High-Tech River Rocks Track Thunderstorms' Strength

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' Walnut Gulch 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 thunderstorms.

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.