Erosion is a naturally occurring process that is accelerated by earth-disturbing projects. Erosion may damage the ecosystem and environment, increase water treatment and maintenance costs and leave the land susceptible to harmful weeds. By executing effective erosion control, it may help reduce the spread of invasive plant species which is one of the four threats to our nation’s forests and grasslands.
Six Principles for Effective Erosion Control are:
- Reduce erosive forces and increase resisting forces. Erosion occurs when the erosive force exceeds the soil’s ability to resist the erosive force. The only methods to reduce erosion are reducing the erosive forces, increase the resisting forces or a combination of the two.
- Apply good erosion control for good sediment control. It is easier to prevent soil from eroding than to remove the soil after it has been deposited somewhere else. Use sediment-control treatments to keep the sediment from leaving the site.
- Effectively designed topography reduces sediment yield and increases vegetation. Shorter and flatter slopes erode less and produce less sediment than longer, steeper slopes. By creating benches, steps or using some soil bioengineering methods can reduce slope length and angle.
- Limit soil exposure since soil is especially prone to erosion during wet seasons. Divert excess water flowing over unprotected soil areas to avoid excessive erosion. Leave vegetation undisturbed when possible because it is one of the most effective ways to reduce erosion. Surface disturbance should only occur when the ground is relatively dry and the site is not subject to frequent storms.
- Keep runoff velocities low by reducing the slope gradient of the water or increasing surface roughness reduces water’s velocity and erosive power.
- Proper installation and maintenance of erosion-controlled treatments should be inspected every 7 days on active sites and 14 days on inactive sites and within 24 hours following rainfall.
There are many different types of erosion and becoming familiar with them will help you with erosion control. The principle agents of erosion include water, gravity, wind, ice and chemical action. The actions of these agents form a continuous spectrum erosion that may be related. The spectrum includes forms that may not be traditionally included in the traditional definition of erosion such as landslides. Complicated and high-risk projects may need specialists such as geotechnical engineers, hydrologists, soil scientists and agronomists. Complicated erosion situations occur in large gullies, coastlines and channels, or steep slopes subject to landslides. Surface erosion includes erosion caused by water, gravity and wind.
Water Caused Erosion
Water erosion is composed is splash erosion, where rain impacts bare soil dislodging the surface soil particles. The splashing can create a crust “seal” on the soil (surface sealing) making it less permeable and reducing the growth of vegetation. The second part of erosion occurs when water forms very shallow surface flow (sheet erosion). This can occur on any soil that is impacted by water drops or where water begins to flow over the soil surface. Where the erosion occurs and the severity of the erosion all depends on soil erodibility, slope length and angel, storm duration rate, duration of snowmelt and vegetative cover. If this is left untreated, it can develop into more severe rill erosion.
Rill erosion is erosion by water in small micro-channels, 0.2-1.2 inches wide and up to 3 inches deep. Rain or snowmelt contacts the bare soil for durations long enough for the water to develop micro-channels. Rill erosion depends on the soil erodibility, slope length and angle, storm duration intensity, rate and duration of snowmelt and vegetation. Rill erosion can occur on any slope with erodible soil, more severe on steeper slopes. The volume of eroded material increases as the number of rills increase. Increasing clay content decreases the chance of rill formation and if untreated, it may develop into more severe gully erosion.
Gully erosion occurs in channels with U or V shaped cross sections and are located in valleys or hill slopes and is characterized by periodic flow and high width to depth ratios. Dimensions can range from millimeters to meters. Untreated rills on slopes may develop into V shaped gullies and are often found on steep forested areas where concentrated flow begins on steep long slopes with erodible soil.
Seepage erosion is the removal of soil particles by water flowing through soil or bedrock which dislodges and transports soil particles. This occurs when permeable soil layers or underlying joined bedrock exist. It can also occur as part of other erosion processes such as channel, mass movement and chemical erosion.
Gravity Caused Erosion
Dry-ravel erosion is the removal and transport of particles downslope by gravity after these particles loses its cohesion from exposure to the elements when moisture is lost. Dry-ravel erosion is recognized by the lack of rills and other water erosion features but with large amounts of eroded material deposited at the base of the slope.
Mass-Movement Erosion is the movement of mass of rock, debris or earth down a slope. This includes landslides and debris flows.
Wind Erosion is the detachment and transport of soil particles by the wind where the particles move suspended in air (suspension), bouncing (saltation) or rolling (surface creep). This can be a more significant erosion source than water in dry climates or windward facing slopes.
Freeze/thaw erosion occurs during the expansion of freezing water and the contraction of thawing ice. This requires freezing temperatures, time for ice to form, soil moisture and frost prone soils. It can loosen and remove rock and soil and displace seeds in a fine-textured soil.
Glacier or Moving Ice Erosion
Glacier or moving ice erosion occurs by large amounts of ice entrapping, grinding and moving soil and rock. It can move soil and rock many miles from its origin.
Chemical erosion is the transport of rock and soil and its transformation into another substance through chemical processes. Rock and soil may be transformed by chemical reactions into another substance and later removed. Rock and soil may be transported by another substance, such as water. Chemical-caused erosion can be complex such as the formation of sink holes in limestone.
In order to be successful in erosion control strategies, the soil properties, erodibility and its capability for soil to support vegetation needs to be established. A standard classification of the soil type is necessary for effective communication. The two most common soil classifications are the USDA Soil Texture Classification and the Unified Soil Classification System. In the right conditions, any soil can be responsive during mass movement. Seepage erosion requires high enough permeability to allow seepage and small particles to be easily moved. Seepage-erosion should be low for gravels (large particles with potentially high permeability) and clays (small particles with low permeability) except for dispersive clays which are very erodible. Loamy sands are prone to surface sealing which increases runoff.
The type of soil also impacts vegetation. Loamy or silty soils are ideal for vegetation to start growing. Sandy gravely soils often lack fines, nutrients and water holding capacity of silty soil. Heavy plastic clay and silt often have poor aeration and resist root penetration, preventing growth. Soil density can also significantly affect the growth of vegetation. Dense soils such as clay and silt have lower permeability and poor aeration that impede root growth. Nutrient and chemical properties (pH) also affect vegetation growth.
Erosion control is a two-step process; short-term erosion control followed by vegetation growth for long-term erosion control. In steep or severe conditions, a structural solution such as a retaining wall is required. The ideal erosion control product promotes germination and plant growth while protecting soil from short-term erosion. There are numerous treatments that may be fitting for a site. The general erosion-control treatment categories are:
Seed, fertilizer and soil amendments
Soil stabilizers and tackifiers
Rolled Erosion-Control Products
Biotechnical stabilization uses mechanical structures and biological elements to prevent severe erosion. These can include non-vegetated structures, like retaining walls. Soil bioengineering, the use of plants in biotechnical slope stabilization. Biotechnical stabilization is a specialized field and a consultation with an expert is strongly recommended.
Proper Treatment Selection
Erosion-control treatment is based on six steps:
Step 1 – Assess project site
Step 2 – Establish objectives
Step 3 – Collect site-specific data
Step 4 – Assess erosion potential
Step 5 – Evaluate alternative treatments
Step 6 – Select treatment
Parameters to consider during project assessment include:
Regulations and policies
Risk and liability
Cost and funding
Controlling erosion is important to preserve the site and minimize the environmental impact that the project has on the surrounding area. BE3 offers a variety of solutions to meet your requirements. Call us today at 716-249-6880.