Controlling erosion and sediment
Earthworks and construction activities disturb soils and create dust and debris. Runoff from landscape construction sites often flows into street gutters and then through drains to creeks or channels ending in rivers, bays or the ocean.
If a site is poorly managed, stormwater runoff will carry soil particles, sediment, dissolved plant nutrients, organic matter and waste, which can block council drains, silt up waterways and kill wildlife.
Law relating to water pollution
Under the POEO Act it is illegal to pollute or cause or permit pollution of waters. Under the Act, 'water pollution' includes introducing litter, wash water, soil, debris, detergent, paint, cement slurry, building materials etc.into waters or placing such material where it is likely to be washed or blown into waters or the stormwater system or percolate into groundwater.
For landscapers this could mean storing materials in a location where they could wash into a road gutter, or failing to install adequate sediment controls.
Before you start work
It's good practice to plan sediment and erosion controls for your site before you start work. The local council may require that you submit a Sediment and Erosion Control Plan (also called a Soil and Water Control Plan, or something similar) as part of a development application.
When you're setting out the site before starting construction or demolition your first tasks might be installing erosion and sediment controls.
Your Sediment and Erosion Control Plan might include a simple sketch of the site showing the types of controls you'll use and where they'll be located.
Erosion and sediment control strategies
You should focus on minimising the amount of dirty water generated by:
- minimising the amount of soil disturbed
- controlling vehicle access, and
- diverting clean water away from disturbed areas.
It's easier to prevent water from becoming dirty in the first place rather than trying to treat large volumes of water.
Minimise cleared areas
Minimise the area to be cleared at any one time and leave as much vegetation intact as possible. Protect these vegetation areas with `no go' fences. Replant vegetation as soon as possible.
Control site access points
Vehicles should not track soil onto the road. Limit vehicle entry and exit to one point on the site. Clearly mark this point with good signage, and stabilise it with a geo-textile fabric and blue metal. Depending on the size of the site and the soil type, you might need to set up a wheel wash.
Install sediment fences
Install sediment fences along the lower side of the site to catch sediment.
Fences should be laid along the contour as much as possible, and 
should consist of a suitable geo-textile fabric supported every three metres (max.) with the lower edge trenched to a depth of 150 mm. Several fences in parallel may be required if there is a large volume of water.
(Picture: Sediment fence on the lower side of the site, trenched)
On small sites with a low waterflow, a continuous line of hay bales, securely pegged, may do the job.
Provide up-slope diversion
Divert clean run-off from undisturbed areas around any disturbed areas. For example, construct cross-slope drainage channels to collect and divert stormwater. At the same time make sure that water does not affect neighbouring properties.
Protect vegetation buffers or create new ones
Areas of grass and vegetation slow the speed of runoff, providing good sediment control especially when used as a final sediment trap. Plan to leave existing buffers where possible, or create new ones.
Stabilise drains and banks
Stabilise all on-site drains and exposed banks with vegetation or erosion control mats.
Use sediment basins
On large sites with high volumes of runoff, water may need to be diverted into a sediment basin. This is a temporary shallow earth dam, which detains water and allows sediment to settle out or be treated if necessary. Note that runoff from sites with clay soils may need to be collected in a dam and treated prior to discharge, as other controls may not be enough to remove fine particles.
Protect kerbside drains
Protect all council kerbside culverts with a `gravel sausage' made from geo-textile fabric rolled and filled with blue metal.
Take care with material stockpiles
Store all material stockpiles within the sediment fences and keep them covered to prevent wind erosion. Get council approval before placing any stockpiles or materials on a nature strip or footpath.
Protect wash down and brick cutting areas
Protect wash down areas and areas where bricks and tiles are cut with local sediment controls. Locate these areas upslope of the site sediment fences. 
Build a trench or small dam below areas used for cutting bricks, tiles or concrete to allow the waste water to collect and infiltrate.
Take care with service trenches
When constructing service trenches, place the excavated material upslope of the trench. Fill and compact the trench immediately after the services have been installed.
Maintaining your controls
Check your erosion and sediment controls every day, and repair them when necessary. To make sure the controls work, remove any trapped sediment and either reuse it on site or dispose of it as waste. Whenever possible, observe how the site controls perform during rain to see how well they work.
Cleaning the footpath
Sweep down the road and footpath everyday and collect the sediment. DO NOT use a hose.
Use design to control erosion and sediment
Many of these erosion and sediment controls can be designed as permanent features in the landscape. For example, earth mounding, grassy swales and garden ponds can all be designed to fulfil a functional as well as an aesthetic purpose.
More information
- Your local council
- Managing Urban Stormwater: Soils and Construction, NSW Department of Housing, 1998
- Department of Lands on (02) 9228 6666
- Yellow Pages, under 'Soil stabilisation'