Controlling Existing Erosion

Once erosion begins, it can accelerate unexpectedly when there’s a particularly heavy rain or strong wind. Don’t expect erosion to follow a linear development path when conditions can change from day to day. Soil conditions that affect erosion also change over time, usually in ways that accelerate mineral loss at some point. While controlling developing erosion is somewhat easier than repair, it’s still harder than prevention efforts in most cases. Make sure to address the soil you’re protecting with a full three-pronged approach rather than a reactive one. These tips on erosion control will prepare you for dealing with the early signs of erosion promptly and without wavering on your chosen approach.

Temporary Options for Erosion Control

Temporary erosion controls are generally bio-degradable, so they break down over time and disappear when no longer needed. This reduces the risk of waste breaking away into the natural environment and reduces labor for removing silt screens and other tools at the end of soil disturbing work. However, many project managers overestimate the use of these temporary measures. A layer of pine straw over a slope may keep soil in place for a few weeks while grass sprouts, but it won’t offer much erosion control six months later. Attempting to constantly reapply short-term solutions for managing erosion can also lead to mechanical damage that causes soil loss itself.

Only turn to temporary methods for erosion control when you’re planning to put in permanent measures within the next few weeks or months. If you’re going to go a year or more before installing other erosion controls, you’ll need more than just the average temporary system. Some popular temporary erosion control techniques include:

  • Spreading various lightweight and bio-degradable cover materials like straw, mulch, pine needles, and jute netting
  • Absorbent fiber-filled socks and straw bolsters designed to reinforce hill edges and trap moving soil
  • Trenching that is filled in later after other work is completed
  • Temporary plastic covers to keep soil, especially loose piled material, from moving in heavy rainstorms.

Permanent Techniques to Control Erosion

Due to the cost and labor required for most erosion control methods, it’s not surprising that there are far more permanent techniques than temporary ones. Some of the most popular older techniques, from decades ago, have recently proven to be anything but permanent. If you’re looking to tackle erosion control once and for all, on a difficult site, you’ll be using one or more of the following techniques.

Shaping and Grading Slopes

Fresh grading and shaping work with heavy equipment is the first step of almost every permanent erosion control effort. Erosion causes soil to collect in steep slopes that are prone to more collapse. Putting geotextiles or other materials over an unstable surface will only help so much. Every slope should be reset to its ideal angle of repose. This is the angle at which gravity and moving water have the least effect on the materials making up the slope. Each material has a different angle of repose, so soil testing and engineering are necessary to design each face or slope of a project. Using a general angle of repose, often recommended as 30 degrees or less, will only lead to failure if the soil is stiffer or looser than average.

Roughening and Tracking

If soil must be left bare during construction or mining work, tracking is a good technique to keep surface erosion under control during normal rainfall. This technique involves running heavy tracked equipment over a slope’s surface to create regular patterns that are a few inches deep. The patterned surface breaks up water before it can collect and gain speed along the slope, while also reducing splash erosion. It’s best used as a temporary technique, but also fits into with the permanent practice of roughening. This fluffs up the soil surface without deep tilling that would lead to a landslide or sheet erosion. Roughening and then tracked soil is easiest to plant seed in since there’s space for roots to take hold and texture to keep the seeds from being washed away.

Wattles, Fences, and Terraces

While most silt fences are temporary, long-term fences and wattles are also recommended to permanently control erosion in sensitive areas. Partially vegetated hills and slopes often respond best to wattles and fencing since there’s less damage done to what cover remains in place. Living materials like willow branches are often used for these techniques since they root and add to the vegetative cover on the slope. If simple rows of woven wattle aren’t enough, to trap sediment and slow water, terraces may be needed. A terrace or retaining wall can work on the steepest slopes that can’t be reshaped or graded. However, they’re also expensive and require engineering to ensure they won’t collapse under the high weight of wet soil.

Vegetative Growth

The gold standard of permanent, erosion control is vegetative growth. As long as there’s some tiny amount of soil, sand, or even gravel that can support plant life, vegetation should be included as part of the erosion control plan. It’s possible to establish the right plants on nearly any eroded area. Of course, plants will need some maintenance over time. If a slope is too unstable to permit much foot or vehicle traffic after being planted, it may be better stabilized with a geotextile and rock blanket instead. Hydroseeding is one of many techniques for getting plant seeds to stay in place on an erosion prone area, so rain can’t disturb the establishment process. Most vegetation projects also require various forms of temporary cover and reinforcement to give the grass, shrubs, and trees time to grow in and develop strong roots.

Riprap, Mulch, and Other Covers

Putting a layer of heavier material over the surface of a slope or flat area, prone to erosion, is one of the best ways to protect it. Materials like chunks of stone (rip rap), gravel, wood chips or other natural mulches, and the rolled products listed below are all good for protecting unstable soil. The water bounces off the larger and heavier mulch, limiting how much reaches the soil below, and ensuring it’s slow enough that it does not carry any particles away. A flood can still disturb most mulch products and weeds can grow through them. Installing a geotextile, under a layer of mulch or riprap, is the best way to establish a complete erosion control solution when plants can’t be established.

Geotextiles

Geotextiles are the most stabilizing, longest lasting, rolled material used to cover and protect surfaces from erosion. While many geotextiles are installed directly over the surface of raw soil, they’re also widely used at the junctions between multiple layers of different soils. When trying to bond sand and heavier clay soil layers together, a geotextile prevents the differences in texture and weight from causing them to delaminate. Geotextile is required for most installations involving cover materials, like rip rap and rock blankets, to keep the heavier materials from sinking into the lighter soil. It’s also an essential part of roadway construction, both for controlling erosion around the sides and for preventing the road itself from coming apart over time. BTL Liners produces a wide range of geotextile products designed specifically for erosion control.

