Measure for Measure
Scientific discovery starts by improving the quality of measurement,” says John Selker. “If you look at the history of science, you’ll see that thermodynamics came about because we made better thermometers.”
Without accurate measurements, you’ll never know whether your approach to fixing the problem works or not, according to Selker, a hydrologist in Oregon State University’s Department of Biological and Ecological Engineering. So Selker and his colleagues have come up with several new tools to study water. They’ve developed ways to calculate how much rainfall is held in tree canopies, to observe how water travels through soil, and to sample water as it passes from topsoil to aquifers. And each new tool has led to new discovery.
For example, if you dig a well to irrigate your field, it takes about 20 years for the irrigation water to cycle through the soil, into the aquifer, and back into your well, Selker says. He and others wanted to see the impact of this year’s agricultural irrigation. “To do that, we had to have an instrument that intercepts water as it travels through the soil.”
It is a passive capillary sampler (PCAPS), basically a box buried about three feet under the surface of a field and a few bottles set upright in the box. Each bottle has a fiberglass wick that absorbs irrigation water at the same rate as the soil and drips the water into the bottles. Tubes suction out the collected water to determine the amount of water draining through the soil and the constituents in that water. With this tool, OSU researchers have been able to help Willamette Valley farmers use less water and fertilizer, and improve the quality of their groundwater.
While the PCAPS seems simple enough, some of Selker’s other measurement tools use cutting-edge technology in wholly new ways. Take fiber optics, for example. “A little tiny bit of the light that you send down a fiber-optic cable gets bounced back, and the color of that bounced light is a function of its temperature,” Selker explains. “I can take a cable that is eight kilometers long, and I can measure the temperature along that cable at every meter to 1/100th of a degree centigrade.” And that ability to precisely gauge temperature has important and practical hydrologic uses.
Selker plans to roll out fiber-optic cable along some Oregon riverbeds to precisely measure the hydrologic profile. Many summer flowing streams are fed by underground springs, Selker says. By using fiber optic cables to get minutely accurate temperature measurement along the length of a stream, researchers will be able to pinpoint those hidden springs, measure their temperature and how much water they pour into a stream, and determine how quickly they respond to rainfall.
Now hydrologists will be able to predict how a stream will fare in an extended drought and when the stream will hit a critically high temperature that could endanger a cold-water species like salmon. This precise measurement could help limit the restriction of water withdrawals to a matter of hours, rather than months and years, “so farmers can grow crops and fish can swim in the streams harmoniously in the same season,” Selker says.
“This is a really new use for fiber optics,” Selker says. He is also testing fiber optics for measuring the rate of evaporation in lakes, studying how glaciers melt, and collecting data on contaminated water in old mine shafts. This process-level understanding, he says, will allow us to predict how water resources might be affected by land use and a changing climate.
“In addition, an instrument can travel around the world,” Selker says. “It is something that I think we should feel very proud of here at Oregon State University: many of the investments that people are making here are adopted around the world to help others improve their water resources.”