Gauge Height vs. River Depth
Gauge height, also called stage, is the height of the water surface above a local reference point at a specific monitoring station.
Gauge height is a local reference
A streamgage continuously measures the elevation of the water surface relative to a station-specific datum. That local reference is what produces a reading such as 4.7 feet or 12.3 feet.
The reading does not mean the entire river is 4.7 or 12.3 feet deep. The actual channel may be much deeper or shallower in different places.
Why 10 feet at one gauge is not 10 feet at another
Each gauge has its own physical channel, reference datum and stage-discharge relationship. A 10-foot stage on one river cannot be treated as equivalent to a 10-foot stage somewhere else.
Gauge height is most useful for tracking whether that specific river location is rising or falling and for comparing the current reading with local flood thresholds.
How stage relates to streamflow
USGS develops a site-specific rating curve that relates stage to discharge. Because channel shape can change after floods or other events, that relationship is maintained and updated for each streamgage.
Keep learning
These guides summarize public technical information in plain English. Measurements and official thresholds should always be checked at their original source when making safety or flood decisions.