Blue River Basin

Division 5 · Water District 36

Auto-mapped

Full diagnostic snapshot pending — this district's weekly-style report (system status, active calls, hydrographs, anomaly flags) is produced by the nightly rotation and appears here after its first run. The tabs above are live now.

Reconstruct conditions as of

Evolution of the network

Gage flow trend & changepoints

What counts as a trend here

Computed 2026-08-20 09:06 from 46 gage(s) with cached period-of-record data. Mann-Kendall (trend) and Pettitt (changepoint) both require at least 8 years spanning at least 10 years of record. A gage below that reports no signal — which is not the same as “no change.”

Of the 46 gages with enough record, 5 are trending down and 1 up, and 7 carry a detected shift. The clearest is BLUE RIVER AT DILLON, CO., -7.6 points of its long-term median per decade over 50 years (p=0.0002). The other 37 show no clear signal either way.

Gage	Trend	Change / decade points of median	Significance	Years	Changepoint
▸ ELLIOTT CREEK FEEDER CANAL TO GREEN MTN RES, CO GREELCCO	↓ decreasing	-87.5	p=0.032	22	—
▸ SNAKE RIVER AT KEYSTONE SKI AREA SNAKEYCO	no clear trend	-8.7	p=0.317	27	~2015
▸ BLUE RIVER AT DILLON, CO. BLUADICO	↓ decreasing	-7.6	p=0.000	50	~1930
▸ SNAKE RIVER AT DILLON, CO. SNADILCO	no clear trend	-7.0	p=0.103	43	~1930
▸ BOULDER CREEK AT UPPER STATION, NEAR DILLON, CO. BOCUPPCO	no clear trend	+6.7	p=0.093	28	~1981
▸ BLUE RIVER AT BLUE RIVER, CO. BLUABLCO	↓ decreasing	-6.5	p=0.016	43	—
▸ TENMILE CREEK AT DILLON, CO. TENDILCO	↓ decreasing	-6.5	p=0.003	40	~1930
▸ TENMILE CREEK BL NORTH TENMILE C, AT FRISCO, CO. TENFRICO	↑ increasing	+4.3	p=0.004	68	~1981
▸ BLUE RIVER BELOW GREEN MOUNTAIN RESERVOIR, CO BLUGRECO	↓ decreasing	-3.7	p=0.012	89	~1986

37 other gage(s) show no significant trend or changepoint (not shown).

How the measurement network itself changed

This basin was not always measured the way it is today — the API-era record is dense and recent, the early record sparse. 15 gage(s) and 211 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1969. Every historical claim below is checked against this: long-term shifts that co-move with the growth of the network carry an explicit measurement-evolution caution, and abandonment screens whose idleness begins before the modern reporting era are flagged †.

Decade	Gages with data (median yr)	Structures reporting (median yr)
1900s	1	0
1910s	3	0
1920s	1	0
1930s	3	0
1940s	15	0
1950s	14	0
1960s	14	66
1970s	15	184
1980s	16	227
1990s	16	176
2000s	15	184
2010s	15	173
2020s	15	204

Mass-balance (network closure) trend

Structure divrec-history backfill coverage as of the last check: 7% of 633 schematic-relevant structures. 0 year(s) clear the 30% coverage gate so far -- the trend activates automatically once qualifying years span a full decade. No action needed; the nightly backfill keeps extending the record.

Reach gain/loss shifts (1950–2026)

Mass-balance kinks computed for every summer month back to 1950 (3195 reach-snapshots) — which reaches gain or lose water, and how that has shifted across decades. Each shift is cross-checked against the observation record above: as more diversions became metered, "unaccounted" water shrinks mechanically, which can masquerade as a hydrologic shift.

BLUE RIVER BELOW GREEN MOUNTAIN RESERVOIR, CO: reach shifted from +268 cfs to +587 cfs summer mean (more gaining, p=0.002, 77 yr) [sedimentary uplands: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records]
TENMILE CREEK BELOW WEST TENMILE CREEK, CO: reach shifted from -55 cfs to -48 cfs summer mean (more gaining, p=0.043, 11 yr) [mountain crystalline canyon: minimal groundwater storage -- large or shifting unaccounted losses here are more consistent with data/measurement issues or unmodeled plumbing than with aquifer exchange]
BLUE RIVER BELOW DILLON, CO.: reach shifted from +207 cfs to -52 cfs summer mean (more losing, p=0.000, 67 yr) [sedimentary uplands: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records] [5 alluvial wells within 2 mi of the gage; pooled water table -2.0 ft (1973–2011, no_trend)]
BOULDER CREEK AT UPPER STATION, NEAR DILLON, CO.: reach shifted from -15 cfs to -5 cfs summer mean (more gaining, p=0.041, 27 yr) [sedimentary uplands: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records]

Groundwater now has its own tab: 29 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 64 reservoir(s), end-of-year storage back to 1964, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 69-year window with full coverage (1958–2026), the dominant shared pattern across 3 gage(s) explains 85% of year-to-year variance (almost certainly a basin-wide climate/snowpack driver).

