If you are working on a construction site of any kind, it’s crucial that you have a sediment and erosion control plan in place. This is part of the building consent process.
Sediment is the most common pollutant in our rivers, streams, lakes and harbour. While sediment naturally finds its way into these waterways, a large percentage comes from human use of land which accelerates erosion. If effects the quality of the waterways, and the stormwater network by:
- filling up drains, sumps, and ponds, which reduces the ability of the network to handle rain events and can cause flooding
- making the water cloudy and settling on the bed of the waterway, interfering with the ability of animals and plants to find or make food, grow and survive in their natural habitats – this can cause a decline in whole food chains
- introducing nutrients such as nitrogen and phosphorous, as well as contaminants such as hydro carbons and heavy metals.
Sediment and silt should therefore not leave the site and should be contained within the site boundary. The downstream sump is not considered part of the site’s primary sediment controls, because any filter put underneath the grate is not monitored and maintained. In a rain event, the sump will clog and block causing flooding, or break and allow sediment laden runoff to enter the stormwater network.
Earthworks are the most likely time that large amounts of sediment could leave the site, normally through runoff from a rain event or via tracking from the entering and exiting of earthworks machinery from the site. Control measures should be in place prior to earthworks commencing.
Reducing the risk
Different sites will require different types of controls to prevent runoff. Flat sites may require minimal containment areas, using bunds and channels to contain any sediment. Sloping sites will likely require silt fencing to contain a larger amount of runoff during a rain event. Ideally on a sloping site a channel is dug for the bottom of the fence to sit in, which is then buried. Regardless of the type of site, there are effective methods for controlling sediment and erosion.
- check and maintain regularly, especially before and after rain events
- ensure subcontractors are informed of their responsibilities
- ensure workers are using containment devices or a wash pit
- only remove controls when the areas they are protecting are stabilised.
For more information on how you can reduce the risk, see the Builders Pocket Guide.
Sediment control best practice flyer (2.4mb pdf)
Last Reviewed: 19/02/2019