Computed 2026-08-20 09:24 from 31 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 293 day(s) old (DWR publishes ~1 year in arrears)
structure coverage	sparse	12% of schematic structures have data

Independent check: PASS — 100.0000% agreement across 122,540 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.

31 gage(s) / 196,311 daily values (1904-01-01–2026-07-06); 624 structure(s) with diversion records; 3562 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. 6 gage(s) and 354 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1979. 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	0
1910s	4	0
1920s	2	0
1930s	1	76
1940s	2	37
1950s	4	97
1960s	8	124
1970s	8	186
1980s	7	220
1990s	6	240
2000s	5	266
2010s	5	302
2020s	6	314

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
▸ WILLIAMS FORK AT MOUTH NEAR HAMILTON☆ WMFKMHCO	↓ decreasing	-281.0%	p=0.000	22	~2017
▸ NORTH FORK ELKHEAD CREEK NEAR ELKHEAD, CO.☆ NOFELKCO	↑ increasing	+49.7%	p=0.018	15	—
▸ MILK CREEK NEAR THORNBURGH, CO.☆ MILTHOCO	↑ increasing	+33.9%	p=0.002	34	~1964
▸ ELKHEAD CREEK NEAR CRAIG, CO☆ ELKCRACO	no clear trend	-32.8%	p=0.078	26	~2018
▸ ELKHEAD CREEK ABOVE LONG GULCH, NEAR HAYDEN, CO☆ ELKLONCO	↓ decreasing	-29.7%	p=0.012	31	~2011
▸ ELKHEAD CREEK NEAR CLARK, CO.☆ ELKHEACO	↑ increasing	+22.8%	p=0.009	17	~1964
▸ ELKHEAD CREEK NEAR ELKHEAD, CO.☆ ELKHENCO	↑ increasing	+13.9%	p=0.040	44	—
▸ YAMPA RIVER NEAR MAYBELL, CO☆ YAMAYBCO	↓ decreasing	-2.9%	p=0.009	111	~1932

23 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: 12% of 547 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 (1953–2026)

Mass-balance kinks computed for every summer month back to 1953 (733 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.

No reach shows a statistically significant long-term gain/loss shift.

Groundwater now has its own tab: 134 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 78 reservoir(s), end-of-year storage back to 1900, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 31-year window with full coverage (1996–2026), the dominant shared pattern across 3 gage(s) explains 95% 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.

The basin's aquifer story, from 711 water-level measurements across 134 monitored well(s) (60 alluvial, 1 bedrock, rest unclassified) — plus 6 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 1 well(s) with enough record for a trend test: 0 declining, 0 rising.

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.

78 reservoir(s) with 4,817 storage measurement(s), 1900–2026. Basin storage as of 2025-10-31 (the record's own end — reservoir records publish ~annually): 17,374 AF across 34 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
▸ ELKHEAD CREEK RESERVOIR (4403902) ☆	16,421	2025-10-31
▸ ROBB PIT (4404436) ☆	807	2004-09-03
▸ FREDRICKSON RES NO 2 (4403732) ☆	720	1982-05-12
▸ RAW WATER RESERVOIR (4403912) ☆	553	2006-05-15
▸ RALPH WHITE RES (4403724) ☆	308	1984-10-17
▸ POOSE CK RES (4403701) ☆	291	2025-10-31
▸ FLAT TOP RES (4403925) ☆	100	2025-10-31
▸ WILSON RESERVOIR (4403674) ☆	85	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: 3979 across 3562 structure(s); 78 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 ~1979 — idleness that begins before then may be unreported use, not nonuse (flagged † below).

• PERRY LUCAS DITCH (4400732)☆ (1903-06-03, 2.3 cfs decreed): last active 1938 — 87 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1979) -- early absence of record is weak evidence of nonuse
• DIAMOND DITCH (4400595)☆ (1903-11-15, 0.5 cfs decreed): last active 1940 — 85 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1979) -- early absence of record is weak evidence of nonuse
• WILLOW CK DITCH (4400508)☆ (1898-05-06, 0.3 cfs decreed): last active 1964 — 61 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1979) -- early absence of record is weak evidence of nonuse
• GOOD SPRING DITCH NO 1 (4400631)☆ (1885-05-20, 0.5 cfs decreed): last active 1966 — 59 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1979) -- early absence of record is weak evidence of nonuse
• GOOD SPRINGS DITCH NO 2 (4400632)☆ (1885-05-20, 1.0 cfs decreed): last active 1966 — 59 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1979) -- early absence of record is weak evidence of nonuse
• CRAIG IRR DITCH (4400580)☆ (1890-03-31, 11.1 cfs decreed): last active 1978 — 47 years idle † predates modern reporting era — last recorded activity predates this basin's modern reporting era (~1979) -- early absence of record is weak evidence of nonuse
• FLOYD BUTTS WELL (4405002)☆ (1954-09-27, 0.2 cfs decreed): last active 1980 — 45 years idle
• MILLER WELL (4405004)☆ (1940-07-31, 0.1 cfs decreed): last active 1980 — 45 years idle
• SJOSTROM SPG NO 1 (4400881)☆ (1977-08-01, 0.1 cfs decreed): last active 1981 — 44 years idle
• OSBORN BARN PUMP (4401055)☆ (1944-06-07, 0.0 cfs decreed): last active 1981 — 44 years idle

