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What
is streamflow?
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perennial vs. ephemeral streams
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There are
two basic types of streams: perennial
and ephemeral.
Perennial
streams flow throughout the year because
they are fed by ample rainfall, snowmelt, and groundwater
sources. Ephemeral
streams do not flow year-round, due
to periods of little or no precipitation or groundwater
discharge. Sabino Creek is an ephemeral stream, flowing
about 293 days per year.
Streamflow
volume is generally measured in either cubic feet per
second, abbreviated as
'cfs,' or cubic meters per second, 'cms.' The following
examples illustrate some common flow rates.
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A typical water fountain
flows at a rate of three ten-thousandths cubic
feet per second (.0003 cfs).
This translates to a
rate of about one hour to pump one cubic foot
of water, or a day and a half to pump a cubic
meter.
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| Fire
hoses, which generate much higher volumes of water,
flow at a rate of 2 cfs. |
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At the heart of the Grand
Canyon, the Colorado River flows at a rate of
18,000 cfs.
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On a
very large scale, the Mississippi River flows
at the impressive rate of 700,000 cfs.
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Because
Sabino Canyon is an ephemeral stream, flow rates
fluctuate dramatically
throughout the year. During a typical year, flow
rates during the winter and spring months are
greater than during the summer monsoon.
While Sabino Creek averages only about 10 cfs,
sometimes the flow rate gets as high as 15,000
cfs.
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As you
can see here, the 1999 monsoon season was extraordinary!
On July 16th of that year, 6 inches of rain fell
in a short period of time on already saturated
ground, higher in the Santa Catalina Mountains.
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In just
over an hour, Sabino Creek went from 218 to 10,700
cfs, the most forceful summer flash flood in 50
years!
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