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Flood study

Cooks River Catchment Flood Study

The purpose of the study is to define flood behaviour throughout the Cooks River stormwater catchment, which is one of the sub-catchments of the main Cooks River catchment, including the analysis of flows within the underground pipe drainage network and surface runoff across the catchment.

The study provides information on flood conditions throughout the catchment for a range of design floods, from relatively frequent events to more extreme floods, for existing catchment conditions as at 2012. The results of the study will form the technical basis for subsequent floodplain management investigations, including the identification of problem areas and assessment of flood mitigation options to reduce the risk and magnitude of flooding. Assistance will be sought from the community to help identify these areas and to derive appropriate solutions.

Responsibilities

The prime responsibility for planning and management of flood prone land in New South Wales rests with local government. The New South Wales Government provides assistance on state-wide policy issues and technical support. Financial assistance is also provided to undertake flood studies and floodplain management studies, and for implementing measures identified in these studies. Funding and technical assistance was provided for this study through Bankstown City Council, the Commonwealth Government under the Natural Disaster Resilience Grants Scheme (NDRGS), and the State Government through the Office of Environment & Heritage (OEH). The study has been undertaken under the direction of Bankstown City Council and their Floodplain Management Committee. The Committee includes Councillors and Council staff, officers from OEH, the State Emergency Service and community representatives.

Study Area

The study area is located in south west Sydney and covers the eastern part of the suburb of Greenacre. It is an urban catchment that drains through a stormwater pipe network in an easterly direction towards the Cooks River in the neighbouring Local Government Area (LGA) of Strathfield. The Cooks River catchment is wholly within the north eastern section of Bankstown City Council Local Government Area.

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;
  • Indicative information on drainage asset performance for various storm events;
  • A property database including surveyed floor levels, flood levels and the resulting floor level immunity, expressed in the magnitude of a storm event;
  • 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 512 stormwater pits and 503 stormwater drainage pipes or culverts. The database also contains model results, including information for each pipe on the design event at which it is running full.

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. The adopted grid size for this study is 2m, whereas the flood studies within Bankstown undertaken prior to 2012 utilise a coarser grid size of 5m. The new grid size has been adopted in line with ongoing improvements in computer technology (in particular speed, memory and storage) to provide higher resolution of the floodplain whilst allowing for manageable model simulation times and file sizes. Full details of the modelling approach, modelling parameters and other assumptions are outlined in the Cooks River Catchment Flood Modelling Report, which is included as Appendix C.

Property Database

This flood study also includes the development of a GIS property database, utilising floor level data collected by Council and comparing these to flood levels for various design flood events. This comparison provides a dataset on floor level immunity, which is a very useful tool for assessing the existing flood risk. Additional information such as property ground levels are also provided as part of the property database. A summary of the property database is presented in Figure 5-1.

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.

Additional Information

Field Value
Title Cooks River Catchment Flood Study
Publication Date 1 November 2012
Themes Land and Resource Management
Spatial Extent
Map data © OpenStreetMap contributors
Council/LGA Canterbury-Bankstown Council
Author/ Prepared by BMT WBM Pty Ltd
Publish date 26 May 2017
Update date 27 June 2017
River Basin 213 - Georges
Place Name Greenacre
Approval State Approved
Submitted for approval 26 May 2017
Submitted by John Silk
Approved 27 June 2017
Approved by dstazic
Data Comment

Report only; no other data. Legacy data; may have been superseded.

Identifier 7ac52182-591c-4629-b322-74d9b9d36625