River Flow Regime Dataset

What this looks like

One real series from the dataset, and real rows from the head of its published extract. Neither is a mock-up: the rows below are the same rows, unchanged, that are in the file you would download.

Sample rows

12 of 10,355,335 rows Taken from the start of observations-river-flow-fi-syke-hydrologia.csv. These are sample rows, not the dataset.

Sample rows from the River Flow Regime Dataset extract
`metric_id`	`subject_id`	`subject_kind`	`value`	`censored`	`censor_operator`	`censor_threshold`	`censor_limit`	`censor_reported`	`unit`	`period_start`	`period_end`	`period_kind`	`basis`	`confidence`	`source_id`	`source_ref`	`qualifier`	`superseded`	`retrieved`
river-flow-mean	fi-syke-0100150	geography	5	—	—	—	—	—	m³/s	1959-01-01	1959-01-01	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	7.8	—	—	—	—	—	m³/s	1959-01-02	1959-01-02	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	7.8	—	—	—	—	—	m³/s	1959-01-03	1959-01-03	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	7	—	—	—	—	—	m³/s	1959-01-04	1959-01-04	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	7.1	—	—	—	—	—	m³/s	1959-01-05	1959-01-05	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	6.3	—	—	—	—	—	m³/s	1959-01-06	1959-01-06	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	6.7	—	—	—	—	—	m³/s	1959-01-07	1959-01-07	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	6.8	—	—	—	—	—	m³/s	1959-01-08	1959-01-08	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	6.6	—	—	—	—	—	m³/s	1959-01-09	1959-01-09	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	5.8	—	—	—	—	—	m³/s	1959-01-10	1959-01-10	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	7.2	—	—	—	—	—	m³/s	1959-01-11	1959-01-11	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26
river-flow-mean	fi-syke-0100150	geography	6.4	—	—	—	—	—	m³/s	1959-01-12	1959-01-12	day	measured	high	fi-syke-hydrologia	0100150	—	—	2026-08-26

Download these rows as CSV — the same twelve, with the column header, for testing a loader before committing to the full file.

Methodology

The duration curve is the gauge’s entire daily record sorted from largest to smallest: Q95 is the discharge equalled or exceeded on 95% of days, which is the standard low-flow measure used in abstraction licensing and environmental flow assessment; Q50 is the median, which on most rivers sits well below the mean because a few days of flood carry a large share of the year’s water; Q10 describes a high but unexceptional day. A curve is drawn only from a record of at least five years that holds at least nine tenths of the days between its first reading and its last, because a curve assumes the days held are a fair sample of the days that happened — an assumption that fails exactly where it matters if a gauge was out of service through a drought. The annual maximum is the largest daily mean within an October-to-September water year, produced only where the year holds at least 355 days with no absent run longer than five, since the largest day of a year nobody read is simply not in the record. Gauges whose discharge is signed — the sluices, locks and pumping stations where a negative value means water moving in reverse — are excluded from all of it, because a duration curve of a managed structure describes the operating regime rather than the river.

What this dataset cannot tell you

Read before relying on these figures

The annual maximum here is the largest daily *mean*, not the instantaneous peak. A flood peak lasting hours is averaged across twenty-four, so this figure sits below the true peak on the same day — slightly on a large slow river, far below on a small fast-responding catchment. It is not a flood peak series and flood frequency analysis needs the publisher’s own instantaneous maxima, which Hydrionis does not yet hold.
A duration curve belongs to the span it was drawn over. It moves as a record lengthens, and one covering a run of years without a drought puts Q95 too high — which matters, because Q95 is the number abstraction licences are set against.
Flow 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, and none of these figures may be attributed to the river.
Rating curves are extrapolated at extreme discharges, so the largest values carry the largest measurement uncertainty. That applies to Q10 and to every annual maximum.
Coverage follows the daily records Hydrionis holds, which are Nordic. This is not a European or global picture of low flow, and the absence of a gauge is an absence of daily data rather than an absence of a river.

Coverage

Subjects	The gauging stations Hydrionis holds at least five years of daily discharge for, which today are in Sweden and Finland — 1,252 held
Period	1847–2024
Units	m³/s
Update cadence	Irregularly, when the publisher releases
Identifier	`river-flow-regime` v1.0.0

Fields

Data dictionary →

Every metric this dataset carries, with the unit it is stored in and the geography level it is reported at. Full definitions are in the data dictionary.

