The Tuggerah Lakes Entrance Management Study has concluded that flooding in Tuggerah Lakes cannot be eliminated, it will likely worsen with sea level rise, and the community should adapt and prepare to live with the impacts of flooding.
In July 2020, the NSW Government’s professional specialist advisor, Manly Hydraulics Laboratory (MHL) was commissioned by Central Coast Council to undertake the study with the aim of developing an interim entrance management procedure based on sound evidence to reduce the risk of life and public health, public and private infrastructure around the low-lying Tuggerah lakes foreshore.
The study says the impacts of flooding will continue even under the implementation of the Interim Entrance Management Procedure and it was important the community in the Tuggerah Lakes floodplain understands the level of flood risk to adapt and prepare to live with the impacts of flooding.
The 232-page comprehensive study covered a review of previous studies, analysis of water levels and the entrance behaviour, management options, results of a stakeholder workshop and options for an Interim Entrance Management Procedure.
It provides a rational decision-making framework for Central Coast Council to approach entrance management works until an Entrance Management Strategy is formalised through the Coastal Management Program process, and alongside other controls identified in the Floodplain Risk Management Study and Plan.
The study found that emergency berm scraping and opening a pilot channel immediately prior to flooding provided the greatest reduction in flood level, however, none of the five interim options nor a wide open, post-flood scoured entrance would eliminate the risk of flooding.
Entrance maintenance dredging was not assessed as an interim management option.
“The interim procedure does not seek to maintain a permanently open entrance,” the study summary said.
“The entrance channel will naturally constrict with sand, particularly during drier periods with low rainfall and scour to a wider entrance during wetter periods with increased rainfall.
“The interim procedure allows natural entrance processes to operate with minimal disturbances in accordance with the Department of Primary Industry’s policy and guidelines for fish habitat conservation and management.
Regular ongoing entrance berm works to continuously maintain flood-ready berm conditions were not considered to be feasible given the highly dynamic nature of the entrance including berm rebuilding and channel infilling processes.
The MHL report said it was vital to review and update flood management procedures including review of sea level rise and coastal inundation impacts on Tuggerah lakes and investigation of entrance shoal dredging to support entrance management for recreational, environmental and social outcomes.
Representatives from Council, the State Emergency Service, NSW Police, and local MPs met on August 23 for “productive dialogue” to improve their joint approach to flood preparedness.
Council’s Director Environment and Planning, Dr Alice Howe, said the meeting was also an opportunity to clarify future actions Council was already, or would be, undertaking.
“Council has received funding from the NSW Government to review and update the 2014 Tuggerah Lakes Flood Study which will inform an updated Floodplain Risk Management Study and Plan,” she said.
“This project is now underway and will allow for an updated understanding of flood risk and behaviour within the Tuggerah Lakes floodplain in order to better identify and mitigate flood risk.
“Community input will be sought as part of upcoming consultation on the Coastal Management Program which is currently in development,” Dr Howe said.
Sue Murray