Computed 2026-08-20 09:32 from 19 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.

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	sparse	19% of schematic structures have data

Independent check: PASS — 100.0000% agreement across 64,889 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 — 99.87% day-level agreement with USGS's own published records for the same gages, across 16 co-listed station(s) and 207,720 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.

19 gage(s) / 255,007 daily values (1930-10-01–2026-07-06); 349 structure(s) with diversion records; 853 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 126 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1974. 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)
1930s	4	0
1940s	8	0
1950s	7	0
1960s	7	49
1970s	9	138
1980s	8	170
1990s	8	168
2000s	8	182
2010s	8	158
2020s	8	123

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
▸ RITO BLANCO NEAR PAGOSA SPRINGS, CO.☆ RITBLACO	↓ decreasing	-92.7%	p=0.034	18	—
▸ RIO BLANCO AT THE MOUTH NEAR TRUJILLO☆ RIOMOUCO	↓ decreasing	-42.7%	p=0.000	56	~1999
▸ SAN JUAN RIVER NEAR ARCHULETA, NM☆ SANARCNM	↓ decreasing	-14.3%	p=0.000	72	~1999
▸ RIO BLANCO BELOW BLANCO DIVERSION DAM NEAR PAGOSA☆ RIOBLACO	↓ decreasing	-10.9%	p=0.004	56	~1998
▸ SAN JUAN RIVER NEAR CARRACAS, CO.☆ SANCARCO	↓ decreasing	-6.2%	p=0.026	64	~1999
▸ SAN JUAN RIVER AT FARMINGTON, NM☆ SANFARNM	↓ decreasing	-4.1%	p=0.031	94	~1999
▸ EAST FORK SAN JUAN RIVER NEAR PAGOSA SPRINGS☆ EASAPACO	no clear trend	+3.3%	p=0.140	54	~1964

12 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: 19% of 497 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 (1555 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.

• RIO BLANCO AT THE MOUTH NEAR TRUJILLO: reach shifted from -575 cfs to -343 cfs summer mean (more gaining, p=0.044, 56 yr) [alluvial valley: real alluvial aquifer -- a decades-long shift toward losing is the classic signature of alluvial pumping and urbanization]
• EAST FORK SAN JUAN RIVER NEAR PAGOSA SPRINGS: reach shifted from -420 cfs to -1914 cfs summer mean (more losing, p=0.016, 41 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]

Groundwater now has its own tab: 37 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 67 reservoir(s), end-of-year storage back to 1970, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 56-year window with full coverage (1971–2026), the dominant shared pattern across 4 gage(s) explains 66% 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 97 water-level measurements across 37 monitored well(s) (23 alluvial, 0 bedrock, rest unclassified) — plus 12 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.

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.

RIO BLANCO AT THE MOUTH NEAR TRUJILLO: 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.

67 reservoir(s) with 4,542 storage measurement(s), 1970–2025. Basin storage as of 2025-09-01 (the record's own end — reservoir records publish ~annually): 75 AF across 4 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
▸ ECHO CANYON RESERVOIR (2903654) ☆	2,150	2011-10-31
▸ MOUNTAIN VIEW RESERVOIR (2903848) ☆	1,010	2006-10-31
▸ MOUNTAIN VIEW RESV (ALT) (2903849) ☆	925	2012-10-31
▸ BORNS LAKE RESERVOIR (2903644) ☆	68	2015-10-29
▸ TURKEY CREEK RANCH R #2 (2903782) ☆	55	2024-08-27
▸ THOMAS RESERVOIR (2903682) ☆	50	2015-10-28
▸ VILLAGE LAKE (2903696) ☆	49	2012-10-30
▸ BROWN PUMPSITE (2901020) ☆	33	2023-10-31

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: 1093 across 853 structure(s); 147 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 ~1974 — idleness that begins before then may be unreported use, not nonuse (flagged † below).

