Hydrohistorian
← Basin trends · All gages in this district
Roaring Fork River Ab Difficult Creek near Aspen
River gage · ROADIFCO · USGS 09073300 · Division 5 · Water District 38 · Pitkin County
Live gage at DWR ↗ · USGS monitoring location ↗ · Download daily record (CSV)
Source DWR administrative record · verify at DWR station ↗ Source Independent agency measurement · verify at USGS ↗ Source Our computation, no independent reference · computed here from the screened record
Two different numbers, deliberately: Flowing now is raw 15-minute telemetry, provisional and unreviewed. Latest cached reading is the end of the verified daily record. They are never merged, and the verified series is the one the trend is computed on.
Extended record — reconstructed, not measured
This gage's own record starts in 1979. A retired gage nearby, ROARING FORK RIVER NEAR ASPEN, CO., ran earlier and overlapped it, so its measurements can be translated onto this gage's scale to extend the picture back roughly 15.0 years. The result before 1979 is a reconstruction. It is not what this gage measured, because this gage did not exist.
| Donor gage | ROARING FORK RIVER NEAR ASPEN, CO., 4.7 km away |
|---|---|
| Overlap used to fit | 17,059 days, 1979-10-01 to 2026-09-29 |
| Agreement (held out) | r² 0.959 |
| Typical error (held out) | 13.7%, bias 3.3% |
| Grade | fair |
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) | 47 1980–2026 | decreasing | 0.00794 | -7.143 cfs |
| ROAASPCO alone (measured, no reconstruction) | 61 1965–2026 | no trend | 0.26376 | -2.909 cfs |
| Extended (with reconstruction) | 62 1965–2026 | no trend | 0.09952 | -2.653 cfs |
The longer record reaches a different conclusion, and the reconstruction's bias does not explain it: a 3.3% bias would tend to manufacture a decreasing trend, which is not what appears. The likeliest reading is statistical power — 47 years cannot detect what 62 can.
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.
The water itself
USGS keeps a sensor here. Latest readings, with the last 30 days of daily means beside each. Provisional: not yet reviewed by USGS, and revised when it is.
Fetched 2026-10-15 03:22 UTC from USGS NWIS (site 09073300). The USGS page has the full sensor record; every Colorado sensor site is listed on one page.
Annual flow & trend
Chart: annual mean flow at Roaring Fork River Ab Difficult Creek near Aspen, water years 1979 to 2026. The measured record is decreasing at -6.64 cubic feet per second per decade. A Pettitt changepoint is detected around 1999. Extended backwards with a reconstruction from ROAASPCO, the 62-year record is no trend (p equals 0.09952). The two records are compared in the table above. The underlying yearly values are available as a CSV download linked at the top of this page.
Where it sits
Location as DWR records it (5.0).
Provenance
DWR station abbreviation ROADIFCO; recorded station name “ROARING FORK RIVER AB DIFFICULT C NR ASPEN, 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.