Study Area

The study area is located in south west Sydney and includes the central part of the suburb of Picnic Point. The northern part of the catchment is predominantly urban; the southern part includes parts of the Georges River National Park, in particular the Yeramba Lagoon. The catchment drains gradually south, through a stormwater pipe network towards the Georges River. The Sydney South Electricity Substation is also located within the Picnic Point catchment. The Picnic Point catchment is wholly within the southern section of Bankstown City Council Local Government Area (LGA).

Outcomes from the Study

The main outcomes from this study include:

• A database of all Council drainage assets within the study area;
• Establishment of a computer model capable of assessing flood behaviour;
• Information on flood behaviour under existing catchment conditions;
• Predicted change in flood levels due to the potential impacts of climate change; and
• A model that can be used to assess flood mitigation options and future development proposals.

Database of Drainage Assets

All drainage asset data collected by Council for the study has been incorporated into a GIS database. This allows the data to be spatially represented across the study area and easily retrieved as required. Information in the database includes data for some 170 stormwater pits and 200 stormwater drainage pipes. Other catchment data, including aerial photography, property cadastre, building footprints and the terrain surface (based on ALS survey) is also incorporated into a GIS database.

Computer Modelling

A numerical computer model was developed for the catchment to simulate flood behaviour, using the software TUFLOW. Surface flows are represented in the model through a two-dimensional grid covering the entire study area. The stormwater pit and pipe network is included as one-dimensional elements within this grid. Full details of the modelling approach, modelling parameters and other assumptions are outlined in the Picnic Point Catchment Flood Modelling Report, which is included as Appendix C.

Existing Flood Behaviour

Design flood behaviour has been computed for a range of floods, ranging from relatively frequent events to more extreme floods.

The model produces a grid of results over the study area providing data on flood levels, flood depths and flood velocities. Flood level contours have also been prepared showing contours of flood heights throughout the study area. This data is provided digitally and can be overlaid on base mapping such as aerial photos and cadastral plans showing property boundaries.

All flood model results have been provided to Council for incorporation into their GIS database. Much of this information is also included as A4 sized plans in Appendix C.

It is understood that once the Flood Study has been adopted by Council, the GIS information resulting from this Flood Study will be used for floodplain management purposes, including assessment of flood-related development constraints on properties. Potential flood mitigation options will be assessed in the Floodplain Risk Management Study phase of the floodplain risk management process.