A sediment trap catches soil and debris in stormwater runoff before it reaches waterways, drains, or neighbouring properties.

Every Australian construction site, landscaping project, and earthworks job needs some form of sediment control. Council requirements are strict, and fines for sediment discharge into waterways start in the thousands.

This article explains how sediment traps work, the different types used on Australian sites, and which products you actually need to build one properly.

What Is a Sediment Trap and How Does It Work

A sediment trap is a temporary erosion control measure that slows stormwater runoff and allows suspended soil particles to settle out before the water leaves a site. The basic principle is simple: slow the water down, give the sediment time to drop, and let cleaner water pass through.

Sediment traps sit at the lowest point of a site or at the point where runoff exits the property. They work by creating a pool or barrier that forces water to spread out and lose velocity.

• Water hits the trap and slows from a concentrated flow to a wide, shallow spread
• Heavier particles (sand, gravel, clay clumps) settle to the bottom within minutes
• Finer particles take longer to settle, which is why trap volume matters
• Filtered water passes through the permeable barrier (silt fence, geotextile, or hay bale) and exits the site

The distinction between a sediment trap and a sediment basin is size. Traps handle catchment areas under 0.5 hectares, while basins are engineered for larger sites.

On residential building sites, a sediment trap usually means a silt fence barrier across the low side of the block. On civil and commercial projects, you might combine multiple trap types along different flow paths.

Types of Sediment Traps Used on Australian Sites

The type of sediment trap you need depends on the size of your site, the gradient, and how much runoff you are managing. Most small to mid-sized projects use one of four common setups.

Silt fence is the most commonly used option across residential and small commercial sites. Coir logs are the better choice where water flows in a concentrated channel rather than as sheet runoff across a slope.

How to Install a Silt Fence Barrier

Silt fence is the backbone of sediment control on most Australian building sites. It works by filtering sheet flow runoff through a woven geotextile fabric that traps soil particles while letting water pass through.

Installation is straightforward, but the details matter. A poorly installed silt fence fails at the first heavy rainfall.

1. Dig a trench 150mm deep along the contour line (across the slope, never down it)
2. Unroll the silt fence into the trench with the fabric facing upslope
3. Drive star pickets or timber stakes every 2 metres on the downslope side of the fence
4. Backfill the trench and compact the soil over the buried fabric
5. Overlap joins by at least 300mm and wrap the overlap around a stake
6. Check that the top of the fence follows the contour, with no low points where water can pool and overtop

When to Use Coir Logs Instead of Silt Fence

Coir logs are rolls of compressed coconut fibre wrapped in coir netting. They work as check dams in drains and swales where water flows in a concentrated channel.

Silt fence cannot handle concentrated flow. If you put silt fence across a drain or channel, the water pressure will push it over or wash underneath within days.

• Use coir logs in drainage swales, table drains, and anywhere water concentrates into a defined channel
• Stack logs for deeper channels (200mm or 300mm diameter depending on flow volume)
• Peg logs in place with timber stakes through the centre or with U-pins at each end
• Space check dams so the top of the downstream log is level with the base of the upstream one
• Coir logs are biodegradable and can be left in place after site stabilisation

The biodegradability factor is a genuine advantage for revegetation projects. The coconut fibre breaks down over 2 to 5 years, adding organic matter to the soil as vegetation establishes.

For large revegetation sites, combining coir logs with coir matting on the slope above gives you both sediment capture in the channel and surface erosion protection on the banks.

Australian Regulations for Sediment Control

Every state and territory in Australia requires sediment control on construction and earthworks sites. The specific requirements vary by council, but the principle is the same everywhere: you cannot discharge sediment-laden water off your site.

According to the Australian Government YourHome guide, sediment controls must be installed before any ground disturbance begins and maintained until the site is fully stabilised with vegetation or hardscape.

• Development approval conditions typically require an Erosion and Sediment Control Plan (ESCP)
• Controls must be inspected after every rainfall event and at least monthly
• Sediment accumulated behind barriers must be removed before it reaches half the barrier height
• Fines for sediment discharge into waterways range from thousands to tens of thousands of dollars depending on the state
• The Australian Department of the Environment oversees federal water quality standards

In practice, the council inspector will check that your silt fences are intact, trenched in properly, and not overloaded. Keeping spare silt fence on site is worth the small cost compared to a stop-work notice.

Maintaining Silt Fences and Coir Logs on Site

A sediment trap that is not maintained is a sediment trap that fails. The most common failure mode is not the product itself but the sediment buildup behind it reducing capacity.

• Remove accumulated sediment when it reaches one-third of the barrier height
• Check silt fence for tears, holes, and undercutting after every rainfall event
• Re-stake any sections where the fence is leaning or sagging
• Replace coir logs that have become compacted or blocked with fine silt
• Clear any debris (leaves, plastic, building waste) that reduces the filtering area

Most failures happen because sediment builds up to the top of the fence and water simply flows over. Regular cleanouts take ten minutes and save you from a council fine that will cost far more than the labour.

After heavy rain, walk the full perimeter of your silt fence and check for undercutting. If water has carved a channel underneath, you need to re-trench that section and compact the soil again.

Keep a spare roll of silt fence on site. Replacing a torn section immediately after a storm is far easier than explaining the sediment in the neighbour's yard to the council inspector.

Choosing the Right Erosion Control Products

The product you need depends on your site conditions. All Stake Supply has stocked erosion control products for 48 years and delivers complete orders anywhere in Australia, guaranteed on time with no partial shipments stalling your project.

• Silt fence for perimeter control and sheet flow: available in 500m rolls for large sites or 50m rolls for smaller jobs
• Coir logs for channel check dams: 150mm, 200mm, and 300mm diameters
• Geotextile filter tubes for drain outlets: 2m lengths or 50m rolls
• Hay bale bags for temporary barriers around stockpiles and site entries

For trade pricing or help specifying the right products for your site, contact the All Stake Supply team directly.