Building a silt fence and bunds | Auckland Council


hi my name’s Sean and today we’re going to look at making silk fences and buns to ensure that soil and concrete stays on the site and doesn’t end up going down our drains stormwater is different to wastewater it’s not treated at all the water goes down the drains into streams and out to sea so it’s really important that only rainwater goes down our drains nothing else there are several reasons to make silt fences and buns you are protecting the environment and being a tidy Kiwi keeping our water clean and clear you save hassle and stress from neighbors and the council you save money through avoiding fines and having fewer council inspections and you increase safety by not tracking mud and other materials onto the road installing silt fences Bunz and a stable entranceway as part of running a good building site and it should be the first thing you do on any job here’s what you need woven 100 micron geotextile cloth don’t use we’d met because we’d met won’t do a good job of containing the sediment Waratahs or posts wire and clips and a post Rama or sledgehammer you need to put yourself in down at the low end of the site where the water will run you want to put it where or keep dirty water on site away from the drains here’s how you make it first mark out where the silt fence will go with dazzle and then mark the Waratahs or posts at 400 millimeter marks then dig a trench that’s about 200 millimeters deep by 100 millimeters wide you’d usually do this with a digger though you can also do it by hand her mistake Waratahs or post at least 400 millimeters deep on the downhill side of the trench no more than 2 metres apart remember to keep the flat side of the water in towards the building site against where the fabric will go the steaks should be 600 millimeters high above the ground if you’re using wire ties thread wire through the holes if you’re using posts use findt staples for the wire unroll your cloth and attach to the wire using clips be sure to pull the fabric tight this is why the fabric needs to go against the flat part of the water keep the cloth nice and tight between the posts or Waratahs leave 200 millimetres of cloth below ground in the trench and then backfill the trench to anchor the silt fence each end of the fence should return up the slope roughly 2 metres to prevent water going around the edges the bottom of the cloth must be buried for it to be effective if you need to join the material here’s how you do it staple the cloth to a stake then wrap the cloth fully around the stake 360 degrees and staple it again take a second stake you’ve already done the same thing to and nail the two steaks together now limb in a way that the material appears to run straight between the two steaks the only other thing is to check it regularly particularly after any major rainfall don’t remove it until the very end of the job dealing with water on-site can be difficult though so it’s much easier to just keep it away this is where buns can be useful not only did I keep your site dry much easier to work on the best location for a Bund is around the upper boundaries of your building site the purpose of the Bund is to divert clean rainwater away from your work site particularly water that will flow down from neighboring sites the bun keeps rain water away from the exposed soil of your site which means that the clean water can flow to the storm water drain diverting the rainwater also keeps your work site drier and safer here’s how to make a Bund compact clay and topsoil and cover it with geotextile cloth grass or mulch also use this method on exposed soil or stock piles and keep stock piles behind silt fences for drains fill a sense up with compost mulch or sand and place above the drain this is your second line of defense remember to remove these when you’re finished so if your site has a silt fence and a Bund that’s going to go a long way towards keeping your site safe and our waterways clear you

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