Avalon Reservoir — storage

Storage now, against this reservoir's own record

4.40 Mm³

Stored, September 2026

93rd

Percentile among 59 Seps on record

+95.4%

Against the Sep 1991–2020 average

+44.2%

Change over the 12 months to 2026-09

Storage in September 2026 was higher than almost every other Sep on record, ranked against 59 other Seps held for this reservoir.

Storage, 1965–2026

Monthly mean storage

715 monthly values, 1965 to 2026

Monthly means of the publisher's daily record. Volume, not percentage of capacity — see below for why.

What the shaded periods are (0 events)

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

240 of 715 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 715 would be longer than this page and unusable with a screen reader.
Period	Avalon Reservoir (Mm³)
October 1965	0.184
January 1966	1.96
April 1966	1.54
July 1966	1.12
October 1966	2.13
January 1967	5.10
April 1967	1.43
July 1967	3.50
October 1967	1.50
January 1968	3.71
April 1968	2.01
July 1968	3.05
October 1969	3.76
January 1970	6.13
April 1970	2.08
July 1970	2.32
October 1970	1.34
January 1971	4.37
April 1971	1.44
July 1971	0.973
October 1971	0.995
January 1972	2.80
April 1972	0.999
July 1972	0.842
October 1972	1.32
January 1973	6.02
April 1973	1.25
July 1973	1.74
October 1973	1.05
January 1974	2.89
April 1974	1.23
July 1974	0.855
October 1974	6.45
January 1975	6.25
April 1975	2.35
July 1975	1.43
October 1975	1.31
January 1976	3.30
April 1976	1.88
July 1976	0.901
September 1976	3.48
December 1976	4.01
March 1977	4.53
June 1977	1.48
September 1977	1.89
December 1977	2.45
March 1978	3.03
June 1978	2.38
September 1978	2.58
December 1978	5.98
March 1979	6.07
June 1979	5.35
September 1979	1.27
March 1980	3.74
June 1980	1.12
September 1980	2.73
December 1980	4.38
March 1981	5.22
June 1981	1.68
September 1981	1.48
December 1981	2.56
March 1982	2.52
June 1982	1.35
September 1982	1.33
December 1982	2.18
March 1983	3.16
June 1983	1.05
September 1983	1.20
December 1983	3.42
March 1984	2.04
June 1984	1.48
September 1984	1.43
December 1984	4.01
March 1985	3.92
June 1985	1.37
September 1985	1.74
December 1985	3.74
March 1986	2.07
June 1986	3.04
September 1986	2.51
December 1986	5.55
March 1987	5.75
June 1987	5.94
September 1987	1.73
December 1987	3.89
March 1988	3.40
June 1988	1.38
September 1988	2.16
December 1988	0.128
March 1989	0.837
June 1989	1.18
September 1989	1.21
December 1989	1.70
March 1990	2.77
June 1990	1.27
September 1990	1.02
December 1990	1.72
March 1991	2.76
June 1991	1.18
September 1991	3.00
December 1991	1.33
March 1992	2.94
June 1992	5.43
September 1992	1.32
December 1992	2.00
March 1993	1.74
June 1993	1.25
September 1993	1.37
December 1993	1.22
March 1994	0.447
June 1994	1.29
September 1994	1.32
December 1994	0
March 1995	2.13
June 1995	1.34
September 1995	1.63
December 1995	0
March 1996	2.03
June 1996	1.09
September 1996	3.92
November 1996	0.979
February 1997	3.26
May 1997	1.18
August 1997	1.59
November 1997	1.37
February 1998	3.86
May 1998	1.67
August 1998	1.88
November 1998	1.77
February 1999	4.59
May 1999	1.22
August 1999	1.38
November 1999	0.146
February 2000	1.01
May 2000	1.32
August 2000	1.52
November 2000	2.05
February 2001	3.94
May 2001	1.51
August 2001	1.56
November 2001	1.79
February 2002	3.19
May 2002	1.36
August 2002	1.50
November 2002	2.95
February 2003	0.159
May 2003	1.58
August 2003	1.94
November 2003	2.00
February 2004	3.10
May 2004	1.73
August 2004	2.90
November 2004	2.32
February 2005	4.33
May 2005	1.52
August 2005	1.94
November 2005	2.09
February 2006	3.11
May 2006	1.75
August 2006	1.55
January 2007	2.75
April 2007	1.67
July 2007	1.54
October 2007	1.45
January 2008	2.75
April 2008	1.40
July 2008	1.72
October 2008	1.69
January 2009	3.02
April 2009	1.45
July 2009	1.52
October 2009	1.33
January 2010	3.13
April 2010	2.01
July 2010	2.52
October 2010	1.55
January 2011	2.62
April 2011	1.56
July 2011	1.61
October 2011	1.61
January 2012	3.04
April 2012	1.81
July 2012	2.24
October 2012	1.96
January 2013	3.35
April 2013	3.00
July 2013	2.46
October 2013	5.40
January 2014	3.78
April 2014	2.39
July 2014	2.27
October 2014	3.84
January 2015	4.11
April 2015	1.72
July 2015	3.67
October 2015	3.98
January 2016	5.62
April 2016	2.41
July 2016	2.08
October 2016	1.51
December 2016	2.47
March 2017	3.34
June 2017	2.44
September 2017	2.39
December 2017	0
March 2018	3.51
June 2018	2.22
September 2018	2.80
December 2018	0
March 2019	1.90
June 2019	2.64
September 2019	2.35
December 2019	0
March 2020	5.01
June 2020	2.24
September 2020	1.49
December 2020	1.93
March 2021	3.08
June 2021	1.62
September 2021	3.87
December 2021	2.50
March 2022	3.48
June 2022	1.81
September 2022	1.49
December 2022	0.0080
March 2023	0.907
June 2023	1.40
September 2023	1.65
December 2023	2.00
March 2024	2.99
June 2024	1.68
September 2024	3.23
December 2024	3.10
March 2025	4.41
June 2025	2.97
September 2025	3.05
December 2025	3.26
March 2026	3.33
June 2026	4.31
September 2026	4.40

