Research finds riparian buffer strips rarely harm streambanks

A new study suggests that saturated riparian buffer strips, a nutrient control technique common in agriculture, could be installed in more places than previously thought.

By expanding the sites where the buffers are placed, farmers could protect more of their local streams. The study was recently published in the Journal of Environmental Quality, a publication of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

“Limiting nutrient transport off of fields and into waterbodies prevents overgrowth of harmful algae and protects in-stream ecosystems,” said Loulou Dickey, researcher at Iowa State University, who led the research.

Current guidelines limit where the riparian buffers should be installed. One cause of this is concern that the redirected flow of water will weaken the streambank. If the streambank erodes and falls into the stream, it hurts water quality and damages the land. The riparian buffers are often limited to banks that are not too tall, in hopes that this protects the banks from damage.

Dickey’s team tested the assumption about bank height. They also looked at how adding in a new riparian buffer affected streambank stability. They combined real-world data collection with models of possible scenarios.

“We wanted to help practitioners and designers to make determinations about site suitability in the future,” said Dickey. “Therefore, we needed to include a wide range of possible site conditions.”

The team found that most streambanks turned out fine once the farmer added a new riparian buffer. Only in about three percent of the scenarios did the new water’s flow through the soil endanger the stability of the bank.

The conditions where the bank failed included sandy soils that didn’t hold together very well and riparian buffers that were less than six feet wide. Those situations are unlikely to happen in the real world, said Dickey.

The biggest predictor of a failing streambank was also one that was already unstable.

“If the streambank is already failing, it is likely to continue to do so, but if the bank is relatively stable, it will likely remain stable even with saturated riparian buffer flow,” Dickey said.

The height of the streambank also didn’t predict the future stability. Instead, a bank that was too steep was more likely to fail. Steep streambanks have always been at risk of erosion. The takeaway is that many sites that used to be off limits could be good candidates for new riparian buffers.

“I hope our work will give farmers and landowners the confidence to install more saturated riparian buffer strips,” says Dickey. “I also hope farmers know how grateful we are to have the opportunity to study these practices because of their support.”

Expanding the use of the saturated riparian buffer could provide a straightforward and cost-effective way to protect surface water quality.