The monitoring network within this area

Hydrionis holds 1,640 values from 2 gauges within it. Discharge is a property of a gauge and its reach, not of this drainage area, so this page reports the network and its records rather than a single figure.

2

Gauges

1,640

Values held

1908–2026

Record spans

Gauges within the Lower Flathead huc8 subbasin

2 monitoring points, positioned as the publisher records them.

Flood peaks, as measured

This gauge's flood record, as measured. Unlike a daily mean it is the discharge at the moment the river was highest, which is the figure flood frequency analysis is built on.

Largest measured flow of each year at Flathead River near Polson MT

The highest instantaneous discharge the publisher recorded in each year — a flood peak as measured, not a daily average of one. 1908–2024.

Show relevant events (1 event)Shading marks when something was recorded, not what caused the line.

Published by the gauge's own operator from its sub-daily record; Hydrionis stores the figure rather than recomputing it. A year the gauge did not cover produces no value rather than a low one, and the gaps are stated below the chart. A peak is a property of this gauge and its reach: a larger flood upstream or downstream of it is not in this series.

What the shaded periods are (1 event)

A shaded period marks when something was recorded, not what caused the shape of the line. Where the two coincide, they coincided.

Documented record — A documented event, compiled from cited sources after it happened. The dates are as good as the record, which for older events can mean the month rather than the day.

Event	Type	Period	Standing	Authority
Hurricane Katrina water and sanitation collapse	Flood	2005-08-29 – 2005-09-30	Documented record	Compiled record

Not shown on this chart

The 1976 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
The 2022 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Yorkshire drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Cantareira water crisis, São Paulo — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Cape Town Day Zero — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
European drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.

View the data behind this chart

Underlying data
Period	Flathead River near Polson MT (m³/s)
1908	1,758
1909	1,665
1910	1,212
1911	1,252
1912	1,034
1913	2,135
1914	1,161
1915	595
1916	2,115
1917	1,674
1918	1,654
1919	1,365
1920	1,252
1921	1,756
1922	1,597
1923	1,583
1924	1,331
1925	1,897
1926	830
1927	2,124
1928	2,345
1929	1,288
1930	898
1931	1,002
1932	1,467
1933	2,212
1934	1,478
1935	1,422
1936	1,441
1937	1,014
1938	1,393
1939	1,300
1940	1,087
1941	629
1942	1,515
1943	1,396
1944	694
1945	1,654
1946	1,430
1947	1,603
1948	2,073
1949	1,458
1950	1,897
1951	1,892
1952	1,184
1953	1,645
1954	1,679
1955	1,396
1956	1,648
1957	1,382
1958	1,744
1959	1,577
1960	1,557
1961	1,563
1962	1,116
1963	1,356
1964	1,892
1965	1,597
1966	1,297
1967	1,382
1968	1,266
1969	1,147
1970	1,254
1971	1,325
1972	1,552
1973	442
1974	1,668
1975	1,563
1976	1,062
1978	915
1979	1,028
1980	1,750
1981	1,410
1982	1,495
1983	1,085
1984	1,116
1985	1,000
1986	1,246
1987	668
1988	391
1989	892
1990	1,203
1991	1,424
1992	394
1993	991
1995	1,563
1996	1,325
1997	1,614
1998	1,107
1999	991
2000	821
2001	527
2002	1,453
2003	776
2004	660
2005	1,371
2006	1,390
2007	940
2008	1,254
2009	688
2010	1,008
2011	1,481
2012	1,589
2013	1,144
2014	1,444
2015	708
2016	858
2017	1,339
2018	1,407
2019	663
2020	1,246
2021	824
2022	1,594
2023	719
2024	719

About this series

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	United States Geological Survey — National Water Information System · US Government work — public domain
How the values came to exist	Measured
Period held	1908–2024
Completeness	98.3% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	2 separate periods inside 1908–2024 hold no value. They are drawn as breaks in the line and are never interpolated across.
Continuity	The record begins in 1908 and is not continuous from it: 117 years separate the first value from the last, and 98% of the years between them are held. The span is not the record.
Last read from the publisher	2026-10-01
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

How much of the rain came back out

A discharge in cubic metres per second cannot be compared with anything: the larger number may only mean the larger catchment. Divided by the area draining to the gauge it becomes a depth of water over that land, which answers a question a reader already has — of the rain that fell here, how much came back out as river?

