Avalon Reservoir — storage

Storage now, against this reservoir's own record

3.41 Mm³

Stored, August 2026

93rd

Percentile among 60 Augs on record

+76.0%

Against the Aug 1991–2020 average

+14.3%

Change over the 12 months to 2026-08

Storage in August 2026 was higher than almost every other Aug on record, ranked against 60 other Augs held for this reservoir.

Storage, 1965–2026

Monthly mean storage

714 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 714 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 714 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
March 1974	3.18
June 1974	1.08
September 1974	2.90
December 1974	6.22
March 1975	5.24
June 1975	1.29
September 1975	1.27
December 1975	2.80
March 1976	3.34
June 1976	1.20
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
May 1989	1.40
August 1989	1.18
November 1989	1.05
February 1990	2.59
May 1990	1.52
August 1990	1.13
November 1990	1.07
February 1991	2.84
May 1991	1.16
August 1991	1.17
November 1991	2.05
February 1992	2.72
May 1992	2.73
August 1992	1.35
November 1992	1.14
February 1993	2.51
May 1993	1.17
August 1993	1.36
November 1993	0.920
February 1994	2.10
May 1994	1.42
August 1994	1.41
November 1994	0.049
February 1995	0.592
May 1995	1.40
August 1995	1.24
November 1995	0.019
February 1996	1.05
May 1996	1.25
August 1996	1.34
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
April 2004	4.40
July 2004	2.50
October 2004	3.35
January 2005	2.20
April 2005	1.61
July 2005	1.63
October 2005	1.86
January 2006	2.49
April 2006	1.52
July 2006	2.13
December 2006	1.35
March 2007	2.91
June 2007	1.49
September 2007	1.58
December 2007	1.96
March 2008	3.22
June 2008	1.58
September 2008	1.70
December 2008	2.34
March 2009	3.31
June 2009	1.58
September 2009	1.54
December 2009	2.44
March 2010	3.95
June 2010	1.56
September 2010	1.94
December 2010	1.85
March 2011	2.96
June 2011	1.62
September 2011	1.61
December 2011	2.43
March 2012	3.49
June 2012	1.56
September 2012	1.80
December 2012	2.80
March 2013	3.84
June 2013	1.79
September 2013	4.43
December 2013	3.05
March 2014	2.97
June 2014	2.10
September 2014	4.06
December 2014	3.22
March 2015	4.23
June 2015	2.79
September 2015	6.34
December 2015	2.80
March 2016	3.58
June 2016	2.28
September 2016	3.68
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
May 2019	2.29
August 2019	2.11
November 2019	0.032
February 2020	3.82
May 2020	2.35
August 2020	2.39
November 2020	1.35
February 2021	2.94
May 2021	1.24
August 2021	5.12
November 2021	1.74
February 2022	3.44
May 2022	1.84
August 2022	1.55
November 2022	0.057
February 2023	0
May 2023	1.35
August 2023	1.67
November 2023	1.47
February 2024	2.77
May 2024	1.58
August 2024	3.14
November 2024	2.89
February 2025	4.95
May 2025	3.23
August 2025	2.99
November 2025	3.19
February 2026	3.55
May 2026	4.09
August 2026	3.41

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	3.41
Sep	2.25	3.05
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

