Study Area

The study area is located in south west Sydney and covers the northern part of the suburb of Chester Hill. It is an urban catchment that drains through a stormwater pipe network in a north-easterly direction to the Parramatta Council Local Government Area (LGA). The Wolumba catchment is one of the sub catchments of Duck River, and is wholly within the north western section of Bankstown City Council (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 160 stormwater pits and 220 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 Wolumba Catchment Flood Modelling Report, which is included as Appendix B.

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 included in Appendix B.

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 current Floodplain Risk Management Study phase of the floodplain risk management process.