Project to reduce streambank erosion is now in its third year

SALINA, Kan. – Along a two-mile stretch of the meandering Smoky Hill River, Kari Bigham is earning a nickname among the locals that she’s pretty proud of.

Bigham, a graduate student at Kansas State University, has been called ‘The Streambank Lady,’ a tribute to her steady work to monitor changes in this part of the river.

“What drives this work,” Bigham says, “is the fact that landowners in general are losing acreage to streambank erosion every year.”

Streambank erosion is a natural process caused by the force of flowing water against the resistance of the bank. When the force of water wins out, adjacent land or sediment essentially ‘falls’ into the waterway and is washed downstream along with sediment-attached pollutants.

Those pollutants create risk to aquatic life and humans, and in some cases, can end up in downstream lakes as well.

Bigham’s work, which began in 2016, aims to slow erosion on parts of the Upper Lower Smoky Hill Watershed. She is currently monitoring six sites on the river between Salina and Lindsborg.

“The goal here is to protect land and improve water quality,” Bigham said.

The team of researchers and engineers began this project nearly three years ago by installing dead trees and similar woody structures into the bottom of the streambank, also called the ‘toe’ of the bank.

“What we’re trying to do by putting these woody structures into the toe of the streambank is to try to dissipate that energy and move that erosive current (called a thalweg) to the center of the bend,” Bigham said. “You’re reducing the energy and the amount of stress being placed on the streambank.”

The team is also looking at the effect that vegetation and re-shaping the slope of the bank has on reducing the rate of erosion.

“We put in these structures and it moves that erosive high-energy current away from the streambank, but what we really want to happen is for the sediment that the stream is carrying to drop and build up between the structures so that vegetation can establish along the bank and protect it from further erosion,” said Trisha Moore, an assistant professor of biological and agricultural engineering at Kansas State University who is supervising Bigham’s doctoral work.

Before beginning classes for the doctoral degree, Bigham worked as a consultant for a company designing streambank stabilization systems, but she says there was no quantitative data collected after a system was installed to show that it works.

In this project, Bigham collected pre-construction data at some of the sites, and has been taking yearly measurements of the sites to determine if the woody structures are helping to reduce the rate of erosion on the streambank.

“It’s a great opportunity to be able to monitor streambank erosion,” Moore said. “A lot of times we use the money to put the structures in, but we don’t get to study. We can’t understand if it’s cost-effective if you don’t have the data.”

Bigham said the results are mixed. The design they have implemented in the sections she’s working in “doesn’t seem to work as well when we have banks with high sand content. That’s not surprising.”

The researchers are also learning more about the force of water around tighter curves in the river, and the benefits of having vegetation on the streambank. They also learned what trees not to use in a woody structure.

“Mulberry trees…beavers like them,” Bigham said. “The beaver went to town on it, so we had to replace it with a hedge. We learned the hard way what species of tree to use.”

Bigham noted she’s also interested in learning more about what effects installing a stabilization system has on areas upstream and downstream.

“My concern is that we are redistributing the energy and causing accelerated erosion downstream,” she said. “I’m looking at a reach scale rather than just one site. Most of the research that’s been done so far looks at just that particular site, and yeah, they work, but are we causing landowner B downstream more problems and that’s why he had to do this project the next year?”

“That’s the part that bugged me when I was working with these designs, I was afraid I was causing more harm than good. I wanted some quantitative data to show that I was or was not. Hopefully we can learn from it and have better solutions, or just keep with this one if it works.”

The current project is expected to continue for at least two more years.

“We’re not just interested in how erosion occurs or why it occurs or that these things are working, but really we want to improve the design of the structures that we are putting out there,” Moore said.

Added Bigham: “This is engineering: Putting something out there to see if it works, and if it doesn’t work, what can we do to fix it. This is applied science.”

Source: KSU extension news release