San Juan River Basin

Source Our computation, no independent reference · computed here from the screened DWR record Source Our computation, no independent reference · no independent reference; see /methods

This year, in context

In the weeks around 2026-09-27 (the newest reading on file), flows at the 7 ranked gages are running at a median 174% of their own long-term norm for this window — 2 below a typical year, 5 at or above. Driest relative to its record: SAN JUAN RIVER NEAR ARCHULETA, NM, ranking 3rd lowest of 72 years.

Gage flow trend & changepoints

Of the 19 gages with enough record, 4 are trending down and 0 up, and 5 carry a detected shift. The clearest is San Juan River near Archuleta, Nm, its annual mean flow changing -82.04 cfs per decade (-10.0% of its median annual flow) over 71 years (p=0.0008). The other 14 show no clear signal either way.

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

How the measurement network itself changed

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 †.

Mass-balance (network closure) trend

Structure divrec-history backfill coverage as of the last check: 20% of 964 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]

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 65-year window with full coverage (1962–2026), the dominant shared pattern across 3 gage(s) explains 85% 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 2026-09-27)

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.

• R-1812 (diversion): +48.9 cfs (17% of that reach's correction)
• R-1811 (diversion): +48.9 cfs (17% of that reach's correction)
• VELASQUEZ DITCH (diversion): +48.9 cfs (17% of that reach's correction)
• ROSA DITCH (diversion): +48.9 cfs (17% of that reach's correction)
• DARLINGTON WASTE WATER D (diversion): +48.9 cfs (17% of that reach's correction)
• PENINSULA DITCH NO 2 (diversion): +48.9 cfs (17% of that reach's correction)
• PSRC #9 (diversion): +0.6 cfs (1% of that reach's correction)
• COUNTY OUTFLOW #1 (diversion): +0.6 cfs (1% of that reach's correction)
• PSRC #8 (diversion): +0.6 cfs (1% of that reach's correction)
• PSRC SPRING 2000-1 (return): +0.6 cfs (1% of that reach's correction)

Source DWR administrative record · verify at DWR groundwater wells ↗ Source DWR administrative record · verify at DWR well permits ↗

97 water-level measurements across 37 monitored well(s) — 23 alluvial, 0 bedrock — plus 12 administered well(s) reporting metered pumping.

Well map

3D aquifer x-ray

Every aquifer unit as its own head surface, animated through time.

Water-table trends

Of 0 well(s) with enough record for a trend test: 0 declining, 0 rising.

Stream corridors — the surface connection

Where a reach's gain or loss has shifted, the wells within two miles of its anchoring gage and what their water table did over the same era.

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.

Source DWR administrative record · verify at DWR structure records ↗

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).

Reservoir map — how full is each vessel?

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 row to chart its full storage history, or open its dossier for rights, documents and dam-safety facts.

Source Independent agency measurement · fetched 2026-10-16 · verify at NRCS report generator ↗ Source Our computation, scored against a reference · NRCS forecast, graded here against the gage record

Snow-water equivalent, WY2027

NRCS SNOTEL, daily. Sites are assigned to the district whose boundary contains them — the snow that feeds this district can also sit in a neighboring headwater district.

Two ways a snow year goes wrong (1979–2026)

A bad snow year here comes in two flavors (both called snow droughtA winter that shorts the snowpack. It happens two ways: a dry one, where the snow never comes, and a warm one, where near-normal snow falls but melts off weeks early -- and the river feels them differently.), and the river feels them differently. In 13 of the last 48 winters the snow never came — the pack peaked below 80% of its median. In 3 more, the snow came but left early — a near-normal peak melted out two weeks or more ahead of its usual date, sending the water down before the season needed it.

The snow never came: 1981, 1988, 1996, 2000, 2002, 2006, 2012, 2013, 2014, 2015, 2018, 2025, 2026. The snow left early: 2020, 2022, 2024.

Computed by this site from 2 SNOTEL sites’ full daily records (NRCS AWDB, back to 1979). Each year is measured against each site’s own multi-decade median — not the 1991–2020 normal the chart above uses — so the 1980s grade against a fair baseline. Peak and melt-out need 85% of the season’s days on the record; thin years are dropped, not guessed. Derived from snow measurements alone — it cannot tell dry-from-warm causes apart, only what the snowpack did.

Runoff outlook — Rio Blanco at Blanco Diversion

NRCS's final issue (2026-06-01) calls it even odds that at least 4 kAF arrives over 06-01 to 07-31 — 23% of a normal season; almost certainly at least 3, probably not more than 11. Our own record at this gage shows 2 kAF actually delivered. New forecasts begin in January. How to read these numbers →

We test a record-based adjustment of the April benchmark at every graded point. Here it did not beat NRCS over 32 replayed seasons (14% typical miss unadjusted vs 14% adjusted), so none is shown — NRCS’s own forecast, unadjusted, is the best April benchmark available for this river. Why we test →

How good are these forecasts here? (1993–2026)

Grading every April issue against what the river then delivered, measured against NRCS’s naturalized volumes (this point forecasts the river as it would run without upstream storage and diversions — which no gage measures) — 33 seasons: the median miss of the 50% forecast is 13%, with a low bias of 0%, and the observed volume landed inside the stated 10–90% band 82% of the time (a calibrated forecast would say 80%).

