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UNION RES

Structure dossier · WDID 0503905 · RESERVOIR · SAINT VRAIN CREEK · DWR record

Union Res is a reservoir on Saint Vrain Creek in Colorado. This page is its public record: the water it has a right to, whether it may take it today, and its history, compiled from the Colorado Division of Water Resources.

Source DWR administrative record · verify at DWR structure ↗ Source DWR administrative record · verify at DWR diversion records ↗ Source Our computation, scored against a reference · scored against DWR's call analysis, see /methods

Where this page's figures come from

Generated 2026-10-15 01:20 by Hydrohistorian. Sources: DWR HydroBase snapshot HydroBase_CO_20260928 (history) + CDSS REST (current), USGS NWIS cross-checks. Engine v0.5.0 (dd58e60) — every figure regenerates from this named code version and data image.

Who owns it

DWR’s own records name no owner for a ditch, reservoir or well, so this comes from the source shown and can be out of date. Organisations only: a private landowner’s name is never listed.

The record and the river

Where this structure is measured

GageFlowing nowRecordHow we know
UNION RESERVOIR OUTLET UNIOUTCO 5.43 cfs 2025–2026, 440 days DWR telemetry mapping

A green link is DWR's own: either its telemetry inventory maps this WDID to that station, or the station is named for this WDID (0700553 → 0700553A). An amber one is ours — the station sits within 250 m and shares a distinctive word with this structure's name, which is a strong hint rather than a DWR statement that this gage meters this structure. Wrong? Tell us.

Flowing now

5.43 cfs as of 2026-10-14 22:45 (2.6 h ago)

Provisional 15-minute telemetry from UNIOUTCO ↗ (UNION RESERVOIR OUTLET). Raw, not the approved record — it is never merged into the diversion history below. DWR publishes the official diversion record after the water year closes and is approved, which is why that record ends months back while this reads minutes ago.

In short

UNION RES holds 19 decreed rights on SAINT VRAIN CREEK. As of 2026-09-27, 18 of them are out of priority under a call at admin 4488.00000 placed by CLOUGH/TRUE DITCH. Its 1 most senior right, back to 1862-04-15, keeps diverting. 7 further calls state no district and sit outside this one, so they are counted here rather than assumed either way. In a median year over its last 12 recorded years it diverts 1,081 acre-feet. It was a party to 4 court cases that also touched 12 other structures.

Assembled from the figures on this page — every number above is checked against them before it is shown (11 checked). The detail, with its method, is in the cards below.

Download this structure

Everything on this page as data you can work with — and a README that makes it citable: the HydroBase snapshot it was built from, the build commit, what every column means, the method behind each derived figure, and that method's stated limits.

⇩ Full record (.zip) Print / save as PDF

Or one table at a time: rights.csv · annual_use.csv · curtailment_now.csv · court_cases.csv · co_parties.csv · call_climatology.csv

What is in the bundle
  • rights.csv — every decreed right, most senior first, with admin numbers, dates, amounts, uses and case numbers.
  • annual_use.csv — recorded diversion by year, with releases accounted separately.
  • curtailment_now.csv — each right's current priority status and how often it was out across analog years.
  • court_cases.csv — the cases attached to its rights.
  • co_parties.csv — the other structures that were parties to those cases. Not available anywhere else.
  • call_climatology.csv — how often each right has been out of priority by week of season, with confidence intervals and the seasons the record could actually judge.
  • README.txt — provenance, methods, limits, disclaimer, and links back to DWR's own records for verification.

Where it sits

Location as DWR records it (storage). Faint dots are the neighbouring water; click any to open it.

Dam safety

⚠ Under an active storage restriction from DWR’s Dam Safety branch.

The State Engineer limits what this dam may impound. DWR publishes no safe-storage figure for it. A low reading on this reservoir can be an order, not a drought; read any storage or fill figure on this page alongside it.

Dam UNION (completed 1902)
Hazard class Significant
Condition at last inspection Satisfactory (2025-07-17)
Storage restriction Yes
Normal storage 12,715 AF
Physical status Active
Emergency action plan Yes

Source: DWR Dam Safety’s jurisdictional-dam inventory (damsafety/damsafetydaminfojd), refreshed weekly. Joined on this structure’s own WDID as DWR records it on the dam. Hazard class describes the consequence of failure, not the likelihood of it. DWR’s dam record.

Current administration

● Junior rights called out — call at SOUTH FLAT DITCH (SAINT VRAIN CREEK, priority 1864-01-01).

● Junior rights called out — call at CLOUGH/TRUE DITCH (SAINT VRAIN CREEK, priority 1862-04-14).

Which of its rights are out of priority?

Under today's controlling call (CLOUGH/TRUE DITCH, priority 1862-04-14): 18 of this structure's 19 rights are out of priority now. (7 call(s) state no district and sit outside this one — not judged, not assumed.) In the 5 past years most like this one (2011, 2015, 2021, 2018, 2012), 3 of the rights shown below were out at least one week in at least one analog year.

