Developers are letting up to 150 tonnes of soil wash into rivers and streams from every hectare of unprotected development site in Brisbane each year, according to an erosion and sediment control expert.
The previous state government environment department was told in 2011 that there was “zero compliance” by construction crews in controlling erosion on construction sites.
That February 2011 study by Marsden Jacobs Associates for the Department of Environment and Resource Management recommended tougher compliance on builders after “pilot audits found 100 per cent of (construction) sites were non-compliant”.
Though the study determined it was “the most cost-effective way” of controlling sediment and nutrient pollution in Brisbane’s rivers, it was never accepted as policy by the Bligh government.
Erosion and sediment control expert Ben Starr, from O2 Environment Consultants, said soil loss from construction sites in urban areas was almost uncontrolled.
“It is quite common to see soil loss rates from a construction site at 150 tonnes per hectare per year and above,” he said.
“Indeed on some of the sites we see as much as 1000 tonnes, or 2000 tonnes per hectare, per year, which can expect to be eroded.”
Mr Starr said while some firms did use erosion fences and sediment basins on development sites, it was rare and checked sporadically by councils and state government.
He said research by Sunshine Coast Regional Council showed best practice steps, such as sediment basins and sediment fences, used to control soil from development sites save only 20 per cent of soil erosion.
“So potentially best practice is still potentially seeing over 100 tonnes per hectare per year off many construction sites,” he said.
Fairfax Media understands Healthy Waterways has begun looking at the issue.
The silt from this soil loss is the leading factor in why the rivers and streams in the Brisbane suburban area declined from a D-minus grade to a F grade in last year’s Healthy Waterways scorecard, experts say.
The not-for-profit community group, which uses scientific experts and local councils to monitor the health of 19 major catchments in south-east Queensland, will release its 2013 scorecard on the condition of the region’s 19 river and stream catchments on Wednesday.
In January 2013, silt from upstream blocked the Mt Crosby Water Treatment plant, putting the city of Brisbane within hours of running out of drinking water.
River health expert Jon Olley described river turbidity as a major issue for Brisbane at last year’s Healthy Waterways scorecard release.
“Mud increases the turbidity or the murkiness of waterways and contains pollutants that have a negative impact on water quality,” Professor Olley said.
The South East Queensland Plan shows 40,000 hectares of land is earmarked for development in the next 20 years.
