Computed 2026-08-20 08:33 from 62 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.

Independent check: PASS — 100.0000% agreement across 133,957 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 — 99.82% day-level agreement with USGS's own published records for the same gages, across 29 co-listed station(s) and 281,373 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.

62 gage(s) / 719,555 daily values (1909-10-01–2026-07-06); 419 structure(s) with diversion records; 1489 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. 42 gage(s) and 0 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 †.

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.

51 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: 2% of 3197 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 (4327 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.

• EF ARKANSAS R AT US HIGHWAY 24, NR LEADVILLE, CO.: reach shifted from -756 cfs to +81 cfs summer mean (more gaining, p=0.013, 37 yr) [sedimentary uplands: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records]
• ARKANSAS RIVER AT BUENA VISTA, CO.: reach shifted from +959 cfs to +792 cfs summer mean (more losing, p=0.027, 23 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] [11 alluvial wells within 2 mi of the gage; pooled water table +1.3 ft (1971–2003, no_trend)]
• ARKANSAS RIVER AT GRANITE, CO.: reach shifted from +700 cfs to +266 cfs summer mean (more losing, p=0.000, 77 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] [measurement-evolution caution: this shift co-moves with the growth of the gage/metering network (rho=-0.42) -- part of it may be unaccounted water becoming accounted, not hydrologic change] [2 alluvial wells within 2 mi of the gage; pooled water table -0.4 ft (1972–1994, no_trend)]
• SOUTH ARKANSAS RIVER NEAR SALIDA, CO.: reach shifted from -47 cfs to -15 cfs summer mean (more gaining, p=0.010, 18 yr) [alluvial valley: real alluvial aquifer -- a decades-long shift toward losing is the classic signature of alluvial pumping and urbanization] [measurement-evolution caution: this shift co-moves with the growth of the gage/metering network (rho=0.62) -- part of it may be unaccounted water becoming accounted, not hydrologic change] [9 alluvial wells within 2 mi of the gage; pooled water table +1.3 ft (1990–2009, no_trend)]
• ARKANSAS RIVER AT SALIDA, CO.: reach shifted from +1277 cfs to -54 cfs summer mean (more losing, p=0.000, 77 yr) [alluvial valley: real alluvial aquifer -- a decades-long shift toward losing is the classic signature of alluvial pumping and urbanization] [measurement-evolution caution: this shift co-moves with the growth of the gage/metering network (rho=-0.59) -- part of it may be unaccounted water becoming accounted, not hydrologic change] [19 alluvial wells within 2 mi of the gage; pooled water table +4.2 ft (1971–2025, decreasing)]
• CLEAR CREEK ABOVE CLEAR CREEK RESERVOIR, CO.: reach shifted from -686 cfs to -426 cfs summer mean (more gaining, p=0.001, 75 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] [2 alluvial wells within 2 mi of the gage; pooled water table -0.4 ft (1972–1994, no_trend)]

Groundwater now has its own tab: 221 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 9 reservoir(s), end-of-year storage back to 1949, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 92-year window with full coverage (1935–2026), the dominant shared pattern across 3 gage(s) explains 61% of year-to-year variance (almost certainly a basin-wide climate/snowpack driver).

TWITUNCO doesn't move with that shared pattern -- a real, localized signal (a new diversion, land-use change, or a gage-specific data problem) worth a closer look, not necessarily noise.

The basin's aquifer story, from 3,234 water-level measurements across 221 monitored well(s) (142 alluvial, 0 bedrock, rest unclassified) — plus 3 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 23 well(s) with enough record for a trend test: 9 declining, 2 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 BUENA VISTA, CO.: 11 alluvial well(s) nearby; pooled water table +1.3 ft (1971–2003, no_trend, p=0.4573)

ARKANSAS RIVER AT GRANITE, CO.: 2 alluvial well(s) nearby; pooled water table -0.4 ft (1972–1994, no_trend, p=0.8267)

SOUTH ARKANSAS RIVER NEAR SALIDA, CO.: 9 alluvial well(s) nearby; pooled water table +1.3 ft (1990–2009, no_trend, p=0.8711). Glover screen: 0.3 cfs of nearby metered alluvial pumping → est. lagged depletion 0.2–0.3 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

ARKANSAS RIVER AT SALIDA, CO.: 19 alluvial well(s) nearby; pooled water table +4.2 ft (1971–2025, decreasing, p=0.0). 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).

