Hydrology Calculators
Calculate runoff, generate hydrographs, and analyze watershed response using industry-standard methods from NRCS, USGS, and other authoritative sources.
Runoff Estimation
Calculate peak discharge and runoff volumes for design storms
Rational Method
Calculate peak discharge using Q = CiA for small watersheds (< 200 acres)
SCS Curve Number
Calculate runoff depth using the NRCS curve number method
Runoff Coefficient Lookup
Look up runoff coefficients (C values) for the Rational Method
Modified Rational Method
Find critical storm duration for detention storage design
Time of Concentration
Calculate travel time for runoff to reach the outlet
Hydrograph Analysis
Generate and analyze storm hydrographs for detention design
SCS Unit Hydrograph
Generate storm hydrographs using the SCS dimensionless unit hydrograph
SCS Triangular Hydrograph
Generate simplified triangular hydrographs for quick estimates
Hydrograph Convolution
Apply unit hydrograph convolution to rainfall excess
Rainfall Distribution
Generate SCS Type I, IA, II, and III 24-hour rainfall distributions
Flood Routing
Route hydrographs through channels and reservoirs
Statistical Hydrology
Frequency analysis and regional estimation methods
Learning Resources
Understand the theory behind the calculations
Understanding the Rational Method
When to use Q = CiA and its limitations
Learn more: Understanding the Rational MethodSCS Curve Number Method Explained
How to select curve numbers for different land uses
Learn more: SCS Curve Number Method ExplainedReading Hydrographs
Creating design hydrographs for detention analysis
Learn more: Reading HydrographsLooking for a different type of calculator?
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