SA Water says a report about the safety of the Whispering Wall dam shows what might happen in only the rarest of scenarios. 

SA Water has released an internal report under Freedom of Information laws by consultants SMEC, which predicts the results of a failure of the Whispering Wall at the Barossa Reservoir. 

In what SA Water describes as an “extreme and worst-case” scenario, the report says that a failure of the wall would cause $1.6 billion in damage, impacting almost 7,000 people, with 25 per cent of the downstream areas Angle Vale and Gawler flooded.

The report looks at the possible outcomes of an “overtopping” event, saying water could erode the wall at its base downstream.

“Three-dimensional crack monitoring points have been installed across one of the cracks,” the review reportedly states.

“The devices are currently not being regularly monitored. Monitoring of the cracks should be undertaken on a six-monthly basis to determine the seasonal performance of the cracks and identify any increasing or worrying trends.”

SA Water’s Senior Manager of Capital Delivery, Peter Seltsikas, says the experts found that the department is managing the wall to standard.

“The standards that are applied to large dams are extremely conservative and the reason for that is that they are important structures that we need to make sure, from an engineering perspective, are adequate and are safe all of the time,” he said. 

Mr Seltsikas says the concerning outcomes would only occur in an “extreme and worst-case” scenario.

“We're talking about a one-in-10-million-year rain event,” he said.

“To put that in perspective ... the floods on the eastern seaboard in recent months, that's a one-in-100-year event. We're talking about an event that is 100,000 times bigger ... an event we may never see.”

Among the documents released to reporters was an upgrade study, covering options to boost the wall’s flood mitigation. It put forth six flood-mitigation options, two of which were rejected over concerns about their impact on the look of the dam wall.

SA Water says some of these options are still being considered.