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Water Questions & Answers
What does the term "river stage" mean?

River stage is an important concept when analyzing how much water is moving in a stream at any given moment. Stage is the water level above some arbitrary point, usually with the zero height being near the river bed, in the river and is commonly measured in feet. For example, on a normal day when no rain has fallen for a while, a river might have a stage of 2 feet (baseflow conditions). If a big storm hits, the river stage could rise to 15 or 20 feet, sometimes very quickly. This is important because, from past records, we might know that when the stage hits 21 feet, the water will start flowing over its banks and into the basements of houses along the river -- time to tell those people to move the dog's bed upstairs!

In this picture, you see a common U.S. Geological Survey (USGS) staff gage—essentially a tall ruler marked in inches. This allows someone to quickly look at the water level and get a pretty accurate reading of the current gage height of the stream.

How high and how fast a river will rise during a storm depends on many things. Most important, of course, is how much rain is falling. But also we have to look at other things, such as the stage of the river when the storm begins, at what the soil is like in the drainage basin where it is raining (is the soil already saturated with water from a previous storm?), and at how hard and in what parts of the watershed the rain is falling. The USGS has studied these things at many places across the country for many years, and thus is often able to make predictions about if and where a flood will occur and how bad that flood will be.

With the advent of modern computer and satellite technology, the USGS can monitor the stage of many streams almost instantly. Since some streams, especially those in the normally arid Western U.S., can rise dramatically in a matter of minutes during a major storm, it is important to be able to remotely monitor how fast water is rising "in real time" in order to warn people that might be affected by a dangerous flood. Recreational users of streams, such as kayakers, also use "real-time" stream-stage data to tell them if certain streams are at the right height for kayaking. The USGS can now gather data on river stage and even produce graphs showing stage as the rain is falling..

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