294 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 294 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 294 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
2003.0833333333333	966
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
2004.4166666666667	967
2004.5833333333333	968
2004.6666666666667	967
2004.75	968
2004.8333333333333	967
2005	967
2005.0833333333333	968
2005.1666666666667	968
2005.25	967
2005.3333333333333	967
2005.5	967
2005.5833333333333	967
2005.6666666666667	967
2005.75	967
2005.9166666666667	967
2006	968
2006.0833333333333	968
2006.1666666666667	967
2006.25	967
2006.4166666666667	967
2006.5	967
2006.5833333333333	967
2006.8333333333333	967
2007	968
2007.0833333333333	968
2007.1666666666667	968
2007.25	967
2007.4166666666667	967
2007.5	967
2007.5833333333333	967
2007.6666666666667	967
2007.75	967
2007.9166666666667	967
2008	968
2008.0833333333333	968
2008.1666666666667	968
2008.3333333333333	967
2008.4166666666667	967
2008.5	967
2008.5833333333333	967
2008.6666666666667	967
2008.8333333333333	967
2008.9166666666667	967
2009	968
2009.0833333333333	968
2009.25	967
2009.3333333333333	967
2009.4166666666667	967
2009.5	967
2009.5833333333333	967
2009.75	967
2009.8333333333333	967
2009.9166666666667	968
2010	968
2010.1666666666667	968
2010.25	967
2010.3333333333333	967
2010.4166666666667	967
2010.5833333333333	967
2010.6666666666667	967
2010.75	967
2010.8333333333333	967
2010.9166666666667	967
2011.0833333333333	968
2011.1666666666667	968
2011.25	967
2011.3333333333333	967
2011.5	967
2011.5833333333333	967
2011.6666666666667	967
2011.75	967
2011.8333333333333	967
2012	968
2012.0833333333333	968
2012.1666666666667	968
2012.25	967
2012.4166666666667	967
2012.5	967
2012.5833333333333	967
2012.6666666666667	967
2012.75	967
2012.9166666666667	968
2013	968
2013.0833333333333	968
2013.1666666666667	968
2013.3333333333333	967
2013.4166666666667	967
2013.5	968
2013.5833333333333	967
2013.75	968
2013.8333333333333	967
2013.9166666666667	968
2014	968
2014.0833333333333	968
2014.25	967
2014.3333333333333	968
2014.4166666666667	967
2014.5	967
2014.6666666666667	968
2014.75	968
2014.8333333333333	967
2014.9166666666667	968
2015	968
2015.1666666666667	968
2015.25	967
2015.3333333333333	967
2015.4166666666667	968
2015.5833333333333	969
2015.6666666666667	969
2015.75	968
2015.8333333333333	967
2016	968
2016.0833333333333	969
2016.1666666666667	968
2016.25	968
2016.3333333333333	968
2016.5	967
2016.5833333333333	968
2016.6666666666667	968
2016.75	967
2016.9166666666667	968
2017	968
2017.0833333333333	968
2017.1666666666667	968
2017.25	968
2017.4166666666667	968
2017.5	968
2017.5833333333333	967
2017.6666666666667	968
2017.8333333333333	964
2017.9166666666667	964
2018	964
2018.0833333333333	964
2018.1666666666667	968
2018.3333333333333	968
2018.4166666666667	967
2018.5	968
2018.5833333333333	968
2018.75	967
2018.8333333333333	965
2018.9166666666667	964
2019	965
2019.1666666666667	967
2019.25	968
2019.3333333333333	967
2019.4166666666667	968
2019.5	968
2019.6666666666667	968
2019.75	968
2019.8333333333333	965
2019.9166666666667	964
2020.0833333333333	968
2020.1666666666667	968
2020.25	967
2020.3333333333333	968
2020.4166666666667	967
2020.5833333333333	968
2020.6666666666667	967
2020.75	967
2020.8333333333333	967
2021	968
2021.0833333333333	968
2021.1666666666667	968
2021.25	967
2021.3333333333333	967
2021.5	968
2021.5833333333333	968
2021.6666666666667	968
2021.75	968
2021.9166666666667	968
2022	968
2022.0833333333333	968
2022.1666666666667	968
2022.3333333333333	967
2022.4166666666667	967
2022.5	967
2022.5833333333333	967
2022.6666666666667	967
2022.8333333333333	964
2022.9166666666667	963
2023	963
2023.0833333333333	963
2023.25	967
2023.3333333333333	967
2023.4166666666667	967
2023.5	967
2023.5833333333333	967
2023.75	967
2023.8333333333333	967
2023.9166666666667	967
2024	968
2024.1666666666667	968
2024.25	967
2024.3333333333333	967
2024.4166666666667	967
2024.5	968
2024.6666666666667	968
2024.75	968
2024.8333333333333	968
2024.9166666666667	968
2025.0833333333333	968
2025.1666666666667	968
2025.25	968
2025.3333333333333	968
2025.5	968
2025.5833333333333	968
2025.6666666666667	968
2025.75	968
2025.8333333333333	968
2026	968
2026.0833333333333	968
2026.1666666666667	968
2026.25	968
2026.4166666666667	968
2026.5	968
2026.5833333333333	968

Rate and persistence

+0.04 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	96.0% 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	2026-09-01
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 2026-09-02, 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

714 monthly observations 1965–2026 Mm³

Spatially aggregatedHigh confidenceAugust 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 September 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.