Go with the flow

Streambeds act as natural water filters by trapping particles and pollutants. To better understand the dynamics of these small yet complex systems, a Carolina hydrologist is creating (and clogging) her own stream.

Kaylyn Gootman observes the water in the racetrack flume.
Kaylyn Gootman observes the water in the racetrack flume, as her undergraduate research assistant Savannah Swinea sets the Acoustic Doppler Velocimeter.

The basement of Chapman Hall is a maze. Wind through several hallways, swipe a UNC OneCard to gain access through a heavy, locked door, and enter the massive chamber of the Joint Applied Math and Marine Sciences Fluids lab.

Turn left, walk past the wind tunnel and the towering 36-meter wave tank, and you’ll see hundreds of gallons of water swirling through an elevated metal structure. Kaylyn Gootman, a Ph.D. candidate in the Curriculum in Environment and Ecology, dumps a large plastic bag full of what looks like flour into the water and watches closely as the contents disperse.

The large oval-shaped metal structure, called a racetrack flume, holds approximately 430 gallons of water, the equivalent of about eight bath tubs. Using an electric trolling motor and an Acoustic Doppler Velocimeter (ADV), Gootman can control the direction and speed of the water. The material that looks like flour is actually finely ground clay — and Gootman is very interested in how it moves.

Gootman calls the set-up a “mock stream.”

“We’re studying the physical impact of a natural pollutant — like how much clay gets embedded in a streambed — and the natural clean-up processes that the water circulation of a stream provides,” she says.

Water movement is complex — in a natural stream, water flows up, down, and all around. To understand the whole system, Gootman, and her undergraduate assistant Savannah Swinea, are examining the individual processes of a stream they built here in the fluids lab.

“Being able to narrow our focus to major physical controls allows us to study a few key processes without much interference,” Gootman says. “That knowledge can then act as a foundation for better understanding in the natural environment where things happen in multiple directions and dimensions all at once.”

Constructing a stream

Think of a streambed as a kidney. “Kidneys filter blood, and streams filter water — both trap toxins,” Gootman says. While kidneys filter toxins like alcohol, streams break down particles from surface water runoff including pollutants from irrigation, construction or industrial agriculture. But just as kidneys can fail, so can streams — a kidney stone is akin to a clogged streambed.

Gootman’s research can help geoscientists, developers and land owners better understand erosion events, especially as they relate to urbanization. How much pollution can a stream filter before the system gets overwhelmed?

Working in the fluids lab allows her to save time and resources — and she’s not harming the environment. “Going out to a stream and dumping a bunch of clay in it would not be very good environmental stewardship,” Gootman says with a smile.

Using a contained system like the racetrack flume also gives her the ability to obtain precise measurements. She can focus on one particular direction of water movement, like down-welling, or the downward flow of water into the streambed. Examining each parameter individually simplifies the inherently complex nature of fluid dynamics.

Read more of this story at the Endeavors website.