// multi-utility computation suite · offline · instant · precise
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sci.flood-frequency-Gumbel Calculator
Calculates flood return period probability using the Gumbel (Type I extreme value) distribution fitted to annual maximum flow data. 100-year flood has 1% annual exceedance probability — it has a 26% chance of occurring at least once in a 30-year design life.
Inputs
Q Mean M3 S
Arithmetic average. Sensitive to outliers — if your data has extreme values, the median may be more representative.
Q Std M3 S
Reference formula or conversion factor shown for context.
Return Period Yr
Time for one complete cycle (s). Period = 1 / frequency. A 50 Hz signal has a 20 ms period.
Results
design flood Q_T (m³/s)
Sample size or count used in the calculation.
Gumbel reduced variate y_T
The value at the specified point or condition.
frequency factor KT
A dimensionless multiplier applied in the calculation.
exceedance probability P = 1/T
Sample size or count used in the calculation.
Q_T = Q̄ + KT·σ
Reference formula or conversion factor shown for context.