All gages in this window move with the shared pattern -- no localized outlier.

Structures most implicated by reconciliation (as of 2026-07-06)

Which structures' data absorbed the most correction when the current mass-balance snapshot was reconciled -- see the Historical tab for the full picture on any date.

DILLON SNOW RETURN FLOW (return): +16.6 cfs (100% of that reach's correction)

Data provenance & quality

Where these numbers come from and how far they can be trusted. Grade D (2/6 points) — the components below are the finding; the letter alone is not. Sources: DWR HydroBase snapshot HydroBase_CO_20260707 (imported 2026-08-19) for history, plus the CDSS REST API for current conditions.

Check	State	What was measured
gage freshness	stale	newest gage reading is 45 day(s) old (target 7)
diversion record	stale	newest diversion record is 658 day(s) old (DWR publishes ~1 year in arrears)
structure coverage	sparse	7% of schematic structures have data

Independent check: PASS — 100.0000% agreement across 37,314 stored values re-checked against DWR's authoritative record (HydroBase_CO_20260707), over 20 structures. 0 disagreement(s) beyond a 0.01 cfs tolerance. Checked 2026-08-19; a rotating sample covers the whole basin across successive runs, and the structures this report cites are checked every time.

Federal cross-check: PASS — 99.89% day-level agreement with USGS's own published records for the same gages, across 40 co-listed station(s) and 414,582 overlapping days (within max(2%, 0.5 cfs) daily). Pre-1950 records at some gages carry known between-agency day-stamp and transcription differences — scored at each year's best ±1-day alignment; residual disagreement is real historical divergence, flagged for review.

46 gage(s) / 442,160 daily values (1904-08-01–2026-07-06); 525 structure(s) with diversion records; 1247 with decreed rights. Methodology has not yet had independent expert review — treat every figure as an advisory screen, not an administrative or legal conclusion.

104 water-level measurements across 29 monitored well(s) — 27 alluvial, 0 bedrock — plus 25 administered well(s) reporting metered pumping.

What is being counted

Observation wells and pumping wells are different populations and are never conflated: water levels come from monitored observation wells, and metered pumping comes from administered wells reporting through diversion records. Click any well to chart its own record.

Well map

3D aquifer x-ray

Every aquifer unit as its own head surface, animated through time.

How the surfaces are built, and what they are not

Alluvial water table on top, Denver Basin members (Dawson, Denver, Arapahoe, Laramie–Fox Hills) stacked beneath where measured, interpolated from measured water levels. Units are never mixed; a surface exists only inside its own unit's well coverage, with no extrapolation; thin epochs are suppressed and say why. Vertical scale is exaggerated for readability and z is head elevation in feet. These are measured heads, not a calibrated groundwater model.

Water-table trends

Of 0 well(s) with enough record for a trend test: 0 declining, 0 rising.

Stream corridors — the surface connection

Where a reach's gain or loss has shifted, the wells within two miles of its anchoring gage and what their water table did over the same era.

How the corridor is assembled

For each reach whose gain/loss has shifted (Trends tab): the wells within 2 miles of its anchoring gage, their pooled water-table history over the same era, and an advisory Glover screen of lagged stream depletion from nearby metered pumping. v1 proximity = distance to the reach's anchoring gage; segment-based reach join is a flagged upgrade.

TENMILE CREEK BELOW WEST TENMILE CREEK, CO: 0 alluvial well(s) nearby. Glover screen: 0.7 cfs of nearby metered alluvial pumping → est. lagged depletion 0.6–0.7 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

BLUE RIVER BELOW DILLON, CO.: 5 alluvial well(s) nearby; pooled water table -2.0 ft (1973–2011, no_trend, p=0.9641)

Wells labeled by administrative world before anything else is said about them: tributary alluvium participates in the priority system; designated-basin and Denver Basin bedrock aquifers are governed differently and are excluded from stream-connection reasoning. Read bedrock declines differently too: deep bedrock aquifers recharge negligibly on human timescales, so a falling bedrock level is storage mining — effectively permanent — not a drought response that a wet year undoes. All screens advisory.

