{"id":"gauge-catchment-areas","slug":"gauge-catchment-areas","name":"Gauge Catchment Area Dataset","description":"The land area draining to 2,257 United States gauging stations, as their operator assesses it. A small dataset that unlocks a large one: it is the denominator that turns a discharge into a depth of water over the catchment, and so into something comparable with rainfall.","methodology":"Read from the USGS station inventory, which publishes the area from its own basin delineation rather than from any measurement Hydrionis makes. Two areas are published and they are not the same quantity: the topographic drainage area is the land that drains to the gauge at the surface, and the contributing drainage area excludes the part that does not deliver water in an ordinary year — closed depressions, karst losing ground, land above a diversion. Where the publisher distinguishes the two, the contributing area is taken, because it is the denominator that makes a runoff depth mean what it says; which of the two a value reports is recorded on it. Square miles are converted to square kilometres and the publisher unit is recorded alongside.","domains":["river-flow"],"metricIds":["catchment-area"],"subjectScope":"The United States Geological Survey streamgauges Hydrionis holds discharge for","cadence":"irregular","version":"1.0.0","released":"2026-08-31","changelog":[{"version":"1.0.0","date":"2026-08-31","summary":"First release: the denominator annual runoff was waiting for.","additions":["Catchment areas for 2,257 stations, each recording whether it is the topographic or the contributing area."]}],"limitations":["The area is the publisher’s delineation, not a Hydrionis measurement, and different agencies delineate differently. Areas from different publishers should not be assumed to mean the same thing.","A catchment area is a statement with a date, and this one does not have the publisher’s. USGS states the area without saying when the basin was assessed, so the date on each value records when Hydrionis read it. A catchment is redrawn when a survey improves or a transfer scheme moves water between basins.","A contributing area and a topographic area can differ greatly on the same river. Dividing a discharge by the wrong one produces a runoff depth wrong by the ratio between them, which is why each value states which it is.","One station published an area larger than any United States basin and was refused rather than stored."],"observationCount":2257,"seriesCount":2257,"subjectCount":2257,"from":2026,"to":2026,"sourceIds":["usgs-nwis"],"units":["km²"],"redistributable":true,"commerciallyReusable":true,"citation":"Hydrionis (2026), Gauge Catchment Area Dataset, version 1.0.0. Retrieved from https://hydrionis.com/data/datasets/gauge-catchment-areas/","downloads":[{"file":"/downloads/observations-river-flow-usgs-nwis.csv","format":"CSV","label":"river-flow observations from USGS (483,211 rows)"}],"apiPath":"/api/v1/datasets/gauge-catchment-areas.json","lastFetched":"2026-08-31","fields":[{"id":"catchment-area","name":"Catchment area","definition":"The land area draining to a gauging station, as the publisher of that station assesses it.","unit":"km²","nativeGeography":["river-gauge"],"comparabilityNotes":"Catchment areas are not all the same quantity. The topographic area drains to the station on the surface; the contributing area excludes parts that do not deliver water to it in an ordinary year — closed depressions, karst losing ground, land above a diversion. On many rivers the two agree and on some they differ greatly, and dividing a discharge by the wrong one produces a runoff depth that is wrong by that ratio. Which figure a value reports is recorded on it. An area is also a statement of its own date: a catchment is redrawn when a survey improves or a transfer scheme moves water between basins."}]}