Pilot Butte Reservoir — storage

Storage now, against this reservoir's own record

29.96 Mm³

Stored, September 2026

82nd

Percentile among 58 Seps on record

+43.3%

Against the Sep 1991–2020 average

+80.0%

Change over the 12 months to 2026-09

Storage in September 2026 was higher than most Seps on record, ranked against 58 other Seps held for this reservoir.

Storage, 1968–2026

Monthly mean storage

696 monthly values, 1968 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 696 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 696 would be longer than this page and unusable with a screen reader.
Period	Pilot Butte Reservoir (Mm³)
October 1968	20.0
January 1969	23.0
April 1969	37.2
July 1969	38.2
October 1969	25.7
January 1970	28.2
March 1970	37.0
June 1970	39.5
September 1970	21.0
December 1970	20.7
March 1971	19.3
June 1971	35.8
September 1971	19.1
December 1971	28.5
March 1972	32.2
June 1972	32.0
September 1972	30.6
November 1972	27.7
February 1973	28.5
May 1973	40.2
August 1973	35.3
November 1973	22.2
February 1974	19.4
May 1974	38.1
August 1974	32.7
November 1974	26.4
February 1975	25.2
May 1975	39.8
July 1975	34.5
October 1975	31.8
January 1976	31.2
April 1976	32.2
July 1976	24.7
October 1976	17.5
January 1977	16.8
April 1977	36.9
July 1977	33.4
October 1977	14.7
January 1978	13.9
March 1978	15.8
June 1978	40.3
September 1978	28.3
December 1978	30.5
March 1979	29.1
June 1979	31.6
September 1979	26.5
December 1979	15.7
March 1980	16.4
June 1980	40.4
August 1980	36.6
November 1980	22.3
February 1981	22.0
May 1981	38.7
August 1981	26.4
November 1981	23.7
February 1982	23.6
May 1982	25.3
August 1982	41.5
November 1982	33.4
February 1983	33.0
April 1983	34.3
July 1983	41.9
October 1983	30.8
January 1984	30.4
April 1984	38.0
July 1984	40.0
October 1984	36.5
January 1985	35.8
April 1985	42.6
July 1985	34.5
October 1985	37.4
December 1985	37.5
March 1986	37.5
June 1986	28.7
September 1986	41.5
December 1986	39.0
March 1987	38.7
June 1987	42.9
September 1987	14.9
December 1987	39.9
March 1988	39.8
June 1988	31.6
August 1988	19.4
November 1988	37.7
February 1989	37.0
May 1989	32.6
August 1989	34.0
November 1989	37.3
February 1990	36.6
May 1990	34.8
August 1990	35.6
November 1990	40.5
February 1991	39.7
April 1991	43.3
July 1991	35.6
October 1991	23.5
January 1992	32.5
April 1992	43.0
July 1992	40.7
October 1992	33.0
January 1993	40.7
April 1993	41.7
July 1993	36.7
October 1993	29.1
December 1993	40.8
March 1994	40.3
June 1994	26.6
September 1994	17.5
December 1994	40.5
March 1995	40.0
June 1995	39.3
September 1995	22.5
December 1995	33.6
March 1996	33.8
June 1996	39.1
August 1996	29.2
November 1996	35.8
February 1997	35.4
May 1997	32.8
August 1997	37.5
November 1997	34.1
February 1998	33.2
May 1998	33.6
August 1998	33.5
November 1998	34.7
January 1999	34.2
April 1999	31.6
July 1999	33.7
October 1999	33.3
January 2000	34.3
April 2000	38.3
July 2000	30.1
October 2000	27.0
January 2001	35.4
April 2001	36.3
July 2001	22.2
September 2001	5.02
December 2001	36.0
March 2002	35.7
June 2002	32.7
September 2002	10.6
December 2002	34.9
March 2003	34.7
June 2003	33.6
September 2003	15.8
December 2003	34.2
March 2004	34.1
May 2004	34.3
August 2004	22.1
November 2004	34.1
February 2005	33.6
May 2005	32.9
August 2005	26.6
November 2005	35.1
February 2006	34.6
May 2006	27.5
August 2006	17.9
November 2006	4.83
January 2007	14.7
April 2007	34.8
July 2007	22.5
October 2007	25.8
January 2008	34.0
April 2008	34.1
July 2008	37.1
October 2008	28.4
January 2009	34.7
April 2009	35.4
July 2009	39.0
September 2009	23.8
December 2009	35.9
March 2010	35.8
June 2010	37.6
September 2010	22.9
December 2010	34.2
March 2011	33.9
June 2011	34.0
September 2011	29.9
December 2011	34.7
March 2012	34.1
May 2012	29.2
August 2012	24.3
November 2012	34.3
February 2013	33.8
May 2013	34.2
August 2013	21.3
November 2013	34.6
February 2014	34.2
May 2014	33.2
August 2014	35.5
November 2014	33.5
January 2015	33.2
April 2015	35.5
July 2015	34.4
October 2015	31.1
January 2016	34.0
April 2016	35.9
July 2016	28.7
October 2016	30.0
January 2017	36.2
April 2017	36.7
June 2017	35.8
September 2017	24.1
December 2017	34.7
March 2018	34.5
June 2018	35.8
September 2018	19.3
December 2018	34.5
March 2019	34.2
June 2019	35.9
September 2019	18.1
December 2019	34.3
February 2020	34.2
May 2020	31.5
August 2020	23.5
November 2020	34.8
February 2021	34.4
May 2021	33.5
August 2021	24.4
November 2021	17.8
February 2022	29.3
May 2022	32.3
August 2022	28.8
October 2022	31.8
January 2023	33.6
April 2023	33.7
July 2023	34.6
October 2023	34.9
January 2024	33.8
April 2024	35.5
July 2024	26.9
October 2024	23.2
January 2025	35.0
April 2025	35.1
June 2025	34.3
September 2025	16.6
December 2025	36.2
March 2026	35.5
June 2026	30.8
September 2026	30.0