64 reservoir(s) with 6,955 storage measurement(s), 1964–2025. Basin storage as of 2024-10-31 (the record's own end — reservoir records publish ~annually): 295,455 AF across 4 reservoir(s).

Why storage matters to the flow network

Storage change is real water the mass balance must credit — a losing reach beside a filling reservoir isn't losing water, it's banking it.

Reservoir map — how full is each vessel?

What “full” is measured against

Bubble size is proportional to a reservoir's record-high storage. Fill is its last recorded storage as a share of its surveyed capacity (USACE National Inventory of Dams) where a confident NID match exists — the tooltip names the matched dam — and as a share of its own record high otherwise. A wrong capacity would be worse than an honest record high, so only confident joins upgrade.

A dashed teal ring marks reservoirs reporting live DWR telemetry: their fill reflects yesterday's storage, is drawn as a dotted tail on charts, and is treated as provisional until the next verified HydroBase snapshot supersedes it.

Basin storage, end of each water year

End-of-water-year totals; per-year reservoir counts shown because reporting coverage varies -- a total is only comparable to years with similar counts.

Largest reservoirs on record

Click a reservoir to chart its full storage history.

Reservoir	Last recorded storage (AF)	As of
▸ DILLON RESERVOIR (3604512)	217,354	2024-10-31
▸ GREEN MOUNTAIN RESERVOIR (3603543)	76,976	2024-10-31
▸ CLINTON GULCH RESERVOIR (3603575)	4,205	2021-10-31
▸ BLACK LAKE AND RESERVOIR (3603533)	1,997	2010-10-31
▸ CATARACT LAKE AND RESERVOIR (3603538)	1,653	2010-10-31
▸ GOOSE PASTURE TARN (3603542)	805	2024-10-31
▸ MIN LAKE MOHAWK NO 2 (3603586)	444	1992-10-31
▸ LOWER BLACK CREEK RESERVOIR (3603556)	400	1988-09-22

Decreed rights on this network run from 1869-07-01 to 2022-08-29. 6 abandonment screens and 171 compliance flags are listed below as leads for review — a screen is not an abandonment and a flag is not a violation.

Rights on file: 2639 across 1247 structure(s); 97 structure(s) carry 0 court-case references. Advisory reading aids on public DWR data — not administrative or legal conclusions.

Abandonment radar (6 screens)

Absolute rights with 10+ years of no recorded diversions. Screens only — storage, alternate points, and plan operations can explain nonuse lawfully. And diversion REPORTING itself only reached its modern level ~1969 — idleness that begins before then may be unreported use, not nonuse (flagged † below).

SODA CREEK DITCH (3600809) (1900-07-01, 2.7 cfs decreed): last active 1969 — 11 years idle
BENTON CREEK NO 1 DITCH (3600522) (1912-10-06, 4.2 cfs decreed): last active 1970 — 10 years idle
BENTON CREEK NO 2 DITCH (3600523) (1904-10-30, 2.2 cfs decreed): last active 1970 — 10 years idle
COULTER NO 1 DITCH (3600575) (1904-08-31, 0.8 cfs decreed): last active 1970 — 10 years idle
COULTER NO 2 DITCH (3600576) (1913-04-24, 0.2 cfs decreed): last active 1970 — 10 years idle
ENGLE DITCH (3600614) (1942-09-25, 4.1 cfs decreed): last active 1970 — 10 years idle

Compliance screens (171 advisory flags)

Screened 279 of 1247 structures with rights (341 have diversion history on file). A flag is a lead for expert review — augmentation plans, exchanges, and free-river conditions can make over-decree diversions lawful and are deliberately not modeled.

