Hydrohistorian
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Left Hand Diversion near Ward
River gage · LEFTHDCO · Division 1 · Water District 5 · Boulder County
Live gage at DWR ↗ · Download daily record (CSV)
Source DWR administrative record · verify at DWR station ↗ 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 1991. A retired gage nearby, SOUTH SAINT VRAIN NEAR WARD, ran earlier and overlapped it, so its measurements can be translated onto this gage's scale to extend the picture back roughly 24.1 years. The result before 1991 is a reconstruction. It is not what this gage measured, because this gage did not exist.
| Donor gage | SOUTH SAINT VRAIN NEAR WARD, 0.4 km away |
|---|---|
| Overlap used to fit | 6,584 days, 1992-05-15 to 2026-09-27 |
| Agreement (held out) | r² 0.949 |
| Typical error (held out) | 13.4%, bias -6.7% |
| 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.
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.
Annual flow & trend
Chart: annual mean flow at Left Hand Diversion near Ward, water years 1991 to 2026. The measured record is insufficient data at cubic feet per second per decade. 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 (4.0).
Provenance
DWR station abbreviation LEFTHDCO; recorded station name “LEFT HAND DIVERSION NEAR WARD”; operated by DWR. 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.