Sediment control

Key points

  • Sediment control aims to stop soils and other sediments from a building site washing into gutters, drains, and waterways.
  • Good sediment control can help keep our waterways healthy, minimise loss from building site stockpiles, and improve building site conditions.
  • Sediment control measures are required by local government in many areas, and you will need to submit a sediment control plan for approval before starting work.
  • The most important action in sediment control is to try to prevent sediment from reaching waterways. The best prevention measure is to minimise site disturbance through careful design and organisation of construction.
  • Cover sand and soil stockpiles on site, use erosion control mats and construct raised exit pads made of crushed rock.
  • Minimise the amount of contaminated water that leaves the site. Use barriers (for example, sediment fences or filter strips) to trap sediment before it can wash away.
  • Divert stormwater away from the disturbed area of the site and install the final stormwater drainage system as early as possible during construction.
  • Consider erosion control after building has finished – use erosion mats and planting on steep slopes, use mulch on garden beds, and minimise the extent of concrete paths and other hard surfaces.

Things to know about sediment control

Sediment control measures are used on building sites to prevent sand, soil, cement, and other building materials from reaching waterways. Even a small amount of pollution from a site can cause significant environmental damage by killing aquatic life, silting up streams, and blocking stormwater pipes.

The objectives of sediment control are to:

  • minimise erosion by minimising site disturbance
  • stabilise disturbed surfaces
  • prevent material stockpiles from collecting or discharging sediment
  • divert uncontaminated water away from the work area.

Whether you need sediment control depends on:

  • soil type — clay soils are more likely to cause environmental harm; sandy soils are more likely to cause traffic hazards and drainage problems. Exposed subsoils generally cause more problems than exposed topsoils
  • slope — the steeper and longer the slope, the greater the potential for erosion and sedimentation
  • extent, nature and duration of the soil disturbance — the greater the disturbance, the greater the risk of erosion and sedimentation
  • climate and season — rainfall and winds influence erosion and sedimentation, depending on their intensity and duration. Rainfall events are intensifying as our climate changes, so the need to mitigate their impacts has become increasingly important
  • size and location of the site — sediment control on small sites is often harder to implement, especially if the slope is towards the street. Large vegetated rural sites may not always require specific controls.

Why is sediment control important?

Successful control measures on building sites trap and retain sediment displaced by up-slope erosion. This results in:

  • cleaner waterways and healthier aquatic life
  • reduced clean-up costs to the community
  • improved site conditions, especially wet-weather working conditions
  • reduced wet-weather construction delays
  • reduced losses from material stockpiles
  • fewer public complaints and less chance of fines from local or state authorities.

A sediment control management plan may need to be submitted to local government for approval before building work begins. The plan should address the location, design, scheduling and maintenance of sediment control measures and details of site rehabilitation.

 

Note

Any sediment control measures should comply with the requirements of local government erosion and sediment control guidelines. It is recommended that advice be obtained from appropriately qualified experts.

How to prevent and control sediment loss

Install sediment control measures before beginning any excavation or earthmoving. Regularly maintain these measures until construction is complete and the site is stabilised. It is vital to ensure that stormwater is not unlawfully diverted or released into neighbouring properties, or allowed to cause erosion at discharge points.

A diagram of a house under construction on a sloping site shows a series of erosion and sediment control measures.

Erosion and sediment control measures on a building site.

Minimise site disturbance

Prevention is better than cure. Careful design and an efficient construction sequence can minimise disturbance to the site, save money, and reduce environmental impact:

  • Design to avoid excessive cut and fill and unnecessary clearing of vegetation.
  • Preserve existing site drainage patterns.
  • Clear only those areas necessary for building work to occur.
  • Preserve grassed areas and vegetation where possible. They help to filter sediment from stormwater before it reaches the drainage system and stop rain turning exposed soil into mud.
  • Delay removing vegetation or beginning earthworks until just before the start of building activities.
  • Avoid building activities that disturb soil during periods of expected heavy or lengthy rainfall.

Divert uncontaminated stormwater

Avoid contamination of stormwater with sediment. Use flow diversion devices to reduce the volume of stormwater reaching the disturbed area on your site.

On compact urban sites, restrict overland flow through the work area by installing the final stormwater drainage system as early as possible in the construction process. Before then, install an up-slope perimeter bank and catch drain to take uncontaminated stormwater directly to the stormwater system. On steep sites, line catch drains with turf or geotextile.

On larger sites, a diversion channel may be used to divert uncontaminated stormwater around the disturbed area. Construct the channel up-slope of the disturbed area with a bank on the lower side. Remove sediment from the channel frequently. Line the channel with erosion control mats or turf to prevent soil erosion, or use check dams constructed from sand or gravel-filled bags.

Uncontaminated stormwater from the channel should discharge to the stormwater system. In some cases, discharge onto non-erodible areas of land is permissible. Check with your local government. Do not allow discharge into neighbouring properties.

Roof drainage must discharge to the stormwater system unless rainwater is being harvested. Complete the final stormwater drainage system before the roof is installed. Connect using temporary or permanent downpipe.

