The Challenge of Steep Slope Erosion

Steep slopes present one of the most demanding erosion control challenges in civil and environmental engineering. As gradients steepen, conventional erosion control products struggle to maintain integrity under the combined forces of gravitational pull, rainfall impact, and high-velocity surface runoff.

The consequences can be severe: loss of structural fill, undermining of roadways and infrastructure, downstream sedimentation, habitat damage, and costly remediation. For highway cut slopes, dam and levee faces, and steep industrial site grading, long-term slope stability is not optional — it is a fundamental design requirement.

Pyramat 75, a High Performance Turf Reinforcement Mat (HPTRM), is a three-dimensional woven polypropylene geotextile engineered specifically for erosion control on steepened slopes and vegetated waterways, where standard products are insufficient.

Why Standard ECBs Fail on Steep Slopes

Standard temporary erosion control blankets (ECBs) — made from straw, coir, wood excelsior, or photodegradable synthetics — are designed for temporary erosion control during vegetation establishment on moderate gradients. Their limitations on steep slopes include:

• Biodegradation: They decompose over a period of months to a few years depending on material. If vegetation does not fully establish during that window, re-erosion occurs.
• Low shear resistance: High-velocity runoff on steep slopes generates hydraulic shear forces that exceed the capacity of lightweight temporary blankets.
• No root reinforcement: Standard ECBs provide no structural interlock with root systems, so even established vegetation may not hold on steep gradients during major storm events.
• Gravity effects: On very steep slopes, even relatively light mats can slide or deform under gravity before anchoring takes effect.

What steep slopes require is a permanent reinforcement system — one that does not degrade, provides structural reinforcement to the vegetation root zone, and maintains functionality throughout the design life of the project.

How Pyramat 75 HPTRM Works on Steep Slopes

Pyramat 75 addresses steep slope erosion through a combination of immediate protection and long-term structural reinforcement.

Immediate Protection

Immediately after installation, the three-dimensional woven polypropylene matrix:

• Reduces rainfall impact energy (splash erosion) at the soil surface
• Creates surface roughness that reduces runoff velocity and hydraulic shear
• Mechanically stabilizes seed and topsoil against displacement
• Promotes infiltration of surface water rather than shedding it downslope

Long-Term Structural Reinforcement

As vegetation establishes, the woven fibres generate very high interlock and reinforcement capacity with both the soil and the developing root system. The result is a composite reinforced turf where mat and vegetation act together to resist shear stress at levels beyond what either could achieve alone. Pyramat 75 is rated to resist both hydraulic and non-hydraulic stresses, and carries a tensile strength of 3,000 lbs/ft.

Because it is a permanent material with superior UV resistance and a design life of up to 75 years, it continues reinforcing the vegetation root system throughout the life of the infrastructure — not just during establishment.

Vegetation Establishment on Steep Slopes

Getting vegetation to establish on steep slopes is notoriously difficult. Seed is easily washed away by runoff before germination; seedlings that emerge are often lost in the first significant rain event; topsoil is thin and prone to drying out between rainfall events.

Pyramat 75 improves seedling survival on steep slopes by:

• Protecting seeds from hydraulic displacement during rain events
• Creating a favourable microclimate with reduced wind at the soil surface and improved moisture retention
• Capturing and holding seed throughout the mat depth, creating multiple germination opportunities rather than a single surface layer
• Providing a physical structure for root systems to anchor into

The mechanism is the patented trilobal X3 Fiber Technology, a matrix of voids designed to lock in seed and promote rapid root mass development while retaining moisture. Vegetation is generally considered established at roughly 60 to 90% cover, at which point the mat-root composite is providing reinforcement and requires minimal maintenance.

Typical Steep Slope Applications

• Highway and freeway cut slopes: The most common application. A design life of up to 75 years aligns with major highway infrastructure service life, and DOT-specific part numbers are available for several state agencies.
• Interstate interchange fill slopes: Large, highly visible fill slopes where aesthetics and long-term stability are both requirements.
• Dam and levee faces: Faces requiring permanent reinforcement against wave action, overtopping, and seepage forces.
• Storm water channels and vegetated waterways: A core application for the product alongside slope work.
• Landfill erosion control: Long-term cap and side-slope protection.
• Mine reclamation slopes: Steep, disturbed soils where long-term vegetation establishment is part of regulatory compliance.
• Arid and semi-arid soil protection: Sites where establishing and holding vegetation is difficult by nature.
• Industrial, commercial and residential grading: Steep cut and fill slopes where local ordinances require permanent erosion control.

Pyramat 75 vs Rock Riprap on Steep Slopes

Rock riprap has historically been the default for steep slope protection when erosion forces exceed the capacity of vegetated systems. Pyramat 75 offers several advantages in many steep slope applications:

• Vegetation: Pyramat 75 produces a fully vegetated slope; riprap suppresses vegetation.
• Verified carbon footprint: Pyramat 75 is the only HPTRM to have its carbon footprint verified by an independent third party. Cradle-to-grave, one square metre is 2.7 kgCO2e — roughly equivalent to driving seven miles — against rock riprap alternatives that run up to 30 times higher. Transportation is the main driver of that gap.
• Cost: Pyramat 75 costs considerably less than rock in many cases, once quarried rock delivery and placement are accounted for.
• Water quality and habitat: A vegetated system removes pollutants from waterways, reduces thermal pollution, and supports wildlife habitat. Hard armouring can raise waterway temperatures, which adversely affects fish populations.
• Aesthetics: A vegetated slope is visually preferred over exposed rock in most contexts.

The Woodley Channel rehabilitation in California is a documented example: the previous rock riprap was replaced with 15,000 square yards of Pyramat 75 HPTRM, chosen because it costs considerably less than rock while offering up to 75 years of design life even when exposed directly to sunlight. Details are on the Pyramat turf reinforcement mats page.

Installation Overview

Proper installation is critical for Pyramat 75 performance on steep slopes. Key principles include:

• Site preparation: Grade the slope to final configuration; remove large rocks, debris, and compaction layers that would prevent mat contact with the soil surface.
• Seeding: Apply seed mix to the slope surface before or concurrent with mat installation, per project specifications. Over-seeding on top of the installed mat supplements the seed below it and helps achieve uniform coverage.
• Anchor trench: Install an anchor trench at the top of the slope. The mat rolls downslope from the trench; this is the most critical mechanical anchor point.
• Securing pins: Anchor the mat with securing pins or U-stakes per specification — typically 12 to 24 inches long depending on soil, with steeper slopes requiring denser anchor patterns.
• Seam overlap: Overlap adjacent runs per manufacturer and specification requirements. Seams are the highest-risk points for hydraulic failure, so plan runs so edge seams do not coincide with runoff concentration zones.
• Check slots: Install check slots — horizontal anchor trenches across the mat face — per specifications to prevent runoff channelling beneath the mat.
• Establishment: Water if irrigation is available and conditions are dry, monitor through the first growing season, over-seed any areas with poor germination, avoid mowing below the mat surface, and inspect after major storm events during the first two years.

For detailed step-by-step guidance, see How to Install Pyramat 75 Turf Reinforcement Mat.

Pyramat 75 for Steep Slopes — Available at Eastgate Supply

Pyramat 75 — 8.5' × 120'

1,020 sq ft coverage, 107 lbs, 0.40" thick. Standard roll. Green or tan.

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Pyramat 75 — 15' × 120'

1,800 sq ft coverage, 168 lbs, 0.40" thick. Wide roll, fewer seams. Green or tan.

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Frequently Asked Questions

Pyramat and X3 are registered trademarks of Propex Operating Company, LLC.