Upper South Platte

Evolution of the network

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 2026-09-07 (the newest reading on file), flows at the 24 ranked gages are running at a median 46% of their own long-term norm for this window — 24 below a typical year, 0 at or above. Driest relative to its record: FOUR MILE CREEK AT BEERY DITCH, ranking 1st lowest of 6 years.

Gage flow trend & changepoints

Of the 50 gages with enough record, 0 are trending down and 3 up, and 4 carry a detected shift. The clearest is South Platte River near Lake George, its annual mean flow changing +7.54 cfs per decade (+8.2% of its median annual flow) over 96 years (p<0.0001). The other 46 show no clear signal either way.

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

46 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. 32 gage(s) and 0 structure(s) report in 2026. 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: 0% of 96 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.

Cross-gage pattern fingerprint

Over the 51-year window with full coverage (1976–2026), the dominant shared pattern across 3 gage(s) explains 70% 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 2026-08-10)

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.

• SPINNEY MTN RESERVOIR (diversion): +45.7 cfs (50% of that reach's correction)
• SOUTH PLATTE RIVER CR 59 PUMP (diversion): +45.7 cfs (50% of that reach's correction)
• CAMP ALEXANDER PUMP (diversion): -13.4 cfs (14% of that reach's correction)
• LAKE GEORGE INTAKE (diversion): -13.4 cfs (14% of that reach's correction)
• LIDDERDALE RES (diversion): -13.4 cfs (14% of that reach's correction)
• ELEVEN MILE CANON D (diversion): -13.4 cfs (14% of that reach's correction)
• CR 90A PUMP (diversion): -13.4 cfs (14% of that reach's correction)
• SOUTH PLATTE RIVER CR 112 PUMP (diversion): -13.4 cfs (14% of that reach's correction)
• SPORTSMENS PARADISE PUMP (diversion): -13.4 cfs (14% of that reach's correction)
• WALKING BEAR PUMP (diversion): +5.6 cfs (100% of that reach's correction)

Source Independent agency measurement · fetched 2026-09-14 · verify at NRCS report generator ↗ Source Our computation, scored against a reference · NRCS forecast, graded here against the gage record

Snow-water equivalent, WY2026

No snow on the ground — normal for the date; the snow year begins in October. The chart shows the full water year just ending.

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 (1999–2026)

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 8 of the last 28 winters the snow never came — the pack peaked below 80% of its median. In 0 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. This year was one of the dry ones: the pack peaked at 33% of median.

The snow never came: 2002, 2012, 2017, 2018, 2022, 2023, 2025, 2026.

Computed by this site from 3 SNOTEL sites’ full daily records (NRCS AWDB, back to 1999). 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 — Antero Reservoir Inflow

NRCS's final issue (2026-06-01) calls it even odds that at least 5 kAF arrives over 06-01 to 09-30 — 46% of a normal season; almost certainly at least 2, probably not more than 7. 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 7 kAF over 04-01 to 09-30. 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 6 kAF.

Computed by this site — not an NRCS number, and shown only because it earned it: replayed over 60 past seasons here (1995–2025), never seeing the year it predicts, the adjustment cut the typical April miss from 33% to 30%. 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 →

Runoff outlook — Spinney Mountain Reservoir Inflow

NRCS's final issue (2026-06-01) calls it even odds that at least 16 kAF arrives over 06-01 to 09-30 — 37% of a normal season; almost certainly at least 7, probably not more than 22. Our own record at this gage shows 6 kAF so far this period (partial record: 91 of 107 days). 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 61 replayed seasons (24% typical miss unadjusted vs 28% 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? (1994–2025)

Grading every April issue against what the river then delivered, measured at this gage’s own record — 31 seasons: the median miss of the 50% forecast is 22%, with a high bias of 1%, and the observed volume landed inside the stated 10–90% band 74% 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 (1999–2026)

Across 28 measured years, the season’s water has loosely followed the April snowpack: a year opening April with 80% of median snow has typically gone on to deliver about 81% 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 0.8). This year opened April at 8% of median snow and delivered 51% of a normal season.

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 — Elevenmile Canyon Reservoir Inflow

NRCS's final issue (2026-06-01) calls it even odds that at least 18 kAF arrives over 06-01 to 09-30 — 41% of a normal season; almost certainly at least 8, probably not more than 25. 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 60 replayed seasons (22% typical miss unadjusted vs 34% adjusted), so none is shown — NRCS’s own forecast, unadjusted, is the best April benchmark available for this river. Why we test →

Source Our computation, no independent reference · computed here from the screened DWR record Source Independent agency measurement · fetched 2026-09-08 · verify at U.S. Drought Monitor ↗

Right now

This is the 34th-driest week 36 in 96 years of record at SOUTH PLATTE RIVER NEAR LAKE GEORGE, CO. (as of 2026-08-31; this week’s flow sits at the 35th 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, Park County is 15% in D4 exceptional drought (2026-09-08).

