Sediment control fences are seen as a “go-to” solution for construction projects across all scales. But are they stacking up in terms of both performance and the environmental benefits they bring?
What is a sediment control fence?
Sediment control fences are often used on construction sites and landscaped areas to prevent sediment from entering watercourses. They are a temporary and cost effective solution used as an environmental control. Also known as a “silt fence” they’re commonly used on construction projects of all sizes from single dwellings to multi-billion-dollar infrastructure builds.
Although they’ve become common place, environmental professionals who frequently specify sediment fence for pollution control are starting to weigh up the cost compared with the benefits. We hope the industry continues to engage in productive discussion about the suitability and effectiveness of sediment fences. Here we look at some of the key factors being considered and discussed.
- Correct installation and maintenance is rare
Unfortunately, sediment fences are rarely installed or maintained correctly. The International Erosion Control Association, Australasian Chapter’s Best Practice Erosion and Sediment Control guidance document identifies sediment fence as a ‘Type 3’ control appropriate for managing sheet flow from small catchments and on all soil types (although it’s only likely to capture particles larger than 0.14mm).
Standard drawings and installation specifications include the requirements to
- place the fence along the contour
- not placing in an area of concentrated flow
- keying fabric into the ground to prevent undercutting
- install returns every 20m etc.
Although these are included in almost every erosion and sediment control plan developed for the construction industry, very few are put in place to these standards and requirements. A correctly installed sediment fence has become a ‘unicorn event’ to many soil conservationists and environmental professionals.
Typical errors include:
- placement location in concentrated flows and close to fill
- not ‘keying in’ the toe of the fence
- insufficient reinforcement and not including returns.
- lack of maintenance causing casual damage and destruction
Unfortunately, the result is many sediment fences are an ineffective token gesture. Often this leads to a culture of any sediment fence, regardless of suitability or effectiveness as being a “good enough” box ticker.
Frustratingly this situation facilitates the perception that environmental protection is in place whilst simultaneously enabling sediment pollution and resulting harm to our aquatic environments.
- Sediment fence materials are bad for the environment
Single use plastics are a leading factor of environmental waste and damage. Sediment fences are undeniably single use plastics. Designed to protect the environment, their production and use is having the reverse effect.
When considered in this light, the sheer volume of sediment fence used for construction projects with large footprints is alarming. Sediment fence is manufactured from either polyester or polypropylene fabric which both rely on fossil fuel extraction and complex chemical processing. Both activities result in
- water pollution and utilisation
- land degradation
- greenhouse gas emissions and harmful by-product generation
- a multitude of social impacts.
Following its use on site, best practice end of life management for sediment fences in Australia simply involves disposal to a municipal landfill facility. Landfilling sediment fences results in the loss of all embedded energy. And slow degradation over hundreds of years generates greenhouse gases and numerous toxic compounds.
This leads us to the question, “Is all this harm offset by the potential avoidance of sediment pollution at the point of use?”
- Pollutes the waterways it’s intended to protect
Sediment fence is often left in place and forgotten about long after a project or package of works is complete, contributing to the global issue of marine and environmental plastics and microplastics. All too often it’s left to either wash away in a high flow event or slowly degrade in-situ into micro-plastics long after the construction team has demobilised from the site.
Many projects focus on rapid demobilisation and site handover, rather than the need to retain sediment controls until the site is stable. Disposing of the sediment fencing appropriately when it is no longer required is rare.
Where to from here?
Despite knowing all this, environmental professionals are finding there is often no suitable alternative to sediment fences. To ‘do nothing’ would attract public scrutiny and regulatory penalties.
We suggest the following:
- Where-ever possible, alternatives to sediment fence should be sought and specified. Using mulch filter bunds are a good example of a viable alternative in the right circumstances and providing suitable mulch (or compost) is readily available and its production is otherwise unavoidable.
Other suggestions include directing sediment laden runoff to higher order (Type 1 and Type 2) controls or ideally, implementing instantaneous and progressive rehabilitation and erosion prevention.
- Where no alternatives to sediment fence are accessible, site staff need to be properly educated on the installation, maintenance, and removal of sediment fence. Let’s put an end to the ‘perception fence’ and ensure that sediment fence is installed to function as designed.
- The industry must raise its voice and pressure manufactures to produce a suitably sourced biodegradable alternative to the petro-chemical based product currently used. A biodegradable product would not solve the problems around installation and maintenance but at least practitioners could be assured that no harm was produced as a result of its application. The catch is that should such a product exist it would likely need to be both performance and cost comparable to the conventional product used today to encourage uptake.
Those within the environmental space of the construction industry have work ahead of them to improve the options available as well as better using the measures they currently have by:
- actively working to find project specific alternatives to sediment fence
- ensuring it is suitably installed, maintained, and removed (where no alternatives exist)
- advocating for the development of a suitably sourced, biodegradable, cost, and performance comparable alternate sediment fence product to be manufactured.
With this action, we can continue to protect our waterways while also reducing the harm caused by sediment fence. GeoLINK provides an integrated mix of environmental, engineering, planning and design services. We’re committed to delivering cost effective, sustainable and innovative solutions to our clients.