The reservoir's year

Seasonal storage profile

Each calendar month's reference average, against the most recent year

1991–2020 average
Most recent 12 months

Twelve separate averages, one per calendar month. A January average describes Januaries only. Months are plotted 1–12.

View the data behind this chart

Underlying data
Period	1991–2020 average (Mm³)	Most recent 12 months (Mm³)
Jan	2.32	3.42
Feb	2.99	3.55
Mar	3.05	3.33
Apr	1.82	4.63
May	1.79	4.09
Jun	1.81	4.31
Jul	1.99	3.44
Aug	1.94	3.44
Sep	2.25	4.40
Oct	2.06	2.87
Nov	1.44	3.19
Dec	1.70	3.26

Why this page shows a volume and not a percentage

Percentage full is a division, and the denominator is missing

“Percentage full” is the figure a drought is discussed in, and it is stored volume divided by capacity. Capacity is published on several different bases — gross, usable, live, and the figure at a particular spillway or licence condition — and dividing a stored volume by the wrong one produces a percentage confidently wrong by the ratio between them, at exactly the moment the number matters most.

Hydrionis holds storage measurements for this reservoir and does not hold a compatible authoritative capacity figure for it, so percentage full is not calculated. The volume above is what was actually measured. Where you need a percentage, take the publisher’s own capacity on its own stated basis and divide it yourself — the source is linked below, and knowing which basis you used is the whole point.

Water level

Monthly mean water surface elevation

295 monthly values

An elevation above a datum, not a depth of water and not a distance below the crest. Levels at different reservoirs are measured against different datums and must not be read against one another; this line is comparable only with its own history. Elevation and volume are not proportional either — a metre near the bottom of a reservoir holds far less water than a metre near the top, because the surface area grows with height.

