Following three weeks close monitoring of the Lake Cathie water levels, Port Macquarie-Hastings Council has made the decision to scrape the sand berm to protect sewer infrastructure and low-lying properties from inundation.
In the weeks since council advised that the lake's water levels had encroached upon the 1.6m level on February 4, staff have undertaken rigorous daily checks of the water levels in an effort to determine the most appropriate course of action - in the best interests of the community and the environment.
While water levels have remained steady up until now at 1.6mAHD, recent and forecasted rain for the coming 10-14 days will likely impact council's sewer infrastructure which becomes inundated at 1.89mAHD (Australian Height Datum).
With the threat of water levels continuing to rise, council has decided that a berm scrape back to 1.75mAHD will be conducted as soon as is reasonably practicable to prevent water entering the sewer network, and the Bonny Hills Sewerage Treatment Plant at Rainbow Beach.
Port Macquarie-Hastings Council Director Community, Planning and Environment, Melissa Watkins, said that following consultation with key government agencies and experts council will now proceed with caution to lower an area of the sand berm by scraping a 10m wide dry channel at 1.75mAHD above the current water level.
"In the weeks since our last update regarding rising water levels at Lake Cathie, we have spent every day monitoring for changes to these water levels to determine the most appropriate course of action in the best interests of the community and the environment," Ms Watkins said.
"With significant rain falling over night and the forecast of further rainfall in the next 10-14 days, it has been determined that these water levels would most likely impact our sewer network, and further impact low-lying properties. That is why council, in consultation with government stakeholders, have agreed to enact a berm scrape that will reduce the height to 1.75mAHD above the water level.
"Based on the current expert advice this is the preferred method for flood mitigation and one that will provide the best chance of allowing rising water levels to flow over the berm and mimic a natural lake overflow before reaching critical sewer assets."
"If we were to enact a full lake opening, it would have detrimental impacts on the state of the lake's health by disturbing the already sensitive acid sulphate material which was exposed during the 2019 drought and after the subsequent opening events in May 2020 and January 2021."
Ms Watkins sad council's stakeholders including the NSW Department of Primary Industries and DPI Fisheries (DPI), the Department of Planning & Environment (DPIE); Biodiversity Conservation Division and Crown Lands, Southern Cross University and NSW Soil Conservation Service all advise that water levels need to remain high and an opening must be avoided if possible.
"Data collected over recent weeks indicates that iron and acid conditions in the lake system point to a high risk of another Iron floc event occurring under the current conditions, if the lake is opened using the traditional method of digging a channel between the ocean and the lake," she said.
"Iron floc events can impact the health of the lake's marine life, and can leave nasty odours. It can also deter recreational activities, such a swimming and boating.
"The recommended emergency measure to prevent this, and to protect sewer infrastructure, is the dry berm scrape. This will minimise the environmental impacts and provides the best opportunity for the lake to remain closed as recommended.
As soon as practicable today, council will begin to deploy earth moving equipment on to the beach to enact the berm scrape. Council requests everyone to please keep a safe distance to allow the works to be undertaken.
Council would also like to remind the community that any unauthorised digging at the berm resulting in an opening is unlawful and may also result in significant safety concerns and environmental impacts.
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