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The Grades of Silt Fences

There are different grades for silt fences

What are Silt Fences?

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Imagine you’re building a sandcastle at the beach, and you build a wall to stop the water from washing it away.

A super silt fence does something similar on construction sites which is like a low wall made of fabric that catches soil and dirt in rainwater before it can reach rivers and lakes.

Normally, a silt fence is not made of just any fabric. It’s a special kind called Geotextile.

a geotextile silt cloth with red ribbon color

(Figure: A 100 gram Geotextile silt cloth)

Geotextile is strong enough to hold back the dirt but lets water pass through and it is usually black and you’ll see it attached to stakes or posts in the ground, forming a barrier around construction sites.

But why do we need silt fences?

  1. When builders work on a site, they often move a lot of earth.
  2. Without plants and grass to hold the soil in place, rain can easily wash it away.

So this is where a silt fence comes in. It acts as a guard, catching the soil and preventing it from polluting nearby streams and lakes.

DOT Grade Silt Fences: Specifications

For construction sites requiring adherence to Department of Transportation (DOT) standards, the choice of silt fence must meet specific criteria.

The DOT grade typically refers to a heavier specification of silt fences, often around 100 grams per square meter.

Below is an example of such specifications, which serve as a guideline for what might be expected from DOT-approved fences:

100 Gram DOT Grade Silt Fence:

  • Weave Pattern: 11×11 weave, providing both strength and permeability.
  • Strength: High grab tensile strength, measured at 135 lbs. x 125 lbs. according to ASTM D 4632 standards.
  • Elongation: Adequate stretchability with 15% elongation to withstand stress.
  • Burst Resistance: Capable of withstanding up to 200 PSI, per ASTM D 3786.
  • Puncture Resistance: A sturdy 50 lbs. of resistance as per ASTM D 4833, to prevent tears and punctures.
  • Tear Resistance: Strong trapezoid tear resistance of 60 lbs. according to ASTM D 4533.
  • Water Flow Rate: Allows 20 gal/min/ft as per ASTM D 4491, balancing soil retention with water passage.
  • Permittivity: Fast water flow through the fabric at 0.1 sec, measured by ASTM D 4491.
  • UV Resistance: Durable with 80% strength retention after 500 hours of UV exposure (ASTM D 4355).

It’s important to note that while the 100-gram weight is a common specification for DOT grade, the exact requirements can differ from one state to another.

However, the 100-gram silt fence is typically considered DOT grade, and it’s vital to consult state-specific DOT standards to ensure compliance.

For the 50-gram and 70-gram silt fences are generally used for less rigorous applications and do not meet the DOT grade requirements.

Compliance with Standards:

Regulations: Meet specific requirements set by the Department of Transportation, ensuring they are suitable for large-scale and impactful construction projects.

Check DOT Spec in California: California Stormwater BMP Handbook

See DOT Spec in Texas: Sediment control fence Design fact sheet

    Also see DOT Spec in Florida: (FDOT) Standard Specifications Library

          Innovations and Case Studies in Silt Fence Usage

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          Silt fences are not just static tools; there are ongoing efforts to improve them. Let’s look at some recent innovations and real-world examples:

          Case Study: Alabama Department of Transportation (ALDOT):

          • Challenge:
            • ALDOT wanted to improve their standard silt fence design to better control sediment on construction sites.
          • Solution:
            • They partnered with Auburn University to test new designs.
          • Outcome:
            • They developed a silt fence with better post spacing and a design that allowed for more effective water and sediment control. This new design was accepted by the Alabama Soil and Water Conservation Committee.
          • Impact of Innovations:
            • Improved Efficiency: New designs and materials are making silt fences more effective at trapping sediment.
            • Environmental Protection: Better fences mean better protection for nearby water bodies and ecosystems.
            • Cost-Effective: Improved designs can also be more cost-effective in the long run, reducing the need for repairs and replacements.

          These innovations and case studies show that silt fences are an evolving tool in environmental protection, with ongoing research and development to enhance their effectiveness.

          See Full Case Study: The Silt Fence: Keeping Sediment Where It Belongs

          Conclusion

          The innovations and case studies, like the one from the Alabama Department of Transportation, show us that there’s always room for improvement.

          These advancements not only make silt fences more efficient but also more cost-effective in the long run.

          Finally, it’s important to remember that practicing good environmental stewardship through tools like silt fences is not just about complying with laws.

          Following these comprehensive best practice recommendations will protect the environment and support compliance with stormwater regulations and SWPPP guidelines.

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