Every year since 1929, week by week

Each thin row is a year at SOUTH PLATTE RIVER NEAR LAKE GEORGE, 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 36 weeks recorded so far, 2026’s weekly trace most resembles 2023 (mean gap 14.8 percentile points; next closest 2018 (15.6), 1992 (17.7)). 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, Park 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 1957 — 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 (754 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.

What drought has cost here

Since 1994, federal crop insurance has paid $182,449 in drought-caused claims across Boulder, Park counties — 4.2% of all insured crop losses there. The worst year was 2022 ($70,070).

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.

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.

Who serves it, who protects it

Two registers the site fetches on their own schedules, read for this district. Neither is a DWR record; each links its own page and its agency.

Public water systems here

Source Register of another agency · fetched 2026-09-08 · verify at EPA SDWIS ↗

10 systems touch this district (10 community systems reporting 4,153 people served, a figure that counts a wholesaler's customers twice); none carries an open health-based violation on EPA's record.

and 2 more; the full directory filters by district.

Instream-flow rights held by the state

Source Register of another agency · fetched 2026-09-13 · verify at CWCB instream flow program ↗

41 reaches over 313.1 miles and 6 natural lake levels, held by the Colorado Water Conservation Board so that water stays in the stream. Every reach, with its schedule and case →

• Middle Fork South Platte River, 28.8 mi: 8 (10/1 - 4/30), 16 (5/1 - 9/30) cfs (appropriated 1980, 80CW0067) · dossier
• Tarryall Creek, 26.0 mi: 20 (1/1 - 12/31) cfs (appropriated 1977, 77W8730) · dossier
• Tarryall Creek, 21.4 mi: 7 (01/01 - 12/31) cfs (appropriated 1976, 76W8229) · dossier
• Michigan Creek, 19.3 mi: 7 (1/1 - 12/31) cfs (appropriated 1976, 76W8230) · dossier
• Fourmile Creek, 17.1 mi: 8 (1/1 - 12/31) cfs (appropriated 1976, 76W8224) · dossier
• Rule Creek, 14.6 mi: 1 (1/1 - 12/31) cfs (appropriated 1980, 80CW0213) · dossier

and 41 more on the district's instream-flow page.

What the water is like -- USGS sensors right now, where it has been sampled, the impaired-waters list, and how the tap water here stands with EPA -- is on the Water quality tab.

Designated groundwater basins are on their own page.

Source Adjudicated record · verify at DWR water-right transactions ↗ Source Adjudicated record · verify at DWR net amounts ↗

Rights on file: 0 across 0 structure(s); 65 structure(s) carry 181 court-case references. Advisory reading aids on public DWR data — not administrative or legal conclusions.

Is the river getting harder to divert from?

Over 1951–2025, administration on this district has been tightening: 2 of 3 measures (days under callA senior water right demanding its water, which requires everyone junior on that stream to stop diverting until it is satisfied., calls set, seniorityColorado shares water by date: the earlier the right, the stronger its claim when the river runs short. "First in time, first in right." of the controlling call) are moving toward more administration, none the other way.

Recent inventory & legal-document changes

• 2026-09-11 — call set: B H EATON DITCH (39462)
• 2026-09-11 — call released: 39455
• 2026-09-11 — call set: B H EATON DITCH (39455)
• 2026-09-11 — call set: BONUS DITCH (39461)
• 2026-09-11 — call released: 39201
• 2026-09-11 — call released: 39439
• 2026-09-09 — call set: COFFIN DAVIS DRY CREEK DIVERSION (39447)
• 2026-09-09 — call set: LAKE DITCH (39446)

Water-court filings this month (division-wide)

16 applications in the 2026-07 resume for this basin's division — new rights, changes, augmentation plans — from the water clerk's statutory monthly notice (C.R.S. 37-92-302), the earliest public signal of a new claim. Filings are division-wide, not district-filtered: check the county column. Full resume PDF at the Judicial Branch →

Anyone affected may file a statement of opposition until 2026-09-30 (15 days left). C.R.S. 37-92-302(3): due by the last day of the second month following the filing month — computed, not legal advice; confirm with the water clerk.

Active substitute water supply plans in this district

Temporary State Engineer approvals to divert out of priority (37-92-308 / 37-90-137). A structure operating under one behaves differently under a call than its decreed rights alone suggest — the priority tables above don't know about these; this list does. Source: DWR’s active-SWSP register, refreshed nightly.

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 2026-09-15 · 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 2026-09-09 · verify at Water Quality Portal ↗

The portal lists 1,047 sampling stations in this district's watershed (South Platte Headwaters 10190001), of which 31 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 (State) (26), Colorado River Watch (4), EPA National Aquatic Resources Survey (NARS) (1). Most-sampled groups: Inorganics, Minor, Metals, Physical, Nutrient, Inorganics, Major, 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 2026-09-09 · verify at EPA SDWIS ↗

10 community systems touch this district. None carries an open health-based violation on EPA's record. EPA sampled 0 of them for PFAS in 2023–25.

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.