St. Vrain Creek

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 44 ranked gages are running at a median 70% of their own long-term norm for this window — 31 below a typical year, 13 at or above. Driest relative to its record: HIGHLAND DITCH AT LYONS, CO, ranking 1st lowest of 23 years.

Gage flow trend & changepoints

Of the 67 gages with enough record, 6 are trending down and 3 up, and 5 carry a detected shift. The clearest is Saint Vrain Creek at Lyons, its annual mean flow changing -4.91 cfs per decade (-3.9% of its median annual flow) over 130 years (p<0.0001). The other 56 show no clear signal either way.

Drought history, cost, and the four-century context moved to the Drought tab.

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

1 of those show a significant trend once extended backwards from a retired neighbour's record: St. Vrain Creek below Boulder Creek at Highway 119 near Longmont (99 yr, increasing, suspect). Those are reconstructions, not measurements — each gage's page shows both.

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. 51 gage(s) and 122 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1975. 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: 5% of 1944 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 (3761 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.

• NORTH SAINT VRAIN CREEK BELOW BUTTONROCK (RALPH PRICE) RESERVOIR: reach shifted from +83 cfs to +32 cfs summer mean (more losing, p=0.037, 14 yr) [crystalline foothills: 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=-0.4) -- part of it may be unaccounted water becoming accounted, not hydrologic change]
• NORTH SAINT VRAIN CREEK ABOVE BUTTONROCK RESERVOIR: reach shifted from +1949 cfs to +77 cfs summer mean (more gaining, p=0.000, 21 yr) [crystalline foothills: minimal groundwater storage -- large or shifting unaccounted losses here are more consistent with data/measurement issues or unmodeled plumbing than with aquifer exchange]
• BONUS DITCH: reach shifted from +85 cfs to -49 cfs summer mean (more losing, p=0.023, 18 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=-0.64) -- part of it may be unaccounted water becoming accounted, not hydrologic change]
• JAMES DITCH: reach shifted from -116 cfs to -68 cfs summer mean (more gaining, p=0.049, 18 yr) [sedimentary plains/foothills: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records]
• MIDDLE SAINT VRAIN AT PEACEFUL VALLEY: reach shifted from -61 cfs to +58 cfs summer mean (more gaining, p=0.017, 29 yr) [alluvial valley: real alluvial aquifer -- a decades-long shift toward losing is the classic signature of alluvial pumping and urbanization]
• BEAVER CREEK ABOVE BEAVER CREEK RESERVOIR: reach shifted from -31 cfs to -66 cfs summer mean (more losing, p=0.034, 16 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=-0.6) -- part of it may be unaccounted water becoming accounted, not hydrologic change]

Groundwater now has its own tab: 258 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 83 reservoir(s), end-of-year storage back to 1950, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 23-year window with full coverage (2004–2026), the dominant shared pattern across 4 gage(s) explains 51% of year-to-year variance (almost certainly a basin-wide climate/snowpack driver).

HIGHLDCO 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.

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.

• L H DICKSON DITCH (diversion): +1.0 cfs (11% of that reach's correction)
• COFFIN DAVIS DITCH (diversion): +1.0 cfs (11% of that reach's correction)
• NIX PUMP (diversion): +1.0 cfs (11% of that reach's correction)
• COLLINS SPRING (return): +1.0 cfs (11% of that reach's correction)
• COLLINS SEEPAGE DITCH (diversion): +1.0 cfs (11% of that reach's correction)
• COX SOUTH SPRING (return): +1.0 cfs (11% of that reach's correction)
• COX NORTH SPRING (return): +1.0 cfs (11% of that reach's correction)
• COFFINS MEADOW DITCH (diversion): +1.0 cfs (11% of that reach's correction)
• MEADOW VALE FARM POND 1 (diversion): +1.0 cfs (11% of that reach's correction)
• BOULDER FEEDER CNL (diversion): -0.2 cfs (2% of that reach's correction)

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

419 water-level measurements across 258 monitored well(s) — 137 alluvial, 41 bedrock — plus 4 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 1 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.

BONUS DITCH: 6 alluvial well(s) nearby

JAMES DITCH: 11 alluvial well(s) nearby

MIDDLE SAINT VRAIN AT PEACEFUL VALLEY: 2 alluvial well(s) nearby

BEAVER CREEK ABOVE BEAVER CREEK RESERVOIR: 1 alluvial well(s) nearby

WEBSTER MCCASLIN DITCH: 10 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 ↗

83 reservoir(s) with 17,291 storage measurement(s), 1950–2026. Basin storage as of 2025-10-31 (the record's own end — reservoir records publish ~annually): 55,341 AF across 27 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 2026-10-14 · 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 (1981–2026)

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 14 of the last 45 winters the snow never came — the pack peaked below 80% of its median. In 5 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, 1982, 1985, 1987, 1989, 1991, 1992, 1995, 1998, 1999, 2001, 2002, 2004, 2026. The snow left early: 1988, 1990, 1996, 2000, 2012.

