Log‑Pearson III Flood Frequency Tool

Quick‑check Log‑Pearson Type III analysis for annual peak flows: computes log‑space mean, standard deviation, skew, and approximate design discharges for selected return periods using a Cornish‑Fisher‑style frequency factor expansion. Units: any consistent flow units (m³/s, cfs, etc.).

1. Data & Options Annual Peaks & Skew

Paste annual peak discharges below (one value per line, or separated by spaces / commas). The tool uses base‑10 logarithms (Log‑Pearson III) and an approximate frequency factor formula; for regulatory work, always cross‑check against your official procedures (e.g. Bulletin 17, regional tools).
Positive values only. Units are arbitrary but must be consistent (e.g. all in m³/s or all in cfs).
Label is cosmetic only; calculations are dimensionless in log‑space.
Comma‑separated values. The tool assumes T‑year event corresponds to non‑exceedance probability p = 1 − 1/T.
Used only in the summary and exports.
Many guidelines recommend a weighted combination of station skew and regional skew. This tool applies a simple choice: either the sample skew or a user‑specified skew value for design purposes.
Log‑space mean & σ Sample skew G Approx. frequency factors K(T) Design Q(T) table