Forest Trail Explorer

US Forest Service and Southern Research Station

Soil Degradation and Sedimentation Due to Transportation

Eroding road
Eroding road
Sediment removal at Lake Junaluska.
Home destroyed when an upslope embankment failed, contributing to a debris flow, January 7, 2009, in Maggie Valley, NC.
Case Camp Ridge forest road, a stable road site.
Subdivision landslide.

Causes and Effects of Soil Loss

Soil loss is caused by a variety of factors, including erosion from wind and water, mechanical tilling, logging, agricultural practices, and poor water management. Erosion and sedimentation, the major effects of soil loss, are widespread and can be devastating.

Erosion

Erosion is a natural process on hill slopes. The rate of erosion is determined by several factors, including soil type, rainfall, and length and percent of slope. Generally, human-induced changes in the landscape lead to higher levels of erosion than would occur naturally. While there are many ways to minimize erosion, vegetative cover is the most effective over the long term. When vegetation is removed, the rate of soil erosion is greatly accelerated, often beyond sustainable levels.

Sedimentation

Eroded soil deposited downslope is referred to as sedimentation. When severe rain or wind events occur or soils are disturbed by human activities, soils are moved off site and deposited on land and in lakes, wetlands, and streams. Sediment, the single largest nonpoint source pollutant, contributes to the decline of surface water quality, imperils aquatic wildlife, and leads to increased stream bank erosion and flooding.Levels of sedimentation increase due to roads, residential and commercial development, agricultural practices, timber harvesting, and any other land-disturbing activity.

The Sedimentation Control Act of 1973 requires operators to implement short- and long-term mitigation measures to reduce erosion on- and off-site. Forest landowners who wish to harvest trees are exempt from these regulations if they comply with forestry practice guidelines, which include erosion control measures and mitigation. Best management practices (BMPs) are voluntary practices that reduce sources of sedimentation and runoff, confine sediment on site, and trap the movement of sediment so that it settles.Although these practices are not required by law, it is estimated that about 85-90 percent of landowners and loggers voluntarily comply with BMPs and regulations. If loggers/landowners are found to be out of compliance, the North Carolina Division of Forest Resources (NCDFR) works with operators to correct problems. If not resolved, the operator may forfeit their exemption under the Sedimentation Control Act and must seek a permit to continue the activity.

According to data generated by the Tennessee Valley Authority’s Integrated Pollutant Source Identification computer models for Haywood County, NC (2000 and 2007), unpaved roads and road banks contribute significantly more sediment loads to streams than nearly all other sources. Roads built on mountainsides for private development are often not built to accommodate steep slopes, eroding soils, heavy vehicular traffic, and water drainages, and can undermine slope stability and lead to increased risk of landslides. Additional issues that can exacerbate erosion include poor maintenance and, in recent years, property foreclosures that leave roads with no maintenance.

 

Cropland

Pasture

Livestock Access

Eroding Streambank

Unpaved Road / Road Bank

Other

Total Tons

2002

1.3% 9.6% 5.5% 47.0% 32.0% 5.8% 4575.470

2007

2.4% 8.7% 6.2% 43.8% 36.9% 2.0% 4226.283

Forest Road Erosion

Forest road erosion and eventual sediment delivery to nearby streams largely depends on soils, climate, traffic intensity, and topography. Erosion rates from forested roads range from about 0.5 to 100 tons per acre per year, while the geologic or natural erosion rate is estimated at 0.1 tons per acre per year. A sustainable range of erosion from disturbance is estimated at 0.4 to 2.0 tons per acre per year. Sediment control can be significantly improved through appropriate road location, drainage systems, and reestablishment of vegetation. These practices effectively trap eroded road sediments and isolate or essentially disconnect roads from stream systems.

In the Southern Appalachians, cut slopes (as opposed to fill slopes) and road beds have been found to account for as much as 75-80 percent of soil loss from the road area, the majority of which occurs during the establishment period for vegetation. These rates decrease significantly, however, following complete reestablishment of vegetative cover.

Steep Slopes and Development

Because building construction was easier and less costly and crop cultivation better in the fertile valleys, human development historically was limited to broad basins, terraces, and floodplains. However, as land became scarcer in the valleys and the demand for uninterrupted mountain views increased, residents slowly began building uphill toward the intermediate and even high mountains. This preference has led to development on steep slopes with few regulations in place to protect those located downslope from soil erosion and landslides.

The above content is a part of the Western North Carolina Vitality Index. To view the full report, visit www.wncvitalityindex.org.

Forest Inventory and Analysis Resources

For more information on FIA, please click here.

References

North Carolina Department of Environment and Natural Resources, Division of Land Resources, Sedimentation Pollution Control Act of 1973. Accessed from: http://www.dlr.enr.state.nc.us/pages/sedimentpollutioncontrol.html.

North Carolina Division of Forest Resources. December 2007. North Carolina Forest Practice Guidelines Related to Water Quality. Leaflet WQ-1. Accessed from: http://www.dfr.state.nc.us/publications/Forestry%20Leaflets/WQ01.pdf.

North Carolina Forest Service, Best Management Practices: Quick Reference Field Guide. Accessed from: http://dfr.nc.gov/publications/WQ0407/01%2002%20Chapters%20Field%20Guide....

North Carolina State University, Department of Soil Science. Accessed from: http://www.soil.ncsu.edu/about/publications.php.

North Carolina Department of Environment and Natural Resources, Land Quality Section, Soil Facts, North Carolina Erosion and Sedimentation Control Program. Accessed from: http://www.soil.ncsu.edu/publications/Soilfacts/AG-439-32/#BasicMandator....

Grace, J.M. 2008. Determining the Range of Acceptable Forest Road Erosion. American Society of Agricultural and Biological Engineers Meeting Presentation, Paper Number 083984. USDA Forest Service, Southern Research Station. Accessed from: http://www.srs.fs.usda.gov/pubs/ja/ja_grace034.pdf.

Photo Credits

Case Camp Ridge Road: Dick Jones.

Landslide in Haywood County, NC: Patrick Parton, Haywood County.