Computed by this site from 3 SNOTEL sites’ full daily records (NRCS AWDB, back to 1981). 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 — St. Vrain Ck at Lyons

NRCS's final issue (2026-06-01) calls it even odds that at least 43 kAF arrives over 06-01 to 09-30 — 57% of a normal season; almost certainly at least 35, probably not more than 54. Our own record at this gage shows 20 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 96 replayed seasons (29% typical miss unadjusted vs 35% 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? (1950–2025)

Grading every April issue against what the river then delivered, measured at this gage’s own record — 75 seasons: the median miss of the 50% forecast is 30%, with a low bias of 6%, and the observed volume landed inside the stated 10–90% band 41% 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 (1984–2026)

Across 38 measured years, April snowpack has explained only part of this river’s season — the dots below scatter widely, so read any single year’s snow number loosely here. In warm, early-melt years the river delivered a median of 55% of a normal season, against 81% 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 2026-10-06 · verify at U.S. Drought Monitor ↗

Right now

This is the 15th-driest week 39 in 131 years of record at SAINT VRAIN CREEK AT LYONS, CO (as of 2026-09-21; this week’s flow sits at the 11th 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, Boulder County is 24% in D4 exceptional drought (2026-10-06). The law agrees: the most senior active call leaves 97% of this district’s decreed flow rights junior to the calling right this week.

Every year since 1895, week by week

Each thin row is a year at SAINT VRAIN CREEK AT LYONS, CO; 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 2002 (mean gap 12.2 percentile points; next closest 2018 (17.3), 2012 (17.6)). 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 Boulder, Weld 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 2004 — 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 (1616 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.

1571–1999: this river before anyone measured it

Tree rings record wet and dry years centuries before the first gage. This is the published reconstruction of annual flow at St. Vrain River at Lyons — 429 years, with its uncertainty band drawn, not implied — and the green line is the measured record at the same gage, water-year totals from DWR’s daily data, carrying the story through 2026. A reconstruction is an estimate, not a measurement: it answers “is this decade unusual in four centuries?”, and nothing in this site’s statistics uses it.

Why the two lines disagree on purpose: the trees were calibrated against naturalized flow — upstream diversions and storage added back — while the gage measures what the ditches left in the river. So the measured line running below the reconstruction is not an error; the gap is, roughly, human use. Over the 103 years both series cover, the river carried a median of 119% of its estimated natural flow past this gage. And because the reconstruction was fit to gage-era data, the overlap shows how well trees track the river (the authors report the models explain 63–76% of gage variance) — it is a calibration, not an independent test.

Woodhouse, C.A. and J.J. Lukas (2006), Multi-century tree-ring reconstructions of Colorado streamflow for water resource planning, Climatic Change 78; data via NOAA NCEI World Data Service for Paleoclimatology / TreeFlow. Source data ↗

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.

What drought has cost here

Since 1991, federal crop insurance has paid $38,554,403 in drought-caused claims across Boulder, Weld counties — 16.7% of all insured crop losses there. The worst year was 2022 ($8,809,218).

USDA crop-insurance indemnities where the recorded cause of loss is drought, summed over the counties this district's gages sit in. Counties overlap water districts imperfectly, and insured-crop claims are a floor on drought damage, not a total. Source: USDA RMA cause-of-loss files.

When this basin claimed its water

Every bar is a year’s new appropriations (1,468 rights across 132 years of shared record), colored by that year’s wetness from the barcode above. Here the correlation is -0.22 — this basin tended to claim water in dry times, under scarcity pressure. 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 2026-10-15 · verify at USGS current conditions ↗

No USGS continuous water-quality sensor reports from inside this district. Statewide sensors →

Where water has been sampled

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

The portal lists 3,782 sampling stations in this district's watersheds (St. Vrain 10190005; Big Thompson 10190006, 3% of the district), of which 187 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: Colorado Dept. of Public Health & Environment-WQCD (95), USGS Colorado Water Science Center (47), Colorado River Watch (32). Most-sampled groups: Physical, Nutrient, Inorganics, Major, Metals, Inorganics, Minor, Metals. 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 ↗

21 community systems touch this district. 1 carries an open health-based violation on EPA's record. EPA sampled 10 of them for PFAS in 2023–25; 1 had PFOA or PFOS at or above the 2024 limit.

and 11 more; the full directory filters by district.

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.