Central Coast Council Administrator, Rik Hart, will meet with members of the communities of the Lower Hawkesbury concerned at a possible major spillage at Mangrove Creek Dam on September 24.
Hart said residents were worried a spillage could result in flooding and although staff think that unlikely, residents wanted to hear more.
River Cares President, Robyn Downham, said the meeting resulted from a conversation she had with Hart at a community barbecue on August 13.
“The dam is still full and we are all nervous about the possibility of another flood in September,” Downham said.
“If both dams commence spilling together again is there a Klaxon warning system in place to alert and notify the residents along Mangrove Creek?”
Downham has also invited Member for Gosford, Liesl Tesch, and Parliamentary Secretary for the Central Coast, Adam Crouch, to the September meeting.
“Historically the dam is at 100 per cent capacity and on Wednesday, July 6, during the recent floods, water was spilling from the dam simultaneously with Warragamba Dam,” Downham said.
She said she was informed at the time by Council that based on current rainfall forecasts from the Bureau of Meteorology and catchment moisture levels, overflow from the dam in the coming days was considered unlikely.
If the dam was to fill to capacity, water would then overflow via the spillway at a rate based on the inflows received, she was told.
“On Tuesday night, August 4, I received an alert stating that the Mangrove Creek holding tank (at Pembertons Hill Rd) had burst and was losing water,” Downham said.
“This was alarming news to say the least.”
She was advised by Council that the incident was the result of an old pressure valve failing to open after 30 years of service.
The tank had not burst but had to be left running to ensure water supply to Somersby treatment plant and the community, she was told.
She was told a new valve had been installed and would be serviced every 12 months.
A Council spokesperson said the operations of Mangrove Creek Dam would be explained at the meeting and the Dam Emergency Plan would be introduced.
“The Emergency Plan provides guidance for the management of various emergencies including flooding,” the spokesperson said.
“The Plan outlines the water levels that trigger activation of the Plan and notification to other agencies, such as the NSW SES.
“Council staff at the meeting will explain the roles and responsibilities for agencies and Council, including who will communicate to the residents in the event of an emergency.”
The spokesperson said Mangrove Creek Dam is a storage dam not a flood mitigation dam.
“Storage dams catch the water from rainfall, as well as run off in the catchment,” the spokesperson said.
“Effectively, what rainfall falls into the dam through rain events also falls into the downstream creek and catchments.
“Communities located along the banks of Mangrove Creek and the Hawkesbury River, regardless of the existence of Mangrove Creek Dam, are vulnerable to flood risk from these large catchments.
“At the meeting on September 24, Council staff will also be able to talk through the functions of the dam in regards to the recent rain event.
The meeting will be held at Spencer Community hall at 9.30am.
Terry Collins