MIN FLOW BLUE RIVER 5 - DILLON TO STRAIG (3602043): Observed p99 daily rate 947.0 cfs (max 1900.0) exceeds total decreed absolute 50.0 cfs across 5100 recorded day(s).
MIN FLOW BLUE RIVER 4 - SWAN RIVER TO DI (3602037): Observed p99 daily rate 528.4 cfs (max 715.0) exceeds total decreed absolute 32.0 cfs across 4986 recorded day(s).
BLUE VALLEY RANCH HYDRO (3600985): Observed p99 daily rate 222.0 cfs (max 222.0) exceeds total decreed absolute 129.0 cfs across 14666 recorded day(s).
MIN FLOW BLUE RIVER 3 - SWAN RIVER UP TO (3602030): Observed p99 daily rate 177.0 cfs (max 339.0) exceeds total decreed absolute 20.0 cfs across 5822 recorded day(s).
ELLIOTT CREEK FEEDER (3600606): Observed p99 daily rate 118.0 cfs (max 200.0) exceeds total decreed absolute 90.0 cfs across 17164 recorded day(s).
MIN FLOW SNAKE RIVER LOW - NORTH FORK TO (3602033): Observed p99 daily rate 107.0 cfs (max 108.0) exceeds total decreed absolute 12.0 cfs across 4350 recorded day(s).
MIN FLOW STRAIGHT CREEK (3602040): Observed p99 daily rate 90.6 cfs (max 125.0) exceeds total decreed absolute 2.5 cfs across 3580 recorded day(s).
CON-HOOSIER SYS MCCULLOUGH DITCH (3604690): Observed p99 daily rate 76.0 cfs (max 128.4) exceeds total decreed absolute 60.0 cfs across 8214 recorded day(s).
CON-HOOSIER TUNNEL (3604699): Observed p99 daily rate 65.7 cfs (max 163.5) exceeds total decreed absolute 20.0 cfs across 26128 recorded day(s).
HOAGLAND CANAL (ELLIOT) (3600662): Observed p99 daily rate 65.0 cfs (max 69.9) exceeds total decreed absolute 25.0 cfs across 9969 recorded day(s).

Seniority (top structures by decreed rate)

Structure	Senior priority date	Rights	Decreed abs (cfs)	Decreed abs (AF)	Conditional?
GREEN MTN HYDRO-ELECTRIC (3600881)	1935-08-01	1	1726.0	0	—
BLUE RIVER DIVERSION PROJECT (3604684)	1946-06-24	1	654.0	0	yes
TOWN OF BRECKENRIDGE WHITEWATER PARK (3607293)	2000-12-21	1	500.0	0	—
CLIMAX INTEGRATED WATER SYSTEM (3604923)	1903-01-01	13	416.5	103	yes
CON-HOOSIER SYS BLUE RIVER DITCH (3604683)	1948-05-13	3	200.0	0	—
BLUE VALLEY RANCH HYDRO (3600985)	1981-03-09	1	129.0	0	—
MIN FLOW BLUE RIVER 9 - BOULDER CK TO SL (3602047)	1904-05-23	3	125.0	0	—
MIN FLOW BLUE RIVER 10 - SLATE CK TO GMR (3602048)	1904-05-23	2	125.0	0	—
MIN FLOW BLUE RIVER 8 - ROCK CK TO BOULD (3602046)	1987-10-02	1	115.0	0	—
ELLIOTT CREEK FEEDER (3600606)	1935-08-01	1	90.0	0	—
CON-HOOSIER EAST HOOSIER DITCH (3604689)	1929-08-05	2	90.0	0	—
MIN FLOW BLUE RIVER 11 - GMR TO COLORADO (3602049)	1987-10-02	1	85.0	0	—
LOBACK DITCH (3600709)	1930-12-31	4	75.8	0	—
MIN FLOW BLUE RIVER 7 - ROCK CK TO WILLO (3602045)	1987-10-02	1	75.0	0	—
CON-HOOSIER SYS MCCULLOUGH DITCH (3604690)	1948-05-13	3	60.0	0	—

No inventory or legal-document changes detected since the daily watch began.

If a call were placed at a given seniority, which structures in this basin would be out of priority, and how much of their decreed rate would be curtailed? Computed from this basin's cached decrees.

What this does and doesn't model. Seniority arithmetic only: every right junior to the call is treated as curtailed. It does not model reach applicability — structures downstream of the calling point are not administered by it — and it applies no futile-call judgment. Read it as “who is junior to this date, and by how much,” not as a prediction of what the Division Engineer would actually order.

Pick a calling right

Real decrees from this basin, ordered by administration number — that is, by actual seniority. The years will look out of order, and that is correct: an administration number encodes the adjudication date as well as the appropriation date, so a right appropriated in 1970 can be administered ahead of one from 1950. A senior call curtails almost everything; a junior one curtails almost nothing.

Or enter an administration number directly

Administration number

DWR administration numbers encode appropriation and adjudication dates; lower is more senior.