February 4, 2013
South Burnett Mayor Wayne Kratzmann says it was heavy local rainfall rather than the overflow from Gordonbrook Dam which sent a torrent through a Wilkesdale woman’s house last Sunday.
Cr Kratzmann said he had enormous sympathy for Dominique Bellonte and her daughter Leana, and council staff would try to contact her.
However the timing of the inundation of her house on Sunday morning showed she was flooded from the huge amount of rain that fell in the downstream catchment rather than water from Gordonbrook.
The Gordonbrook spillover would have added to the flow later in the day.
Cr Kratzmann agreed that lessons could be learned from the Australia Day weekend floods, especially the possible consequences when parts of the South Burnett receive 400-500mm of rain over a very short period of time.
“It’s highlighted that when we receive that amount of rain there will be some real issues arising in the region,” he said.
He was also particularly concerned about what had happened in the Byee and Silverleaf areas.
Cr Kratzmann said a system could be put in place where council staff would contact one key person in a locality who had local knowledge, and that person could pass on alerts to people known to be at risk.
“We had put in place a system for a one-in-100 year event; but this was really different,” he said.
South Burnett Water and Sewerage Manager Russell Hood said that at 10:30am on Sunday (January 27) the level of water going over the spillway at Gordonbrook Dam was 1.5m, which required the Emergency Action Plan to be activated.
“This is well below the 2011 flood level of 2.5m over the spillway,” he said.
“The flooding that is shown in the photos at Ms Bellonte’s property at 12:30pm is likely to have been caused predominantly from downstream inflow and flooding, as at 12:30pm the level over the dam was 1.9m, still below the 2011 flood level.
“I commenced ringing downstream residents at 11:40am on that day, working from the dam downstream but not all could be reached.
“Obviously and unfortunately for Ms Bellonte, this was too late due to the higher downstream flooding and significant inflows from areas downstream of the dam, particularly Reedy Creek and Home Creek, not as a result of the water level going over the Gordonbrook Dam spillway.”
Mr Hood pointed to an extract from the Gordonbrook Dam Emergency Action Plan:
“Limitations: The EAP covers only the situation at the storage itself. The effect of a dam failure on the downstream residents (a Failure Impact Assessment carried out by Worley Parsons in June 2008) is included in the analysis data provided by SBRC. The evacuation of downstream residents will be undertaken by the Queensland Police Service. It should be noted that severe flooding potentially requiring evacuations can occur without failure of the dam.”
“The last part of this extract is critical and in hindsight is what has likely occurred on January 27 from what was a significant rain event that resulted in fast rises in the Stuart River downstream of the dam,” Mr Hood said.
“Prior to this rainfall event, Gordonbrook Dam was 1m below the spillway so would have provided some buffering of the flood levels in taking up this initial inflow until the storage was full.
“Taking lessons from this event, properties such as this and others in the Silverleaf area are obviously at risk of flood inundation irrespective of dam overflow or failure risks.
“Either early self-evacuation or assisted evacuation during significant rainfall events such as these will ensure at-risk persons can be relocated to safe locations more promptly and easily.”
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