Identifier	Field	Unit	Reported at
`river-flow-q95`	Q95 low flow The flow exceeded 95% of the time — a standard measure of low-flow conditions.	m³/s	river-gauge
`river-flow-q50`	Q50 median flow The flow exceeded half of the time — the middle of the flow duration curve.	m³/s	river-gauge
`river-flow-q10`	Q10 high flow The flow exceeded 10% of the time — the wet end of the flow duration curve, describing a high but not exceptional day.	m³/s	river-gauge
`river-flow-annual-max-daily`	Annual maximum daily flow The highest daily mean discharge recorded at a gauging station in a water year.	m³/s	river-gauge

Rights and access

Licence position

Open with attribution. Derivative use true; redistribution true; commercial reuse true.

Permitted uses

Public display
Derived analysis
API delivery
Bulk download
Commercial use

Available to: Public, Developer, Research, Professional, Enterprise. These follow from the rights of the contributing publishers, not from a Hydrionis pricing decision — no access tier can widen what a publisher withheld.

Contributing sources

Attribution and citation

Cite and reuse →

Two different obligations, deliberately kept apart. One is a condition of somebody else's licence; the other is a request Hydrionis has no standing to enforce.

Attribution you are required to give

These are conditions of the licences the underlying data is published under. They are obligations to the publishers, not to Hydrionis, and they apply to you directly whether or not you mention Hydrionis at all.

Contains data from the Finnish Environment Institute (Syke), licensed under CC BY 4.0. Data from Sveriges meteorologiska och hydrologiska institut, used under CC BY 4.0.

Suomen ympäristökeskus (Finnish Environment Institute) — CC BY 4.0 (licence text)
Sveriges meteorologiska och hydrologiska institut — CC BY 4.0 (licence text)

Suggested citation for Hydrionis

Hydrionis (2026), River Flow Regime Dataset, version 1.0.0, accessed 2026-09-02, hydrionis.com/data/datasets/river-flow-regime/

Cite Hydrionis where you rely on values Hydrionis computed, on the method that produced them, or on the compilation itself. The underlying measurements remain the publishers’ and their attribution requirements apply to you directly.

Recommended, not required. Hydrionis does not claim rights over unmodified public data it relayed, and doing arithmetic on somebody else’s measurements does not make them Hydrionis’s. Cite the version and the access date: River Flow Regime Dataset changes as publishers release and as methods are revised, and a citation without both cannot be checked later. Full guidance is on cite and reuse.

Changelog

Version 1.0.0 — 2026-08-31

First release: flow duration curves and annual maxima from the daily records.

Method version: flow-duration-percentile 1.0.0, annual-maximum-of-daily 1.0.0

Additions

Q95, Q50 and Q10 for every gauge with a long enough and dense enough daily record.
Annual maximum daily flow by water year, so a winter flood belongs to one year rather than being split across two.

Use this data

Every bulk extract ships with a companion metadata file carrying this dataset’s version, its sources, their licences, the attribution you are required to give and the suggested citation — so the terms travel with the file rather than staying on this page.

About this data

The fields a professional user needs to judge whether this is fit for a particular purpose. Deliberately not a score.

About this data

Everything below is a property of the data rather than a rating of it. There is deliberately no single confidence score: how much a gap matters depends on what you are about to do with the series, and only you know that.

Source	Suomen ympäristökeskus (Finnish Environment Institute) — Hydrologiarajapinta — Finnish national hydrological archive · CC BY 4.0 Sveriges meteorologiska och hydrologiska institut — Swedish hydrological observations · CC BY 4.0
How the values came to exist	Derived Computed by Hydrionis
Period held	1847–2024
Known gaps	The annual maximum here is the largest daily mean, not the instantaneous peak. A flood peak lasting hours is averaged across twenty-four, so this figure sits below the true peak on the same day — slightly on a large slow river, far below on a small fast-responding catchment. It is not a flood peak series and flood frequency analysis needs the publisher’s own instantaneous maxima, which Hydrionis does not yet hold. A duration curve belongs to the span it was drawn over. It moves as a record lengthens, and one covering a run of years without a drought puts Q95 too high — which matters, because Q95 is the number abstraction licences are set against. Flow 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, and none of these figures may be attributed to the river.
Continuity	Version 1.0.0, released 2026-08-31. 1 recorded version; breaking changes and corrections are listed in the changelog above.
Last read from the publisher	not recorded · publisher updates irregularly, when the publisher releases
Redistribution	Permitted by the upstream licences
Commercial reuse	Permitted by the upstream licences. No Hydrionis access tier can widen this.
Methodology	How this was produced