Other Rolled Products

Many other erosion control mats and nets look similar to geotextiles, but they’re not quite as versatile. They may be used in conjunction with a solid or woven textile to add more support and soil stabilization. Some of the most common rolled erosion products include:

  • Finely matted blankets of coir, excelsior, natural wool, synthetic fiber, and other materials
  • Loose nets made from coir or synthetic fibers that help anchor mulches to the surface
  • Rolled geogrids that have pockets that are a few inches across to hold cover material
  • Short-term straw mats designed to give cover to seeds or other plants.

Tackifiers and Soil Engineering

If the soil itself is too loose or unstable to remain reposed regardless of the slope, the project may require the use of tackifiers, stabilizing chemicals, and other soil engineering products. Some of the products are organic in nature and break down rapidly, but most are synthetic or polymer-based and last for years at a time. By trapping the soil surface with a spray or soak, it’s possible to give plants weeks to months to establish before any erosion resumes. Many hydroseeding products include tackifiers that glue both the grass seeds and the soil surface together to resist erosion until the roots penetrate.

Brushlaying and Branchpacking

For steep and vegetated slopes, where the least disturbance as possible is recommended, laying down layers of brush and branches is often the best way to control erosion. When the natural material is packed down tightly against the surface and held in place with pins or poles, it’s capable of both keeping sediment from moving and interrupting the splashing process. While this method is technically temporary, because the natural materials will break down over time, plants generally establish themselves in time to create a permanent cover.

Erosion control methods don’t work as well if tried one after another. If you think you might need more than one approach to prevent soil loss and damage, you’ll likely need to install them all at once for the best effects. This list of methods is far from comprehensive, but it does cover all of the most common techniques used for residential development, mining sites, logging operations, and national parks alike.

What Materials Work Best for Geotextiles?

If you’ve decided that a geotextile is necessary for all or part of your erosion control plan, you still need to narrow down the options based on material and design. Both non-woven and woven textiles are available from most of the common polymers used for membrane production. Features vary greatly between the various materials and designs.

Woven vs Non-Woven Geotextiles

Non-woven geotextiles are made from the same polymers as the woven varieties, but they’re made out of solid materials with techniques like needle punching and calendaring. Non-woven geotextiles are more impermeable and better at controlling water movement, typically making them the better choice for erosion control projects. If water penetration is desired through the layer of geotextile, stick with a woven material instead. Woven materials can be somewhat stronger and tear resistant in the beginning, but well-manufactured non-woven geotextiles often offer the same features. They also stretch over time and lose shape, which isn’t a problem with non-woven materials. Reinforced materials, in particular, offer the longest lifespan; regardless of the style of manufacturing or polymer type.

Material Options

Whether woven or non-woven materials are right for you, there are plenty of material options to choose from among them. Polyethylene is one of the most common materials, sold in both high density (HDPE) and low density (LDPE) varieties. Unfortunately, when used on their own, these materials can suffer from a mix of flexibility, durability, and chemical resistance issues when used for erosion control. Reinforced polyethylene (RPE) is the best choice for any geotextiles intended for permanent erosion control. This material offers superior tear resistance, long term stretch control, and high levels of impermeability when made in a non-woven method. You can find out more about the benefits of RPE for geotextiles by contacting us here at BTL Liners.

Choosing Cover Materials for Geotextiles

If you simply cover a bare hillside with a layer of slick geotextile, you’ll find that water still rushes down the slope to cause erosion or flooding issues elsewhere. Covering the geotextile with a rough and heavy material like the chunks of rock, known as rip rap, solves this problem by breaking up and slowing down the flow of water. It also keeps the geotextile in place and protects it from breaking down due to UV exposure. However, the cover material matters as much as the geotextile when it comes to erosion control. Undersized or lightweight materials will float, roll, or blow away and leave the textile exposed. On the flip side, using very large, heavy, and sharp materials could cut or tear the textile and leave it leaking below. Most geotextile manufacturers will recommend types of cover material for each product they sell to help you find the right combination for each erosion situation. If you’re not sure what works best with BTL Liners geotextiles, our team is happy to help you.

Combining Geotextiles with Geogrids and Geonets

There’s no need to limit an erosion control project to a single type of reinforcement fabric. Geotextiles may work well to stabilize the surface of the soil, but it’s not enough on its own to hold seeds in place or keep cover material from sliding. Geonets and geogrids work well installed over the top of geotextiles, especially when there’s at least a small layer of soil in between the various materials. The geotextile acts as the backbone of the design to prevent large amounts of soil loss and movement, while the nets and grids on the surface disrupt the flow of water and protect everything below from wind. The anchor pins and posts, commonly used to reinforce larger geogrids and nets, can penetrate through geotextiles without any risk of damage if the system is designed to work together.

While geotextiles and other permanent erosion control methods work well for various types of erosion, individual methods work best for specific applications. For example, it’s unlikely that a farm can cover their entire crop fields in geotextiles and rip rap and still get a good crop with efficient harvesting. On the flip side, vegetation and wind breaks may not work so well on a steep slope above a busy freeway. Choosing the right erosion control tactics simply means adapting a combination of them to the specific challenges of your project. Whether you’re dealing with steep slopes, large amounts of water, or very loose soils, there’s a solution available to permanently control erosion.


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