Water leaving the catchment above Flathead River near Polson MT, as a depth

The year's flow spread over the land draining to this gauge, in millimetres — the same unit rainfall is measured in. 1939–2024.

Show relevant events (1 event)Shading marks when something was recorded, not what caused the line.

Computed by Hydrionis from the published annual mean flow and the catchment area the station's own publisher states. It is not a water balance: the difference between rainfall and runoff is not evaporation alone but also change in groundwater storage, water abstracted and taken elsewhere, and water imported by transfer schemes — which is why a catchment can yield more runoff than the rain that fell on it without anything being measured wrongly. A different area figure rescales every value here by the ratio between them.

What the shaded periods are (1 event)

A shaded period marks when something was recorded, not what caused the shape of the line. Where the two coincide, they coincided.

Documented record — A documented event, compiled from cited sources after it happened. The dates are as good as the record, which for older events can mean the month rather than the day.

Event	Type	Period	Standing	Authority
Hurricane Katrina water and sanitation collapse	Flood	2005-08-29 – 2005-09-30	Documented record	Compiled record

Not shown on this chart

The 1976 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
The 2022 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Yorkshire drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Cantareira water crisis, São Paulo — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Cape Town Day Zero — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
European drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.

View the data behind this chart

Underlying data
Period	Flathead River near Polson MT (mm)
1939	493
1940	333
1941	300
1942	490
1943	670
1944	276
1945	433
1946	614
1947	701
1948	636
1949	504
1950	758
1951	771
1952	526
1953	476
1954	691
1955	559
1956	721
1957	532
1958	424
1959	849
1960	614
1961	630
1962	557
1963	492
1964	676
1965	750
1966	602
1967	624
1968	540
1969	645
1970	520
1971	706
1972	701
1973	411
1974	814
1975	603
1976	640
1977	370
1978	556
1979	513
1980	447
1981	621
1982	567
1983	552
1984	479
1985	544
1986	512
1987	423
1988	386
1989	528
1990	664
1991	737
1992	406
1993	492
1994	377
1995	493
1996	810
1997	791
1998	462
1999	536
2000	497
2001	267
2002	592
2003	407
2004	476
2005	515
2006	604
2007	508
2008	593
2009	451
2010	511
2011	837
2012	716
2013	572
2014	695
2015	492
2016	537
2017	677
2018	658
2019	403
2020	560
2021	470
2022	632
2023	355
2024	417

About this series

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	United States Geological Survey — National Water Information System · US Government work — public domain
How the values came to exist	Derived Computed by Hydrionis
Period held	1939–2024
Completeness	100.0% of the periods in that span are held.
Continuity	Continuous: every year from 1939 to 2024 is held.
Inputs last read	2026-10-01 · when the records this was computed from were last read from their publishers
Calculation date	2026-08-24 · when the calculation method was last versioned, not a reading of any publisher
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

The snow standing above this water

3 automated snow stations sit inside this drainage area, weighing the snowpack rather than measuring how deep it is.

1,742

Fullest snowpack recorded at North Fork Jocko, in 1997 (mm of water)

677

Thinnest, in 2024 (mm of water)

April

Month the pack is usually at its fullest

July

Month the pack has gone by, in half of years

Peak snowpack at North Fork Jocko

Water years 1990–2026. Each point is the fullest month of that snow season.

A water year runs October to September and is named for the year it ends, so the snow of one winter stays in one point. The value is the fullest month, not the fullest day: a pack that peaked sharply mid-month reads lower here than a single measurement taken at the right moment would.

