Crest Gage: A Quick Way to Measure River Stage

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The maximum height rivers reach during storms and floods is an important "data point" to document. In places where there are not dedicated monitoring equipment, the U.S. Geological Survey (USGS) often uses "crest stage gages" to record a one-time measurement of the flood peak.

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Crest Gage: A Quick Way to Measure River Stage

A crest stage gage in Texas.

A crest-stage gage: the wooden rod and cork are inside the pipe.

The metal pipe bolted to the side of the bridge in this picture is a crest-stage gage. It is a low-tech device made of solely of a metal pipe, a wooden pole, and crushed cork that is invaluable to providing a one-time measurement of the maximum height (stage) that a stream hits during a high-water event. 

During a storm event, you might hear the peak stage of a river announced on news as "So-And-So Creek reached a peak today of 23.5 feet." Sometimes that peak stage was recoded using a crest-stage gage.

 

How Do Crest Stage Gages Work?

There are holes drilled in the bottom of the pipe to allow water to enter. Inside the pipe is a wooden rod with markings in feet and inches. The technician puts some ground cork in the pipe and when it rains both the creek water and the water in the pipe rises, thus floating the cork in the pipe. When the water stops rising, and then falls, the cork sticks to the wooden rod at the highest point where the water was.

This device allows the technician to pull the rod out of the pipe and make a quick estimate of the highest gage height the stream reached during a storm. Gage heights are important because it is used to determine stream discharge, which is the amount of water flowing in a stream at any particular moment.

 

Photo of a cork line from a crest-stage gage

Photo of a cork line from a crest-stage gage.

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