Attachment I - Flood Assessment

Cooroy Hinterland Park Flood Assessment



4          COOROY CREEK FLOOD MODELLING
Cooroy Creek flood modelling has been carried out based on the flood models produced by WMA
Water for the 2018 Six Mile Creek Flood Study. Minor updates have been undertaken as
necessary to ensure the existing site is adequately represented in its current form.

A summary of the established flood model details is provided below for reference.

      •    Hydraulic modelling has been carried out using TUFLOW software developed by BMT in
           Brisbane. TUFLOW is a computational engine that provides one-dimensional (1D) and
           two-dimensional (2D) solutions for the free-surface flow equations to simulate flood and
           tidal wave propagation.
      •    Ground levels and hydraulic roughness values are represented using a 5m grid.
      •    Ground levels in the model are primarily based on Aerial LiDAR Survey (ALS)
      •    Hydrologic modelling of the catchment has been carried out using WBNM software
           developed jointly by the University of Wollongong, Rienco Consulting and Balance R & D.


This report presents results of two hydraulic modelling scenarios as follows:

      •    Existing Case – This is the base case for the impact assessment and reflects the site in
           its existing condition.
      •    Proposed Case – Incorporates the hinterland playground in its proposed form
           represented by changes to model ground levels and hydraulic roughness values.



4.1       Existing Case
Council’s established TUFLOW model used for the 2018 Six Mile Creek Study has been updated
for this investigation as follows:

      •    The TUFLOW model has been updated to a more recent version of TUFLOW and is now
           run using the HPC solution scheme which allows significantly reduced model runs times.
      •    Hydraulic roughness mapping of the existing site has been refined based on a recent site
           visit in conjunction with recent aerial imagery. A Manning’s ‘n’ hydraulic roughness value
           of 0.06 has been applied to cleared areas of the existing site which is the value applied to
           ‘open space’ in the model.

Model ground levels of the existing site have been compared to site survey and found to be a close
match.

The existing case model has been run for the following design flood events.

      •    1% AEP event for future climate conditions at year 2100 (major event).
      •    10% AEP
      •    50% AEP (minor event)

This provides an appreciation of Cooroy Creek flood characteristics during a minor, intermediate
and major flood event.

Results of the updated Existing Case model have been compared to those of Council’s established
results and found to be a close match (within +/- 100mm). Therefore, the updates made to the
model have not altered peak flood level predictions at the site.

Peak flood depth and velocity mapping of the existing case results are provided in Appendix A.


J00318R1V1                                                                                          6