• DRY GULCH DITCH - USFS (2900586)☆ (1944-10-06, 1.5 cfs decreed): last active 1965 — 60 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1974) -- early absence of record is weak evidence of nonuse
• POND DITCH (2900693)☆ (1911-12-31, 0.0 cfs decreed): last active 1965 — 60 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1974) -- early absence of record is weak evidence of nonuse
• TOWN OF PAGOSA SPRINGS PIPELINE & RESERV (2903695)☆ (1902-05-15, 3.0 cfs decreed): last active 1965 — 60 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1974) -- early absence of record is weak evidence of nonuse
• TEAL LAKE DITCH (2900735)☆ (1959-06-02, 0.5 cfs decreed): last active 1967 — 58 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1974) -- early absence of record is weak evidence of nonuse
• AT LAST SPRING NO 2 (2900511)☆ (1910-06-01, 0.0 cfs decreed): last active 1974 — 51 years idle
• BROWN-BENNETT P L (2900545)☆ (1968-06-30, 1.0 cfs decreed): last active 1974 — 51 years idle
• BROWN SPRING & PIPELINE (2900547)☆ (1951-10-01, 0.1 cfs decreed): last active 1974 — 51 years idle
• STINKING SPRING D NO 1 (2900726)☆ (1962-06-01, 2.0 cfs decreed): last active 1974 — 51 years idle
• STINKING SPRINGS D NO 2 (2900727)☆ (1962-06-01, 1.0 cfs decreed): last active 1974 — 51 years idle
• BLAYLOCK PUMP & PIPELINE (2905002)☆ (1969-08-01, 0.0 cfs decreed): last active 1974 — 51 years idle

Compliance screens (194 advisory flags)

Screened 253 of 853 structures with rights (297 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.

• C H LOUCKS DITCH (2900550)☆: Observed p99 daily rate 130.0 cfs (max 130.0) exceeds total decreed absolute 6.8 cfs across 16783 recorded day(s).
• WHITE CREEK NO 1 DITCH (2900753)☆: Observed p99 daily rate 70.0 cfs (max 70.0) exceeds total decreed absolute 5.0 cfs across 12843 recorded day(s).
• PARK DITCH (2900686)☆: Observed p99 daily rate 60.2 cfs (max 82.2) exceeds total decreed absolute 60.0 cfs across 23257 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• COLTON AND MONTROY DITCH (2900566)☆: Observed p99 daily rate 15.4 cfs (max 27.4) exceeds total decreed absolute 4.5 cfs across 19697 recorded day(s).
• LONG HORN AND MEE DITCH (2900653)☆: Observed p99 daily rate 14.4 cfs (max 15.0) exceeds total decreed absolute 14.2 cfs across 8702 recorded day(s).
• MURPHY DITCH (2900672)☆: Observed p99 daily rate 12.2 cfs (max 12.7) exceeds total decreed absolute 3.0 cfs across 4522 recorded day(s).
• CARR DITCH (2900555)☆: Observed p99 daily rate 12.0 cfs (max 13.0) exceeds total decreed absolute 8.6 cfs across 14912 recorded day(s).
• KELLY'S LAKE DITCH (2901028)☆: Observed p99 daily rate 11.6 cfs (max 11.6) exceeds total decreed absolute 10.0 cfs across 3868 recorded day(s).
• SAN JUAN DITCH (2900706)☆: Observed p99 daily rate 10.4 cfs (max 12.2) exceeds total decreed absolute 1.6 cfs across 1570 recorded day(s).
• SISSON-STEPHENS DITCH (2900716)☆: Observed p99 daily rate 10.3 cfs (max 13.9) exceeds total decreed absolute 10.0 cfs across 10439 recorded day(s).

Seniority (top structures by decreed rate)

Structure	Senior priority date	Rights	Decreed abs (cfs)	Decreed abs (AF)	Conditional?
PARK DITCH (2900686)☆	1886-07-01	8	60.0	0	yes
SAN JUAN RIVER MIN FLOW (2901900)☆	1980-01-30	1	50.0	0	—
CHAPSON AND HOWE DITCH (2900560)☆	1890-10-31	5	45.6	0	—
SNOWBALL DITCH (2900718)☆	1896-06-27	4	38.5	0	—
FOUR-MILE DITCH (2900601)☆	1890-10-15	5	34.0	0	—
RIO BLANCO MIN FLOW (2900768)☆	1974-12-04	1	29.0	0	—
MESA DITCH (2900669)☆	1891-01-12	5	28.5	0	—
ECHO DITCH (2900588)☆	1881-05-01	7	27.8	0	—
DUTTON COLLECTION DITCH (2902007)☆	1912-12-31	2	25.5	0	—
WEST FK SAN JUAN R MIN F (2901902)☆	1980-01-30	1	25.0	0	—
EAST FK SAN JUAN R MIN F (2901904)☆	1980-01-30	1	25.0	0	—
DUTTON DITCH (2902005)☆	1909-06-03	2	22.9	0	—
EAST FK SAN JUAN R MIN F (2901903)☆	1980-01-30	1	15.0	0	—
LONG HORN AND MEE DITCH (2900653)☆	1899-12-31	3	14.2	0	—
FISH CREEK DITCH (2900597)☆	1897-06-01	4	14.0	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.