Erosion Control
Table of Contents
Erosion control protects water quality, maintains the structural integrity of the roadway, protects germinating seed and helps counties and cities comply with National Pollutant Discharge Elimination System (NPDES) Phase II regulations. It is among the most important goals of a roadside program. Permanent vegetation is the long-term solution, but short-term erosion control is necessary to protect exposed soil while vegetation matures.
Types of erosion
Soil erosion can occur through different processes. Those of greatest concern to a roadside manager are splash, sheet and rill erosion on slopes and channel erosion in concentrated flow areas.
- Splash erosion occurs when raindrops dislodge exposed soil particles. These particles settle in soil pores and when dry, form a crust, reducing infiltration during subsequent rains.
- Sheet erosion occurs in heavier rains on uniformly smooth soil surfaces. Dislodged particles become suspended and are transported downslope.
- Rill erosion occurs when slight differences in soil surface elevation cause runoff to concentrate and form a pattern of cuts or rills. It is more likely to occur than sheet erosion since slopes are rarely uniformly smooth.
- Channel erosion occurs in concentrated flow areas and is caused by downward scour due to flow shear stress. Many, if not all, roadsides are conduits for concentrated flow.
Planning for erosion control
Erosion control objectives should be considered in the planning stage of each roadside project. Many factors affect a site’s erosion potential. Some also affect how quickly vegetation will establish and provide stabilization. The following interconnected factors should be analyzed to determine what, if any, erosion control practices are necessary:
- Time of year (How long will soil be exposed?)
- Soil type and fertility
- Slope length, grade and aspect
- Off-site surface flow onto project area
- Type of seed mix (Warm season establishes slower than cool season.)
- Weather forecast
Other considerations: the consequences of failure and the presence of sensitive areas (e.g., wetlands, sensitive waterways and critical habitats for threatened and endangered species).
Erosion control and IRVM
Some IRVM programs will be more involved in erosion control than others. Sediment control and long-term erosion control may be the responsibility of other departments or contracted out.
All IRVM programs will be responsible for short-term soil protection provided by proper site preparation, nurse/stabilizer crops and mulches.