Computed by this site: NRCS's archived April issues (their period as issued each year) against NRCS’s own naturalized monthly volumes; years missing any month are dropped, not summed. A grade of the forecast, never of the forecasters — these are hard rivers. How this point ranks among every graded Colorado forecast point →

What April snow has meant for this river (1979–2026)

Across 48 measured years, the season’s water has closely followed the April snowpack: a year opening April with 80% of median snow has typically gone on to deliver about 75% of a normal season (a snow-to-runoff elasticityHow strongly one number moves with another. A snow-to-runoff elasticity of 1.5 means a 10% shortfall in April snowpack has typically become a 15% shortfall in the season's water. of 1.1). In warm, early-melt years the river delivered a median of 73% of a normal season, against 136% in typical years — the timing of the melt matters, not just its size.

Computed by this site: the district’s April 1 SWE (% of each SNOTEL site’s own-record median) against the observed April–July volume at this gage (% of its median season) — a fixed window every year, unlike the forecast grades above, which use each issue’s own period. The slope is fit so single wild years can’t steer it (Theil–Sen, log space); years missing 10% of their days are dropped.

Runoff outlook — San Juan R nr Carracas

NRCS's final issue (2026-06-01) calls it even odds that at least 25 kAF arrives over 06-01 to 07-31 — 19% of a normal season; almost certainly at least 13, probably not more than 62. Our own record at this gage shows 16 kAF actually delivered. New forecasts begin in January. How to read these numbers →

The record-adjusted April benchmark

NRCS’s April issue (2026-04-01) called even odds at 85 kAF over 04-01 to 07-31. Re-anchoring that number on this river’s own history — how its April issues have verified, the winter’s baseflow, and the district’s April 1 snowpack — moves it to 84 kAF. The river delivered 82 kAF.

Computed by this site — not an NRCS number, and shown only because it earned it: replayed over 66 past seasons here (1966–2025), never seeing the year it predicts, the adjustment cut the typical April miss from 31% to 21%. At points where it does not beat NRCS, no adjusted number appears. Coefficients are frozen each August; the model never changes mid-season. Method and honest limits →

How good are these forecasts here? (1965–2025)

Grading every April issue against what the river then delivered, measured at this gage’s own record — 60 seasons: the median miss of the 50% forecast is 35%, with a high bias of 34%, and the observed volume landed inside the stated 10–90% band 56% of the time (a calibrated forecast would say 80%).

Computed by this site: NRCS's archived April issues (their period as issued each year) against the observed volume in DWR’s published record; years with under 90% daily coverage are dropped, not summed. A grade of the forecast, never of the forecasters — these are hard rivers. How this point ranks among every graded Colorado forecast point →

What April snow has meant for this river (1979–2026)

Across 48 measured years, the season’s water has closely followed the April snowpack: a year opening April with 80% of median snow has typically gone on to deliver about 65% of a normal season (a snow-to-runoff elasticityHow strongly one number moves with another. A snow-to-runoff elasticity of 1.5 means a 10% shortfall in April snowpack has typically become a 15% shortfall in the season's water. of 1.3). In warm, early-melt years the river delivered a median of 63% of a normal season, against 128% in typical years — the timing of the melt matters, not just its size.

Computed by this site: the district’s April 1 SWE (% of each SNOTEL site’s own-record median) against the observed April–July volume at this gage (% of its median season) — a fixed window every year, unlike the forecast grades above, which use each issue’s own period. The slope is fit so single wild years can’t steer it (Theil–Sen, log space); years missing 10% of their days are dropped.

Source Our computation, no independent reference · computed here from the screened DWR record Source Independent agency measurement · fetched 2026-10-13 · verify at U.S. Drought Monitor ↗

Right now

This is the 68th-driest week 39 in 93 years of record at SAN JUAN RIVER AT FARMINGTON, NM (as of 2026-09-21; this week’s flow sits at the 73rd percentileRank against the record: a river at its 5th percentile is lower than it was in 95 of the past 100 years on this same date. for the date). On this week’s US Drought Monitor, Mineral County is 57% in D2 severe drought (2026-10-13). The law agrees: the most senior active call leaves 95% of this district’s decreed flow rights junior to the calling right this week.

