Upper Yampa River

Evolution of the network

Gage flow trend & changepoints

What counts as a trend here

Computed 2026-08-20 09:31 from 55 gage(s) with cached period-of-record data. Mann-Kendall (trend) and Pettitt (changepoint) both require at least 8 years spanning at least 10 years of record. A gage below that reports no signal — which is not the same as “no change.”

Of the 55 gages with enough record, 7 are trending down and 0 up, and 5 carry a detected shift. The clearest is YAMPA RIVER ABOVE ELKHEAD CREEK NEAR HAYDEN, CO, -30.4 points of its long-term median per decade over 23 years (p=0.0018). The other 48 show no clear signal either way.

Gage	Trend	Change / decade points of median	Significance	Years	Changepoint
▸ YAMPA RIVER ABOVE ELKHEAD CREEK NEAR HAYDEN, CO☆ YAMELKCO	↓ decreasing	-30.4	p=0.002	23	~2019
▸ YAMPA RIVER ABOVE STAGECOACH RESERVOIR, CO☆ YAMSTACO	↓ decreasing	-22.1	p=0.005	38	~2016
▸ WALTON CREEK NEAR STEAMBOAT SPRINGS, CO.☆ WLTNCKCO	↓ decreasing	-14.9	p=0.004	36	~2015
▸ YAMPA RIVER BELOW STAGECOACH RESERVOIR, CO☆ YAMBSRCO	↓ decreasing	-4.2	p=0.027	63	~2000
▸ ELK RIVER AT CLARK, CO.☆ ELKLARCO	↓ decreasing	-3.9	p=0.004	73	~1947
▸ ELK RIVER NEAR MILNER, CO.☆ ELKMILCO	↓ decreasing	-3.2	p=0.005	57	—
▸ YAMPA RIVER AT STEAMBOAT SPRINGS, CO☆ YAMSTECO	↓ decreasing	-1.8	p=0.033	119	—

48 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. 33 gage(s) and 465 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1941. 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)
1900s	2	1
1910s	4	0
1920s	2	0
1930s	2	82
1940s	3	259
1950s	4	264
1960s	6	295
1970s	6	314
1980s	12	357
1990s	12	394
2000s	11	439
2010s	14	441
2020s	15	429

Mass-balance (network closure) trend

Structure divrec-history backfill coverage as of the last check: 8% of 857 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 (1408 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.

• LAKE CATAMOUNT SPILLWAY: reach shifted from -90 cfs to -200 cfs summer mean (more losing, p=0.037, 27 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: 92 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 277 reservoir(s), end-of-year storage back to 1901, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 42-year window with full coverage (1985–2026), the dominant shared pattern across 3 gage(s) explains 69% 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 2026-07-06)

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.

• HEART THERMAL SPRING RETURN FLOW (return): +57.5 cfs (100% of that reach's correction)

157 water-level measurements across 92 monitored well(s) — 57 alluvial, 0 bedrock — plus 50 administered well(s) reporting metered pumping.

What is being counted

Observation wells and pumping wells are different populations and are never conflated: water levels come from monitored observation wells, and metered pumping comes from administered wells reporting through diversion records. Click any well to chart its own record.

Well map

3D aquifer x-ray

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

Load 3D x-ray

How the surfaces are built, and what they are not

Alluvial water table on top, Denver Basin members (Dawson, Denver, Arapahoe, Laramie–Fox Hills) stacked beneath where measured, interpolated from measured water levels. Units are never mixed; a surface exists only inside its own unit's well coverage, with no extrapolation; thin epochs are suppressed and say why. Vertical scale is exaggerated for readability and z is head elevation in feet. These are measured heads, not a calibrated groundwater model.

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.

How the corridor is assembled

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.

LAKE CATAMOUNT SPILLWAY: 3 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).

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.

277 reservoir(s) with 21,062 storage measurement(s), 1901–2026. Basin storage as of 2025-10-31 (the record's own end — reservoir records publish ~annually): 72,013 AF across 129 reservoir(s).

Why storage matters to the flow network

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?

What “full” is measured against

Bubble size is proportional to a reservoir's record-high storage. Fill is its 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 as a share of its own record high otherwise. A wrong capacity would be worse than an honest record high, so only confident joins upgrade.

A dashed teal ring marks reservoirs reporting live DWR telemetry: their fill reflects yesterday's storage, is drawn as a dotted tail on charts, and is treated as provisional until the next verified HydroBase snapshot supersedes it.

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
▸ STAGECOACH RESERVOIR (5804213) ☆	28,490	2025-10-31
▸ STEAMBOAT LAKE (5803787) ☆	22,274	2025-10-31
▸ LAKE CATAMOUNT (5803631) ☆	6,276	2025-10-01
▸ LESTER CK RESERVOIR (5803521) ☆	5,656	2025-10-31
▸ YAMCOLO RESERVOIR (5804240) ☆	3,235	2025-10-31
▸ FISH CREEK RESERVOIR (5803508) ☆	2,329	2025-10-31
▸ HAHNS PEAK RES (5803512) ☆	865	2025-10-31
▸ STILLWATER NO. 1 RESERVOIR (5803540) ☆	863	2025-10-31

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.