{"id":"us-reservoir-operations","slug":"us-reservoir-operations","name":"Reclamation Reservoir Operations Dataset","description":"Monthly storage, water level, inflow and release for the federal reservoirs of the western United States, including Lake Mead and Lake Powell, whose decline is the Colorado River shortage. Where the Geological Survey record says what is in a reservoir, this says how it is being operated.","methodology":"Aggregated by Hydrionis from the daily values published by the Bureau of Reclamation. Storage is published in acre-feet and converted to millions of cubic metres using the exact definition of the acre-foot; elevations are converted from feet, and inflow and release from cubic feet per second. A month is published only where at least twenty days of record exist. Reservoirs need twenty years of record, and at most twenty-five are taken from each Reclamation region. Inflow and release are taken only where the publisher states them as a rate: the same quantities are also published as daily volumes in acre-feet, which are a different measurement, and those series are left alone rather than divided by a day length the publisher did not state.","domains":["reservoir"],"metricIds":["reservoir-storage-volume","reservoir-water-level","reservoir-inflow","reservoir-release"],"subjectScope":"Bureau of Reclamation reservoirs with 20+ years of record, capped at twenty-five per Reclamation region","cadence":"monthly","version":"1.0.0","released":"2026-09-01","changelog":[{"version":"1.0.0","date":"2026-09-01","summary":"First release. Adds the operated western reservoirs, and with them reservoir water level, inflow and release as measures Hydrionis holds for the first time.","additions":["Monthly storage, water level, inflow and release for federal reservoirs of the western United States."]}],"limitations":["No percentage full is published, because no capacity is. The Bureau publishes what is in each reservoir but not what it holds when full — of the 782 quantities in its catalogue, the only ones named capacity are the generating capacity of the powerplants — so the denominator does not exist and is not invented.","Water levels are elevations against each operator’s own datum, and those datums are not a common surface: Lake Mead is published against a local datum established at Hoover Dam in 1912. Levels are comparable within one reservoir’s record and never between reservoirs.","A level is not a proxy for storage. The same one-metre fall releases far more water from a full reservoir, where the surface is wide, than from a nearly empty one.","Inflow is usually inferred from the change in storage and what was released rather than gauged, so it carries the errors of both and can be negative where the balance does not close.","A release is an operating decision rather than a catchment response, and is not the natural flow of the river below the dam.","Reservoir storage is managed as well as observed: a drawdown may record a flood-control rule curve or a scheduled release rather than a shortage."],"observationCount":222763,"seriesCount":273,"subjectCount":91,"from":1905,"to":2026,"sourceIds":["us-bureau-reclamation"],"units":["Mm³","m","m³/s"],"redistributable":true,"commerciallyReusable":true,"citation":"Hydrionis (2026), Reclamation Reservoir Operations Dataset, version 1.0.0. Retrieved from https://hydrionis.com/data/datasets/us-reservoir-operations/","downloads":[{"file":"/downloads/observations-reservoir-us-bureau-reclamation.csv","format":"CSV","label":"reservoir observations from USBR (223,788 rows)"}],"apiPath":"/api/v1/datasets/us-reservoir-operations.json","lastFetched":"2026-09-01","fields":[{"id":"reservoir-storage-volume","name":"Reservoir stored volume","definition":"Volume of water held in a reservoir at a given time.","unit":"Mm³","nativeGeography":["reservoir-site"],"comparabilityNotes":"Storage is strongly seasonal and is managed, not merely observed: an operator drawing a reservoir down for flood control produces the same reading as a drought would. A month should be compared with the same month in other years, and a fall in storage should not be read as a supply signal without knowing the operating rule."},{"id":"reservoir-water-level","name":"Reservoir water level","definition":"Elevation of the water surface in a reservoir, above the datum the operator uses.","unit":"m","nativeGeography":["reservoir-site"],"comparabilityNotes":"Each reservoir’s level is measured against the datum its operator uses, and those datums are not a common surface: some are national levelling datums, and some are local references established at the dam itself. Two reservoirs reading the same elevation are not at the same height, and the difference between two datums can be larger than the drawdown being described. Read a level against that reservoir’s own record, never against another reservoir’s, and never subtract one reservoir’s level from another’s."},{"id":"reservoir-inflow","name":"Reservoir inflow","definition":"Rate at which water enters a reservoir from its catchment.","unit":"m³/s","nativeGeography":["reservoir-site"],"comparabilityNotes":"Inflow is commonly derived from the storage change rather than gauged, so it inherits every error in the storage record and can be negative on days when the balance does not close. Compare a month against the same month in other years at the same reservoir."},{"id":"reservoir-release","name":"Reservoir release","definition":"Rate at which water is released from a reservoir to the river below it.","unit":"m³/s","nativeGeography":["reservoir-site"],"comparabilityNotes":"A release is an operating decision, not a catchment response, and must not be read as the natural flow of the river below the dam. Where a publisher reports releases through separate outlets, a total is not the sum of the ones Hydrionis happens to hold."}]}