Erosion control blankets are temporary protective layers applied to exposed soil surfaces to prevent soil loss and promote the establishment of vegetation. Composed of organic fibers held together by a net, they are deployed on disturbed land, such as steep slopes or newly graded areas, where soil is highly vulnerable to the forces of wind and water. Their primary purpose is to stabilize the soil immediately after seeding, creating a shielded environment until the root systems of new plants provide the necessary long-term stabilization role.
Core Functionality
A primary function of these blankets is to dissipate the kinetic energy of falling raindrops, creating a physical barrier that intercepts rain before it strikes the bare earth. This significantly reduces the impact and subsequent displacement of topsoil. This shielding effect is particularly important on slopes where detached soil particles are easily carried away by surface runoff.
The fibrous matrix of the blanket also works to slow the velocity of water flowing across the ground, a process known as reducing sheet flow erosion. As runoff encounters the blanket’s surface texture, friction increases, causing the water to lose speed and reducing its capacity to carry sediment. Slowing the flow allows more time for water to infiltrate the soil rather than running off, which helps mitigate the formation of rills and gullies.
The blanket creates a favorable microclimate at the soil surface, supporting seed germination and early plant growth. The material acts as a mulch layer, retaining moisture by reducing direct evaporation. This moisture retention, combined with the insulation provided by the fibers, helps to stabilize soil temperature, preventing extreme fluctuations that can stress vulnerable seedlings. This protection encourages the rapid establishment of vegetation.
Material Composition and Types
Erosion control blankets are broadly classified by their expected lifespan, which is directly tied to their material composition.
Temporary Blankets
Temporary blankets are the most common and utilize organic fibers designed to degrade naturally once vegetation is established. These products include materials like straw, offering protection for 6 to 12 months, and wood excelsior, which may last up to 24 months. For sites requiring longer-term temporary protection, such as steeper slopes or areas with moderate water flow, coconut coir or straw-coir blends are used. Coconut coir fibers are stronger and more decay-resistant, providing effective erosion control for two to five years before completely biodegrading. The fibers are held together by netting, which can be either photodegradable or fully biodegradable.
Permanent Blankets
Permanent blankets, often called Turf Reinforcement Mats (TRMs), are reserved for areas facing severe conditions, such as high-velocity water channels or extremely steep slopes. These mats are typically made from non-degradable, three-dimensional synthetic fibers, such as polypropylene, which provide a permanent matrix. The permanent mat reinforces the root structure of the growing vegetation, offering structural resistance to high shear stress.
Proper Installation Techniques
Successful erosion control depends heavily on correct preparation of the soil surface before the blanket is applied. The area must first be fine-graded to a smooth contour, removing large rocks, clods, and debris that could prevent the blanket from maintaining firm contact with the soil. Once graded, the area should be seeded according to project specifications, ensuring the seeds are placed directly onto the prepared soil.
The blanket must be laid out in the direction of the water flow, meaning it is unrolled vertically down a slope or parallel to the flow path in a channel. Installation requires several key steps:
- The upstream edge must be secured in a trench called a check slot to prevent water from undermining the blanket at the top of the slope.
- This trench is typically excavated six inches deep and six inches wide. The blanket is anchored inside it with staples, and the trench is then backfilled and compacted.
- Adjacent blankets must be overlapped to form a continuous protective layer, preventing water from finding an exposed seam.
- A horizontal overlap of two to six inches is recommended along the side edges. On a slope, the higher blanket must shingle over the lower one to shed water correctly.
- The entire blanket is secured using U-shaped staples or pins, which must be driven flush with the ground to hold the material firmly against the soil.
- A minimum anchoring rate of approximately 1.5 staples per square yard is generally used across the body of the blanket, with greater density along overlaps and edges.
- Staples are typically placed no more than 12 inches apart along all terminal ends and check slots, ensuring the blanket remains taut and in consistent contact with the soil surface.
This careful installation prevents movement during rainfall, allowing the seeds beneath to germinate without being washed away.