Whispering Wall: Barossa Dam reservoir wall fails flood-modelling test, homes under threat

The Whispering Wall has failed a critical safety test, but SA Water has moved to reassure the public that minor works are already under way.

The 120-year-old dam wall that holds back a 4510-megalitre reservoir has failed a safety test, which showed in floods it could burst and put a quarter of Gawler and Angle Vale under water.

SA Water has reassured residents the Whispering Wall – the retaining wall of the Barossa Reservoir, in Williamstown – is safe under normal conditions, and is undergoing work.

The report was only released on the SA Water website last week and given to an FOI applicant, but was received by SA Water in March last year.

The consultant SMEC report states “overtopping” “might destabilise and result in failure of the dam” by eroding where concrete meets the landscape at both sides.

“It was estimated that approximately 25 per cent of Gawler (16km away) and 25 per cent of Angle Vale (25km away) would be inundated,” the report states.

Deputy Premier Susan Close said she had sought assurances from SA Water about safety issues and the report should have been made public a year ago.

“Gawler and Angle Vale residents deserve reassurance that they will not be impacted by any potential future flooding events,” she said. 

The dam holds 10 times the volume of the Torrens Lake in the CBD of Adelaide. The “consequences” of wall failure could be up to 6581 people flooded and up to 141 lives lost, the report found.

The estimated cost of failure was $1.6bn.

The Whispering Wall dam. Pic Mike Burton.

SA Water moved to reassure the public after The Advertiser revealed the secret report on Sunday; “We have comprehensive management practices in place to safely release water, to balance inflows with the reservoir’s capacity, and avoid an overtopping event and maintain regular contact with the Bureau of Meteorology to inform these decisions”.

The study ruled the dam safe during normal flows such as the present, and SA Water said 32 minor works recommended are already under way.

An SA Water spokesman said the modelling was for a one-in-10,000-year flood to a one-in-10,000,000-year flood.

The problem is created because the dam does not have a slipway like more modern ones, allowing rapid release of water during flood. An SA Water spokesman said a retrofitted slipway was being considered as a result of the report.

The Whispering Wall reservoir dam wall at Williamstown. Picture: Mike Burton