MCU14-0039 Flood report and flood man Plan rev August 2015

Como Glasshouse P/L C/‐ Martoo Consulting P/L
Flood Impact Assessment – 305 Lake McDonald Drive Cooroy


2.2              Available Data
The following data has been sourced and used in this assessment: ‐
         LiDAR topographical data sourced from the Department of Natural Resources and Mines
          (DNRM);
         A partial detailed survey of the subject site (provided by Martoo); and
         Digital flood models and associated model files for the Six Mile Creek (Cooroy Flood Study)
          sourced from Noosa Council.
By way of background to the Council flood model, the hydrological and hydraulic model developed for
Six Mile Creek as part of the Cooroy Flood Study was originally prepared by Water Technology on
behalf of the Sunshine Coast Council (SCC). The study was documented in the report entitled “Cooroy
Flood Study”, Water Technology, July 2013. The work included model calibration tasks relating to the
historical flood events which occurred in 1999, 2009 and 2012. The models developed in 2013 (XP‐
RAFTS and TUFLOW) were subsequently used by Hydrology & Water Management Consulting Pty Ltd
(HWMC) under commission from SCC in 2013 and extended to include design flood assessments for
the 1 in 2 AEP to PMF flood events. This work was documented in the report entitled “Cooroy Design
Flood Modelling” by Hydrology & Water Management Consulting Pty Ltd, November 2013 (report
J00147Lt1). We understand that the digital flood model data purchased and subsequently provided
by Council for the purposes of this current assessment is the same model prepared by HWMC in
November 2013. This model, namely the TUFLOW model, has been adopted for the purposes of this
investigation and remains fundamentally un‐changed in respect to the model details applied for this
assessment other than that the minor changes that have been outlined in this report.

2.3              Hydraulic Assessment
The Council provided TUFLOW hydraulic model was used as a basis for this investigation and revised
for the purposes of this assessment to reflect the following scenarios:‐
         Existing conditions (no greenhouse structure or associated site earthworks); and
         Developed case (representing the inclusion of the greenhouse structure and associated site
          earthworks).
For the existing condition, the model topography was supplemented with detailed survey information
of the immediate site and surrounds. The detailed survey was included to otherwise more accurately
reflect site topography in respect to the LiDAR information contained within the model. As the
detailed survey reflects the current site conditions and therefore includes since constructed works at
the site (i.e. greenhouse, pond and associated earthworks including existing bunds), it was necessary
to modify the survey information to otherwise exclude the since constructed works and to reflect a
pre‐development site arrangement. This ensured that a representative topographic condition was
included in the existing case model with associated enhancement using the detailed site. No other
change was made to the model for the purposes of the existing case scenario. The revised model was
subsequently re‐analysed for the 10% AEP and 1% AEP design flood events to provide base case
existing flood information at the site and on which comparisons would be made to the developed case
site conditions to quantify impacts.
For the developed case, a number of model scenarios have been analysed in an iterative manner and
for the purposes of minimising flood impacts from the since constructed works. This has included: ‐
          Inclusion and exclusion of since constructed earthwork bunds at the site (i.e. these being
           bunds 1, 2 and 3 as illustrated on the site layout plan included in Appendix A); and
          Inclusion of the greenhouse structure itself (i.e. again, illustrated on the site layout plan
           included in Appendix A).


3917‐01 / R01 v02 ‐ 31/08/2015                                                                        5