Computed 2026-08-20 08:39 from 57 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 C (3/6 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.

Independent check: PASS — 100.0000% agreement across 667,373 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 — 95.75% day-level agreement with USGS's own published records for the same gages, across 17 co-listed station(s) and 225,167 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.

57 gage(s) / 584,090 daily values (1912-04-01–2026-07-06); 175 structure(s) with diversion records; 1909 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. 43 gage(s) and 49 structure(s) report in 2026, but structure reporting only reached half its modern level around ~2017. 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 †.

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.

39 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: 1% of 2617 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 (4051 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.

• ARKANSAS RIVER AT LA JUNTA, CO: reach shifted from +302 cfs to -135 cfs summer mean (more losing, p=0.000, 77 yr) [sedimentary plains/foothills: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records] [74 alluvial wells within 2 mi of the gage; pooled water table +2.3 ft (1959–2018, increasing)]
• ARKANSAS RIVER AT LAS ANIMAS, CO.: reach shifted from -93 cfs to +329 cfs summer mean (more gaining, p=0.000, 77 yr) [sedimentary plains/foothills: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records] [measurement-evolution caution: this shift co-moves with the growth of the gage/metering network (rho=0.51) -- part of it may be unaccounted water becoming accounted, not hydrologic change] [43 alluvial wells within 2 mi of the gage; pooled water table +0.3 ft (1955–2023, no_trend)]
• TIMPAS CREEK AT MOUTH NEAR SWINK, CO.: reach shifted from -270 cfs to +82 cfs summer mean (more gaining, p=0.000, 58 yr) [alluvial valley: real alluvial aquifer -- a decades-long shift toward losing is the classic signature of alluvial pumping and urbanization] [33 alluvial wells within 2 mi of the gage; pooled water table +2549.3 ft (1959–2023, no_trend)]
• HOLBROOK CANAL AT MILE 3.4 NEAR ROCKY FORD: reach shifted from -7 cfs to +125 cfs summer mean (more gaining, p=0.010, 41 yr) [sedimentary plains/foothills: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records] [measurement-evolution caution: this shift co-moves with the growth of the gage/metering network (rho=0.44) -- part of it may be unaccounted water becoming accounted, not hydrologic change] [19 alluvial wells within 2 mi of the gage; pooled water table -0.3 ft (1960–2011, decreasing)]
• PURGATOIRE RIVER NEAR LAS ANIMAS, CO.: reach shifted from -43 cfs to -255 cfs summer mean (more losing, p=0.001, 77 yr) [alluvial valley: real alluvial aquifer -- a decades-long shift toward losing is the classic signature of alluvial pumping and urbanization] [17 alluvial wells within 2 mi of the gage; pooled water table +1585.6 ft (1959–2023, no_trend)]
• HORSE CREEK AT HIGHWAY 194: reach shifted from -114 cfs to +23 cfs summer mean (more gaining, p=0.000, 34 yr) [sedimentary plains/foothills: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records] [measurement-evolution caution: this shift co-moves with the growth of the gage/metering network (rho=0.6) -- part of it may be unaccounted water becoming accounted, not hydrologic change] [21 alluvial wells within 2 mi of the gage; pooled water table +95267.5 ft (1958–2018, increasing)]

Groundwater now has its own tab: 1087 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 22 reservoir(s), end-of-year storage back to 1950, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 88-year window with full coverage (1939–2026), the dominant shared pattern across 4 gage(s) explains 84% 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.

• COLO CANAL RETURN FLOWS (return): +57.8 cfs (50% of that reach's correction)
• CITY OF ROCKY FORD WWTP RETURNS (return): +57.8 cfs (50% of that reach's correction)
• BENT FORT WWTP RETURNS (return): -16.9 cfs (100% of that reach's correction)
• LAS ANIMAS R/O RETURN FLOWS (return): +9.3 cfs (100% of that reach's correction)

The basin's aquifer story, from 21,337 water-level measurements across 1087 monitored well(s) (917 alluvial, 29 bedrock, rest unclassified) — plus 5 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.

Water-table trends

Of 287 well(s) with enough record for a trend test: 54 declining, 70 rising.

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.