What the shaded periods are (0 events)

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

240 of 295 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 295 would be longer than this page and unusable with a screen reader.
Period	Avalon Reservoir (m)
2002	968
2002.0833333333333	968
2002.1666666666667	968
2002.3333333333333	967
2002.4166666666667	967
2002.5	968
2002.5833333333333	967
2002.75	967
2002.8333333333333	968
2002.9166666666667	967
2003	966
2003.1666666666667	967
2003.25	967
2003.3333333333333	967
2003.4166666666667	967
2003.5	967
2003.6666666666667	967
2003.75	967
2003.8333333333333	967
2003.9166666666667	967
2004.0833333333333	968
2004.1666666666667	968
2004.25	968
2004.3333333333333	967
2004.5	968
2004.5833333333333	968
2004.6666666666667	967
2004.75	968
2004.8333333333333	967
2005	967
2005.0833333333333	968
2005.1666666666667	968
2005.25	967
2005.4166666666667	967
2005.5	967
2005.5833333333333	967
2005.6666666666667	967
2005.8333333333333	967
2005.9166666666667	967
2006	968
2006.0833333333333	968
2006.1666666666667	967
2006.3333333333333	967
2006.4166666666667	967
2006.5	967
2006.5833333333333	967
2006.9166666666667	967
2007	968
2007.0833333333333	968
2007.1666666666667	968
2007.3333333333333	967
2007.4166666666667	967
2007.5	967
2007.5833333333333	967
2007.6666666666667	967
2007.8333333333333	967
2007.9166666666667	967
2008	968
2008.0833333333333	968
2008.25	967
2008.3333333333333	967
2008.4166666666667	967
2008.5	967
2008.5833333333333	967
2008.75	967
2008.8333333333333	967
2008.9166666666667	967
2009	968
2009.1666666666667	968
2009.25	967
2009.3333333333333	967
2009.4166666666667	967
2009.5833333333333	967
2009.6666666666667	967
2009.75	967
2009.8333333333333	967
2009.9166666666667	968
2010.0833333333333	968
2010.1666666666667	968
2010.25	967
2010.3333333333333	967
2010.5	968
2010.5833333333333	967
2010.6666666666667	967
2010.75	967
2010.9166666666667	967
2011	968
2011.0833333333333	968
2011.1666666666667	968
2011.25	967
2011.4166666666667	967
2011.5	967
2011.5833333333333	967
2011.6666666666667	967
2011.8333333333333	967
2011.9166666666667	968
2012	968
2012.0833333333333	968
2012.25	967
2012.3333333333333	967
2012.4166666666667	967
2012.5	967
2012.5833333333333	967
2012.75	967
2012.8333333333333	968
2012.9166666666667	968
2013	968
2013.1666666666667	968
2013.25	968
2013.3333333333333	967
2013.4166666666667	967
2013.5833333333333	967
2013.6666666666667	968
2013.75	968
2013.8333333333333	967
2013.9166666666667	968
2014.0833333333333	968
2014.1666666666667	968
2014.25	967
2014.3333333333333	968
2014.5	967
2014.5833333333333	968
2014.6666666666667	968
2014.75	968
2014.9166666666667	968
2015	968
2015.0833333333333	968
2015.1666666666667	968
2015.25	967
2015.4166666666667	968
2015.5	968
2015.5833333333333	969
2015.6666666666667	969
2015.8333333333333	967
2015.9166666666667	968
2016	968
2016.0833333333333	969
2016.25	968
2016.3333333333333	968
2016.4166666666667	967
2016.5	967
2016.5833333333333	968
2016.75	967
2016.8333333333333	967
2016.9166666666667	968
2017	968
2017.1666666666667	968
2017.25	968
2017.3333333333333	967
2017.4166666666667	968
2017.5833333333333	967
2017.6666666666667	968
2017.75	967
2017.8333333333333	964
2017.9166666666667	964
2018.0833333333333	964
2018.1666666666667	968
2018.25	967
2018.3333333333333	968
2018.5	968
2018.5833333333333	968
2018.6666666666667	968
2018.75	967
2018.9166666666667	964
2019	965
2019.0833333333333	967
2019.1666666666667	967
2019.25	968
2019.4166666666667	968
2019.5	968
2019.5833333333333	967
2019.6666666666667	968
2019.8333333333333	965
2019.9166666666667	964
2020	964
2020.0833333333333	968
2020.25	967
2020.3333333333333	968
2020.4166666666667	967
2020.5	967
2020.5833333333333	968
2020.75	967
2020.8333333333333	967
2020.9166666666667	967
2021	968
2021.1666666666667	968
2021.25	967
2021.3333333333333	967
2021.4166666666667	967
2021.5	968
2021.6666666666667	968
2021.75	968
2021.8333333333333	967
2021.9166666666667	968
2022.0833333333333	968
2022.1666666666667	968
2022.25	967
2022.3333333333333	967
2022.5	967
2022.5833333333333	967
2022.6666666666667	967
2022.75	967
2022.8333333333333	964
2023	963
2023.0833333333333	963
2023.1666666666667	966
2023.25	967
2023.4166666666667	967
2023.5	967
2023.5833333333333	967
2023.6666666666667	967
2023.8333333333333	967
2023.9166666666667	967
2024	968
2024.0833333333333	968
2024.1666666666667	968
2024.3333333333333	967
2024.4166666666667	967
2024.5	968
2024.5833333333333	968
2024.75	968
2024.8333333333333	968
2024.9166666666667	968
2025	968
2025.1666666666667	968
2025.25	968
2025.3333333333333	968
2025.4166666666667	968
2025.5	968
2025.6666666666667	968
2025.75	968
2025.8333333333333	968
2025.9166666666667	968
2026.0833333333333	968
2026.1666666666667	968
2026.25	968
2026.3333333333333	968
2026.5	968
2026.5833333333333	968
2026.6666666666667	968

