Central Coast Council has adopted the Woy Woy Peninsula Floodplain Risk Management Study and Plan (FRMSP), setting out measures to prepare for future flooding events.
The plan will serve as a guide for priorities for Council, communities and the State Emergency Service (SES).
Prepared by DHI Pty Ltd, the plan encompasses the Woy Woy Peninsula including the Kahibah Creek catchment.
The FRMSP quantifies the nature and extent of existing flooding issues and recommends actions to better manage the existing, future, and continuing flood risk.
It also seeks to build community resilience to flooding and includes flood mitigation works, emergency management plans, flood warning processes, land-use planning and suitable design of infrastructure and buildings.
The draft documents were on public exhibition from January 18 to February 15, with submissions evaluated and proposed amendments for flood management made to the final FRMSP.
The final report said the area was impacted by flooding from Brisbane Water as a result of ocean storm surge events and tidal inundation and catchment flooding as a result of rainfall events.
“Ocean storm surge events result in the elevation of the Brisbane Water estuary levels and can lead to flooding of the low-lying areas of the peninsula,” it said.
“During Brisbane Water flooding events, flood levels typically rise and fall over several hours, with inundation occurring for approximately five hours in a one per cent AEP (Annual Exceedance Probability) event.
“Flood depths can be up to 0.9m at the peak of the one per cent AEP flood event in the areas with the lowest elevations.”
The report found that risks associated with tidal inundation were not as significant on the Woy Woy Peninsula as other mechanisms of flooding.
“However, in the future, as a result of sea level rise, a large proportion of the low-lying regions of the study area will be subjected to frequent inundation from high tides,” it said.
“For example, in 2100, the lowest areas of the Woy Woy CBD will experience daily tidal depths of approximately 0.4m and king tide depths of approximately 0.7m.
“This will compromise the liveability of some portions of the suburbs through flooding of roads, services and private properties.
“Flooding from Brisbane Water can also impact to capacity of the existing drainage system … with elevated flood levels restricting flow discharging from local catchment flooding.”
Measures suggested in the plan include the installation of six infiltration devices along low-lying streets with a history of ponding and nuisance flooding due to lack of drainage or drainage capacity even in minor flood events.
It also suggests a review of evacuation centre locations and flood warning systems, the erection of more flood warning signage, flood education programs and recommendations on land use and development control planning.
The most significant issues raised in the submissions included: the fact sea level rise predictions are not informed by the latest International Panel on Climate Change (IPCC) reports; insufficient consideration with respect to evacuation routes and access to Gosford Hospital; and general concern about the degree of development on the Woy Woy Peninsula and the increase in impervious surfaces on private property.
A report to Council’s June 27 meeting said all submissions were considered by staff and consultants with minor amendments and clarifications made to the final version.
Now that it has been adopted, the recommended actions identified within the FRMSP are eligible for grant funding from various external departments including the DPE under the NSW Floodplain Risk Management Program.
Read the final report at https://www.yourvoiceourcoast.com/sites/default/files/2023-06/woywoyfrms_final2.1_mainvolume_r1.pdf
Terry Collins