Big Thompson River

Evolution of the network

Gage flow trend & changepoints

Of the 72 gages with enough record, 6 are trending down and 2 up, and 10 carry a detected shift. The clearest is WIND RIVER NEAR ESTES PARK, +21.0 points of its long-term median per decade over 54 years (p<0.0001). The other 61 show no clear signal either way.

61 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. 51 gage(s) and 123 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1994. 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 1391 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 (5701 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.

• LITTLE THOMPSON RIVER AT MILLIKEN, CO.: reach shifted from -30 cfs to +24 cfs summer mean (more gaining, p=0.021, 14 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=-0.56) -- part of it may be unaccounted water becoming accounted, not hydrologic change] [10 alluvial wells within 2 mi of the gage; pooled water table +2.2 ft (1962–2004, decreasing)]
• HANSEN FEEDER CANAL LOVELAND TURNOUT: reach shifted from -172 cfs to -21 cfs summer mean (more gaining, p=0.000, 26 yr) [alluvial valley: real alluvial aquifer -- a decades-long shift toward losing is the classic signature of alluvial pumping and urbanization]
• USBR POWER PLANT AT BIG THOMPSON CANYON MOUTH: reach shifted from +221 cfs to +117 cfs summer mean (more losing, p=0.006, 30 yr) [sedimentary plains/foothills: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records]
• MINER LONGAN DITCH: reach shifted from -143 cfs to -135 cfs summer mean (more gaining, p=0.043, 11 yr) [alluvial valley: real alluvial aquifer -- a decades-long shift toward losing is the classic signature of alluvial pumping and urbanization]
• RYANS GULCH EXCHANGE DITCH: reach shifted from -60 cfs to -17 cfs summer mean (more gaining, p=0.001, 17 yr) [sedimentary plains/foothills: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records]
• WIND RIVER NEAR ESTES PARK: reach shifted from +185 cfs to -41 cfs summer mean (more losing, p=0.000, 65 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=-0.49) -- part of it may be unaccounted water becoming accounted, not hydrologic change]

Groundwater now has its own tab: 91 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 38 reservoir(s), end-of-year storage back to 1950, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 79-year window with full coverage (1948–2026), the dominant shared pattern across 3 gage(s) explains 45% of year-to-year variance (almost certainly a basin-wide climate/snowpack driver).

BTBLESCO 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 2026-08-15)

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.

• BTM DITCH BROWNWOOD RETURN (return): -75.1 cfs (100% of that reach's correction)
• WIENS RANCH RETURN FLOW OBLIGATION REACH (return): -61.2 cfs (100% of that reach's correction)
• HANDY DITCH SYLVAN DALE RANCH RETURN (return): +19.3 cfs (100% of that reach's correction)
• HILL & BRUSH AUG RETURN (return): +15.1 cfs (100% of that reach's correction)
• HILLSBOROUGH DITCH MILLIKEN RETURN VIA N (return): +13.8 cfs (100% of that reach's correction)

6,963 water-level measurements across 91 monitored well(s) — 60 alluvial, 5 bedrock — plus 16 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 4 well(s) with enough record for a trend test: 4 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.

LITTLE THOMPSON RIVER AT MILLIKEN, CO.: 10 alluvial well(s) nearby; pooled water table +2.2 ft (1962–2004, decreasing, p=0.0015). Glover screen: 0.1 cfs of nearby metered alluvial pumping → est. lagged depletion 0.0–0.1 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

MINER LONGAN DITCH: 1 alluvial well(s) nearby. Glover screen: 0.0 cfs of nearby metered alluvial pumping → est. lagged depletion 0.0–0.0 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

RYANS GULCH EXCHANGE DITCH: 6 alluvial well(s) nearby. Glover screen: 0.2 cfs of nearby metered alluvial pumping → est. lagged depletion 0.1–0.2 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

WIND RIVER NEAR ESTES PARK: 0 alluvial well(s) nearby. Glover screen: 0.0 cfs of nearby metered alluvial pumping → est. lagged depletion 0.0–0.0 cfs (uncalibrated T/S ranges; flagged for SPDSS calibration, AWAS cross-check, and expert review — DWR's AWAS is the authority).

BIG THOMPSON RIVER BELOW HILLSBOROUGH DIVERSION: 6 alluvial well(s) nearby; pooled water table -2.2 ft (1941–1986, decreasing, p=0.0017)

BIG THOMPSON RIVER ABOVE LAKE ESTES: 0 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.

38 reservoir(s) with 16,980 storage measurement(s), 1950–2025. Basin storage as of 2024-10-31 (the record's own end — reservoir records publish ~annually): 139,543 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 reservoir to chart its full storage history.

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.