Driving OHVs through Streams

Some effects depend on local conditions

Researchers survey a stream crossing. Photo by Virginia McDaniels, U.S. Forest Service.
Researchers survey a stream crossing. Photo by Virginia McDaniels, U.S. Forest Service.

Millions of people enjoy nature while riding all-terrain vehicles, utility or recreational off-highway vehicles, or off-highway motorcycles. Collectively, these vehicles are called off-highway vehicles or OHVs, and in the southeastern U.S. – especially in Arkansas – much of this vehicle use occurs on U.S. Forest Service lands or other public lands.

In Arkansas, increased off-highway vehicle use on Forest Service lands began in the early 1990s, when existing unpaved logging roads began to be converted into recreational trails. However, by the late 1990s, scientists and land managers started becoming concerned about erosion, soil compaction, vegetation loss, and sediments washing into rivers. In some areas of the Ouachita River in Arkansas, threatened and endangered mussel species could be harmed.

“Balancing the desire to provide recreation opportunities to off-highway vehicle users and promote related economic benefits to local communities against the mandate to prevent adverse environmental change presents a growing challenge to public-land managers,” says Daniel Marion,  research hydrologist at the Forest Service Southern Research Station (SRS) Center for Bottomland Hardwoods Research who recently collaborated with researchers from the University of Kentucky to see whether off-highway vehicle trails impact water quality and stream channels at ford-type stream crossings. Their study was published in the journal Geomorphology. The study was led by Jonathan Phillips of the University of Kentucky, and the Forest Service National Stream and Aquatic Ecology Center provided funding.    

The study took place in the Wolf Pen Gap Trail Complex, a popular recreational area in the Ouachita Mountains of western Arkansas. In 2011, when sampling was conducted, approximately 25 miles of trails were open to recreational vehicles. Originally, all these trails crossed streams using ford-type crossings, which are essentially areas of a stream or river that are shallow enough to drive through. While three crossings at the widest stream sections were replaced with bridges in 2005, and many fords on very small streams have recently been replaced with culvert and fill structures, ford crossings are still common. Marion and his colleagues compared the upstream and downstream areas of 15 crossings.

Some of the crossings had been active for more than 20 years, while others had been closed for more than 5 years. “However, all of the sites designated for off-highway vehicle use have lost about a foot to a foot and a half of soil on the trail segments on both sides of the stream crossing, and bedrock in many of these areas is exposed,” says Marion. Even after bedrock was exposed, sedimentation continued to be a problem in many of the streams.

Although every stream in the study area was affected by off-highway vehicles, the type of response varied between sites. The most consistent impacts involved mud coating and sediment deposition downstream of the crossings. Other changes, such as stream bank erosion and changes in streams’ width-to-depth ratio were more variable. “Off-highway vehicle use can negatively impact stream channel condition and water quality,” says Marion, “but specific effects are strongly contingent on local geology and channel structure, and only limited generalizations are evident.”

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For more information, email Daniel Marion at dmarion@fs.fed.us