Computed 2026-08-20 09:26 from 33 gage(s) with cached period-of-record data. Statistical tests (Mann-Kendall trend, Pettitt changepoint) require at least 8 years spanning at least 10 years of record -- gages below that report no signal, not "no change."

Data provenance & quality

Where these numbers come from and how far they can be trusted. Grade B (4/6 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	expected-lag	newest diversion record is 293 day(s) old (DWR publishes ~1 year in arrears)
structure coverage	partial	53% of schematic structures have data

Independent check: PASS — 100.0000% agreement across 100,670 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 — 99.98% day-level agreement with USGS's own published records for the same gages, across 28 co-listed station(s) and 164,636 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.

33 gage(s) / 191,617 daily values (1904-05-01–2026-07-06); 723 structure(s) with diversion records; 1262 with decreed rights. Methodology has not yet had independent expert review — treat every figure as an advisory screen, not an administrative or legal conclusion.

Read this first: the measurement network itself evolved

This basin was not always measured the way it is today — the API-era record is dense and recent, the early record sparse. 5 gage(s) and 387 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1973. 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	7	0
1910s	1	0
1920s	6	0
1930s	10	0
1940s	10	0
1950s	4	32
1960s	2	0
1970s	4	344
1980s	4	412
1990s	4	436
2000s	5	482
2010s	6	428
2020s	5	291

Gage flow trend & changepoints

Every located gage with a period of record — dot size scales with the strength of its flow trend (|Sen slope| in %/decade, the same statistic as the table below), color with direction. An amber ring marks a detected Pettitt changepoint. Click a gage to chart its trend and shift.

Gage	Trend	Change / decade	Significance	Years	Changepoint
▸ ILLINOIS CREEK AT WALDEN, CO.☆ ILLWALCO	↓ decreasing	-103.9%	p=0.004	25	~1932
▸ NORTH PLATTE RIVER NEAR WALDEN, CO.☆ NOPLWACO	no clear trend	-15.2%	p=0.094	26	~1930
▸ MICHIGAN RIVER AT WALDEN, CO.☆ MICWLDCO	↓ decreasing	-13.0%	p=0.000	43	~1933

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

Mass-balance (network closure) trend

Structure divrec-history backfill coverage as of the last check: 53% of 123 schematic-relevant structures. Kink count trend: increasing (p=0.000), kink magnitude trend: increasing (p=0.003) across 48 qualifying year(s).

Reach gain/loss shifts (1974–2026)

Mass-balance kinks computed for every summer month back to 1974 (244 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.

• MICHIGAN RIVER AT WALDEN, CO.: reach shifted from +13 cfs to -47 cfs summer mean (more losing, p=0.012, 24 yr) [sedimentary uplands: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records] [2 alluvial wells within 2 mi of the gage; pooled water table -0.1 ft (1976–2024, no_trend)]

Groundwater now has its own tab: 52 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 204 reservoir(s), end-of-year storage back to 1974, click-to-chart histories.

Cross-gage pattern fingerprint

Not enough gages with a long enough common-coverage window yet to fingerprint shared patterns.

The basin's aquifer story, from 326 water-level measurements across 52 monitored well(s) (17 alluvial, 12 bedrock, rest unclassified) — plus 4 administered well(s) reporting metered pumping through diversion records. Observation wells and pumping wells are different populations and are never conflated. Click a well to chart its record.

Well map

Every monitored well with a location — hover for identity, click to chart its water-level record below. ● alluvial   ● bedrock / confined (Denver Basin, High Plains, etc. — one-way, no human-timescale recharge)   ● unclassified — marker size scales with the strength of the well's water-level trend (|Sen slope| in ft/decade — the same Mann-Kendall/Sen statistic as the trends table below); the smallest, faintest dots have too little record to test.

3D aquifer x-ray

Every aquifer unit as its own 3D head surface — alluvial water table on top, Denver Basin members (Dawson, Denver, Arapahoe, Laramie–Fox Hills) stacked beneath where measured — interpolated from measured water levels and animated through time. Units are never mixed; surfaces exist only inside each unit's well coverage (no extrapolation); thin epochs are suppressed with their reason shown. Vertical scale exaggerated for readability; z is head elevation in feet. Advisory — measured heads, not a calibrated model.

Load 3D x-ray

Water-table trends

Of 4 well(s) with enough record for a trend test: 1 declining, 1 rising.

Fastest-declining wells	Setting	ft / decade	Span	p
▸ NP-03☆	unknown	-10.65	33 yr	0.0131

Stream corridors — the surface connection

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.

MICHIGAN RIVER AT WALDEN, CO.: 2 alluvial well(s) nearby; pooled water table -0.1 ft (1976–2024, no_trend, p=0.6922). Glover screen: 0.3 cfs of nearby metered alluvial pumping → est. lagged depletion 0.3–0.3 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

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.

204 reservoir(s) with 16,908 storage measurement(s), 1974–2026. Basin storage as of 2025-10-31 (the record's own end — reservoir records publish ~annually): 21,106 AF across 62 reservoir(s). 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?

