Silt logs are one of the most practical sediment control tools available for construction sites, disturbed slopes and waterway stabilisation across Australia. They slow runoff, trap suspended sediment and allow water to filter through while the ground re-establishes. Unlike silt fences, they do not require trenching and can be installed on uneven terrain in minutes.
This guide covers what silt logs are made from, how they work, which size to use for your site conditions, step-by-step installation, and what you need to do to keep them effective throughout a project.
A silt log is a cylindrical roll of compressed natural fibre wrapped in woven netting. Most silt logs sold in Australia are made from coconut coir fibre, which is why they are also called coir logs or coir rolls. The outer netting holds the fibre in place while allowing water to pass through the body of the log.
When placed across a slope or drainage line, silt logs act as a permeable barrier. Runoff water hits the log and slows down. As the flow velocity drops, suspended soil particles fall out of the water and settle on the uphill side of the log. The filtered water continues through and past the log at a reduced speed. Over time, trapped sediment builds up and vegetation can establish in the accumulated soil.
Silt logs are also referred to as sediment logs, filter logs, coir logs, erosion control logs and fibre rolls. They all describe the same type of product, though the fill material can vary between coconut coir, straw and wood fibre.
Because they are made entirely from natural materials, coir silt logs are 100% biodegradable. A standard coir log will break down over 2 to 5 years depending on moisture levels and UV exposure. This makes them suitable for sites where the control measure can be left in place permanently as the landscape revegetates.
Silt logs are used wherever sediment-laden runoff needs to be slowed and filtered before it reaches a waterway, stormwater drain or neighbouring property. Their flexibility makes them suitable for uneven ground where rigid barriers would leave gaps.
On construction sites in NSW, the NSW EPA Guidelines for Erosion and Sediment Control on Building Sites require an Erosion and Sediment Control Plan (ESCP) for any works disturbing the ground surface. Silt logs are a recognised control measure within these plans.
Silt logs come in several diameters and lengths. The right size depends on the slope gradient, the volume of runoff you expect, and the length of the area you need to protect. A log that is too small will be overtopped during heavy rainfall. One that is too large adds unnecessary cost.
| Log Size | Best Used For | Typical Slope |
|---|---|---|
| 150mm x 3m | Light sheet flow, garden beds, minor slopes | Less than 2:1 |
| 200mm x 2m | Moderate runoff, residential construction sites | 2:1 to 3:1 |
| 200mm x 3m | Longer runs on moderate slopes, swale check dams | 2:1 to 3:1 |
| 300mm x 3m | High-flow areas, steep slopes, creek bank stabilisation | Greater than 3:1 |
For most residential construction sites and landscaping projects, a 200mm diameter log is the standard choice. The 300mm diameter is reserved for steeper gradients or areas with concentrated water flow, such as gullies and drainage lines.
Tip: If you are covering a long run, the 3m length logs are more efficient than 2m logs because you have fewer joins to manage. Fewer joins means fewer potential weak points where sediment can escape.
One of the main advantages of silt logs over silt fencing is the simplicity of installation. There is no trenching required. The logs sit directly on the ground surface and are held in place with wooden stakes. A two-person crew can install a 50-metre run in under an hour.
For a more detailed walkthrough with diagrams, see our guide on how to install coir log silt berms.
On slopes, silt logs are typically installed in rows across the face of the slope. The spacing between rows depends on the gradient and the soil type. Closer spacing is needed on steeper slopes and highly erodible soils.
| Slope Gradient | Recommended Spacing Between Rows |
|---|---|
| Less than 10% | 15 to 20 metres |
| 10% to 25% | 8 to 15 metres |
| 25% to 50% | 4 to 8 metres |
| Greater than 50% | 2 to 4 metres |
These spacings are general guidelines. On sandy or silty soils that erode easily, reduce the spacing by 25 to 30%. On clay soils that hold together better, you may be able to increase it. The Australian Government's YourHome guide on sediment control provides additional context on matching control measures to site conditions.
A silt log that is installed and forgotten will eventually fail. Sediment builds up, the log shifts, or the stakes loosen over time. Regular inspection and basic maintenance keeps the barrier working for the full duration of your project.
Compliance note: Under Section 120 of the Protection of the Environment Operations Act 1997 (NSW), it is an offence to cause or permit waters to be polluted. Failing to maintain sediment controls on a construction site can result in fines. Keep a dated record of every inspection.
Both silt logs and silt fence are sediment control measures, but they work differently and suit different situations. Here is a practical comparison.
| Factor | Silt Logs | Silt Fences |
|---|---|---|
| Installation | No trenching, stakes only | Requires 150 to 200mm trench |
| Terrain | Handles uneven and rocky ground well | Needs relatively smooth ground for a tight seal |
| Flow type | Filters water through the log body | Blocks flow against the fabric |
| Lifespan | 2 to 5 years (biodegradable) | 6 to 12 months typical |
| Concentrated flow | Better for swales and channels | Not suitable for concentrated flows |
| Re-use | Single use (biodegrades in place) | Can be removed and reused if undamaged |
| Cost per metre | Higher upfront | Lower upfront |
| Maintenance | Less frequent (permeable design) | More frequent (fabric clogs) |
Many Erosion and Sediment Control Plans specify both products working together. Silt fence along the perimeter of a site, with coir silt logs placed across internal slopes and around drainage inlets. For more on choosing the right silt fence for your project, see our guide on how to choose the right silt fence.
All Stake Supply stocks coir silt logs in 150mm, 200mm and 300mm diameters, along with hardwood stakes, silt fencing, coir matting and geotextile filter tubes for complete sediment control setups. All products ship Australia-wide from the St Marys warehouse in western Sydney.
Browse the full sediment control range at All Stake Supply, or contact the team for trade pricing and bulk orders.
