{"id":"us-flood-peaks","slug":"us-flood-peaks","name":"United States Flood Peak Dataset","description":"The instantaneous maximum discharge of each water year at 2,236 long-record United States gauging stations, dated to the day it happened, from 1867 onward. This is the annual maximum series flood estimation rests on — the true peak, not the average of the day containing it.","methodology":"Collected from the USGS peak streamflow service, which publishes one instantaneous maximum per water year for each station together with the codes that qualify it. Those codes decide what may be held. A peak the publisher marks as itself a maximum daily average is not an instantaneous peak and is not held under this measure, because a daily average is systematically smaller than the peak of the same day and a series mixing the two understates every flood it covers. A peak marked as bounded rather than measured — the discharge known only to be above or below a figure, because backwater or an out-of-range stage made it unmeasurable — is held as a censored observation carrying that bound rather than as a number nobody measured. Peaks the publisher marks as estimates are held, because an estimated peak is its best account of a real flood, and the qualification travels with the series. Where a water year lists more than one peak, the larger is that year’s maximum. A peak dated to an unknown day is not held, because placing it on the first of the month would be inventing the date of a flood. Cubic feet per second are converted to cubic metres per second and the publisher unit is recorded alongside.","domains":["river-flow"],"metricIds":["river-flow-annual-max"],"subjectScope":"United States Geological Survey streamgauges whose daily discharge record opens before 1930 and spans at least fifty years","cadence":"annual","version":"1.0.0","released":"2026-08-31","changelog":[{"version":"1.0.0","date":"2026-08-31","summary":"First release: the instantaneous annual maximum series.","additions":["175,008 instantaneous annual peaks at 2,236 stations, each dated to the day it occurred.","Peaks the publisher bounds rather than measures are held as censored observations carrying the bound."]}],"limitations":["Rating curves are extrapolated at extreme discharges, so the largest value in a peak series carries the largest measurement uncertainty. That is inherent to the measurement and applies to every published annual maximum series, not to this one particularly.","A peak belongs to a gauge on a reach, never to a river as a whole. Two gauges on the same river can differ by an order of magnitude.","This is not a flood frequency analysis and Hydrionis publishes no return periods. A return period is a statistical claim requiring a stated distribution, a stated fitting method and a sample long enough to support both, and presenting one without those would put a confident number on the least certain part of the record.","Some peaks are affected by regulation, diversion or dam failure, and some occurred before the station was operated systematically. The publisher’s codes record this; a peak series is a record of what happened at a gauge, not of what a natural catchment would have produced.","Coverage is the United States. The absence of a gauge elsewhere is an absence of collected peak data rather than an absence of floods."],"observationCount":175008,"seriesCount":2236,"subjectCount":2236,"from":1806,"to":2025,"sourceIds":["usgs-nwis"],"units":["m³/s"],"redistributable":true,"commerciallyReusable":true,"citation":"Hydrionis (2026), United States Flood Peak Dataset, version 1.0.0. Retrieved from https://hydrionis.com/data/datasets/us-flood-peaks/","downloads":[{"file":"/downloads/observations-river-flow-usgs-nwis.csv","format":"CSV","label":"river-flow observations from USGS (483,211 rows)"}],"apiPath":"/api/v1/datasets/us-flood-peaks.json","lastFetched":"2026-08-31","fields":[{"id":"river-flow-annual-max","name":"Annual maximum river flow","definition":"The highest instantaneous discharge recorded at a gauging station in a water year.","unit":"m³/s","nativeGeography":["river-gauge"],"comparabilityNotes":"The annual maximum series is the basis of flood frequency analysis. It belongs to a specific gauge on a specific reach, and cannot be attributed to a river as a whole. Rating curves are extrapolated at extreme flows, so the largest values carry the largest uncertainty."}]}