Computed 2026-08-20 08:48 from 23 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 B (4/6 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	partial	62% of schematic structures have data

Independent check: PASS — 100.0000% agreement across 221,012 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 — 98.16% day-level agreement with USGS's own published records for the same gages, across 8 co-listed station(s) and 49,495 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.

23 gage(s) / 170,340 daily values (1914-05-01–2026-07-06); 144 structure(s) with diversion records; 1041 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. 18 gage(s) and 102 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1950. 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)
1910s	1	0
1920s	2	0
1930s	2	0
1940s	2	0
1950s	3	61
1960s	2	64
1970s	3	65
1980s	4	73
1990s	8	88
2000s	9	82
2010s	9	95
2020s	16	98

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
▸ SOUTH CHANNEL NORTON DRAIN DITCH NEAR LA SAUSES☆ NORDSCCO	↓ decreasing	-70.5%	p=0.000	37	~2001
▸ ALAMOSA RIVER BELOW TERRACE RESERVOIR, CO.☆ ALABELCO	↓ decreasing	-12.6%	p=0.000	80	~1987
▸ NORTON DRAIN NEAR LA SAUSES☆ NORDLSCO	↓ decreasing	-12.4%	p=0.004	56	~1999
▸ LAJARA CREEK AT GALLEGOS RANCH NEAR CAPULIN☆ LAJCAPCO	↓ decreasing	-5.4%	p=0.002	80	~1999
▸ ALAMOSA RIVER ABOVE TERRACE RESERVOIR, CO.☆ ALATERCO	↓ decreasing	-2.8%	p=0.018	104	—

18 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: 62% of 76 schematic-relevant structures. Kink count trend: increasing (p=0.000), kink magnitude trend: increasing (p=0.000) across 47 qualifying year(s).

Reach gain/loss shifts (1990–2026)

Mass-balance kinks computed for every summer month back to 1990 (155 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.

• SOUTH CHANNEL NORTON DRAIN DITCH NEAR LA SAUSES: reach shifted from -8 cfs to -21 cfs summer mean (more losing, p=0.002, 28 yr) [sedimentary uplands: moderate groundwater connectivity -- gain/loss shifts can be real aquifer response; corroborate with nearby well records] [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]

Groundwater now has its own tab: 76 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 3 reservoir(s), end-of-year storage back to 1975, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 56-year window with full coverage (1971–2026), the dominant shared pattern across 3 gage(s) explains 55% 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 5,009 water-level measurements across 76 monitored well(s) (27 alluvial, 33 bedrock, rest unclassified) — plus 0 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 15 well(s) with enough record for a trend test: 7 declining, 0 rising.

Fastest-declining wells	Setting	ft / decade	Span	p
▸ NA03500907CCC CON 1☆	unknown	-5.79	54 yr	0.0
▸ NA03601001DAD RG67☆	alluvial	-0.65	48 yr	0.0134
▸ NA03400905ABA RG85A☆	alluvial	-0.63	44 yr	0.0003
▸ NA03500813DCD☆	alluvial	-0.46	55 yr	0.0001
▸ NA03601026CBB☆	alluvial	-0.45	56 yr	0.0001
▸ NA03501016CBB☆	alluvial	-0.39	57 yr	0.0001
▸ NA03501006DDD RG74☆	alluvial	-0.29	45 yr	0.0014

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.

SOUTH CHANNEL NORTON DRAIN DITCH NEAR LA SAUSES: 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.

3 reservoir(s) with 13,039 storage measurement(s), 1975–2026. Basin storage as of 2025-10-31 (the record's own end — reservoir records publish ~annually): 5,996 AF across 3 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
▸ TERRACE RESERVOIR (2103583) ☆	4,322	2025-10-31
▸ LA JARA RESERVOIR (2103582) ☆	1,623	2025-10-31
▸ SUMMITVILLE DAM IMPOUNDMENT (SDI) (2103591) ☆	51	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: 1136 across 1041 structure(s); 33 structure(s) carry 0 court-case references.

Abandonment radar (9 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 ~1950 — idleness that begins before then may be unreported use, not nonuse (flagged † below).

