Why is Council doing these flood studies?
We’re doing these flood studies to improve safety for residents. The outcomes and recommendations will improve protection for properties, assist planning for residential growth and development and improve management of our waterways.
Under NSW planning laws, councils are responsible for managing local flood planning. Council has engaged a consultant, WMA Water, to complete studies on eight minor tributary catchments where a flood study has not previously been undertaken.
These eight remaining un-modelled tributary catchments that flow into the Lake Macquarie waterway have a history of flooding or have otherwise been identified on Council’s records as having the potential to flood. We need to be prepared. The flood study will establish hydrologic and hydraulic computer models of the study area which then are used to design flood levels, extents and velocities within this study area, and map areas affected by flood events in a range of scenarios.
The flood study will be used to inform a floodplain risk management study and plan later in the flood management process.
What community consultation has taken place to develop these flood studies?
In early 2020, we collected information on community flood experiences and overall concerns on flooding issues. It also allowed Council to receive ideas on potential floodplain management measures. There were 74 responses received to the survey.
Approximately half of the respondents (36 responses) had experienced some flooding of their property and six respondents had experienced above floor flooding. Some of the respondents were able to provide photographs or descriptions of flooding that were suitable for use in the model verification process.
Without community input we would have lost a significant aspect of real-life information and impacts contributing to the studies. This information helped greatly to inform the flood study for each catchment.
How do these flood studies contribute to flood management in Lake Macquarie?
This project improves our methods of floodplain management and forward planning through tailored flood controls and accurate flood planning levels in the study areas. It will provide valuable information about appropriate areas of residential growth and development and identify properties that are potentially affected by flooding events, but are located outside the extent of existing flood studies.
On completion, Council will have a better understanding of flooding over approximately 98 per cent of the flood-liable lands in the City. The study for each identified tributary catchment will utilise appropriate hydraulic modelling and a history of past flooding to identify areas with flooding concerns. The results of this study, combined with land zoning and growth plans, will enable Council to identify areas that are flood affected and those which may require more detailed assessments of flood risks, which will be undertaken on a priority basis.
What is the effect of lake flooding and sea level rise?
The flood studies will consider the impacts of climate change upon flood levels for the rainfall increase scenarios and the effects of elevated water levels in Lake Macquarie waterway due to sea level rise.
How do these flood studies relate to Council’s current Local Adaptation Planning programs?
Local adaptation plans (LAP) are often recommended as an outcome of a flood risk management study and plan. For example, the Lake Macquarie Waterway Floodplain Management Study and Plan (2012) recommended that Council work with local communities to develop a LAP for low lying areas on the eastern side of the lake including Belmont South, Marks Point, Pelican, Blacksmiths and Swansea.
Local adaptation plans need to take account of flood studies to help determine the level of current and future flood risk in the catchment.
What is a tributary?
A tributary is a river or stream flowing into a larger river or lake.