflow hydrograph, peak attenuation, and translation time.
Open CalculatorGradually Varied Flow Calculator
Calculate water surface profiles using the Direct Step Method.
Open CalculatorCompound Channel Calculator
Calculate flow in compound channels with multiple subsections using the divided channel method.
Open CalculatorFull Calculator Library by Category
Hydrology (15 calculators)
Hydraulics (24 calculators)
Stormwater BMP (8 calculators)
Standards and References Used
Our calculators implement methods from these authoritative sources. For how each method is selected, implemented, and validated against published examples, see our methodology page.
NRCS TR-55
Urban Hydrology for Small Watersheds
FHWA HEC-22
Urban Drainage Design Manual
FHWA HEC-14
Hydraulic Design of Energy Dissipators
ASCE Manual of Practice
Design and Construction of Urban Stormwater Systems
USGS Bulletin 17C
Flood Frequency Analysis
Manning's Equation
Open channel and pipe flow calculations
SCS Curve Number Method
Runoff estimation for ungauged watersheds
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