How to read a USGS gauge before you tow

Gauge height is not flow

Gauge height (USGS parameter 00065) is the water surface, in feet, above an arbitrary local datum set when the gauge was installed. It is not depth, and 3.0 ft at one gauge has no relationship to 3.0 ft at another. What it is good for is comparison with itself: if you know your ramp is usable at 2.5 ft and it reads 1.8 ft, you know something useful.

Discharge (parameter 00060) is the volume passing the gauge, in cubic feet per second. It is comparable across sites and across years, which is why USGS publishes historical percentiles for discharge and not for stage.

Why our pages say "lower than normal for this date" about flow only

Where a gauge reports discharge, we compare today's value with that gauge's own record for today's calendar day — at some sites a record running back to the 1940s — and put it in a band: much lower, lower, about normal, higher, much higher than normal. That judgement is about flow, and we label it as such. Presenting it as though it described the water level would be a subtle falsehood, and it is the kind that sends someone to a ramp they should not use.

The gauge is not the ramp

• A gauge sits where the hydrologists needed one, which may be miles from where you launch. Every reading on our pages shows the gauge name and its distance so you can judge that yourself.
• Where we could not confirm the gauge is on the same water as the ramp, the page says so in as many words rather than hiding it behind a small print disclaimer.
• Reservoirs behave nothing like rivers. A dam release changes the tailwater in an hour and the pool not at all.
• After heavy rain, a gauge upstream of you is a forecast; one downstream is history.

Work out the numbers that matter for the ramps you use, once, and write them down. "Usable above 1.4 ft, sketchy below 1.0" beats any general rule anyone can give you.