Minimise the potential for erosion

Construct a single vehicle entry and exit pad to minimise tracking of sediment onto roadways. Use a 150mm (minimum) layer of 40mm crushed rock. A raised hump across the entry and exit pad can be used to direct stormwater into a sediment trap to the side of the pad.

Protect materials that may erode, particularly sand and soil stockpiles, with waterproof coverings. Contain waste in covered bins or traps made from geotextile.

Locate stockpiles of building materials away from drainage paths and up-slope of sediment barriers. Use an up-slope perimeter bank to divert runoff around stockpiles unavoidably located in drainage paths.

Use biodegradable erosion control mats to protect exposed earth. These mats are particularly useful on high-risk soils and steep sites where there is a delay in building or site rehabilitation.

Site plan of a suburban block shows drainage control down the uphill side, sediment barriers on the downhill edges, stockpiles inside the sediment barriers on the downhill corners and a stabilised entry with flow control hump on the downhill side.

Sediment control layout on a compact urban site

 

Minimise contaminated water leaving the site

Use barriers to trap coarse sediment at all points where stormwater leaves the site before it can wash into gutters, drains and waterways. Install sediment fences down-slope of the disturbed area, usually along the lowest site boundary with the ends returning up-slope. Inspect barriers after storms and remove sediment. Stockpile extra sediment fencing on site for emergency repairs.

Regularly sweep adjacent streets and gutters clean – do not hose them. Relocate sediment on site or dispose of it suitably. Remove accidental spills of soil or other material immediately.

Maintain kerbside vegetation in a healthy state as it can function as an additional filter for sediment. Do not use nature strips or footpaths for parking or stockpiling unless unavoidable. Council permission is required.

Cut bricks, tiles or masonry on a pervious surface such as grass or loosened soil within the property boundary. The same applies when cleaning equipment. Waste concrete, paint and other solutions used on site should be properly disposed of, so they do not contaminate stormwater.

Use sediment control devices

Woven sediment fences

These are generally the most efficient barriers for building sites. Constructed from geotextile attached to posts, these fences trap sediment but allow water through. On small-frontage sites with limited access, use steel posts and wire-tied fences that can be readily unhooked to unload materials.

Diagram of a woven fence on sloped ground trapping sediment on the uphill (disturbed) side of the barrier. Posts are 2000mm apart, barrier is 700mm high and sunk 200mm into the ground.

Woven sediment fences trap sediment but allow water through

 

Vegetated filter strips

Vegetated filter strips are useful as a secondary measure but generally are not a substitute for sediment barriers. Strips of turf or vegetation are used to trap sediment, acting as a buffer zone between the site and the gutter. The nature strip is often used for this purpose.

Stormwater inlet traps

Stormwater inlets are not usually found in residential building lots but may occur on larger development sites. Construct a temporary sediment fence around on-site stormwater inlet grates. Wrap geotextile around posts fitted at each corner of the drainage grate. Embed the base of the fabric into the soil.

Off-site sediment traps

For safety and efficiency, do not locate sediment barriers outside property boundaries, particularly on roads. Anything placed on a road requires the permission of the road owner, whether it is the local government or the developer.

Sediment barriers in front of roadside stormwater inlets are rarely effective and usually only result in the sediment being washed down the street into the nearest gully inlet.

As a last resort, use off-site sediment traps, made from sand or geotextile gravel bags. Ensure they do not fully block the gully inlet. Check daily and remove accumulated sediment.

Post-construction erosion control

To minimise the potential for ongoing soil erosion, stabilise the site as soon as possible after construction, or while the last trades are finishing.

Integrate your landscaping strategy with sediment control. For example, diversion channels and trenches that filter sediment can be used with rubble in the base to create a deep root planting opportunity.

Turf lawns are commonly used to stabilise soil, but their high water consumption can be an environmental burden. For considerably lower water use:

  • plant native ground cover plants to stabilise soil
  • avoid replacing native vegetation with turf.

Mulch (straw, chip bark or other material) can be used on open garden beds to protect soil and support plant growth. Mulch spread to a depth of 75–100mm minimises soil and water loss and controls weed growth. Mulch may be less suitable on steep sites and in high-wind areas.

Temporary, quick germinating grasses such as rye and oats can be used to stabilise soil until slower growing plants can be established. This method is only effective after the grass seeds have germinated and established a root structure.

Semi-permeable paving can be used to stabilise areas of the site. Avoid excessive use of hard surfaces that create inappropriate water flows and prevent stormwater percolating into the ground. Biodegradable erosion control mats are useful when revegetating steep slopes.

References and additional reading

Learn more

  • Refer to Choosing and using a site to find out more about protecting your site
  • Explore Waste minimisation for more ideas on reducing, reusing and recycling when building or renovating
  • Explore Stormwater to integrate your strategy for sediment control with the design of your stormwater system 

Authors

Original author: Caitlin McGee

Contributing author: Chris Reardon

Updated: Paul Downton 2013