Compliance screens (267 advisory flags)

Screened 403 of 3562 structures with rights (498 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.

• D D & E DITCH (4400586)☆: Observed p99 daily rate 60.1 cfs (max 64.4) exceeds total decreed absolute 49.3 cfs across 12394 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• MILK CREEK DITCH (4400706)☆: Observed p99 daily rate 40.0 cfs (max 45.0) exceeds total decreed absolute 20.0 cfs across 12166 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• WISCONSIN DITCH (4400511)☆: Observed p99 daily rate 32.8 cfs (max 35.5) exceeds total decreed absolute 32.0 cfs across 15023 recorded day(s).
• SMITH DITCH (4400763)☆: Observed p99 daily rate 30.1 cfs (max 30.1) exceeds total decreed absolute 21.0 cfs across 10590 recorded day(s).
• CRAIG IRR DITCH (4400580)☆: Observed p99 daily rate 30.0 cfs (max 30.0) exceeds total decreed absolute 11.1 cfs across 5156 recorded day(s).
• MCKINLAY DITCH NO 1 (4400699)☆: Observed p99 daily rate 30.0 cfs (max 30.0) exceeds total decreed absolute 8.3 cfs across 8842 recorded day(s).
• MCKINLAY DITCH NO 2 (4400700)☆: Observed p99 daily rate 30.0 cfs (max 46.4) exceeds total decreed absolute 25.7 cfs across 10130 recorded day(s).
• DEER CK & MORAPOS D (4400590)☆: Observed p99 daily rate 28.3 cfs (max 34.2) exceeds total decreed absolute 19.5 cfs across 16043 recorded day(s).
• EGRY MESA DITCH (4400607)☆: Observed p99 daily rate 27.0 cfs (max 40.0) exceeds total decreed absolute 22.9 cfs across 41448 recorded day(s).
• D D FERGUSON D NO 2 (4400587)☆: Observed p99 daily rate 26.8 cfs (max 30.0) exceeds total decreed absolute 18.3 cfs across 11558 recorded day(s).

Seniority (top structures by decreed rate)

Structure	Senior priority date	Rights	Decreed abs (cfs)	Decreed abs (AF)	Conditional?
MAYBELL CANAL (4400694)☆	1899-10-02	3	149.0	0	—
DEEP CUT IRRIGATING DITCH (4400589)☆	1884-05-13	6	68.7	0	—
JUNIPER MOUNTAIN TUNNEL AND IRRIGATION D (4400675)☆	1890-04-02	5	67.0	0	—
MARTIN CK DITCH (4400692)☆	1900-05-30	3	62.0	0	—
D D & E DITCH (4400586)☆	1888-03-01	6	49.3	582	—
CRAIG STATION DITCH AND PIPELINE NO1 (4400522)☆	1895-06-25	25	44.9	0	yes
LILY PARK DITCH NO 1 (4400500)☆	1886-04-10	1	36.7	0	—
WISCONSIN DITCH (4400511)☆	1888-05-19	3	32.0	0	—
NORVELL DITCH (4400724)☆	1885-05-14	2	30.0	0	—
WILLIAMS FORK RIVER MSF (4401448)☆	1992-09-16	1	30.0	0	—
SYNTHETIC PRODUCTS DITCH (4400779)☆	1895-06-25	25	26.8	0	—
MCKINLAY DITCH NO 2 (4400700)☆	1890-05-01	4	25.7	0	—
VAUGHN PUMP (4401122)☆	1984-04-18	1	25.0	0	—
ELKHEAD CREEK (LOWER) IS (4402557)☆	2017-01-24	1	24.0	0	—
HUSTON DITCH (4400657)☆	1892-08-10	2	23.5	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.