Data sources & methodology

GageLog is a normalization layer over public hydrologic data. This page states plainly what that data is, how fresh it is, and what we do — and deliberately don't do — to it.

Sources

Readings come from the agencies that operate the stations:

  • USGS NWIS — the bulk of the registry: instantaneous discharge (and stage where reported) from the national network.
  • State agencies — for example Washington Ecology's telemetry and flow-monitoring files and Oregon WRD's near-real-time portal, which also serves as an independent path to stations it shares with USGS.
  • District telemetry — irrigation-district SCADA feeds for diversion gages that no federal or state network carries.

Every gage's detail page names its source and station ID and links to the agency's own record. The underlying data is public.

Cadence and freshness

Native resolution is 15 minutes for most stations. GageLog sweeps sources on a fixed schedule (hourly), so a reading is typically visible within an hour of the agency publishing it — but publishing lag varies by source, from minutes (USGS) to hours (some state telemetry). Where a source has a known publish delay, the gage's Today tab says so instead of showing an empty morning.

Normalization and quality flags

All sources are mapped to one schema: a timestamped discharge (and stage, where available) per station. Readings that fail basic validity checks — negative discharge is the common case, usually an agency sentinel value — are kept but flagged. Flagged readings plot in red and are excluded from every average, percentile, daily summary, and monitor evaluation. We do not correct, interpolate, or infill values beyond what the source itself publishes.

Provisional data. Agencies publish near-real-time data as provisional and may revise it during finalization — USGS states this on every real-time page, and state sources finalize on their own schedules. Small differences between GageLog statistics and an agency's finalized record are expected, and the agency's finalized record governs for regulatory purposes.

Daily summaries

Alongside raw readings, GageLog maintains per-day mean/min/max summaries (UTC calendar days, unflagged readings only). Long-horizon charts — year-over-year, water-year comparison, percentile envelope, annual statistics — read from these summaries. The Charts & statistics page states each chart's exact construction.

Storage horizon

Recent water years stay in hot storage and are instantly queryable. Older readings move to long-term storage and come back on demand via archive restore (see Tracked gages). Daily summaries are retained for the full record either way, so annual statistics and envelopes always use the whole history.