ARKANSAS RIVER AT LA JUNTA, CO: 74 alluvial well(s) nearby; pooled water table +2.3 ft (1959–2018, increasing, p=0.0). Glover screen: 0.0 cfs of nearby metered alluvial pumping → est. lagged depletion 0.0–0.0 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

ARKANSAS RIVER AT LAS ANIMAS, CO.: 43 alluvial well(s) nearby; pooled water table +0.3 ft (1955–2023, no_trend, p=0.0527). Glover screen: 0.0 cfs of nearby metered alluvial pumping → est. lagged depletion 0.0–0.0 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

TIMPAS CREEK AT MOUTH NEAR SWINK, CO.: 33 alluvial well(s) nearby; pooled water table +2549.3 ft (1959–2023, no_trend, p=0.6098)

HOLBROOK CANAL AT MILE 3.4 NEAR ROCKY FORD: 19 alluvial well(s) nearby; pooled water table -0.3 ft (1960–2011, decreasing, p=0.0029)

PURGATOIRE RIVER NEAR LAS ANIMAS, CO.: 17 alluvial well(s) nearby; pooled water table +1585.6 ft (1959–2023, no_trend, p=0.8575)

HORSE CREEK AT HIGHWAY 194: 21 alluvial well(s) nearby; pooled water table +95267.5 ft (1958–2018, increasing, p=0.0002)

APISHAPA RIVER NEAR FOWLER, CO: 47 alluvial well(s) nearby; pooled water table +0.1 ft (1959–2023, no_trend, p=0.7412)

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.

22 reservoir(s) with 10,582 storage measurement(s), 1950–2024. 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.

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: 2077 across 1909 structure(s); 71 structure(s) carry 0 court-case references.

Abandonment radar (20 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 ~2017 — idleness that begins before then may be unreported use, not nonuse (flagged † below).

• CLUTE SPRING DITCH (1700627)☆ (1948-07-31, 1.0 cfs decreed): last active 1980 — 45 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• FOULK DITCH & IRRIG SYS (1700564)☆ (1954-01-01, 3.0 cfs decreed): last active 1982 — 43 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• 1700575☆ (1948-12-02, 5.0 cfs decreed): last active 1983 — 42 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• CROWLEY COUNTY WELL NO 3 (1706019)☆ (1981-08-31, 0.6 cfs decreed): last active 1983 — 42 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• ADOBE CREEK FEEDER (1700674)☆ (1906-01-25, 17262.0 cfs decreed): last active 2007 — 18 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• MUSTANG RESERVOIR CANAL (1700608)☆ (1902-03-17, 5.0 cfs decreed): last active 2009 — 16 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• MCCABE DITCH NO 1 (1700660)☆ (1905-09-09, 10.0 cfs decreed): last active 2010 — 15 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• MCCABE DITCH NO 2 (1700688)☆ (1905-09-09, 10.0 cfs decreed): last active 2010 — 15 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• DOUGLAS - GORDON RES (1703912)☆ (1919-04-16, 0.0 cfs decreed): last active 2010 — 15 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse
• DAWN POND (1703508)☆ (1964-10-22, 0.0 cfs decreed): last active 2011 — 14 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~2017) -- early absence of record is weak evidence of nonuse

Compliance screens (19 advisory flags)

Screened 59 of 1909 structures with rights (71 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.

• CROOKED ARROYA DITCH (1700578)☆: Observed p99 daily rate 1710.0 cfs (max 1710.0) exceeds total decreed absolute 27.2 cfs across 12241 recorded day(s).
• BEST DITCH HEADGATE 1 (1700605)☆: Observed p99 daily rate 301.3 cfs (max 325.0) exceeds total decreed absolute 50.0 cfs across 196 recorded day(s).
• BEER DITCH (1700561)☆: Observed p99 daily rate 230.0 cfs (max 230.0) exceeds total decreed absolute 100.0 cfs across 166 recorded day(s).
• HORSE CREEK & BLACK DRAW DITCH (1700592)☆: Observed p99 daily rate 225.0 cfs (max 255.0) exceeds total decreed absolute 190.5 cfs across 180 recorded day(s).
• MUSTANG RESERVOIR CANAL (1700608)☆: Observed p99 daily rate 151.2 cfs (max 152.0) exceeds total decreed absolute 5.0 cfs across 218 recorded day(s).
• LAS ANIMAS CONSOLIDATED (1700556)☆: Observed p99 daily rate 131.3 cfs (max 190.0) exceeds total decreed absolute 94.6 cfs across 70259 recorded day(s).
• 1700541☆: Observed p99 daily rate 131.0 cfs (max 442.0) exceeds total decreed absolute 129.4 cfs across 74187 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• ROCKY FORD DITCH (1700558)☆: Observed p99 daily rate 120.0 cfs (max 631.0) exceeds total decreed absolute 116.2 cfs across 81054 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• MCCABE DITCH NO 1 (1700660)☆: Observed p99 daily rate 90.0 cfs (max 90.0) exceeds total decreed absolute 10.0 cfs across 60 recorded day(s).
• CROWLEY COUNTY WELL NO 3 (1706019)☆: Observed p99 daily rate 37.2 cfs (max 37.2) exceeds total decreed absolute 0.6 cfs across 46 recorded day(s).

Seniority (top structures by decreed rate)

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.