Right (priority)NowAnalog years outMajority out by
1862-04-15 4488 ● in priority 0 of 5 —
1862-05-15 4518 ● out 0 of 5 —
1862-10-01 4657 ● out 0 of 5 —
… 13 more rights between these …
2009-12-22 58430 ● out 5 of 5 2026-09-27
2020-10-27 62392 ● out 5 of 5 2026-09-27
2021-12-07 62798 ● out 5 of 5 2026-09-27
How this table is built, and what it is not

“Now” compares each right's admin number with today's most senior applicable active call. The outlook uses flows at LAST CHANCE DITCH around 2026-09-27 (the newest reading on file) — currently 97% of that gage's own median for this window — to pick the 5 most similar past years with complete administration records (2004–2026). Only calls that verifiably apply count: DWR's own district statements in the call's set comments, a caller located in this district, or — on the same stream, where DWR records both stream miles (measured from the mouth) — a caller DOWNSTREAM of this structure. An upstream senior cannot demand water this diversion never deprives it of. Calls that state nothing and sit elsewhere are counted as unjudged rather than assumed, which also means the verified record is shorter than the raw one: early calls rarely state districts. For each week it finds the most senior call then in force; a right is out in that week exactly when that call is senior to it, which is why one line prices every right and juniors can be out while seniors keep diverting. “Majority out by” is the first week out in more than half the analog years. A frequency among named historical years, not a probability from a model, and not a forecast of what the division engineer will do. It says how often years whose flow resembled this one were under a call senior to this right in a given week. Snowpack, storage, and the actual administrative decisions of a given season are not modelled. Check the analog years listed: if they do not resemble this year to you, the outlook does not either.

Where it sits in line

Priority 1862-04-15 — 42nd most senior of the 1290 structures with decreed rights in this water districtDWR's administrative subdivision of a river basin; the unit calls are usually stated in..

Under prior appropriationColorado's rule for sharing water: first in time, first in right. Age decides, not proximity or need., everything ahead of it in this line is satisfied in full before it receives any water. Immediately ahead: GOLDEN PONDS DIVERSIONS STRUCTURE (1862-04-15). Immediately behind: COPELAND RES (1862-04-15).

On MAINSTEM at river mile 17.9, it is 363rd of 476 down the reach. Immediately upstream: HERGENREDER SEC 33 DIVR. Immediately downstream: MEAD RES 4.

Position on the modelled network, not a claim about whose water this is — a stream carries water from many rights at once, and diverted water returns to it.

Decreed rights (20)

Admin noDWR's numeric encoding of a water right's seniority. Smaller is more senior; the integer part counts days from 1849-12-31 to the date that ranks the right. AppropriatedWhen water was first put to beneficial use. It sets seniority unless a prior adjudication date is later. AdjudicatedWhen the water court confirmed the right. A use decreed in 1975 was not a decreed use in 1955, however old the appropriation is. AbsoluteA right actually put to use, as opposed to conditional -- a placeholder for a use not yet made. ConditionalA right reserving a place in line for a use not yet made; it must be diligently pursued or it lapses. Alt-pointAn absolute amount decreed at another structure that may be diverted here instead -- an alternate point of diversion or an exchange. DWR calls this the APEX amount; a right showing 0.0 absolute but an alt-point amount is exercised here under another structure's decree. Decreed forWhat the court said this water may be used for -- irrigation, municipal supply, augmentation and so on.Case
4488.00000 1862-04-151882-06-02 0.0 cfs 0.0 0.39 cfs Irrigation, Municipal +8 01CW0188
4518.00000 1862-05-151882-06-02 0.0 cfs 0.0 0.97 cfs Irrigation, Municipal +8 01CW0188
4657.00000 1862-10-011882-06-02 0.0 cfs 0.0 3.27 cfs Irrigation, Municipal +8 01CW0188
4853.00000 1863-04-151882-06-02 0.0 cfs 0.0 0.46 cfs Irrigation, Municipal +8 01CW0188
5996.00000 1866-06-011882-06-02 0.0 AF 0.0 300.4 AF Irrigation, Municipal 00CW0240
6339.00000 1867-05-101882-06-02 0.0 AF 0.0 2804.6 AF Municipal 07CW0330
6339.00000 1867-05-101882-06-02 0.0 cfs 0.0 15.14 cfs Municipal 07CW0330
7012.00000 1869-03-131882-06-02 0.0 AF 0.0 368.0 AF Irrigation, Municipal 00CW0241
7640.00000 1870-12-011882-06-02 0.0 AF 0.0 450.6 AF Irrigation, Municipal 00CW0240
7822.00000 1871-06-011883-02-21 0.0 AF 0.0 1608.0 AF All beneficial uses 87CW0231
8464.00000 1873-03-041882-06-02 0.0 AF 0.0 368.0 AF Irrigation, Municipal 00CW0241
19271.00000 1902-10-061907-03-13 13219.0 AF 0.0 — Irrigation, Domestic +4 02CW0172, 05CW0318 +5
19273.00000 1902-10-081907-03-13 0.0 AF 0.0 2460.0 AF Municipal, All beneficial uses 87CW0253
20890.19756 1904-02-031926-06-01 0.0 AF 0.0 923.9 AF All beneficial uses 87CW0231
29219.00000 1929-12-311951-07-23 0.0 AF 0.0 2460.0 AF Municipal, All beneficial uses 87CW0253
46386.45046 1973-05-011977-12-31 5879.0 AF 0.0 — Irrigation, Augmentation +3 W7486, 87CW0222 +5
49974.00000 1986-10-281986-12-31 0.0 AF 19802.0 AF — Irrigation, Municipal +8 86CW0394
58430.00000 2009-12-222009-12-31 0.0 cfs 0.0 17.3 cfs Irrigation, Municipal +8 09CW0271
62392.00000 2020-10-272020-12-31 0.0 cfs 0.0 12.04 cfs Storage, Irrigation +3 20CW3179
62798.00000 2021-12-072021-12-31 0.0 AF 6889.0 AF — Municipal, Augmentation +1 21CW3209