View the data behind this chart

Underlying data
Period	North Fork Jocko (mm)
1990	1,075
1991	1,413
1992	898
1993	900
1994	835
1995	784
1996	1,323
1997	1,742
1998	854
1999	1,269
2000	1,062
2001	815
2002	1,466
2003	1,055
2004	959
2005	709
2006	1,242
2007	855
2008	1,180
2009	1,123
2010	884
2011	1,586
2012	1,153
2013	1,081
2014	1,358
2015	886
2016	916
2017	968
2018	1,600
2019	823
2020	1,219
2021	914
2022	1,157
2023	1,068
2024	677
2025	1,160
2026	942

Read against the river

North Fork Jocko and Flathead River near Polson MT both sit in this drainage area, and their records overlap by 35 years. That is the span the two have in common, not a count of years both actually hold — either record may have gaps inside it. The two are shown separately rather than on one axis: millimetres of stored water and cubic metres per second are not commensurable, and a difference between them would mean nothing.

Being in the same drainage area does not put the snowpack upstream of the gauge. A subbasin is an area, and snow on one tributary can join the river below a gauge on another — so a weak relationship here may say more about which tributary was measured than about the snow.

Every gauge Hydrionis holds within this area

Gauges within the Lower Flathead and what each holds
Gauge	Measures	Values	Record
Flathead River near Polson MT	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	326	1908–2026
Big Knife Creek near Arlee MT	catchment area, annual maximum river flow	30	1982–2026

How these gauges were attached to this water

Assigned by the publisher to a numbered basin Every gauge here is assigned to this drainage area by its own publisher, which issues the area an official code — 17010212. A drainage area is not a river: it contains the tributaries as well as the main channel, and a gauge in it may be on any of them.

What each gauge’s link to this water rests on
Gauge	Evidence	Established
Flathead River near Polson MT	Stated by the publisher — USGS site service, huc_cd field — https://waterservices.usgs.gov/nwis/site/ ; named from the USGS Watershed Boundary Dataset 8-digit HU (Subbasin) layer — https://hydro.nationalmap.gov/arcgis/rest/services/wbd/MapServer/4	2026-10-02
Big Knife Creek near Arlee MT	Stated by the publisher — USGS site service, huc_cd field — https://waterservices.usgs.gov/nwis/site/ ; named from the USGS Watershed Boundary Dataset 8-digit HU (Subbasin) layer — https://hydro.nationalmap.gov/arcgis/rest/services/wbd/MapServer/4	2026-10-02

What this record holds

Hydrionis decides which waters get a page, and which of those are offered to search, from what is actually held rather than from how the page reads. Five signals are counted; this record has 4 of them, which makes it a full profile.

Information-gain signals held for this water body
Signal	Held	Counts
Gauges holding a real record	1	no
Years spanned	119	yes, 20 or more
Values held	1,640	yes, 1000 or more
Distinct measurements	6	yes, 2 or more
Publishers measuring it	2	yes, 2 or more
Official identifiers	1	recorded, not counted

Use this data

Machine-readable JSON /api/v1/observations/by-subject/gauge-usgs-12372000.json
How to cite this, and who you must credit
How these figures were produced
Request this at a different scale, format or geography

No bulk download is offered here, which is a licence position rather than a product one: at least one contributing publisher does not permit redistribution. The values can be read on the page, cited, and pointed to at source.

Attribution and citation

Suggested citation for Hydrionis

Hydrionis (2026), Lower Flathead gauge records, accessed 2026-10-05, hydrionis.com/waters/united-states-lower-flathead/

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: the Lower Flathead gauge records 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.

None of the contributing licences requires attribution. Crediting the publishers is still good practice and they are listed above.

Where these figures come from

MeasuredHigh confidence2024-06-14

Source: USGS — National Water Information System, USGS site 12372000, annual peak streamflow. Licence: Open.

Method: The instantaneous maximum discharge of each water year as published by USGS, dated to the day it occurred. One value per October-to-September water year; where the publisher lists both a systematic and a historic peak for a year, the larger is the annual maximum. Values the publisher marks as maximum daily averages are not held here, because they are not instantaneous peaks. Values marked as bounded rather than measured are held as censored observations carrying the bound. Cubic feet per second are converted to cubic metres per second and the publisher unit is recorded alongside.

Rating curves are extrapolated at extreme discharges, so the largest values in a peak series carry the largest measurement uncertainty. Data from the U.S. Geological Survey National Water Information System, a work of the United States government and therefore in the public domain.

Retrieved 1 October 2026.