Rate and persistence

+0.11 Mm³

Mean change per month over 12 months

0 of 24

Recent months below the 20th percentile for their own month

Rates are computed only across an unbroken run of months, so a rate is never divided by a period in which some of the change was not observed. Percentile counts compare each month with the same calendar month in every other year held.

Location

Avalon Reservoir

Gauge location

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	United States Bureau of Reclamation — Reservoir operations and Colorado River data · US Government work — public domain
How the values came to exist	Measured
Period held	1965–2026
Completeness	96.1% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	Storage is a managed quantity. A falling line can be a rule curve, a scheduled release or a transfer to another system rather than a shortage of water, and nothing here distinguishes them. No capacity figure on a stated basis is held for this reservoir, so no percentage of capacity is computed.
Continuity	96% of the months between 1965 and 2026 are held. Monthly means of the publisher's own daily 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

Use this data

Machine-readable JSON /api/v1/observations/by-subject/reservoir-usbr-267.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), Avalon Reservoir reservoir records, accessed 2026-10-05, hydrionis.com/reservoirs/reservoir-usbr-267/

Cite Hydrionis where you rely on the compilation, the normalisation, the eligibility judgements or a chart. Where you use an unmodified published value, the publisher’s attribution is the one that is required; crediting Hydrionis as well is welcome and is not something Hydrionis can require of you.

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 Avalon Reservoir record 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 this comes from

715 monthly observations 1965–2026 Mm³

Spatially aggregatedHigh confidenceSeptember 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 139. Licence: Open.

Method: Monthly mean of the daily values published by the Bureau of Reclamation in acre-feet, converted to Mm³. Months with fewer than 20 days of record are not published rather than averaged from a partial month.

Stored as a volume and not as a share of capacity: the operator publishes what is in the reservoir but not what it holds when full, so a percentage cannot be computed without inventing the denominator.

Retrieved 1 October 2026.

Monthly mean of the daily values published by the Bureau of Reclamation in acre-feet, converted to Mm³. Months with fewer than 20 days of record are not published rather than averaged from a partial month.