CLEAR CREEK ABOVE CLEAR CREEK RESERVOIR, CO.: 2 alluvial well(s) nearby; pooled water table -0.4 ft (1972–1994, no_trend, p=0.8267)

LAKE FORK CREEK BELOW SUGAR LOAF DAM NEAR LEADVILLE: 1 alluvial well(s) nearby

LAKE CREEK BELOW TWIN LAKES RESERVOIR: 1 alluvial well(s) nearby

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.

9 reservoir(s) with 17,935 storage measurement(s), 1949–2018. Basin storage as of 2018-04-30 (the record's own end — reservoir records publish ~annually): 103,958 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.

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: 1934 across 1489 structure(s); 119 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).

• BLOW DITCH - EMPIRE CREEK (1100729)☆ (1890-12-01, 2.0 cfs decreed): last active 1912 — 109 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• IRON SILVER MINING CO-EVANS GULCH BRANCH (1100757)☆ (1904-06-02, 0.3 cfs decreed): last active 1912 — 109 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• RESURRECTION DITCH (1100758)☆ (1904-06-01, 3.3 cfs decreed): last active 1912 — 109 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• EGGLESTON DITCH (1100846)☆ (1885-04-20, 1.0 cfs decreed): last active 1913 — 108 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• PINON CANON DITCH (1100847)☆ (1886-09-01, 3.4 cfs decreed): last active 1913 — 108 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• ROCK CLIFF DITCH (1100852)☆ (1890-01-30, 2.0 cfs decreed): last active 1913 — 108 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• LIPPARD DITCH (1100853)☆ (1895-05-01, 2.0 cfs decreed): last active 1913 — 108 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• TOWN DITCH (1100854)☆ (1895-05-01, 1.5 cfs decreed): last active 1913 — 108 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• SCANGA DITCH (1100856)☆ (1896-07-01, 2.8 cfs decreed): last active 1913 — 108 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse
• WILLIAMS DITCH (1100876)☆ (1877-04-30, 1.0 cfs decreed): last active 1913 — 108 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1973) -- early absence of record is weak evidence of nonuse

Compliance screens (179 advisory flags)

Screened 260 of 1489 structures with rights (281 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.

• TURQUOISE RESERVOIR (1103500)☆: Observed p99 daily rate 804.3 cfs (max 1260.9) exceeds total decreed absolute 3.0 cfs across 12875 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• OTERO PUMP STATION (1100529)☆: Observed p99 daily rate 180.5 cfs (max 180.7) exceeds total decreed absolute 1.7 cfs across 4079 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• SALIDA "OLD" GALLERY (1100882)☆: Observed p99 daily rate 76.5 cfs (max 110.2) exceeds total decreed absolute 2.5 cfs across 3126 recorded day(s).
• CHAMP DITCH (ARK) (1100517)☆: Observed p99 daily rate 52.8 cfs (max 52.8) exceeds total decreed absolute 5.0 cfs across 10598 recorded day(s).
• BOWEN DITCH (1100691)☆: Observed p99 daily rate 50.0 cfs (max 55.5) exceeds total decreed absolute 44.5 cfs across 7630 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• BUSK-IVANHOE SYSTEM (1104612)☆: Observed p99 daily rate 49.6 cfs (max 74.7) exceeds total decreed absolute 17.5 cfs across 13026 recorded day(s).
• HELENA DITCH (1100535)☆: Observed p99 daily rate 40.0 cfs (max 50.5) exceeds total decreed absolute 36.0 cfs across 16496 recorded day(s).
• MCFARLAND DITCH (1100702)☆: Observed p99 daily rate 40.0 cfs (max 40.0) exceeds total decreed absolute 0.4 cfs across 6452 recorded day(s).
• STEVENS & LEITER WELL (1100759)☆: Observed p99 daily rate 36.0 cfs (max 36.0) exceeds total decreed absolute 1.1 cfs across 4698 recorded day(s).
• FISH DITCH (1100546)☆: Observed p99 daily rate 25.0 cfs (max 25.0) exceeds total decreed absolute 0.2 cfs across 7432 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.