The Shadow
BLACKSBURG, Va. – As flooding intensifies worldwide, streambanks are most prone to erosion in the days after a storm. But, another vulnerable window is often overlooked: the period between reconstruction and when vegetation is established.
Without roots to hold soil in place, newly graded banks are highly susceptible to erosion from rainfall and fast‑moving water. This creates excess sediment that can smother habitat for fish and macroinvertebrates, degrade water quality, and increase treatment costs for drinking water and wastewater facilities.
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. This substance acts 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 densities and allowed to sit for several weeks to encourage microbial activity. The mixtures then will be tested in a laboratory flume to measure how well they withstand erosion.
“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
Many restoration projects currently rely on plastic mesh or rock armoring to stabilize banks. While effective in the short term, these methods can create long‑term challenges. Plastic mesh can break down into microplastics, and rock armoring can increase water velocity downstream, shifting erosion onto neighboring properties.
By giving vegetation more time to establish, the soil‑glue approach could reduce dependence on these 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.”
