How We Calculate River Conditions
What "Low / Normal / High / Flood Risk" means
The current gauge height is at or below the 10th percentile of historical readings for this date. The river is running below its typical range.
The gauge height is between the 10th and 90th percentile — within the river's typical operating range for this time of year.
The gauge height is above the 90th percentile. The river is running above its typical range and may present challenging or technical conditions.
The gauge height has reached or exceeded the NWS-published flood stage for this station. This is a serious hazard — consult official NWS flood warnings.
Data window and refresh cadence
Current readings are fetched dynamically using the modernized USGS Water Data for the Nation (WDFN) OGC API. The timestamp displayed on each page is the exact measurement time reported by the USGS sensor, not our fetch time. Historical statistics are pulled via the USGS OGC Daily Values API to determine the statistical means. Additionally, we actively query the National Weather Service (NWS) API using the precise latitude and longitude of each gauge to instantly surface authentic, localized flood watches and warnings directly on the gauge page.
How thresholds are set — and their limitations
Thresholds are statistically derived per gauge from its own historical daily-mean data (10th percentile = Low, 90th percentile = High threshold; flood stage = NWS published flood stage where available). These are descriptive statistics, not safety certifications. A "Normal" verdict does not mean the river is safe to enter. Conditions on the water are always affected by factors not captured by a single gauge reading: water temperature, wood debris, access-point hazards, individual paddler skill, and weather upstream.
If a gauge has insufficient historical data to derive a threshold, we report "Insufficient data" rather than guessing. We will never fabricate a threshold.
How to verify current NWS flood stage directly
The National Weather Service publishes official flood stage data at NWPS (National Water Prediction Service). Each gauge page on ClearGauge includes a direct link to the official USGS station page where you can verify current readings independently.