What is streamflow?

perennial vs. ephemeral streams

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.

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.

Fire hoses, which generate much higher volumes of water, flow at a rate of 2 cfs.

At the heart of the Grand Canyon, the Colorado River flows at a rate of 18,000 cfs.

On a very large scale, the Mississippi River flows at the impressive rate of 700,000 cfs.

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.

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.

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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