Christian Braudrick, William Dietrich and colleagues in California have built a physical model of a meandering stream in the laboratory that successfully meanders without straightening out or turning into a braided stream.

Braudrick and Dietrich from UC Berkeley, along with colleagues at San Francisco State University and Berkeley-based Stillwater Sciences, reported their results last week in the online edition of the journal Proceedings of the National Academy of Sciences.

By reverse-engineering a meandering stream, the researchers have shown two ingredients to be very important: “vegetation to reinforce banks and prevent erosion, and sand to build point bars and block off cut-off channels and chutes.”

According to Braudrick in the news release Alfalfa sprouts hold the line on meandering streams,  “We found that you need enough vegetation on the outer bank to slow down erosion and let the bars grow on the inner bank; otherwise, the stream cuts through the point bars and creates a braided river.”  Their scale model used alfalfa sprouts to represent deep-rooting vegetation and light-weight plastic particles to represent sand.

The release notes, “as with trees and other vegetation along natural rivers, the roots of the alfalfa sprouts provide strength to the soil and, when exposed, protect the banks from the force of the water, preventing banks from washing away too quickly.”

This study should underline for all of us the critical importance of restoring riparian buffers and native stream bank vegetation on all river restoration projects.  And it begs the question, why are so many in the industry continuing to rely on invasive strategies like hard armor stabilization if creating a stable, self-maintaining channel is an important goal?

Read more in this month’s Water Matters: Biotechnical Stabilization Can Yield Big Benefits