10 Aug 2011

Site Establishment and Site Erosion

Posted by bcsands

When you establish a construction site in Australia it is your responsibility to ensure that no dirt runs off your site to pollute gutters, drains or waterways. Heavy on-the-spot fines may be charged if your local council identifies you as an offender.

Perimeter protection, drain protection, stockpile containment, slope stabilization and stormwater management all fall under the general heading of site establishment. There are a range of traditional and newer ways of achieving these aims, but essentially they boil down to two things – filtering and blocking dirty water, so that the only water that flows off your site is clean and goes just where it should.

Silt fence, straw bales and filter sock

Silt fence is one of the most popular ways of protecting the perimeter of a site. However, made from filter fabric secured with metal star pickets, silt fence is a labour-intensive product to install and can easily fail. To work effectively, the filter fabric must be buried into the ground to a depth of around 150mm, so that dirty water flows through the fence rather than underneath it. This means digging a trench before setting up the fence. Silt fence also notoriously flimsy – often the storm conditions which a silt fence is set up to combat simply demolish it. Fences can also deteriorate rapidly and should be regularly checked for tears, holes, sagging and slippage.

Straw bales are another traditional option – set up around the perimeter of the site and held in place with star pickets. However, they are only suitable for a low flow of water – fast-flowing water will simply run around them and they do not filter water particularly effectively.

Filter socks or filter are increasing in popularity. This is a type of tubing, which can be filled with blue metal or sand. Blue metal in 10mm or 20mm is used to filter the water, with 10mm for a slow flow rate and 20mm for a faster rate. Filter socks can also be filled with sand to block and redirect water, for example, to protect a stormwater drain or to direct clean water towards it, or to create a channel that you want to encourage water to flow down.

BioSock

A newer option on the market is BioSock, which manages to combine the best elements of all of the other three methods.

On the outside, BioSock looks like a slightly bigger filter sock, but the main difference is that BioSock is intended to be filled with mulch, screened to an optimum size. This makes it more environmentally friendly and easier to handle than filter sock and the sock itself is stronger, with two layers.

BioSock is a much tougher solution than silt fence and it can be used in exactly the same way – but with no trenching. BioSock is simply laid in place, with pre-made 2m lengths that fit in most site fencing blocks. 6m lengths are also available for use elsewhere on site – and it’s robust enough for vehicles to drive over (although this may shorten its life). Unlike silt fence, BioSock won’t blow or be washed away in storms – in most cases its low profile and weight means that it simply stays in place, although anchor systems are also available for sloping or difficult sites.

BioSock is also ideal in an emergency situations – the ready made lengths can be dropped into place, exactly where you need them, even in the middle of a storm.

Simple tips for better erosion control

  • Check your erosion control measures every day to ensure they are in good order
  • Double check when the weather forecast is for rain or storms – and introduce additional measures if necessary
  • Keep your site clean – sweep away as much loose soil and debris as possible and dispose of it properly
  • Don’t keep any more loose material on site than you will actually use
  • Always check all your installed erosion control devices after a storm and repair or renew any that have failed


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