Whenever we see plumes of building sand in our suburban lakes, waterways and parklands, we can easily see some of the environmental impact of poor erosion and sediment management practices from local building sites.
These visible cues are often the catalyst for action, but many people are unaware that the economic costs associated with managing the effects of poor building practices are borne by local governments, and ultimately paid by ratepayers.
Examples of the financial implications to Local Governments in WA of poor erosion and sediment control practices during urban development
Local Government can expend large amounts of money and time managing sediment loss and sand drift from subdivision, building and construction sites by sweeping roads, repairing and maintaining stormwater management systems, responding to public complaints and remediating or restoring rivers, wetlands and parks.
The financial implications and potential financial risk for Local Governments in WA of poor erosion and sediment control practices can be significant, as can be demonstrated by the following examples:
Drainage infrastructure maintenance and street sweeping budget for three “high growth” LGAs
|1.||The City of Swan’s maintenance team carries out regular drainage maintenance and has spent a significant amount of time clearing drainage systems in new subdivision areas where houses are being built on individual lots. 462 work requests related to drainage were received by the City’s Assets Management Department during 2018.
For the 2019/2020 financial year, the City is budgeting approximately $267,000 for street sweeping costs for new subdivision stages following residential building site works and approximately $375,000 for cleaning drainage pits and lines full of sand within new subdivisions.
This equates to an annual budget of $642,000; a substantial cost being borne by the City of Swan and its ratepayers.
|2.||The City of Bayswater estimates that $15,000 is budgeted for the maintenance of drainage infrastructure where builders’ sediment has run-off from building, subdivision and constructions sites and been captured, requiring removal. This cost represents approximately 10% of the City’s annual drainage maintenance budget.
|3.||The City of Armadale acknowledges that the cleaning of the drainage pits and pipes in areas where new development is occurring can cause huge issues to their drainage systems. This is particularly an issue when a new subdivision is completed, and the drainage system is not cleaned prior to hand over to Council.
Waste materials like concrete, sand and other rubbish that blow off building sites can render a drainage system useless very quickly. Depending on the pipe size, the costs to clean the systems varies greatly. The following two examples are provided by the City of Armadale in relation to the costs of removing (primarily building) sediment from stormwater drains:
“In-fill” Local Government examples of costs of manual “cleaning” of iconic wetlands
|1.||In 2017, the City of Subiaco was forced to undertake a clean-up of Lake Mabel Talbot in Jolimont in order to remove the build-up of sediments forming at the bottom of the Lake which were threatening the health of the Lake and impeding water flow. Seven tonnes of sediments were removed from the Lake during this manual clean-up, at a cost of over $36,000.
|2.||The City of Bayswater estimate that the annual maintenance cost (sediment removal) of the Gross Pollutant Trap at Eric Singleton Bird Sanctuary is $16,000. The estimated maintenance cost of the sedimentation basin (sediment removal) is $17,500 every ten years.
How is this happening?
Sediment that moves off building and construction sites typically enters stormwater drains untreated, thereby clogging the stormwater system and transporting attached pollutants including oils, heavy metals and hydrocarbons into local waterways.
Most urban development in Western Australia disturbs the natural environment and this, in combination with the common practice of importing sand fill from coastal areas, results in soils that are susceptible to erosion. In many cases, current subdivision, residential and commercial building and construction practices are resulting in considerable environmental impacts and financial cost.
Often sand from smaller scale subdivisions and residential building lots is transferred onto the road during building construction activities and makes its way into stormwater systems. In WA, builders have been observed tipping sand for construction directly onto the road, particularly in laneways. Sometimes sand is tipped directly on top of or adjacent to a gully grate or side entry pit, which is immediately inundated with sand.
Significantly, in many municipalities, the installation of sediment control fencing or other sediment control treatments is not a common practice. In addition, smaller land developers who infrequently carry out subdivision works are not as familiar with processes and practices for preventing sediment loss.
There is also evidence of a lack of effective erosion control from formed access driveways on steep sites, which results in soil erosion after heavy rain events, inundating roads. The impacts of erosion are predominantly experienced during winter when stormwater runs down driveways that are unsealed, where loose gravel, clay and sand pad fill washes onto the road. In the summer, sand drift is an issue as builders report dust control fencing impedes site access, and is often destroyed as a result.
These issues are compounded by the frequent and reliant use of building subcontractors, who can be less concerned about site requirements and demonstrate less responsibility towards sediment loss and waste management.
What is being done?
Many local governments are sharing information with each other through the Sediment Taskforce, coordinated by Perth NRM.
The goal is to create a consistent approach to erosion and sediment management, which provides certainty for local governments and the building industry.
The Taskforce is compiling case studies on the most successful management techniques for local governments, and is working to create information tools in collaboration with the building industry to create greater awareness of best management practices and the costs of poor sediment and erosion control.
These resources are made available online and through participating local government partners.