HydrionisGlobal Water Intelligence
Monitored reservoir

Horseshoe Reservoir At Horseshoe Dam, AZ

United States Geological Survey reservoir gauge 09509501 in AZ, with published storage from 1974.

Storage record09509501

Storage now, against this reservoir's own record

29.55 Mm³
Stored, September 2026
71st
Percentile among 52 Seps on record
+60.9%
Against the Sep 1991–2020 average
-58.1%
Change over the 12 months to 2026-09

Storage in September 2026 was higher than most Seps on record, ranked against 52 other Seps held for this reservoir.

Storage, 1974–2026

Monthly mean storage
624 monthly values, 1974 to 2026
Monthly mean storageMonthly mean storage: Horseshoe Reservoir At Horseshoe Dam, AZ in Mm³, from 1974.75 to 2026.6666666666667.050100150200Mm³1974.751981.251987.751994.252000.752007.252013.752020.25Year

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 624 periods, evenly spaced across the record. Every value is in the download and the API; a table of all 624 would be longer than this page and unusable with a screen reader.
PeriodHorseshoe Reservoir At Horseshoe Dam, AZ (Mm³)
October 19742.62
January 19754.36
March 197510.3
June 197518.0
August 19753.08
November 19753.76
February 197693.9
April 197627.2
July 19764.09
September 19764.37
December 19762.30
March 19779.11
May 197733.1
August 197748.2
October 197739.4
January 197826.4
April 1978169
June 1978126
September 197817.6
December 1978122
February 197998.1
May 1979144
July 197967.2
October 19790.592
January 198059.3
March 1980120
June 1980134
August 19806.05
November 19801.77
February 19812.95
April 19814.05
July 19811.93
September 19812.07
December 19812.54
March 1982122
May 198279.5
August 19822.15
October 19829.90
January 198369.6
April 1983156
June 1983137
September 198313.0
November 198346.5
February 1984104
May 198422.7
July 19842.49
October 19843.21
January 198598.6
March 1985141
June 1985127
August 198547.9
November 198518.1
February 198659.6
April 1986149
July 1986110
September 1986104
December 198657.9
March 1987128
May 1987158
August 198763.7
October 198726.5
January 198896.6
April 1988116
June 1988116
September 198854.2
November 198825.7
February 198919.3
May 19899.49
July 19892.54
October 198915.2
December 198911.8
March 19902.12
June 19900.611
August 19901.40
November 19900.794
February 19911.64
April 1991155
July 1991133
September 199182.5
December 199148.6
March 1992134
May 1992159
August 1992128
October 199295.8
January 199399.7
April 1993152
June 1993125
September 199336.7
November 199329.9
February 199445.1
May 199495.8
July 199414.3
October 199413.7
December 199418.6
March 1995137
June 199510.8
August 19959.01
November 19959.32
January 199615.5
April 19969.51
July 199614.8
September 199644.1
December 199651.0
February 199746.5
May 199723.5
August 199711.8
October 199714.3
January 199820.5
April 1998156
June 199875.6
September 199823.5
November 199813.8
February 199915.0
May 199931.8
July 199927.5
October 199974.2
December 19998.27
March 20003.52
June 20002.64
August 200014.6
November 200046.2
January 20019.98
April 200120.3
July 20010
September 20010
December 20010.041
February 20020.022
May 20020.0006
August 20020
October 20020.040
January 20030.024
March 200344.2
June 200312.0
September 20030.089
November 20030.756
February 200426.9
May 200437.8
July 200410.4
October 20044.03
December 200449.1
March 2005133
June 200589.6
August 20055.53
November 20050.658
January 20060.161
April 20060.072
July 20060.043
September 20061.74
December 20060.182
February 20070.384
May 200711.6
August 20077.89
October 20070.450
January 200849.0
March 2008134
June 200873.2
September 20080.221
November 20080.436
February 200947.3
April 200962.6
July 20090.053
October 20094.33
December 200920.1
March 2010127
May 2010132
August 201022.1
November 201034.4
January 201119.3
April 201132.9
July 20110.186
September 20110.212
December 20110.395
February 20120.323
May 20120.062
August 20121.68
October 20120.143
January 20137.51
March 201372.8
June 20131.76
September 201310.3
November 20130.140
February 201445.3
April 201482.4
July 20140
October 20140
December 20140.048
March 201581.3
May 201512.8
August 201537.0
November 201565.9
January 201672.0
April 201654.7
June 201623.4
September 20162.29
December 20169.22
February 2017127
May 201755.5
August 201715.2
October 201716.4
January 201815.8
March 201811.0
June 20184.90
September 20185.73
November 20186.35
February 201983.5
April 2019114
July 20195.09
October 201914.9
December 201946.0
March 202098.5
May 2020125
August 20200.263
November 20208.66
January 20218.00
April 20215.51
June 20210.308
September 202136.1
December 20218.91
February 202219.4
May 20224.86
July 20224.91
October 202210.6
January 202362.8
March 2023111
June 2023127
September 202399.6
November 202373.5
February 202484.2
April 2024102
July 202486.5
October 202472.4
December 202477.4
March 202570.8
May 202575.6
August 202577.5
November 202582.7
January 202694.1
April 202670.2
June 202661.7
September 202629.6

