Computed 2026-08-20 09:31 from 55 gage(s) with cached period-of-record data. Statistical tests (Mann-Kendall trend, Pettitt changepoint) require at least 8 years spanning at least 10 years of record -- gages below that report no signal, not "no change."

Data provenance & quality

Where these numbers come from and how far they can be trusted. Grade C (3/6 points) — the components below are the finding; the letter alone is not. Sources: DWR HydroBase snapshot HydroBase_CO_20260707 (imported 2026-08-19) for history, plus the CDSS REST API for current conditions.

Check	State	What was measured
gage freshness	stale	newest gage reading is 45 day(s) old (target 7)
diversion record	expected-lag	newest diversion record is 294 day(s) old (DWR publishes ~1 year in arrears)
structure coverage	sparse	8% of schematic structures have data

Independent check: PASS — 100.0000% agreement across 183,484 stored values re-checked against DWR's authoritative record (HydroBase_CO_20260707), over 20 structures. 0 disagreement(s) beyond a 0.01 cfs tolerance. Checked 2026-08-19; a rotating sample covers the whole basin across successive runs, and the structures this report cites are checked every time.

Federal cross-check: PASS — 99.26% day-level agreement with USGS's own published records for the same gages, across 25 co-listed station(s) and 210,656 overlapping days (within max(2%, 0.5 cfs) daily). Pre-1950 records at some gages carry known between-agency day-stamp and transcription differences — scored at each year's best ±1-day alignment; residual disagreement is real historical divergence, flagged for review.

55 gage(s) / 276,852 daily values (1904-10-01–2026-07-06); 1020 structure(s) with diversion records; 3097 with decreed rights. Methodology has not yet had independent expert review — treat every figure as an advisory screen, not an administrative or legal conclusion.

Read this first: the measurement network itself evolved

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

Gage flow trend & changepoints

Every located gage with a period of record — dot size scales with the strength of its flow trend (|Sen slope| in %/decade, the same statistic as the table below), color with direction. An amber ring marks a detected Pettitt changepoint. Click a gage to chart its trend and shift.

Gage	Trend	Change / decade	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).

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)

The basin's aquifer story, from 157 water-level measurements across 92 monitored well(s) (57 alluvial, 0 bedrock, rest unclassified) — plus 50 administered well(s) reporting metered pumping through diversion records. Observation wells and pumping wells are different populations and are never conflated. Click a well to chart its record.

Well map

Every monitored well with a location — hover for identity, click to chart its water-level record below. ● alluvial   ● bedrock / confined (Denver Basin, High Plains, etc. — one-way, no human-timescale recharge)   ● unclassified — marker size scales with the strength of the well's water-level trend (|Sen slope| in ft/decade — the same Mann-Kendall/Sen statistic as the trends table below); the smallest, faintest dots have too little record to test.

3D aquifer x-ray

Every aquifer unit as its own 3D head surface — alluvial water table on top, Denver Basin members (Dawson, Denver, Arapahoe, Laramie–Fox Hills) stacked beneath where measured — interpolated from measured water levels and animated through time. Units are never mixed; surfaces exist only inside each unit's well coverage (no extrapolation); thin epochs are suppressed with their reason shown. Vertical scale exaggerated for readability; z is head elevation in feet. Advisory — measured heads, not a calibrated model.

Load 3D x-ray

Water-table trends

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

Stream corridors — the surface connection

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). 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?

Each reservoir drawn as a vessel: bubble size ∝ its record-high storage, fill level = 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 of its own record high otherwise (a wrong capacity would be worse than an honest record high, so only confident joins upgrade). Hover for numbers, click to chart its history below the map. A dashed teal ring marks reservoirs reporting live DWR telemetry — their fill reflects yesterday's storage, drawn as a dotted tail on charts and treated as provisional until the next verified HydroBase snapshot supersedes it. ● <25% ● 25–60% ● 60–90% ● >90%

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

Decrees, seniority, and administrative calls connected to this basin's flow network. Advisory reading aids on public DWR data — not administrative or legal conclusions. Rights on file: 3942 across 3097 structure(s); 101 structure(s) carry 0 court-case references.

Abandonment radar (25 screens)

Absolute rights with 10+ years of no recorded diversions. Screens only — storage, alternate points, and plan operations can explain nonuse lawfully. And diversion REPORTING itself only reached its modern level ~1941 — idleness that begins before then may be unreported use, not nonuse (flagged † below).