Every year since 1930, week by week

Each thin row is a year at SAN JUAN RIVER AT FARMINGTON, NM; each cell is one week’s flow ranked against the same calendar week of every other year — warm means dry for the date, blue wet, so seasonality cancels and droughts appear as warm bands. Gaps are missing record, never a dry river. Click a year to reconstruct it on the Historical tab.

This year against its analogs

Over the 39 weeks recorded so far, 2026’s weekly trace most resembles 2003 (mean gap 12.6 percentile points; next closest 2013 (13.1), 2025 (13.1)). The analog’s remainder is drawn as context — its ending is what happened to it, not a forecast for this year.

The Drought Monitor’s view since 2000

Mean share of area in each class across Archuleta, Mineral, San Juan counties — the counties this district’s gages sit in, which overlap the district imperfectly. The Drought Monitor weighs soils, vegetation and local reports; it is CONTEXT beside the river’s own record above, not the water-rights picture.

The law’s own drought gauge

When water runs short, administration answers: calls reach further back in time, and more decreed rights go junior to the calling right. This is that response, weekly since 2002 — the share of this district’s decreed flow rights junior to the most senior active call. Watch it spike in the named droughts below, and linger after the river recovers.

Computed from DWR’s call record (53 calls touching this district) against the district’s rights index. Scoping is deliberately coarse — a call’s own district, or districts named in its comments — and this is administration’s RESPONSE, not a per-structure verdict (each dossier’s curtailment card does that, with stream miles). A deepening call can also reflect growing demand, not only shrinking supply.

This basin’s droughts, by its own record

Detected mechanically: the 26-week smoothed percentile below the 30th for at least 20 weeks; recovered on regaining the 50th. The water-table clock compares each monitoring well against its own pre-drought median (the 3 years before onset) and dates the year the median well got back — the aquifer remembers longest, and “still below” is a finding, not a gap. The knobs are stated because the episode list depends on them — a different reasonable choice merges or splits episodes at the edges. Names are attached where an episode overlaps a drought Colorado already talks about.

When this basin claimed its water

Every bar is a year’s new appropriations (782 rights across 96 years of shared record), colored by that year’s wetness from the barcode above. Here the correlation is +0.14 — essentially no wet-dry pattern; here, law and settlement set the pace, not the weather. Across the state both behaviors exist: ephemeral southwest basins file after wet demonstrations, transbasin-source basins under drought — and the biggest statewide filing waves sat in the 1950s drought and after 2002, not in the wet 1980s–90s.

Appropriation dates are the CLAIMED initiation of a right, not the courthouse filing date; the record is survivor-biased (abandoned claims are absent, so failed dry-era scrambles are undercounted); and the big 1960s and 2000s spikes sit on legal events — the pre-1969-Act adjudication era and 2000s legislation — not on weather. A correlation here is a description, never a cause.

New to how a dry winter becomes a call on the river? Anatomy of a drought walks the chain in four minutes — snow to rivers to reservoirs to calls to the water table.

The water itself, in this district

Four registers, each on its own schedule: what USGS sensors read right now, where samples have been taken, which stretches the state lists as impaired, and how the tap water of the systems here stands with EPA. None is a DWR record; each links its own page.

Right now

Source Provisional telemetry · fetched 2026-10-16 · verify at USGS current conditions ↗

1 USGS sensor reports temperature, conductance, dissolved oxygen or turbidity from inside this district; provisional readings, never merged into the verified record.

Where water has been sampled

Source Register of another agency · fetched 2026-10-08 · verify at Water Quality Portal ↗

The portal lists 670 sampling stations in this district's watershed (Upper San Juan 14080101), of which 78 reported a sample in the last 5 years on the state and tribal side (USGS activity is in the station count, not in that figure). Most active: Southern Ute Tribe (37), Colorado Dept. of Public Health & Environment-WQCD (16), Mountain Studies Institute (MSI) (14). Most-sampled groups: Inorganics, Major, Metals, Physical, Nutrient, Organics, Other. Every station as a file ↗

Results themselves are not fetched here; USGS samples added after March 2024 may not be in the portal's legacy profiles yet.

Drinking water

Source Register of another agency · fetched 2026-10-07 · verify at EPA SDWIS ↗

3 community systems touch this district. None carries an open health-based violation on EPA's record. EPA sampled 1 of them for PFAS in 2023–25; none had PFOA or PFOS at or above the 2024 limit.

EPA's record carries violations and lead/copper percentiles; nitrate and disinfection by-product results are not in it. UCMR 5 samples are monitoring, not compliance, and the 2024 PFOA/PFOS limits equal its reporting limit, so any detection of those two is at or above them.

Impaired waters

Source Register of another agency · verify at EPA ATTAINS ↗

The state's 303(d) impaired-waters list has not been joined to this basin's own watershed boundary yet, so nothing is shown rather than a guess; the basins with a join carry the full list here. Why the join is geometry, not a name match.