Each reservoir drawn as a vessel: bubble size ∝ its record-high storage, fill level = 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 of its own record high otherwise (a wrong capacity would be worse than an honest record high, so only confident joins upgrade). Hover for numbers, click to chart its history below the map. A dashed teal ring marks reservoirs reporting live DWR telemetry — their fill reflects yesterday's storage, drawn as a dotted tail on charts and treated as provisional until the next verified HydroBase snapshot supersedes it. ● <25% ● 25–60% ● 60–90% ● >90%

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
▸ LAKE JOHN (4703750) ☆	7,092	2025-10-31
▸ MACFARLANE RES (4703614) ☆	2,732	2025-10-31
▸ LAUNE RESERVOIR (4703742) ☆	2,602	2025-10-31
▸ NORTH MICHIGAN CK RES (4703753) ☆	1,090	2025-10-31
▸ WALDEN RESERVOIR (4703627) ☆	902	2025-10-31
▸ MEADOW CREEK RES (4704335) ☆	872	2025-10-31
▸ BIG CREEK RESERVOIR (4703595) ☆	730	2025-10-31
▸ LAKE JOHN ANNEX (4703699) ☆	692	2025-10-31

Decrees, seniority, and administrative calls connected to this basin's flow network. Advisory reading aids on public DWR data — not administrative or legal conclusions. Rights on file: 1869 across 1262 structure(s); 60 structure(s) carry 0 court-case references.

Abandonment radar (25 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 ~1973 — idleness that begins before then may be unreported use, not nonuse (flagged † below).

• SURPRISE DITCH (4700913)☆ (1902-09-12, 10.0 cfs decreed): last active 1975 — 49 years idle
• ANTELOPE NO 1 DITCH (4701012)☆ (1908-05-01, 5.5 cfs decreed): last active 1976 — 48 years idle
• HUGH GRIFFITH DITCH (4700677)☆ (1888-05-01, 5.4 cfs decreed): last active 1998 — 26 years idle
• SHEARER SPRING RES #2 (4703639)☆ (1989-11-30, 0.0 cfs decreed): last active 2004 — 20 years idle
• DWR SPG (4702001)☆ (1935-05-10, 0.0 cfs decreed): last active 2005 — 19 years idle
• SHEARER SPRINGS RES #1 (4703638)☆ (1939-12-31, 0.0 cfs decreed): last active 2005 — 19 years idle
• ROBBIES POND (4703670)☆ (1967-07-15, 0.0 cfs decreed): last active 2005 — 19 years idle
• SOUTH CASE CONTOUR (4703682)☆ (1977-12-31, 2.0 cfs decreed): last active 2005 — 19 years idle
• DEER CREEK SPRING (4701076)☆ (1955-12-31, 0.0 cfs decreed): last active 2006 — 18 years idle
• BLUEBILL POND (4703544)☆ (1967-08-15, 2.0 cfs decreed): last active 2006 — 18 years idle

Compliance screens (390 advisory flags)

Screened 566 of 1262 structures with rights (648 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.

• MUTUAL DITCH (4700786)☆: Observed p99 daily rate 167.4 cfs (max 177.1) exceeds total decreed absolute 158.0 cfs across 9366 recorded day(s).
• MIDLAND DITCH (4700774)☆: Observed p99 daily rate 150.0 cfs (max 212.7) exceeds total decreed absolute 90.0 cfs across 20235 recorded day(s).
• INDEPENDENT DITCH (4700684)☆: Observed p99 daily rate 120.0 cfs (max 120.0) exceeds total decreed absolute 113.0 cfs across 9367 recorded day(s).
• STAPLES DITCH 1 (4700895)☆: Observed p99 daily rate 105.0 cfs (max 116.1) exceeds total decreed absolute 100.0 cfs across 7914 recorded day(s).
• INDEPENDENCE DITCH (4700683)☆: Observed p99 daily rate 95.0 cfs (max 95.0) exceeds total decreed absolute 52.0 cfs across 7431 recorded day(s).
• SENECA DITCH (4700868)☆: Observed p99 daily rate 91.4 cfs (max 93.0) exceeds total decreed absolute 73.0 cfs across 7206 recorded day(s).
• LITTLE NELLIE DITCH (4700730)☆: Observed p99 daily rate 91.0 cfs (max 101.4) exceeds total decreed absolute 89.2 cfs across 6409 recorded day(s).
• MALLON DITCH NO 2 (4700748)☆: Observed p99 daily rate 88.0 cfs (max 100.0) exceeds total decreed absolute 80.0 cfs across 7296 recorded day(s).
• LEWIS DITCH (4700723)☆: Observed p99 daily rate 80.0 cfs (max 80.0) exceeds total decreed absolute 40.0 cfs across 6628 recorded day(s).
• BIG GRIZZLY DITCH (4700512)☆: Observed p99 daily rate 78.0 cfs (max 96.7) exceeds total decreed absolute 66.7 cfs across 7574 recorded day(s).

Seniority (top structures by decreed rate)

Structure	Senior priority date	Rights	Decreed abs (cfs)	Decreed abs (AF)	Conditional?
MICHIGAN DITCH (4704603)☆	1902-07-10	5	275.0	0	—
WOLFER DITCH (4700961)☆	1888-05-08	5	218.5	0	—
BUDDY'S POND (4703546)☆	1972-12-31	2	206.0	29	—
ROSS POND (4703582)☆	1982-12-31	2	204.5	14	—
NORTH HACKLEY POND (4703685)☆	1986-12-31	2	204.5	5	—
SOUTH HACKLEY POND (4703686)☆	1986-12-31	2	204.5	4	—
RODRIQUEZ POND (4703687)☆	1986-12-31	2	204.5	40	—
SCHROEDER POND (4703697)☆	2002-12-31	2	185.0	3	—
MUTUAL DITCH (4700786)☆	1888-08-29	4	158.0	0	—
HOWARD DITCH (4700672)☆	1888-05-25	5	136.0	0	yes
INDEPENDENT DITCH (4700684)☆	1888-09-01	3	113.0	0	—
OVERLAND DITCH (4700819)☆	1888-05-31	9	108.3	0	—
SQUIBOB DITCH (4700893)☆	1888-04-30	7	106.5	0	—
DARBY DITCH (4700584)☆	1901-05-31	3	103.9	0	—
HUBBARD DITCH 2 (4700674)☆	1889-04-02	7	103.0	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.

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
Simulate

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