Fire risk has been underestimated at the proposed site for the Ginninderry housing development, according to a University of NSW Canberra report.
The report, commissioned by the Ginninderra Falls Association, has prompted the grass-roots opponents to the cross-border development to call for the Yass Valley Council to delay any decision to rezone land on the NSW side of the project.
University of NSW Canberra scientist Jason Sharples has written a report which asserts fire risk has been underestimated for Ginninderry. Photo: Katherine Griffiths
The report asserts current Australian standard, AS 3959 for construction in bush fire prone areas does not account for recent scientific insights into extreme fire development and the effect of intense wind, steep terrain and ember storms, which could be expected on the north-western edge of the Ginninderry development.
The author of the report, UNSW bushfire scientists and associate professor of applied mathematics Jason Sharples, said the detailed bushfire management strategy for the Ginninderry region was compiled by EcoLogical in 2014 in full compliance with relevant guidelines.
Map of elevation around the Ginninderry region, with the land subject to rezoning in dark shading. The red pixels indicate locations with slopes above 20°, that are prone to extreme fire behaviour. Photo: UNSW Canberra
"The Australian standards have fallen behind the state of the science," Dr Sharples said.
"The particular concern with Ginninderry was the river corridors. Work we have done in the last few years shows that sort of landform is really prone to producing fire behaviour that will throw up a lot of embers and cause fires to burn in a way that fires aren't assumed to burn in the standard."
Dr Sharples argued current standards were underpinned by the assumption radiant heat was the biggest threat to homes, yet aftermath of Canberra bushfires in Duffy demonstrated ember attack did far more damage.
Half of the homes lost in Duffy were more than 100m from the forest edge - data Dr Sharples uses in his case for a reconsideration of how asset protection zones widths are drawn up.
Black pixels show steep lee-facing slopes (assuming NW winds), which would be prone to extreme fire behaviour under strong winds. The red shading provides a conservative estimate of where embers originating from lee-facing slopes would fall under extreme fire danger conditions. Photo: UNSW Canberra
Figure 15 in the report showed the northern-most border of the Ginninderry project was prone to atypical fire spread and conservative modelling showed embers could fly 3.5km into the housing precinct causing potential spot fires across most of the NSW portion and the top-third of the ACT land.
EcoLogical's Rod Rose conducted the 2014 bushfire management strategy for the site and said it was reasonable to assume best-practice guidelines may change before buildings were constructed in the NSW section in 2025, but the claims within the report were untested.
"There needs to be proper peer review of the work the report is releasing," he said. "This is just a report of one person to a lobby group."
Mr Rose disagreed with the premise of the report that current standard didn't adequately account for variables such as ember attack and said the west belconnen development proposal was based on best practice and included setbacks based on worst case scenario extreme fire events.
He said using data on the homes lost in Duffy in 2003 as a predictor for Ginninderra was an oversimplification and failed to account for factors such as landscape and active defense by home owners.
Ginninderra Falls Association member Robyn Coughlan she felt the report findings were reason enough to delay the Yass Valley Council's decision on rezoning land on the NSW side of the precinct.
"A more thorough assessment of the threat from bushfires is needed," she said.
"Rezoning this environmental land to urban could not only potentially put people in harm's way, it could also increase pressure to burn the surrounding forest for the protection of property, putting the fragile ecosystem and threatened species at risk."