Computed 2026-08-20 09:11 from 17 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 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	3% of schematic structures have data

Independent check: PASS — 100.0000% agreement across 182,862 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 — 99.46% day-level agreement with USGS's own published records for the same gages, across 13 co-listed station(s) and 44,916 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.

17 gage(s) / 90,139 daily values (1921-04-01–2026-07-06); 347 structure(s) with diversion records; 1758 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. 8 gage(s) and 85 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1950. 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)
1920s	1	0
1940s	1	28
1950s	2	122
1960s	0	113
1970s	2	120
1980s	2	161
1990s	5	162
2000s	4	94
2010s	4	93
2020s	7	86

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
▸ ELK CREEK AT NEW CASTLE, CO.☆ ELKNEWCO	↓ decreasing	-17.9%	p=0.012	14	—
▸ RIFLE CREEK BELOW RIFLE GAP RESERVOIR☆ RIFRGRCO	↓ decreasing	-15.5%	p=0.033	39	—
▸ GRASS VALLEY CANAL NEAR RIFLE FALLS, CO☆ GRSVALCO	↓ decreasing	-14.4%	p=0.000	39	~2008

14 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: 3% of 832 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 (1955–2026)

Mass-balance kinks computed for every summer month back to 1955 (170 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.

No reach shows a statistically significant long-term gain/loss shift.

Groundwater now has its own tab: 35 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 73 reservoir(s), end-of-year storage back to 1965, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 24-year window with full coverage (2003–2026), the dominant shared pattern across 3 gage(s) explains 48% 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.

The basin's aquifer story, from 96 water-level measurements across 35 monitored well(s) (21 alluvial, 1 bedrock, rest unclassified) — plus 11 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 0 well(s) with enough record for a trend test: 0 declining, 0 rising.

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.

73 reservoir(s) with 3,268 storage measurement(s), 1965–2022. Basin storage as of 2021-10-31 (the record's own end — reservoir records publish ~annually): 2,936 AF across 2 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
▸ HARVEY GAP RESERVOIR (3903510) ☆	2,400	1971-10-01
▸ RIFLE GAP RESERVOIR (3903508) ☆	2,241	2021-10-31
▸ GRASS VALLEY CANAL (3900563) ☆	1,559	2009-10-01
▸ MEADOW CREEK RESERVOIR (3903940) ☆	984	2008-10-31
▸ FRAVERT RESERVOIR (3903504) ☆	719	1970-11-01
▸ GRASS VALLEY RESERVOIR (3903505) ☆	695	2021-10-31
▸ PARK RESERVOIR (3903507) ☆	215	2008-10-31
▸ CHAMBERS POND NO 2 (3904000) ☆	200	2004-10-31

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: 2463 across 1758 structure(s); 88 structure(s) carry 0 court-case references.

Abandonment radar (22 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 ~1950 — idleness that begins before then may be unreported use, not nonuse (flagged † below).

• HAZELTON SPRING NO 1 (3900820)☆ (1997-03-10, 0.0 cfs decreed): last active 1953 — 34 years idle
• VETTER DITCH (3900683)☆ (1888-10-27, 0.3 cfs decreed): last active 1956 — 31 years idle
• HUBBARD SPRING AND PL (3900720)☆ (1942-10-03, 0.1 cfs decreed): last active 1957 — 30 years idle
• MEADOW CREEK RES INLET D (3900722)☆ (1954-09-13, 2.0 cfs decreed): last active 1957 — 30 years idle
• MILE POND DITCH (3900725)☆ (1902-11-07, 0.4 cfs decreed): last active 1957 — 30 years idle
• DURAND SPRING & PIPELINE (3900711)☆ (1913-05-15, 0.1 cfs decreed): last active 1964 — 23 years idle
• DOW E MIDDLE FORK PL (3900707)☆ (1883-05-17, 6.5 cfs decreed): last active 1967 — 20 years idle
• DOW MIDDLE FK PIPELINE (3900708)☆ (1883-05-17, 8.9 cfs decreed): last active 1968 — 19 years idle
• THE PUMPING PIPELINE OF THE UNION OIL CO (3900728)☆ (1883-02-15, 11.5 cfs decreed): last active 1968 — 19 years idle
• ANDERSON STOCKWATER PL (3900502)☆ (1930-05-01, 0.2 cfs decreed): last active 1971 — 16 years idle

Compliance screens (151 advisory flags)

Screened 257 of 1758 structures with rights (288 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.

