Gluing streambanks could help restore healthy rivers

As flooding intensifies worldwide, buildings and roads are more vulnerable to severe streambank erosion. While streambanks can be rebuilt, the banks are more likely to erode immediately after reconstruction by restoration crews, before vegetation has time to establish.

Without roots to hold soil in place, newly graded banks are highly susceptible to erosion from future floods, potentially creating excess sediment that can smother fish eggs and macroinvertebrates, degrade water quality, and increase drinking water treatment costs.

One undergraduate researcher, Keegan O'Hara, a senior and accelerated master's degree student in the Department of Biological Systems Engineering, is supported by research funding from the Global Change Center as he develops a “recipe” to encourage soil microorganisms to create substances that act like glue, quickly strengthening reconstructed streambanks until vegetation can grow. 

“The less erosion you have from a bank, the healthier the water will be,” he said.

Creating a sticky recipe 

The project builds on the previous work of Daniel Smith Ph.D. '22 and Michael Snead '22 in the lab of Tess Thompson, associate professor in biological systems engineering. Earlier research showed that adding small amounts of organic matter to soils can rapidly stimulate the growth of soil microorganisms and increase the amount of extracellular polymeric substances. These substances act like a natural sticky adhesive, binding soil particles together and reducing erosion.

To test how this process might support stream restoration, O’Hara is evaluating three organic materials: wood chips, straw, and a hemp‑based substrate. Each material will be mixed into soil at different amounts to encourage microbial activity. The mixtures will then be tested in a laboratory flume to measure how well they withstand erosion over time.

“We’re hoping to identify one or two mixtures that noticeably improve soil cohesiveness,” O’Hara said. “If we can show that, it could become a simple, low‑cost addition to restoration work.” 

Because the materials being tested are inexpensive and widely available, the approach could be easily integrated into existing construction workflows. Straw, for example, is already used on many sites as a surface layer to reduce splash erosion.

"By determining how streambank erosion resistance changes with different types and amounts of readily available organic matter,” said Thompson, “the results of Keegan's research will be directly applicable to the stream restoration practice, improving the success of restoration projects."  

A sustainable alternative

Traditionally, large rocks have been used to stabilize banks. While this "rip-rap" is immediately effective, it can create long‑term challenges. As compared to streamside forests, rock armoring does not provide habitat and can increase water velocity downstream, shifting erosion onto neighboring properties.

By rapidly increasing soil erosion resistance, the soil‑glue approach could reduce dependence on hard materials and encourage engineers and restoration companies to consider organic soil-stabilizing mixtures as a supplemental tool to reduce erosion during the most vulnerable stage of restoration. 

“This is something that could help balance ecological goals with infrastructure needs,” O’Hara said. “And in the future, it could be applied beyond streams to other construction areas that face erosion challenges.”