Amounts marked cfs are flow rates; AF are stored volumes (storage rights are decreed in acre-feet). An absolute amount of 0.0 beside an alt-point amount is not a dead right: the water is decreed at another structure, and that row records permission to divert it here instead (an alternate point or exchange). A case listing several numbers reflects the original decree plus later change cases.

How often is it out of priority?

Across the 11 seasons whose call record is complete enough to judge this structure (2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025, 2026), week by week from April.

most senior right · admin 4488.00000 · never out of priority in these seasons
AprMayJunJulAugSep
middle right · admin 8464.00000 · peaks at 11 of 11 seasons
AprMayJunJulAugSep
most junior right · admin 62798.00000 · peaks at 11 of 11 seasons
AprMayJunJulAugSep

Snow sets the clock here. In the driest third of snow years (3 seasons), the call settled in for the season around June 17 (June 3 to June 17 across those years). In the middle third (5 seasons), the call settled in for the season around June 24 (June 17 to June 24 across those years); in 3 of them it never lifted at all. In the wettest third (3 seasons), the call settled in for the season around July 8 (June 17 to July 8 across those years).

Snow years ranked by the district’s April 1 snow-water percentile across 3 SNOTEL sites; 11 seasons carry both a snow reading and a judgeable call record. How the past played out, not a forecast.

Why only 11 seasons, and what the bars mean

Each bar is one week: how many of those seasons that right was out of priority under a call this site can lawfully attribute to this structure. Green is never, red is every season on record.

The short record is a property of DWR's data, not of the river. A call only counts against a structure when we can establish it applies — by the districts named in its set comments, or by stream mile on the same source. DWR did not begin stating affected districts routinely until about 2015: fewer than one call in ten can be judged before then, against roughly two in three since. A season we cannot judge is not a season without calls, so it is dropped rather than counted as quiet — 12 seasons dropped here.

This is a frequency over past seasons, not a forecast. It says nothing about what the division engineer will do this year.

Recorded use (last 15 years on record)

Years far under the decreed amount? That gap has a name — paper water vs. wet water, explained on this structure.

In a median year this structure has a recorded diversion of 1,081 AF. Its most recent year on record, 2025, came in at 357 AF — 33% of that, and 2nd lowest of the 12 years with a recorded volume.

This structure records both diversions and reservoir releases — they are separate water movements and are accounted separately below.

YearDiverted (AFA volume: one acre covered a foot deep, about 326,000 gallons -- roughly a suburban household's outdoor use for a year.)Compared with its own recordReleased (AF)Days recordedPeak (cfs)
2011 595 3rd lowest of 12 · 55% of median — 11 32.2
2012 — no recorded volume 613 0 —
2013 804 6th lowest of 12 · 74% of median 2,101 57 17.9
2014 748 5th lowest of 12 · 69% of median 7,988 46 12.0
2015 1,358 7th lowest of 12 · 126% of median 3,390 34 48.6
2016 730 4th lowest of 12 · 68% of median 6,168 33 30.0
2017 — no recorded volume 8,469 0 —
2018 24 1st lowest of 12 · 2% of median 8,212 2 6.3
2019 4,543 11th lowest of 12 · 420% of median 10,876 163 43.4
2020 5,954 12th lowest of 12 · 551% of median 8,196 148 63.1
2021 — no recorded volume 6,049 0 —
2022 4,110 10th lowest of 12 · 380% of median 6,989 65 50.0
2023 2,157 9th lowest of 12 · 200% of median 10,059 40 40.9
2024 1,410 8th lowest of 12 · 130% of median 6,442 56 18.2
2025 357 2nd lowest of 12 · 33% of median 3,785 13 15.0

How good is our record of it?

Grade B (8/10 points) — the components below are the finding; the letter alone is not.

The rubric, component by component
CheckStateDetail
identity complete name, type, and water source all on file
decreed rights on file 20 right(s), seniority decoded
diversion record current 1527 measured days, newest 331 day(s) before the data's end (DWR publishes ~1 year in arrears)
record continuity sparse 14% of the irrigation seasons in 1974-2025 carry measured days
published-record stability stable no upstream revisions recorded against this structure

Advisory reading aid on public data — not an administrative or legal conclusion, not a title opinion, and not a substitute for DWR administration or an engineer's analysis. Methodology review status is disclosed at hydrohistorian's basin pages.

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