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	34.6	36.0
Feb	34.7	35.8
Mar	35.1	35.5
Apr	36.3	36.1
May	33.7	33.6
Jun	34.6	30.8
Jul	33.5	34.5
Aug	26.3	32.7
Sep	20.9	30.0
Oct	28.1	29.8
Nov	34.0	36.5
Dec	34.2	36.2

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

696 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 696 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 696 would be longer than this page and unusable with a screen reader.
Period	Pilot Butte Reservoir (m)
1968.75	1,656
1969	1,657
1969.25	1,662
1969.5	1,662
1969.75	1,658
1970	1,659
1970.1666666666667	1,662
1970.4166666666667	1,662
1970.6666666666667	1,656
1970.9166666666667	1,656
1971.1666666666667	1,656
1971.4166666666667	1,661
1971.6666666666667	1,655
1971.9166666666667	1,659
1972.1666666666667	1,660
1972.4166666666667	1,660
1972.6666666666667	1,660
1972.8333333333333	1,659
1973.0833333333333	1,659
1973.3333333333333	1,663
1973.5833333333333	1,661
1973.8333333333333	1,657
1974.0833333333333	1,656
1974.3333333333333	1,662
1974.5833333333333	1,660
1974.8333333333333	1,658
1975.0833333333333	1,658
1975.3333333333333	1,663
1975.5	1,661
1975.75	1,660
1976	1,660
1976.25	1,660
1976.5	1,658
1976.75	1,655
1977	1,655
1977.25	1,662
1977.5	1,661
1977.75	1,654
1978	1,653
1978.1666666666667	1,654
1978.4166666666667	1,663
1978.6666666666667	1,659
1978.9166666666667	1,660
1979.1666666666667	1,659
1979.4166666666667	1,660
1979.6666666666667	1,658
1979.9166666666667	1,654
1980.1666666666667	1,654
1980.4166666666667	1,663
1980.5833333333333	1,662
1980.8333333333333	1,657
1981.0833333333333	1,657
1981.3333333333333	1,662
1981.5833333333333	1,658
1981.8333333333333	1,657
1982.0833333333333	1,657
1982.3333333333333	1,658
1982.5833333333333	1,663
1982.8333333333333	1,661
1983.0833333333333	1,661
1983.25	1,661
1983.5	1,663
1983.75	1,660
1984	1,660
1984.25	1,662
1984.5	1,663
1984.75	1,662
1985	1,661
1985.25	1,663
1985.5	1,661
1985.75	1,662
1985.9166666666667	1,662
1986.1666666666667	1,662
1986.4166666666667	1,659
1986.6666666666667	1,663
1986.9166666666667	1,662
1987.1666666666667	1,662
1987.4166666666667	1,663
1987.6666666666667	1,654
1987.9166666666667	1,663
1988.1666666666667	1,663
1988.4166666666667	1,660
1988.5833333333333	1,656
1988.8333333333333	1,662
1989.0833333333333	1,662
1989.3333333333333	1,660
1989.5833333333333	1,661
1989.8333333333333	1,662
1990.0833333333333	1,662
1990.3333333333333	1,661
1990.5833333333333	1,661
1990.8333333333333	1,663
1991.0833333333333	1,663
1991.25	1,664
1991.5	1,661
1991.75	1,657
1992	1,660
1992.25	1,664
1992.5	1,663
1992.75	1,660
1993	1,663
1993.25	1,663
1993.5	1,662
1993.75	1,659
1993.9166666666667	1,663
1994.1666666666667	1,663
1994.4166666666667	1,658
1994.6666666666667	1,655
1994.9166666666667	1,663
1995.1666666666667	1,663
1995.4166666666667	1,662
1995.6666666666667	1,657
1995.9166666666667	1,661
1996.1666666666667	1,661
1996.4166666666667	1,662
1996.5833333333333	1,659
1996.8333333333333	1,663
1997.0833333333333	1,662
1997.3333333333333	1,662
1997.5833333333333	1,663
1997.8333333333333	1,662
1998.0833333333333	1,662
1998.3333333333333	1,662
1998.5833333333333	1,662
1998.8333333333333	1,662
1999	1,662
1999.25	1,661
1999.5	1,662
