Answer:
Stream
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 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." 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
out!
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
basin 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 stream stage and
even produce graphs showing stage as the rain is falling.
In fact, some of these real-time data and graphics are
being made available for you to use via the World Wide
Web.
