Water, wind, and gravity can combine to completely erode a hill or slope’s structural integrity, especially in terrains with steep grades or little vegetation.
No matter your role in the stability project, you can’t allow slope failure. It could cause millions of dollars in landscape, civilian, and property damage.
And you and your professional reputation will be to blame.
Our team recommends using vegetation to support your efforts. But is the quantity and quality of vegetation the primary determinant of a slope’s integrity and stability?
Below are some factors that impact your slope project, common slope stabilization methods, and an analysis of how vegetation impacts slope stability.
What Kinds of Vegetation Stabilizes Slopes?
For slopes of all sizes, vegetation is one of the most common and effective stabilization techniques.
Slopes without any natural vegetation, such as grasses, shrubs, or trees, have nothing naturally connecting the soil particles and area and nothing to reduce the amount of water that flows above and below the surface.
But what kind of vegetation actually supports a slope? Put simply, all vegetation types can provide varying levels of stabilization to a slope.
For instance, grasses, while they don’t have deep root systems, provide some texture and roughness to the surface, helping to prevent runoff channels from developing.
On the opposite side of the spectrum, full-grown trees with extensive root systems can physically stabilize a slope and reduce the impacts of wind and rain.
Mid-size plants, including bushes and shrubs, provide the same benefits to varying degrees depending on their species and physical condition.
How Does Vegetation Prevent Soil Erosion?
So we’ve established what types of vegetation can help stabilize a slope, but how does that process actually work? Below are the five primary ways that plants on a slope can prevent soil erosion and preserve the slope’s integrity.
Interception
One of the primary causes of erosion is rainfall dislodging pieces of soil, which can cause landslides and crusting. Vegetation helps prevent this by intercepting or blocking those raindrops before they arrive at the surface.
Restraint
Another way that vegetation provides slope stabilization is by physically restraining soil particles and holding them together. Root systems and the plants themselves both play a role in this process.
Retardation
Whether it be grasses, small shrubs, or trees, plants serve as a deterrent, slowing down any runoff and preventing large channels from forming. This process is called retardation.
Infiltration
Having plants on a slope increases the available channels, or pathways, for water that lands on the surface to enter the soil. The more vegetation on a slope, the easier it will be for water to infiltrate the soil, making runoff less likely.
Transpiration
While the rate varies greatly depending on the size and species, plants of all sizes absorb water from the soil and use it for general processes. This process, which is called transpiration, reduces the amount of moisture in the soil and, as a result, the chances for oversaturation.
Improving Slope Stability with Vegetation
There are two primary ways that vegetation can improve the integrity and stability of a slope: mechanically improving the slope and reducing the impacts of water.
1). Mechanical Stabilization
Plants and vegetation on a slope help to physically stabilize the soil. While grass and other ground-level foliage can provide some slope stability, most of this stabilization is a result of the roots.
Runoff
Strong, interconnected root systems bind soil particles together, improving the slope’s ability to withstand runoff. The larger the plants and their root systems, the more stability they provide over a larger area.
For instance, a small bush will provide some connectivity and strengthen the soil in a relatively small area, whereas the roots of a fully-grown tree will provide even more stability over a larger area.
Wind
That mechanical stabilization from the roots is particularly important for resisting winds. Soils without any vegetation are susceptible to wind throws. The vegetation mechanically stabilizes the soil and provides cover against the wind.
Vegetation as a slope stabilization method is a long-term solution because it can take many years for a sturdy, widespread root system to grow.
2). Water Stabilization
In addition to physically and mechanically stabilizing a slope, vegetation provides water stabilization. Water-related slope erosion occurs when rainfall creates runoffs and seals soil particles, causing a crust to form.
The water stabilization that vegetation creates works in a few different ways.
Below the Surface
Plants have roots, and roots absorb water from the soil around them. The more vegetation there is on a slope, the more water these plants will absorb, which reduces the likelihood of erosion.
But the water stabilization that plants provide doesn’t only occur below the surface.
On the Surface
On the surface, having vegetation changes the physical landscape, making it rougher and less smooth. Whether it be grass, foliage, or trees, plants increase the roughness and variance of the surface, which slows the velocity and decreases the volume.
Above the Surface
Vegetation, especially trees and plants with lots of foliage, can also intercept rainfall before it ever reaches the surface. During a significant rainstorm, many of the raindrops will land on the vegetation and evaporate back into the air, never touching the surface.
How Vegetation Works with Other Stabilization Methods
In most cases, some type – or types – of vegetation provide some slope stabilization. Plants also work well with other, more involved slope stabilization methods.
For instance, erosion control blankets work especially well when combined with natural vegetation. With an open weave, you can seed the hill through the industrial jute netting for vegetation to grow.
Terraces, which reduce both the velocity and volume of soil and water runoff and control where the water does flow, work best with large plants installed on the flat areas.
Retaining walls are another common stabilization option for complex and steep slopes. There are a variety of types of retaining walls, including natural vegetative and gravity retaining walls. In almost every case, retaining walls function best when paired with vegetation.
Stabilize Any Slope with Geocell
When it comes to stabilizing a slope, having interconnected, native, and durable vegetation is one of the best tools.
As someone who works with slopes, you know that it isn’t always that simple. For especially steep slopes, or those that are barren and need a solution that will work in the short-term and long-term, vegetation alone won’t work.
For those especially difficult slopes, geocell grids are the most effective solution. By applying lateral forces across the entire system, geocell allows you to enhance the mechanical integrity of a slope.
Geocell will stabilize the slope, improve drainage and water flows below the surface, and help vegetation grow.
Vegetation with Geocell for Extra Slope Support
Our team has installed geocell panels on slopes across the world. During a project evaluation, we can provide more details about the role of vegetation in slope stabilization and help you identify the best solutions for your slope.
Want to learn more about how geocells can stabilize any slope? Give us a call at (888)-511-1553.