• SPRING OVFL D (2100597)☆ (1889-05-24, 1.7 cfs decreed): last active 1988 — 37 years idle
• ARROYA SPRG D (2100610)☆ (1902-02-11, 19.5 cfs decreed): last active 1999 — 26 years idle
• SOUTH SIDE ARROYA D (2100596)☆ (1889-05-25, 43.5 cfs decreed): last active 2000 — 25 years idle
• L D ESKRIDGE IRR D (2100548)☆ (1889-05-25, 6.5 cfs decreed): last active 2001 — 24 years idle
• AGUA CALIENTE D (2100501)☆ (1875-05-05, 15.4 cfs decreed): last active 2004 — 21 years idle
• CROWTHER BROS D (2100515)☆ (1942-06-15, 6.3 cfs decreed): last active 2004 — 21 years idle
• LEIGH F PETERSON SEPG WD (2100555)☆ (1947-02-03, 15.0 cfs decreed): last active 2009 — 16 years idle
• J H VALDEZ D (2100717)☆ (1995-06-15, 5.0 cfs decreed): last active 2009 — 16 years idle
• LE MITA D 3 (2100554)☆ (1874-06-15, 6.2 cfs decreed): last active 2015 — 10 years idle

Compliance screens (44 advisory flags)

Screened 79 of 1041 structures with rights (83 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.

• LOWLAND D (2100558)☆: Observed p99 daily rate 230.0 cfs (max 462.0) exceeds total decreed absolute 69.9 cfs across 9525 recorded day(s).
• EMPIRE CANAL-ALAMOSA (2100522)☆: Observed p99 daily rate 201.4 cfs (max 283.0) exceeds total decreed absolute 85.0 cfs across 12065 recorded day(s).
• EMPIRE CANAL-LA JARA (2100521)☆: Observed p99 daily rate 183.4 cfs (max 331.0) exceeds total decreed absolute 30.0 cfs across 16989 recorded day(s).
• HEAD OVFL D 5 (2100539)☆: Observed p99 daily rate 175.6 cfs (max 503.8) exceeds total decreed absolute 155.7 cfs across 15054 recorded day(s).
• LOWLAND OVERFLOW NORTH BRANCH (2100575)☆: Observed p99 daily rate 102.0 cfs (max 148.6) exceeds total decreed absolute 42.0 cfs across 4418 recorded day(s).
• HANSEN LA JARA OVFL D 3 (2100536)☆: Observed p99 daily rate 46.0 cfs (max 71.0) exceeds total decreed absolute 21.3 cfs across 12184 recorded day(s).
• TERRACE RESERVOIR (2103583)☆: Observed p99 daily rate 43.8 cfs (max 473.6) exceeds total decreed absolute 3.5 cfs across 66569 recorded day(s). Structure holds an Augmentation-use decree -- diversions above the direct-flow decree can be lawful under plan operations; interpret with care.
• SCANDINAVIAN CNL (2100593)☆: Observed p99 daily rate 43.6 cfs (max 55.6) exceeds total decreed absolute 43.6 cfs across 3102 recorded day(s).
• ALAMOSA SPRG CR D (2100505)☆: Observed p99 daily rate 36.5 cfs (max 37.0) exceeds total decreed absolute 30.3 cfs across 9186 recorded day(s).
• CAPULIN D (2100510)☆: Observed p99 daily rate 32.6 cfs (max 62.6) exceeds total decreed absolute 31.4 cfs across 25214 recorded day(s).

Seniority (top structures by decreed rate)

Structure	Senior priority date	Rights	Decreed abs (cfs)	Decreed abs (AF)	Conditional?
USFS QP27C (2100730)☆	1907-03-02	1	1113.0	0	—
USFS QP27G (2100735)☆	1905-06-03	1	742.6	0	—
HEAD OVFL D 5 (2100539)☆	1874-05-03	10	155.7	0	—
TERRACE MAIN CNL (2100601)☆	1867-08-01	8	138.2	0	—
EMPIRE CANAL-ALAMOSA (2100522)☆	1890-04-01	1	85.0	0	—
ALAMOSA CR CNL (2100503)☆	1867-08-01	7	78.7	0	—
MILLER D-ALAMOSA (2100561)☆	1873-04-13	4	74.9	0	—
VALDEZ D (2100604)☆	1870-04-10	2	71.2	0	—
LOWLAND D (2100558)☆	1881-04-01	2	69.9	0	—
UNION D (2100602)☆	1876-05-20	3	69.5	0	—
MILLER D-LA JARA (2100560)☆	1886-11-11	1	66.4	0	—
NORTH ALAMOSA D (2100571)☆	1877-06-14	3	63.1	0	—
AROYA D (2100506)☆	1875-07-01	1	53.1	0	—
NORLAND D (2100570)☆	1885-06-12	1	48.6	0	—
SCANDINAVIAN CNL (2100593)☆	1887-07-07	1	43.6	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.