Can unpaved roads and watersheds co-exist? Researchers wade into the question

Visualize a dump truck unloading 13 tons of soil into Brush Creek, a vital waterway supplying northwest Arkansas' primary drinking water reservoir, Beaver Lake. This substantial amount of sediment was measured entering the stream as runoff following a single significant storm event.

Assessing the volume of storm-derived sediment entering Brush Creek was a central objective of a recent study titled "Watershed-scale controls outweigh local crossing effects on sediment loss from unpaved roads," published in the Journal of Environmental Quality.

Water quality scientist Shannon Speir noted that this study emerged from ongoing stream monitoring initiatives. She and her research team routinely explore the watersheds of northwest Arkansas, investigating runoff, sedimentation, and other factors influencing local rivers, creeks, and lakes.

"We were already engaged in routine sampling—wading through the creek and collecting water samples across the watershed—and we consistently traversed these unpaved roads to access our research sites," remarked Speir. "It was difficult to overlook the ruts, loose gravel washing toward the stream, and ditches directing runoff straight toward the water."

Speir serves as an assistant professor in the Department of Crop, Soil, and Environmental Sciences at the Dale Bumpers College of Agricultural, Food and Life Sciences, part of the University of Arkansas and the Arkansas Agricultural Experiment Station.

Northwest Arkansas presents a unique juxtaposition; it ranks among the 20 fastest-growing metropolitan areas in the U.S. while simultaneously retaining a largely rural character marked by the hills and valleys of the Ozarks that support cattle and poultry farming. The region is defined by dirt roads that traverse its pastures, farms, and forests, while its waterways feature low-water crossings, culverts, and direct crossings where vehicles traverse the watercourses.

"We recognized that 85% of Arkansas county roads are unpaved," Speir stated. "Much of the existing research regarding unpaved road impacts has been conducted primarily in the Pacific Northwest's forestry contexts—not within pasture-dominated, rural watersheds like ours.

"We were in an ideal position to investigate related questions, and the study evolved naturally as a crucial extension of our work," she added.

Testing the hypothesis

In collaboration with lead author and program associate Kathleen Cutting, Bumpers College master's student Karessa De La Paz, recent University of Arkansas graduate Caroline Anscombe, and Alana Strauss, a program associate at the Division of Agriculture, Speir's team aimed to determine how road crossings impacted water quality.

The researchers collected water samples from Brush Creek to analyze total suspended solids, which included silt, clay, animal wastes, and other particulates present in the water. They conducted their analyses both upstream and downstream of the road crossings.

"We hypothesized that sediment yields would increase downstream of a road crossing, with direct road crossings being the most detrimental," Speir explained.

However, contrary to their expectations, "the data did not support that assumption unequivocally," she added. "What proved to be significantly influential was the overall conditions at the watershed scale, including the extent of the unpaved road network within a sub-watershed, the amount of pastureland, and the prevailing flow conditions.

"While crossings are relevant locally under certain circumstances, the larger narrative emerged from the overall watershed dynamics," Speir concluded.

Broader focus, next steps

According to Speir, the study's outcomes prompted "a consequential shift in management priorities."

"It emphasizes shifting the focus from simply 'fix the crossing' to considering the entire landscape when water flows through it," she stated.

The study will integrate seamlessly with ongoing initiatives.

"Within Brush Creek, we have accrued nearly three years of baseline water quality data, and we are building upon it through Project BEACON, which investigates the use of biochar-amended poultry litter to mitigate nutrient runoff at both farm and watershed levels," Speir articulated.

Biochar, a carbon-rich substance derived from agricultural residues via a specific heating process, when combined with poultry litter and applied to pastures, acts as a sponge—absorbing nutrients and minimizing runoff into adjacent water bodies.

"The insights gained from our research on unpaved roads will inform more strategic deployment of on-farm conservation practices in conjunction with optimal management approaches for roads and pasturelands to achieve the greatest beneficial impact," Speir mentioned.

Consequences

Speir highlighted that "the study demonstrates that sediment loading to streams is already substantial under present conditions. During major storm events, we recorded sediment losses of up to 13 tons in a single day—essentially the equivalent of an entire dump truck of sediment" entering the waterway.

In line with the mission of land-grant institutions, Speir is committed to disseminating the research findings through the Cooperative Extension Service and other channels that can translate this information into practices that enhance local water quality.

"We are dedicated to ensuring that this research reaches individuals equipped to take action," she emphasized. "This involves collaboration with extension agents, the Arkansas Unpaved Roads Program, and organizations such as the Beaver Watershed Alliance, which has already estimated that the implementation of road best management practices could potentially reduce sediment loads to Beaver Lake by over 800 tons annually. These findings underline the importance of targeted investments in these areas."