Silt Fencing

When I walk out onto a construction site, often I’m greeted with the familiar site of silt fencing installed or maintained incorrectly. Fences flapping in the breeze, pushed over by bulldozers, located in strange places, I’ve seen it all.

Silt (or sediment) fences are barriers constructed from geosynthetic material placed to intercept and control sheet flow from disturbed lands. Silt fences are not designed to filter particles, rather they create a containment system to allow the deposition of particles.

Where do you use it?

  • At the toe of cut and fill slopes
  • Around inlets
  • As small sediment containment systems
  • Around the perimeter of disturbed areas

[ad#125-right]What do you need to watch out for?

  • Are the stakes installed on the downhill side?
  • Is the fabric embedded in the ground?
  • Does/can water flow under the fabric?
  • Will water flow around the fence?
  • Stakes should be no more than 2.5 meters apart.
  • The fabric should be a minimum of 600mm high.
  • J-Hooks as shown above can be installed to locally trap muddy water as it flows down a section of fence.
  • Silt fences should not be installed in areas where concentrated flows are expected.
  • Don’t install silt fences in channels or ditches.
  • Don’t install silt fences uphill of areas of bare soil.
  • Regular maintenance is required to ensure that silt fences operate as required.

These are some pretty simple suggestions, and considering how often this product is installed, you’d think it would be easy to get it right.

Picture from the Kentucky Erosion Prevention and Sediment Control Field Guide

Published by Mike Thomas

Mike Thomas P.Eng. ENV SP, is the author of and Director of Engineering at the City of Revelstoke in the Interior of British Columbia, Canada.

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