Extended record — reconstructed, not measured

This gage's own record starts in 1999. A retired gage nearby, EAGLE RIVER AT RED CLIFF, CO., ran earlier and overlapped it, so its measurements can be translated onto this gage's scale to extend the picture back roughly 70.0 years. The result before 1999 is a reconstruction. It is not what this gage measured, because this gage did not exist.

Donor gage	EAGLE RIVER AT RED CLIFF, CO., 17.9 km away
Overlap used to fit	9,777 days, 1999-10-01 to 2026-09-29
Agreement (held out)	r² 0.912
Typical error (held out)	21.3%, bias 5.8%
Grade	weak

How this was built, and what it cannot tell you

• The two gages had to overlap. Without shared days there is nothing to measure the relationship against, and no extension is offered at all — that rule rejected the overwhelming majority of candidate pairs.
• The relationship is fitted in log space, because the ratio between two gages changes with flow. On Clear Creek the downstream gage reads 95% of the upstream one at low flow but 88% at high flow, because ditches in between take more when there is more to take. A single scale factor would get both ends wrong.
• It is scored out of sample: fitted on half the overlap, tested on the other half. The numbers above are from the half it never saw.
• Reconstruction never replaces a real observation. Every day in the series is labelled measured or reconstructed, and the overlap itself stays measured.
• The trends published on this site still use the measured record only. This extension is offered for reading the longer shape, not as an input to the statistics.
• DWR's published record is the authority. A reconstruction is an estimate of what this location would have read, not a measurement of it.

What the longer record says

Record used	Years	Trend	p	Change / decade
Measured only (what the site publishes)	27 2000–2026	no trend	0.38126	-31.286 cfs
EAGREDCO alone (measured, no reconstruction)	96 1911–2025	decreasing	1e-05	-2.613 cfs
Extended (with reconstruction)	97 1911–2026	decreasing	0.0	-36.695 cfs

The strongest evidence needs no reconstruction at all. EAGREDCO shows decreasing across its own 96 measured years (1911–2025, p = 1e-05) — that is a measurement of this reach, not an estimate. The extended record mostly inherits it, which is why the long view differs from the 27-year modern one.

Treat this difference as suspect. The reconstruction runs 5.8% high against the held-out half of the overlap. A reconstruction that reads high lifts the early years up and can manufacture exactly the decreasing trend seen here. The longer record may be right, but this pairing cannot distinguish a real change from its own bias.

This pairing is graded weak, so its extended trend is shown for interest only and should not be used as a result. Extending changes the conclusion for roughly half the gages that have a reconstruction — which is why both rows are here and neither replaces the other. Every trend published elsewhere on this site uses the measured record only.

The record

Readings come from the weekly-refreshed cache, never fetched live — the date beside the value says exactly how fresh it is. The live gage is one click up.

Provenance

DWR station abbreviation EAGAVOCO; recorded station name “EAGLE R BLW WASTEWATER TREATMENT PLANT AT AVON, CO”; operated by USGS. Daily flows from the DWR HydroBase snapshot plus CDSS REST updates, refreshed on the weekly cycle. Trend statistics are Mann-Kendall (Hamed-Rao corrected) with Sen's slope in native cfs, the same numbers as the basin Trends tab.