Transcript of the Building a silt fence or bunds video
[video: Auckland Council logo (pōhutukawa flower over water). Music plays. Title ‘Building Silt Fences’ shows over shot of a silt fence on a building site adjacent to a partially completed housing development.]
[video: Presenter Sean, a man in late 20s. He is wearing workwear (cap, waterproof jacket) and is standing in front of digger.]
Sean: Hi, my name's Sean and today we're going to look at making silt fences and bunds, to ensure that soil and concrete stays on the site and doesn't end up going down our drains.
[video: Graphic of a house showing wastewater going to a treatment station, while stormwater flows out to sea.]
Sean: Stormwater is different to waste water 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 rain water goes down our drains, nothing else.
[video: Water flowing out to a stormwater pipe, across the sand and into the sea. An island that looks like Rangitoto in the background. Camera zooms in closer to the sea. Woman power-walking along the shoreline. Caption shows: ‘Protect the environment.’]
Sean: There are several reasons to make silt fences and bunds. You are protecting the environment and being tidy Kiwis, keeping our water clean and clear. You save hassle and stress from neighbours and the council.
[video: Camera sweeps along wet street in front of housing development. Caption shows: ‘Protect the environment. Save hassle and stress. Save money. Increase safety’.]
[video: Sean in front of digger adjacent to housing development.]
Sean: 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, bunds and a stable entranceway is part of running a good building site, and it should be the first thing you do on any job.
[video: Wooden posts, staple gun and other such materials neatly lined up on concrete.]
Sean: Here's what you need: woven 100 micron geotextile cloth. Don't use weed mat, because weed mat won't do a good job of containing the sediment.
[video: Cloth and wooden posts, then wire and clips, then a post rammer.]
Sean: Waratahs or posts, wire and clips and a post rammer or sledgehammer.
[Video: Silt fence on a building site adjacent to a partially completed housing development.]
Sean: You need to put your silt fence down at the low end of the site where the water will run.
[video: Silt fence constructed at the low end of a site, rain falling, arrows to show water diversion.]
Sean: You want to put it where it will keep dirty water on site away from the drains.
[video: Sean in high vis vest marking the silt fence site by spraying bright pink ‘dazzle’ from a spray can onto the grass. Sean measuring the wooden posts and marking them with the ‘dazzle’.]
Sean: 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 400mm marks.
[video: Digger digging at bright pink ‘dazzle’ line on building site.]
Sean: Then, dig a trench that's about 200mm deep by 100mm wide.
[video: Sean digging the at the same site with a spade.]
Sean: You'd usually do this with a digger but you can also do it by hand.
[video: Sean driving posts into the trench.]
Sean: Hammer stake Waratahs or posts at least 400mm deep on the downhill side of the trench, no more than two metres apart.
[video: Closeup of Waratah held by Sean, with Sean indicating flat side.]
Sean: Remember to keep the flat side of the Waratah in towards the building site against where the fabric will go.
[video: Sean threading wire through Waratahs dug into trench.]
Sean: The stakes should be 600mm high above the ground. If you're using Waratahs, thread wire through the holes. If you're using posts, use fence staples for the wire. Unroll your cloth and attach to the wire using clips.
[video: Sean and his colleague unrolling cloth and attaching it to one of the Waratahs. Colleague attaches a clip to the cloth.]
Sean: Be sure to pull the fabric tight: this is why the fabric needs to go against the flat part of the Waratah. Keep the cloth nice and tight between the posts or Waratahs.
[video: Sean and his colleague attaching cloth, showing the bottom edge inside the trench.]
Sean: Leave 200mm of cloth below ground in the trench and then backfill the trench to anchor the silt fence.
[video: Sean digging soil back onto the other side of the cloth, into and slightly above the trench. Sean’s colleague smoothing the soil with a spade. Sean applying bright yellow caps to the ends of the Waratahs.]
Sean: Each end of the fence should return up the slope roughly 2m 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.
[video: Sean and his workmate using a staple gun to attach cloth to a stake. They turn the cloth over and wrap/roll it around the stake and then staple it again.]
Sean: Staple the cloth to a stake, then wrap the cloth fully around the stake 360 degrees and staple it again.
[video: Sean and his workmate use a nailgun to attach two such stake/cloth arrangements together. Closeup of the nailed-together stakes with the cloth appearing to run straight through the middle of the two stakes.]
Sean: Take a second stake you've already done the same thing to and nail the two stakes together. Nail them in a way that the material appears to run straight between the two stakes.
[video: Sean walks along the length of the silt fence they have built, wiggling the stakes to checking they are securely inserted and pulling the cloth to make sure it is taught.]
Sean: 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.
[video: digger over a long mound of earth on the building site adjacent to the incomplete housing development. Music plays. Caption shows: ‘Making a bund.’ Sean on the building site standing over a mound covered with dry grass.]
Sean: Dealing with water on site can be difficult though so it's much easier to just keep it away. This is where bunds can be useful - not only do they keep your site dry, much easier to work on.
[Shot of the work site with the silt fence and bottom left and the mound of earth – we can now presume it is a bund – at top right. Arrow graphics over the bund to show rain water being diverted by it.]
Sean: The best location for a bund is around the upper boundaries of your building site. The purpose of the bund is to divert clean rain water away from your worksite, particularly water that will flow down from neighbouring sites. The bund keeps rainwater away from the exposed soil of your site, which means that the clean water can flow to the stormwater drain. Diverting the rainwater also keeps your worksite dryer and safer.
[video: Digger moving earth into a long mound. Sean covering the mound with dry grass. Sean covers mound with cloth and hammers the cloth into the ground.]
[video: Here’s how to make a bund. Compact clay and topsoil and cover it with geotextile cloth, grass or mulch.]
Sean: Also, use this method on exposed soil or stockpiles, and keep stockpiles behind silt fences.
[video: Sean carries tubes of filled material and places them above drains at the kerbside.]
Sean: For drains, fill a sand sock with compost, mulch or sand, and place above the drain. This is your second line of defence. Remember to remove these when you are finished.
[video: Closeup of drain with inscription ‘PUMP NO WASTE, FLOWS TO SEA’. Music plays. Sean standing next to bund and silt fence.]
Sean: So if your site has a silt fence and a bund, it’s going to go a long way towards keeping your site safe, and our waterways clear.
[video: Auckland Council logo.]