High-Tech River Rocks Track Thunderstorms'
Strength By Marcia Wood
October 30, 2003
Downpours from sudden summer thunderstorms in the typically
parched American Southwest can quickly fill a dry streambed, loosening pebbles
and stones to send them rolling and tumbling downstream. But no one really
knows precisely how far and fast these rocks travel.
To find out, Agricultural
Research Service scientists have substituted approximately 200 high-tech,
electronically equipped rocks in place of natural rocks. And, they're tracking
the electronic rocks' journeys. They're doing the work at three small
streambeds in the rugged shrub-grasslands of ARS'
Experimental Watershed outside Tombstone, Ariz.
Their discoveries should, for example, provide the basis for
mathematical formulas that could help reservoir managers estimate the amount of
rock and sediment that might make its way to their reservoirs after
ARS hydraulic engineer Mary H. Nichols designed the research
rocks in her laboratory at the Southwest Watershed Research Center in
Tucson, Ariz. Each sphere, about the size of a racquetball, is made of concrete
and weighs about the same as a natural rock of the same size. But each lab-made
rock houses a tiny, glass-enclosed transponder, an electronic device similar to
those that commuters attach to their vehicles for prepaid passage through
bridge or highway toll gates.
Nichols and co-researchers quickly and easily found and
individually identified--electronically--all the research rocks after
rainstorms during Arizona's 2002 and 2003 "monsoon" seasons. They did that by
sweeping a battery-powered antenna over the streambeds. The signal sent from
the antenna is picked up by the transponders, then sent to and recorded by a
handheld personal digital assistant or PDA. Portable global positioning
equipment logs the exact location of each electronic stone.
Though the idea of electronic rocks isn't new, Nichols' are
likely among the best performing, most numerous and most economical.
Nichols discussed the experiments earlier this week with
researchers participating in an international conference and tour honoring the
50th anniversary of the world-famous Walnut Gulch Experimental Watershed.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.