San Miguel River Basin

Evolution of the network

Gage flow trend & changepoints

What counts as a trend here

Computed 2026-08-20 09:01 from 25 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 25 gages with enough record, 5 are trending down and 0 up, and 1 carries a detected shift. The clearest is SAN MIGUEL RIVER AT NATURITA, CO., -8.5 points of its long-term median per decade over 53 years (p=0.0022). The other 20 show no clear signal either way.

Gage	Trend	Change / decade points of median	Significance	Years	Changepoint
▸ BEAVER CREEK NEAR NORWOOD, CO.☆ BEANORCO	↓ decreasing	-40.7	p=0.004	32	—
▸ FALL CREEK NEAR FALL CREEK, CO.☆ FALCRECO	↓ decreasing	-39.5	p=0.019	18	—
▸ SAN MIGUEL RIVER AT BROOKS BRIDGE NEAR NUCLA CO☆ SANBROCO	↓ decreasing	-35.5	p=0.005	32	—
▸ WEST NATURITA CREEK NEAR NORWOOD, CO.☆ WENATNCO	↓ decreasing	-32.6	p=0.021	19	—
▸ SAN MIGUEL RIVER AT NATURITA, CO.☆ SMGNATCO	↓ decreasing	-8.5	p=0.002	53	~1948

20 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. 6 gage(s) and 169 structure(s) report in 2026, but structure reporting only reached half its modern level around ~1974. 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)
1890s	1	0
1910s	1	0
1920s	1	0
1930s	1	0
1940s	7	0
1950s	7	0
1960s	4	0
1970s	7	166
1980s	2	210
1990s	2	226
2000s	4	112
2010s	7	148
2020s	6	159

Mass-balance (network closure) trend

Structure divrec-history backfill coverage as of the last check: 6% of 931 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 (830 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.

• SAN MIGUEL RIVER AT BROOKS BRIDGE NEAR NUCLA CO: reach shifted from -38 cfs to +139 cfs summer mean (more gaining, p=0.036, 32 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: 53 monitored well(s), water-table trends, stream corridors, and the advisory depletion screen.

Reservoirs now has its own tab: 12 reservoir(s), end-of-year storage back to 1991, click-to-chart histories.

Cross-gage pattern fingerprint

Over the 15-year window with full coverage (2012–2026), the dominant shared pattern across 3 gage(s) explains 89% 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.

• TAYLOR DITCH & WTR RT (return): +9.2 cfs (33% of that reach's correction)
• COLUMBIA S&P MILL WTR RT (return): +9.2 cfs (33% of that reach's correction)
• TMV/TSG SNOWMAKING RETURN FLOWS (return): +9.2 cfs (33% of that reach's correction)

223 water-level measurements across 53 monitored well(s) — 35 alluvial, 2 bedrock — plus 4 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 1 well(s) with enough record for a trend test: 0 declining, 1 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.

SAN MIGUEL RIVER AT BROOKS BRIDGE NEAR NUCLA CO: 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.

12 reservoir(s) with 4,636 storage measurement(s), 1991–2024. Basin storage as of 2024-04-10 (the record's own end — reservoir records publish ~annually): 1,800 AF across 1 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
▸ MIRAMONTE RESERVOIR (6003512) ☆	7,696	2022-04-25
▸ BLUE LAKE RESERVOIR (6003505) ☆	4,435	2015-10-31
▸ NATURITA CANAL (6000707) ☆	2,664	2005-10-31
▸ TROUT LAKE RESERVOIR (6003527) ☆	2,013	2021-10-31
▸ GURLEY RESERVOIR (6003507) ☆	1,800	2024-04-10
▸ PAXTON RESERVOIR (6003519) ☆	575	2008-05-24
▸ LAKE HOPE RESERVOIR (6003509) ☆	427	2002-09-05
▸ LONE CONE RESERVOIR (6003511) ☆	316	2021-08-10

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.