Hydrohistorian
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Roberts Tunnel at East Portal near Grant
Transbasin diversion gage · ROBTUNCO · USGS 09050590 · Division 1 · Water District 80 · Park 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.
What this gage meters
This is not a natural stream record. The Harold D. Roberts Tunnel moves water from Blue River at Dillon Reservoir (Div 5) into North Fork South Platte River near Grant (Div 1), operated by Denver Water — so this record is a ledger of those deliveries. Trends here reflect operational and demand decisions, not the basin's hydrology, and the basin trends page marks it accordingly (⇆). All of Colorado's curated transbasin diversions are collected at /transbasin.
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 Roberts Tunnel at East Portal near Grant, water years 1963 to 2026. The measured record is increasing at 10.24 cubic feet per second per decade. A Pettitt changepoint is detected around 1988. The underlying yearly values are available as a CSV download linked at the top of this page.
This gage measures the Harold D. Roberts Tunnel, water carried across the Continental Divide. It is taken from Blue River at Dillon Reservoir (Div 5) and delivered to North Fork South Platte River near Grant (Div 1) — so what this gage reads leaves one river basin for good and arrives in another.
The two ends: Montezuma Shaft - Roberts Tunnel (source, on Snake River); Roberts Tunnel (receiving, on North Fork South Platte)
- Decree in case 08CW0159 ↗ · imaged 2014-04-09 · filed under the receiving end, Roberts Tunnel
- Decree in case CA3286 ↗ · imaged 2006-09-05 · filed under the receiving end, Roberts Tunnel
The ditch’s mapped channel is drawn on the map below where the USGS has surveyed it. Every crossing →
Where it sits
Location as DWR records it (4.0).
Provenance
DWR station abbreviation ROBTUNCO; recorded station name “ROBERTS TUNNEL AT EAST PORTAL NEAR GRANT”; 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.