The reservoir's year

Seasonal storage profile
Each calendar month's reference average, against the most recent year
Seasonal storage profileSeasonal storage profile: 1991–2020 average, Most recent 12 months in Mm³, from 1 to 12.0255075100Mm³123456789101112Month1991–2020 average 1: 32.6 Mm³1991–2020 average 2: 48.7 Mm³1991–2020 average 3: 66.1 Mm³1991–2020 average 4: 70.1 Mm³1991–2020 average 5: 58.1 Mm³1991–2020 average 6: 39.2 Mm³1991–2020 average 7: 21.7 Mm³1991–2020 average 8: 16.7 Mm³1991–2020 average 9: 18.4 Mm³1991–2020 average 10: 18.1 Mm³1991–2020 average 11: 16.8 Mm³1991–2020 average 12: 21.0 Mm³Most recent 12 months 1: 94.1 Mm³Most recent 12 months 2: 74.3 Mm³Most recent 12 months 3: 96.4 Mm³Most recent 12 months 4: 70.2 Mm³Most recent 12 months 5: 73.3 Mm³Most recent 12 months 6: 61.7 Mm³Most recent 12 months 7: 45.5 Mm³Most recent 12 months 8: 40.0 Mm³Most recent 12 months 9: 29.6 Mm³Most recent 12 months 10: 70.7 Mm³Most recent 12 months 11: 82.7 Mm³Most recent 12 months 12: 81.4 Mm³
  • 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
Period1991–2020 average (Mm³)Most recent 12 months (Mm³)
Jan32.694.1
Feb48.774.3
Mar66.196.4
Apr70.170.2
May58.173.3
Jun39.261.7
Jul21.745.5
Aug16.740.0
Sep18.429.6
Oct18.170.7
Nov16.882.7
Dec21.081.4

Why this page shows a volume and not a percentage

Rate and persistence

-3.42 Mm³
Mean drawdown 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

Horseshoe Reservoir At Horseshoe Dam, AZ
Gauge location
Horseshoe Reservoir At Horseshoe Dam, AZHorseshoe Reservoir At Horseshoe Dam, AZ — 29.55 Mm³Horseshoe Reservoir At Horseshoe Dam, AZ — 29.55 Mm³

About this data

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 Geological Survey — National Water Information System · US Government work — public domain
How the values came to existMeasured
Period held1974–2026
Completeness98.1% 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.
Continuity98% of the months between 1974 and 2026 are held. Monthly means of the publisher's own daily record.
Last read from the publisher2026-10-01
RedistributionPermitted by the upstream licences
Commercial reusePermitted by the upstream licences. No Hydrionis access tier can widen this.
MethodologyHow this was produced

Use this data

Use this data

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), Horseshoe Reservoir At Horseshoe Dam, AZ reservoir records, accessed 2026-10-05, hydrionis.com/reservoirs/reservoir-usgs-09509501/

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 Horseshoe Reservoir At Horseshoe Dam, AZ 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

624 monthly observations 1974–2026 Mm³
Spatially aggregatedHigh confidenceSeptember 2026

Source: USGS — National Water Information System, 09509501. Licence: Open.

Method: Monthly mean of daily reservoir storage published by the USGS in acre-feet and converted to millions of cubic metres. Months with fewer than 20 days of record are not published rather than averaged from a partial month.

Reservoir storage is managed as well as observed: a drawdown may reflect an operating rule, flood-control rule curve or scheduled release rather than a shortage. Compare a month against the same month in other years, and do not read a fall as a supply signal without knowing the operating regime.

Retrieved 1 October 2026.

Monthly mean of daily reservoir storage published by the USGS in acre-feet and converted to millions of cubic metres. Months with fewer than 20 days of record are not published rather than averaged from a partial month.

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