May 27, 2002 COLLEGE STATION - Turns out that picturesque mountain stream you've always admired doesn't just burble randomly down the hillside: It marches to the measured cadence of its own drummer. Geographer Anne Chin has discovered that like their flatland cousins, mountain streams meander too. It's just that they meander vertically, dropping from pool to pool at a rhythmic, periodic rate.
Chin, a professor in the College of Geosciences at Texas A&M University, will publish an article on her research, titled "The Periodic Nature of Step-Pool Mountain Streams," this summer in The American Journal of Science.
"Mountains cover a sizable portion of the earth's surface, and as urbanization encroaches on mountain ecosystems, the streams there assume greater importance," Chin said. "Both policy-makers and the public are becoming concerned with how to manage mountain habitats and protect them from damage by human activities.
"The problem is that scientists don't fully understand the energetics and form-process interactions of high-gradient mountain streams," she continued. "Since most of these streams are located in steep, rugged terrain, access to them has been limited, and hydrologists and geomorphologists have tended to ignore them. Now, however, we realize that the theories about how lowland streams interact with the environment may not explain what's happening in the mountains."
Chin is the first scientist to advance the idea that mountain streams are organized in a regular, periodic pattern. Focusing on the pools and rocky drop-downs such streams create in their beds as they move downhill, she applied spectral analysis to the problem and discovered mountain stream step-pool sequences proceed in a rhythmic, staircase-like pattern.
"Mountain streams are more complex than those in the flatlands," Chin said. "Mountain streams work to accomplish different tasks, moving rocks from pebbles to heavy boulders. Such streams change more slowly, over a longer time scale, so their adjustment to environmental change takes longer. Thus their responses to both natural and anthropogenic disturbances are more difficult to understand.
"Mountain streams are confined by narrow valleys and can't move laterally," she observed. "They can only move vertically, for the most part, and this takes away a degree of freedom in their ability to adjust to energy conditions in the stream system. At the same time, the steepness of the stream's course gives them a high level of energy, which they must regulate. Lowland streams manage their energy more uniformly and efficiency through meandering over the face of the landscape, but mountain streams can only adjust vertically, so they create step-pool sequences to dissipate energy."
Chin, whose research interests center on fluvial geomorphology and hydrology, is conducting projects in the arid and semi-arid basins around Arizona's McDowell Mountains and the Santa Monica Mountains in California. She's also studying the impacts of roads and trails on stream channel dynamics in the Ouachita National Forest in Arkansas, collaborating with the U.S. Department of Agriculture Forest Service.
"The idea that mountain streams' vertical adjustment takes place in a periodic fashion is a new one, and that's exciting," Chin said. "No one has ever said this before."
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