Flagging Doggy Doo

Public spaces should be respected and kept clean for the enjoyment of all; and around here, there is a group of people who are not all pulling their weight – Dog Owners.

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Rain Barrels

The idea of collecting water from the roof of our home elicits some primeval response related to survival – we need water, we need security, it is natural to want to be able to grow things. The crazy suburban fiesta of the past 40 or 50 years has removed us from the realities of food and survival, with centralization and expansion of everything being the theme of the era.

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Silt Fencing Done Right

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

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

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Erosion First

Most construction sites seem to focus on installing huge sediment basins and miles of silt fences, but allow whole hillsides of material to remain at the mercy of the wind and the rain.

The simple fact is that controlling the very erosion that can cause the sedimentation in the first place is more than half the battle if you bother to follow some simple guidelines.

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  1. The majority of construction site erosion comes from sheet flow
  2. Gullies (at the bottom of the picture above) can transport more than ten times more soil than sheet flow.
  3. Splashing from raindrops is a major contributor to erosion
  4. Soil covered by vegetation is the least susceptible to the effects of erosion.
  5. Mulch is effective in reducing erosion, as is roughing the soil material, however this may increase the wind erosion potential.

Once you’ve got the erosion sorted out, then you can worry about the fact that the particles are being transported, and use best practices to detain and or filter sediment from water.

More about that soon.

Picture from the Kentucky Erosion Prevention and Sediment Control Field Guide

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Not Just Silt Fences

While working in the consulting side of Civil Engineering I was able to see a lot of different erosion and sediment control techniques in practice. What baffles me is that something this simple can be done so badly, or not at all!

2178809039_5c9dd2bfd1_m While written from a US perspective the Field Manual on Sediment and Erosion Control Best Management Practices for Contractors and Inspectors is one of the best resources available to contractors to ensure they are installing the right control structures in the right situations, and that they are doing it properly.

There are a lot of mistakes seen commonly in erosion and sediment control, here are my top three…

  • Relying on sediment control, with no mitigation of erosion.
  • Over-reliance on silt fencing.
  • Improper installation of silt fencing.

Check out the book at amazon.com if you are involved in the management or inspection of erosion and sediment control.

I’ll write more on each of these, and maybe more in the coming weeks.

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