• LOWER CACTUS VALLEY DITCH (3900612)☆: Observed p99 daily rate 55.0 cfs (max 65.5) exceeds total decreed absolute 53.0 cfs across 47860 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• WARE AND HINDS DITCH (3900687)☆: Observed p99 daily rate 54.0 cfs (max 60.0) exceeds total decreed absolute 47.3 cfs across 44192 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• WILLIAMS CANAL (3900825)☆: Observed p99 daily rate 35.6 cfs (max 38.3) exceeds total decreed absolute 31.0 cfs across 26593 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• THOMPKINS DITCH (3900672)☆: Observed p99 daily rate 26.0 cfs (max 27.6) exceeds total decreed absolute 21.0 cfs across 29221 recorded day(s).
• CLOUGH NO 1 DITCH (3900532)☆: Observed p99 daily rate 22.2 cfs (max 23.2) exceeds total decreed absolute 17.8 cfs across 10852 recorded day(s).
• CORYELL JOINT STOCK IRRI (3900540)☆: Observed p99 daily rate 20.5 cfs (max 21.6) exceeds total decreed absolute 15.0 cfs across 9880 recorded day(s).
• GRANLEE DITCH (3900562)☆: Observed p99 daily rate 16.1 cfs (max 20.0) exceeds total decreed absolute 12.7 cfs across 18524 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• WEST FORK DITCH (3900691)☆: Observed p99 daily rate 16.0 cfs (max 35.0) exceeds total decreed absolute 8.0 cfs across 10852 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• RIFLE FALLS HTC SPG COLL (3905398)☆: Observed p99 daily rate 16.0 cfs (max 16.0) exceeds total decreed absolute 11.7 cfs across 3574 recorded day(s).
• NELSON DITCH (3900627)☆: Observed p99 daily rate 15.0 cfs (max 15.0) exceeds total decreed absolute 0.8 cfs across 2700 recorded day(s).

Seniority (top structures by decreed rate)

Structure	Senior priority date	Rights	Decreed abs (cfs)	Decreed abs (AF)	Conditional?
WILLCOX CANAL (3900752)☆	1901-09-01	1	200.0	0	—
GRASS VALLEY CANAL (3900563)☆	1887-07-20	2	124.0	0	—
EAST RIFLE CR PL NO 2 (3900649)☆	1953-03-12	1	90.0	0	—
LOWER CACTUS VALLEY DITCH (3900612)☆	1887-03-23	3	53.0	0	—
WARE AND HINDS DITCH (3900687)☆	1883-10-01	7	47.3	0	—
RIFLE CREEK CANON DITCH (3900645)☆	1882-05-15	14	41.0	0	—
SILT PUMP CANAL (3900663)☆	1956-11-21	2	36.1	0	yes
DEWEESE DITCH (3900548)☆	1897-11-15	3	35.0	0	—
WILLIAMS CANAL (3900825)☆	1886-03-15	20	31.0	0	yes
DOW PUMPING PLANT AND PIPELINE (3900709)☆	1883-05-17	14	30.9	0	yes
GRAND TUNNEL DITCH (3900574)☆	1882-05-15	11	28.5	0	—
PIERSON AND HARRIS DITCH (3900638)☆	1898-09-27	3	28.1	0	—
LOW COST DITCH (3900610)☆	1887-01-04	7	27.9	0	—
PARACHUTE DITCH (3900635)☆	1886-02-01	6	27.2	0	—
DAVENPORT DITCH (3900546)☆	1889-05-01	6	21.4	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.