Controlling sediment loss during house construction benefits communities
18th June, 2024
Sediment laden runoff and sand drift from construction sites can cause water pollution when site soil erosion and sediment controls are absent or ineffective.
A small-scale project (the project) was coordinated by Perth NRM in partnership with the Department of Biodiversity, Conservation and Attractions, Richard Noble & Company and the City of South Perth. The project was undertaken between 2020-2023 at Cygnia Cove in Waterford (Perth) to observe a housing developments’ sediment control mechanisms and the potential environmental impacts of poor industry practices.
This project was funded by the Australian Government Swan Canning River Recovery Project Three and was informed by research commissioned by the Sediment Task Force to quantify sediment loss during an urban development. Completed in 2020 by the Cooperative Research Centre for Water Sensitive Cities (CRC-WSC) and the University of Western Australia (UWA), their research concluded that 17 tonnes of builders sand and other construction related sediment can escape into the environment, our storm drains, rivers and waterways for every hectare of building development per year, especially after significant weather events.
Cygnia Cove’s “First Cygnets”. Photo credit: Richard Noble & Company
The Cygnia Cove project resulted in initial interest from landholders and builders in using the free erosion and sediment control products on offer, and to help determine which were most effective. However, due to the impacts from COVID, concerns about additional building delays, taking on new or changing building practices, and potential increased labour costs there was no uptake of the products. This outcome provides some insight to barriers in achieving best practice erosion and sediment control.
Project redirection included installing silt sausages at stormwater inlets to quantify sediment loss prior to entering the drainage network, quantifying sand drift from building sites and awareness raising initiatives.
A Keep Soil and Sand on Site signage trial enacted during this study resulted in some improved sediment management practices. The new signs proved quick and easy to install, very cost-effective and a useful tool for the building site supervisors involved to remind all trades that a tidy site includes no sand on roads or down the drain and that the government and the community expect this too. https://www.perthnrm.com/blog/2023/06/22/stopping-site-sediment-pollution/.
Overall, however, non-compliance of legislative requirements for sediment control was often observed and there was limited voluntary adoption of best practice by residential builders.
Partial dumping of bulk sand onto the road becomes a sediment pollution risk if this sand is not placed back on site immediately. Photo credit: Perth NRM
Measurement of soil and sand leaving site where the source was known facilitated the quantification of the impact of poor industry practices if sediment is not controlled. For example, lots being hydro-mulched and seeded soil with rye-grass after subdivision and a reduced level of fill behind semi-mountable verge curbing, one tonne of wind-blown sand left one 442m2 vacant block lot over 444 days. https://www.perthnrm.com/blog/2024/06/04/dont-curb-your-enthusiasm-for-sustainable-subdivision-design/
Other examples include:
- Almost one tonne of builders sand was dumped partially onto the road during one bulk sand delivery
- Half a tonne of sand leaving one lot over one day during landscaping of the verge after one house had been constructed
- 240kg (0.16m3) leaving one 462m2 lot on one day, due to builders sand being allowed to drift onto the road, into the gutters and down the drain
- 242kg (0.16 m3) sand leaving one 450m2 lot on one day due to a digger tracking sand from site onto the road
- 150kg (0.1 m3) sand lost on one day from one 455m2 lot due to the lot being driven on to deliver building materials and for parking
Uncontrolled builders sand that was allowed to leave site and make its way to the drain resulted in sedimentation of Cygnia Cove’s connecting channel, prior to draining into the Canning River.
Photo credit: Perth NRM
This project concluded that frequent non-compliance with legislative requirements for sediment management has resulted in a cumulative environmental impact, namely the pollution of Cygnia Cove’s retained wetland, constructed wetland, stormwater retention basin, drainage channel and the Canning River.
The Sediment Control at Cygnia Cove, Waterford Stakeholder Summary Report contains further details and a list of recommendations for subdivision and the construction of residential housing (lot development) to improve sediment management practices. You can download this report and other useful sediment control resources at https://www.perthnrm.com/resource/sediment-management/
For further information, please email [email protected]