1999.75	1,662
2000	1,662
2000.25	1,663
2000.5	1,661
2000.75	1,660
2001	1,662
2001.25	1,663
2001.5	1,658
2001.6666666666667	1,649
2001.9166666666667	1,663
2002.1666666666667	1,663
2002.4166666666667	1,662
2002.6666666666667	1,653
2002.9166666666667	1,662
2003.1666666666667	1,662
2003.4166666666667	1,662
2003.6666666666667	1,656
2003.9166666666667	1,662
2004.1666666666667	1,662
2004.3333333333333	1,662
2004.5833333333333	1,658
2004.8333333333333	1,662
2005.0833333333333	1,662
2005.3333333333333	1,662
2005.5833333333333	1,660
2005.8333333333333	1,662
2006.0833333333333	1,662
2006.3333333333333	1,660
2006.5833333333333	1,656
2006.8333333333333	1,649
2007	1,655
2007.25	1,662
2007.5	1,658
2007.75	1,659
2008	1,662
2008.25	1,662
2008.5	1,663
2008.75	1,660
2009	1,662
2009.25	1,662
2009.5	1,663
2009.6666666666667	1,659
2009.9166666666667	1,663
2010.1666666666667	1,663
2010.4166666666667	1,663
2010.6666666666667	1,658
2010.9166666666667	1,662
2011.1666666666667	1,662
2011.4166666666667	1,662
2011.6666666666667	1,661
2011.9166666666667	1,662
2012.1666666666667	1,662
2012.3333333333333	1,661
2012.5833333333333	1,659
2012.8333333333333	1,662
2013.0833333333333	1,662
2013.3333333333333	1,662
2013.5833333333333	1,658
2013.8333333333333	1,662
2014.0833333333333	1,662
2014.3333333333333	1,662
2014.5833333333333	1,662
2014.8333333333333	1,662
2015	1,662
2015.25	1,662
2015.5	1,662
2015.75	1,661
2016	1,662
2016.25	1,663
2016.5	1,660
2016.75	1,661
2017	1,663
2017.25	1,663
2017.4166666666667	1,663
2017.6666666666667	1,659
2017.9166666666667	1,662
2018.1666666666667	1,662
2018.4166666666667	1,663
2018.6666666666667	1,657
2018.9166666666667	1,662
2019.1666666666667	1,662
2019.4166666666667	1,663
2019.6666666666667	1,657
2019.9166666666667	1,662
2020.0833333333333	1,662
2020.3333333333333	1,661
2020.5833333333333	1,659
2020.8333333333333	1,662
2021.0833333333333	1,662
2021.3333333333333	1,662
2021.5833333333333	1,659
2021.8333333333333	1,656
2022.0833333333333	1,661
2022.3333333333333	1,662
2022.5833333333333	1,660
2022.75	1,661
2023	1,662
2023.25	1,662
2023.5	1,662
2023.75	1,662
2024	1,662
2024.25	1,662
2024.5	1,660
2024.75	1,658
2025	1,662
2025.25	1,662
2025.4166666666667	1,662
2025.6666666666667	1,656
2025.9166666666667	1,663
2026.1666666666667	1,662
2026.4166666666667	1,661
2026.6666666666667	1,661

Rate and persistence

+1.11 Mm³

Mean change per month over 12 months

2 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

Pilot Butte 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	1968–2026
Completeness	98.3% 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	98% of the months between 1968 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-435.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), Pilot Butte Reservoir reservoir records, accessed 2026-10-05, hydrionis.com/reservoirs/reservoir-usbr-435/

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 Pilot Butte 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

696 monthly observations 1968–2026 Mm³

Spatially aggregatedHigh confidenceSeptember 2026

Source: USBR — Reservoir operations and Colorado River data, RISE catalogue item 648. 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.