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GREAT WESTERN RESERVOIR

Structure dossier · WDID 0203861 · RESERVOIR · WALNUT CREEK · DWR record · probably BROOMFIELD CITY AND COUNTY OF’s (matched on DWR’s contact or an EPA intake name; verify below)

Great Western Reservoir is a reservoir on Walnut 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 20:52 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DWR’s own records name no owner for a ditch, reservoir or well, so this comes from the source shown and can be out of date.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
GREAT WESTERN RESERVOIR INLET FROM MCKAY DITCH 0203861A — — named for this WDID

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.

In short

GREAT WESTERN RESERVOIR holds 8 decreed rights on WALNUT CREEK. No active call senior to its rights reaches its district today (18 active calls checked), so it is in priority now. 8 further calls state no district and sit outside this one, so they are counted here rather than assumed either way. That is today's position; the weeks ahead cannot be projected for it: this structure is not on the modelled flow network, so no reference gage can honestly stand in for it. In a median year over its last 11 recorded years it diverts 2,207 acre-feet.

Assembled from the figures on this page — every number above is checked against them before it is shown (5 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

Dam GREAT WESTERN (completed 1903)
Hazard class High
Condition at last inspection Conditionally Satisfactory (2025-03-25)
Storage restriction None on file
Normal storage 2,200 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

● In priority — no active call senior to this structure's rights affects its district (18 active call(s) checked).

8 further calls state no district and sit outside this one, so they are counted here rather than assumed either way.

Which of its rights are out of priority?

The outlook for the weeks ahead is not computable for this structure: this structure is not on the modelled flow network, so no reference gage can honestly stand in for it. Today’s position is a separate question, and it is answered in Current administration above — that screen reads the district’s active calls and needs no reference gage.

Where it sits in line

Priority 1878-12-31 — 863rd most senior of the 21886 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: WILLIAMS DITCH 1 (1895-07-01). Immediately behind: POITZ RES (1884-10-01).

Decreed rights (8)

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
16718.10592 1878-12-311936-05-13 98.0 AF 0.0 — Irrigation 84CW0390
16718.13468 1886-11-151936-05-13 198.0 AF 0.0 — Municipal W9411
16718.14124 1888-09-011936-05-13 21.25 AF 0.0 — Municipal W9411
16718.14595 1889-12-161936-05-13 154.0 AF 0.0 — Municipal W9411
19468.00000 1903-04-211918-08-02 1595.74 AF 1595.74 AF — Irrigation CA40750
20188.19468 1903-04-211907-03-13 296.0 AF 0.0 — Irrigation, Municipal +4 CA4842
27930.19468 1903-04-211943-02-09 1757.0 AF 0.0 — Irrigation, Municipal +4 CA10584
47931.00000 1981-03-251981-12-31 736.0 AF 25264.0 AF — Irrigation, Municipal +6 88CW0009, 81CW0463

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 16718.10592 · peaks at 10 of 11 seasons
AprMayJunJulAugSep
middle right · admin 19468.00000 · peaks at 10 of 11 seasons
AprMayJunJulAugSep
most junior right · admin 47931.00000 · peaks at 10 of 11 seasons
AprMayJunJulAugSep
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 12 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 2,207 AF. Its most recent year on record, 2025, came in at 1,931 AF — 88% of that, and 4th lowest of the 11 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)
1997 — no recorded volume 318 0 —
1999 187 1st lowest of 11 · 8% of median — 21 6.8
2016 2,207 6th lowest of 11 · 100% of median — 258 32.1
2017 1,516 3rd lowest of 11 · 69% of median — 130 11.5
2018 970 2nd lowest of 11 · 44% of median 509 97 10.0
2019 3,266 8th lowest of 11 · 148% of median 1,942 230 33.2
2020 2,376 7th lowest of 11 · 108% of median 602 300 19.2
2021 3,825 10th lowest of 11 · 173% of median 1,537 298 57.0
2022 3,571 9th lowest of 11 · 162% of median 634 263 45.1
2023 3,866 11th lowest of 11 · 175% of median 2,452 304 99.2
2024 2,120 5th lowest of 11 · 96% of median 518 366 18.6
2025 1,931 4th lowest of 11 · 88% of median 441 304 21.9

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 8 right(s), seniority decoded
diversion record present 2571 measured days; currency unknown (no data-coverage date to compare against)
record continuity patchy 42% of the irrigation seasons in 1997-2025 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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