Hydrohistorian
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Alva B. Adams Tunnel at East Portal near Estes Park
Transbasin diversion gage · ADATUNCO · USGS 09013000 · Division 1 · Water District 4 · Larimer 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 Alva B. Adams Tunnel moves water from Colorado River headwaters at Grand Lake (Div 5) into Big Thompson River at Estes Park (Div 1), operated by Northern Water / USBR (Colorado-Big Thompson) — 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 Alva B. Adams Tunnel at East Portal near Estes Park, water years 1947 to 2026. The measured record is no trend at 10.07 cubic feet per second per decade. The underlying yearly values are available as a CSV download linked at the top of this page.
This gage measures the Alva B. Adams Tunnel, water carried across the Continental Divide. It is taken from Colorado River headwaters at Grand Lake (Div 5) and delivered to Big Thompson River at Estes Park (Div 1) — so what this gage reads leaves one river basin for good and arrives in another.
The two ends: Cbt Alva B Adams Tunnel (source, on East Inlet); Adams Tunnel (receiving, on Colorado River)
- Decree in case CA2782 ↗ · imaged 2018-02-16 · filed under the source end, Cbt Alva B Adams Tunnel
- Decree in case 16CW3193 ↗ · imaged 2020-02-05 · filed under the receiving end, Adams Tunnel
- Decree in case 02CW0082 ↗ · imaged 2006-04-12 · filed under the receiving end, Adams 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 (5.0).
Provenance
DWR station abbreviation ADATUNCO; recorded station name “ALVA B. ADAMS TUNNEL AT EAST PORTAL NEAR ESTES PARK”; operated by NWBOR. 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.