Expert witnesses clash over what led to McCrae landslide
A scientific showdown has erupted at the McCrae landslide inquiry, with experts divided over what caused the catastrophic collapse that destroyed multiple homes.
A burst water main was the “only credible” water source that could have triggered a Mornington Peninsula landslide that destroyed a house and damaged 19 others, an inquiry into the disaster has been told.
Experts engaged by the local council for a Board Inquiry into the McCrae landslides believe the burst pipe at Bayview Ave had a “significant to major influence” on an earlier landslide on January 5 and the catastrophic event on January 14.
Dane Pope PSM principal geotechnical engineer Dane Pope and Australian Environmental Auditors principal hydrogeologist Phil Hitchcock held the view that while it was impossible to determine exactly how the water from the leak site arrived at the landslide location there were “credible flow paths” including through sewer trenches and permeable shallow aquifers.
The pair argued the water’s chemistry could have been altered as it travelled which would explain the chemistry of the water issued from the headscarp after the January landslides.
The view was shared by Board Inquiry experts WSP technical director engineering geology Darren Paul and WSP hydrogeologist Stephen Makin.
But South East Water’s expert team disagreed, arguing the water did not have enough time to travel from the leak to the landslide site.
Court documents revealed SMEC senior associate engineer David Hartley and Technical Principal Hydrogeologist Hugo Bolton found the chemistry of water taken from the landslide headscarp suggested it did not come from the burst water main.
Mr Hartley and Mr Bolton concluded that domestic irrigation was a “major contributor” to the water that cause the landslides based on the high water usage measured at multiple View Point Rd properties.
However, the shire’s barrister Kathleen Foley SC put it to Mr Hartley that SMEC did not have a viable alternative theory for what caused the landslide.
“Instead of asking yourselves as scientists what was the most likely cause, what you’ve done is say what could it have been other than South East Water,” Ms Foley said.
“You don’t have a viable alternative theory for what happened.”
Mr Hartley said the suggestion was “a little bit unfair”.
“We are being scientifically robustly testing the theories,” he said.
“The geochemistry really foxed us.
“We couldn’t work how you can get a flow of water that picks up a chemical footprint and gets to the (landslide location).”
Ms Foley asked Mr Hartley if, after hearing all the evidence of the past two days, SMEC’s position it “couldn't have been our water” was no longer a viable position,
“I still stand by that, but in all likelihood no,” Mr Hartley said.
The rating of potential cases of the landslide was included in a report prepared after six experts involved in the inquiry took part in a two day conclave ahead of hearings resuming on Monday.
A conclave is closed to the public and allows witnesses to discuss and attempt to resolve differences in their expert opinions.
The aim is to identify areas of agreement and disagreement – ultimately producing a joint report that provides further clarity on key issues.
The landslide Board Inquiry conclave was unable to reach a consensus on five points including the impact of water from the Bayview Rd leak and domestic irrigation as well as the roles played by “old fill” present in the gully prior to the landslide and the View Point Rd retaining wall.
The Board Inquiry hearings will continue on August 18.