• WILLIAM G HERSOM GUNN D (5800941)☆ (1911-09-12, 0.3 cfs decreed): last active 1940 — 85 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1941) -- early absence of record is weak evidence of nonuse
• BAER DITCH (5800517)☆ (1902-05-02, 1.2 cfs decreed): last active 1948 — 77 years idle
• FOLDEN DITCH (5800646)☆ (1922-10-30, 2.0 cfs decreed): last active 1951 — 74 years idle
• DEER CREEK DITCH (5800609)☆ (1889-10-31, 1.7 cfs decreed): last active 1953 — 72 years idle
• STUKEY PIPELINE (5800891)☆ (1903-05-12, 5.0 cfs decreed): last active 1954 — 71 years idle
• FETCHER SPRINGS (5800635)☆ (1955-10-02, 0.1 cfs decreed): last active 1962 — 63 years idle
• STUKEY SODA CR D (5800889)☆ (1903-05-12, 11.8 cfs decreed): last active 1962 — 63 years idle
• BASHOR DITCH 1 (5800525)☆ (1902-06-30, 3.0 cfs decreed): last active 1964 — 61 years idle
• HOGUE SPRING 7 (5801267)☆ (1977-05-30, 0.0 cfs decreed): last active 1965 — 60 years idle
• BUSTER SPG 3 (5801283)☆ (1963-06-25, 0.0 cfs decreed): last active 1965 — 60 years idle

Compliance screens (448 advisory flags)

Screened 665 of 3097 structures with rights (868 have diversion history on file). A flag is a lead for expert review — augmentation plans, exchanges, and free-river conditions can make over-decree diversions lawful and are deliberately not modeled.

• STAGECOACH HYDROELECTRIC (5801583)☆: Observed p99 daily rate 115.0 cfs (max 181.5) exceeds total decreed absolute 110.0 cfs across 27885 recorded day(s).
• STILLWATER DITCH (5804685)☆: Observed p99 daily rate 51.7 cfs (max 67.9) exceeds total decreed absolute 30.8 cfs across 30035 recorded day(s).
• ELK VALLEY DITCH CO. D. (5800626)☆: Observed p99 daily rate 47.0 cfs (max 51.6) exceeds total decreed absolute 21.2 cfs across 18495 recorded day(s).
• BIG MESA DITCH (5800539)☆: Observed p99 daily rate 41.1 cfs (max 74.0) exceeds total decreed absolute 28.0 cfs across 21389 recorded day(s).
• MANDALL DITCH (5800763)☆: Observed p99 daily rate 38.3 cfs (max 72.1) exceeds total decreed absolute 31.1 cfs across 29070 recorded day(s).
• WOOLERY DITCH (5800944)☆: Observed p99 daily rate 37.4 cfs (max 39.1) exceeds total decreed absolute 37.4 cfs across 22430 recorded day(s).
• KELLER DITCH (5800714)☆: Observed p99 daily rate 30.3 cfs (max 34.5) exceeds total decreed absolute 25.4 cfs across 33185 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• STAFFORD DITCH (5800879)☆: Observed p99 daily rate 28.3 cfs (max 31.8) exceeds total decreed absolute 21.1 cfs across 14421 recorded day(s).
• MORIN DITCH (5800783)☆: Observed p99 daily rate 25.4 cfs (max 35.3) exceeds total decreed absolute 21.0 cfs across 25147 recorded day(s).
• BUCKINGHAM MANDALL DITCH (5800564)☆: Observed p99 daily rate 25.0 cfs (max 31.2) exceeds total decreed absolute 22.7 cfs across 23117 recorded day(s).

Seniority (top structures by decreed rate)

Structure	Senior priority date	Rights	Decreed abs (cfs)	Decreed abs (AF)	Conditional?
STEAMBOAT SPRINGS BOATING PARK (RICD) (5802591)☆	2003-12-16	1	1400.0	0	—
STAGECOACH HYDROELECTRIC (5801583)☆	1982-10-13	1	110.0	0	—
FOUR COUNTIES D3HG8 (5802813)☆	1958-06-02	2	81.9	0	yes
WALTON CREEK DITCH (5800920)☆	1887-07-20	14	75.5	0	yes
YAMPA RIVER MSF (5802164)☆	2001-07-24	1	72.5	0	—
ELK RIVER MSF-L (5801355)☆	1977-09-23	1	65.0	0	—
ELK RIVER MSF-U (5802219)☆	1977-09-23	1	65.0	0	—
SUTTLE DITCH (5800897)☆	1888-10-29	5	52.1	0	—
BAXTER DITCH (5800530)☆	1888-10-29	4	49.6	0	—
WESSELS CANAL (5802120)☆	1954-07-05	2	45.7	0	yes
SARVIS DITCH (5804684)☆	1911-05-24	1	43.0	0	—
WOOLERY DITCH (5800944)☆	1885-06-14	2	37.4	0	—
MANDALL DITCH (5800763)☆	1885-10-20	5	31.1	0	—
STILLWATER DITCH (5804685)☆	1903-09-23	1	30.8	0	—
ENTERPRISE DITCH (5800627)☆	1887-10-08	6	29.0	0	—

No inventory or legal-document changes detected since the daily watch began.

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.