Erosion Control Cloth: An Overview

“Erosion control cloth” often refers to a permeable geotextile fabric used as a separation and filtration layer under riprap, gravel, and soil interfaces. In plain terms: it helps keep soil where it belongs while still letting water pass through—reducing washouts, undermining, and sediment movement that can ruin a slope or rock-lined channel.

What Erosion Control Cloth Is (and What It’s Not)

Erosion control cloth (geotextile) is an engineered fabric placed between soil and aggregate (or soil and soil) to limit material mixing and soil loss. It’s designed to be permeable—water passes through, but many soil particles do not.

How It Works: Separation + Filtration + Protection

Most erosion failures start when soil moves. Soil can migrate up into stone (making the stone bed “disappear”), or it can wash out from underneath riprap and slope armor (creating voids and slumps). Erosion control cloth reduces those pathways.

• Under riprap: water can pass through rock, but the fabric helps keep the subgrade from piping out.
• Under gravel on slopes: fabric helps prevent the cover layer from mixing into the slope soil over time.
• In drainage features: fabric reduces fines intrusion that can clog stone voids and reduce flow capacity.

Photo 1: Geotextile fabric under riprap to reduce soil loss and undermining

Real-world example: why riprap needs a filter layer

Riprap looks stable—but water moves through the voids between rocks. Without a filter layer, that flow can pull fine soil particles out from underneath, creating voids that eventually lead to settling, slumping, or a “sinkhole” effect behind the rock line. A properly installed erosion control cloth acts like a breathable filter so the rock stays supported.

Practical tip: if you’re seeing rock “disappear” into the soil, that’s often a separation problem—not a rock-size problem.

Best Applications for Erosion Control Cloth

1) Riprap banks, shorelines, ditches, and outfalls

• Helps prevent subgrade washout under rock armor
• Improves long-term stability by maintaining support under the stones

2) Gradual slopes with aggregate cover

• Helps reduce soil migration and mixing under gravel
• Supports a cleaner, more stable cover layer

3) Separation beneath gravel access and drainage stone

• Helps keep aggregate from sinking into soft soil
• Maintains void space for drainage performance

How to Choose the Right Fabric for the Job

Selection comes down to the forces at play: soil type (fine vs coarse), water conditions (intermittent vs constant), and installation environment (angular stone, equipment traffic, and depth).

Quick selection logic

• Need separation + filtration under rock: a robust non-woven geotextile is a common choice.
• Higher installation abuse (angular rock, deeper excavation): choose a heavier-duty fabric and protect it during placement.
• Fine soils (silts/clays): filtration performance matters—avoid “cheap” fabrics that tear or clog easily.

Step-by-Step Installation

Step 1: Prepare the subgrade

1. Remove loose organics, roots, and protruding rocks that could puncture fabric.
2. Grade to the planned profile—smooth, consistent, and without sudden dips.
3. Compact lightly where appropriate (especially under stone sections).

Step 2: Place and align the fabric

1. Unroll fabric in the direction that minimizes seams.
2. Keep it smooth (no wrinkles) and maintain contact with the subgrade.
3. Overlap seams (commonly 12"+) and keep overlaps “shingled” downslope where applicable.

Photo 2: Erosion control cloth used as a separation and filtration layer

Step 3: Anchor the fabric (so it doesn’t shift during rock placement)

Anchor spacing depends on slope, wind, and cover material. As a practical baseline, place extra anchors at: seams, corners, edges, and any transition points. The goal is simple: keep the fabric from moving while you place aggregate.

Step 4: Place cover material without damaging the fabric

For riprap and angular stone, avoid dragging rock across exposed fabric. If possible, place stone carefully and build up coverage so the fabric is protected before final grading and positioning.

Step 5: Finish and protect the system

• Under riprap: ensure full coverage and avoid exposed fabric edges that can catch flow.
• Under gravel: maintain consistent depth to protect the fabric and keep loads distributed.
• At edges: consider trenching/terminating fabric edges to reduce undermining and uplift.

Common Mistakes That Cause Erosion Failures

Mistake #1: Not enough overlap (or overlaps oriented the wrong way)

Seams are the weak link. Increase overlap and orient it so water flow doesn’t “catch” the seam and pull it open.

Mistake #2: Fabric left exposed

Exposed edges can be lifted by flow or wind. Terminate edges properly and ensure full coverage with the specified material.

Mistake #3: Poor subgrade prep

Wrinkles, voids, and sharp debris can lead to punctures and settlement. A smooth, consistent base is a reliability multiplier.

Mistake #4: Using the wrong erosion product for steep or high-velocity conditions

Geotextile separation fabric is excellent for many permanent separation and filtration needs, but high-velocity channels and steep slopes may require engineered armoring or reinforcement products per spec.

Case Study: Riprap Bank Edge That Stopped Undermining

What was installed

• Subgrade reshaped and smoothed along the bank face.
• 8 oz non-woven erosion control cloth installed as a continuous filter layer with overlapped seams.
• Riprap placed carefully to avoid tearing, then keyed in to provide stable coverage.

Why it worked

1. Filtration + drainage: water moved through the system without carrying soil fines out.
2. Maintained support: the rock stayed “on top” instead of slowly sinking into the subgrade.
3. Better seam control: overlaps and anchoring reduced the risk of seam pull-open during peak flow.

Outcome

After heavy rain events, the riprap remained stable with noticeably less voiding and settlement. The bank line held shape longer, and maintenance shifted from repeated rock resets to periodic inspections—exactly what you want from a permanent erosion-control separation layer.

Photo 3: Laying erosion control cloth at the jobsite prior to cover placement

Takeaway: treat the fabric like structural prep, not an accessory

The fabric layer is easy to overlook because it disappears when the job is finished. But it’s doing the long-term work—maintaining separation, controlling fines migration, and protecting the slope or bank from undermining forces that only show up after multiple storms.

Pro tip: the most durable installs pay attention to terminations—edges, transitions, and seams—because that’s where water tries to find a shortcut.

FAQ: Erosion Control Cloth