Athens, Ohio
Climatological Data Archive
Weather and Precipitation Observations, Stream Stage/Flow,
Flood Potential Monitoring, Historic Events, Research References

Understanding "Flow" value calculations:

The Hocking River "flow" values contained in the accompanying data are computed values, based on a mathematical stage-discharge relationship (or "rating") that, in turn, is based on actual periodic current-meter measurements of the stream. USGS makes current-meter measurements about every 6 weeks at most stream gauges, with extra measurements during times of especially high or low flows to define the extreme ends of the rating. It commonly takes about a year's worth of current-meter measurements before an initial rating can be established, and the rating is constantly being reviewed and adjusted as needed because stream-channel geometry changes over time.

Although technology is being developed to measure stream velocity remotely (thus making for even more reliable real-time flow data), "flows" at most stations are based strictly on stage, with the latest rating programmed into the system for each gauging station. In the water-year-end review of data, USGS technicians judge how representative these initial flows actually are, and they revise data as needed to arrive at a set of edited and approved daily mean flows, which become the official record for the stream gauge for that water year.

In summary, users can take the "stage" values for what they are (usually representative of reality but sometimes erroneous due to equipment malfunctions, ice or log jams), and "flow" values as the best immediate estimates based on stage, but provisional and subject to revision.  It should also be noted that all the decimal places shown for some of the computed flows do not represent true USGS confidence in their accuracy.

(excerpted with permission and thanks from material provided by:)
The Ohio District, Water Resources Discipline, U.S. Geological Survey
Athens Ohio Climatological Data Archive
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