Wednesday, November 17, 2010

Erosion and Sediment Control with Recycled Organic Waste - Berms

The following is very pertinent to the Top End of the NT today, as we experience a major 100mm per hour storm across the Dariwn region.

Where is your soil going today??

Erosion and sediment control, particularly on civil construction sites often seems to start and end with using a silt fence.

While silt fences can be effective, to be so, they require correct installation, and ongoing maintenance. While there are machines to install silt fencing [yes, they do exist!] rarely have I seen one in Australia, and especially on smaller civil works sites, they are, as they say, as rare as hen’s teeth!

Installing a silt fence is a tedious job, particularly the preparation of the footings, in which a lower area is buried, as well as refilling the trench. Mostly, and somewhat sadly, it is often done poorly, and the silt fence is often relatively ineffective.

In Australia with high summer storm rains, and especially so in the tropics, it is quite common to see a silt fence struggle with high rainfall intensity, and they sometimes breach. There are other options that can be simple and easy to install, and repair if necessary.

Top among the options is using a mulch or compost berm or contour bank. Many regions have mulched green waste available, and creating a berm is relatively simple using readily available on site equipment such as a bobcat or small backhoe. Accessing the greenwaste is often through the local council, or sometimes even using on site available cleared green materials can be useful too.
Ideally, pasteurised mulch is the preferred material, with coarse materials suitable. Ground woody waste, even small woody branches are usable. However, where pasteurised mulch is NOT available, unpasteurised mulch can do, although there will be a need to spray and kill any weeds that emerge within the berm – glyphosate is the normal option. Plants developing from the pasteurised mulch are very slow to almost none, although a few plants might be expected from blown in seeds, after a while.

There are some excellent resources on line, but the simple plan is to develop several berms across a slope, on the contour. They should be lightly keyed into the ground, often by building on a ripped base area or similar simple disturbance. Unlike an earth bank, they are supposed to be porous........just that all the water does not flow through at once, and sediment is collected and deposited along the way.

More information here: from Georgia in the US; a sub tropical region of the US - a very comprehensive overview of berm use and construction - shows how to build a system

When the project is completed, the berm can then be used as part of the organic materials often used on site as part of the landscaping, or often left in place in small drainage lines to continue to function until there is improved cover on the nearby soil areas.

They work extremely well, are cheap to construct and maintain, and VERY environmentally friendly!

1 comment:

0s0-Pa said...

At least governments are finally starting to address sediment control concerns... hopefully all of environmental issues and safety hazards can be reduced for a greater emphasis on this area of concern.