2016-07-18 General Committee Meeting - Item 3 - Attachment 1 - Flood Management Plan

5.3 Six Mile Creek                                                  5.3.2       Cooroy Creek




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Currently Council’s flooding information for the main               In 2013 the Sunshine Coast Council commissioned Water




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watercourse and floodplain of Six Mile Creek is limited to          Technology11 to develop hydrologic and hydraulic models




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the findings of the Six Mile Creek Flood Study Upgrade9             for the township of Cooroy. The primary purpose of this
undertaken by Sunshine Coast Council in 2013 as a                   study was to prepare and calibrate a hydrologic (XP-
part of their regional flood hazard mapping project. The            RAFTS) and hydraulic model (TUFLOW) for the greater
flood model utilised by the Sunshine Coast Council was              Cooroy township area such that Council could then use
based upon an existing flood model originally developed             the model to undertake further analyses.
in 2001 by JWP10 to investigate a dam break scenario at
Lake Macdonald. This base model utilises coarse, sparsely           The hydrologic model included the analysis of the greater
spaced cross section data and does not include details of           catchment areas that contribute to the Cooroy Township
local road crossings. This 15 year old base model is a one          as well as immediate surrounds. Specifically, this included
dimensional hydraulic model which utilises the MIKE 11              Cooroy Creek, Six Mile Creek Left Branch, Cudgerie
modelling platform.                                                 Creek as well as tributaries and sections of the Six Mile
                                                                    Creek main branch. The hydraulic model developed as
The SCC 2013 model updates for Six Mile Creek include               part of this study extends approximately 1km upstream of
model scenarios for both existing and future climates.              the Bruce Highway downstream to approximately 500m
Future climate scenarios were used as the basis for the             downstream of the confluence of the Six Mile Creek main
2016 amendment to the Planning Scheme flood hazard                  branch and Six Mile Creek left branch. The model includes
area. Existing climate scenarios are used to inform the
                                                                    24 separate hydraulic structures located throughout the
disaster management mapping for the Noosa River.
                                                                    model area.

5.3.1      Lake Macdonald                                           In late 2013 Hydrology and Water Management
                                                                    Consulting Pty Ltd (HWMC) was engaged12 by Sunshine
In 2001 consultants JWP were engaged to determine flood
                                                                    Coast Council to undertake further updates to the Cooroy
levels downstream of the dam as a result of severe flooding
                                                                    flood model previously prepared by Water Technology.
combined with embankment failure. The model is a one
                                                                    The results of this model form the basis for the current
dimensional hydraulic model which utilises the MIKE 11
                                                                    disaster management mapping.
modelling platform.

In a 2007 update of a Failure Impact Assessment, the                Recent upgrades to the Bruce Highway have delivered
MIKE11 model was extended a further 15km downstream                 flood mitigation benefits to some properties immediately
in accordance with Department of Natural Resources and              downstream of the highway. The Cooroy flood study
Water (NRW) guidelines and recommendation from the                  model has been amended to include these works and
Sunwater Dam Safety Review.                                         the resulting inundation extents for the 1% AEP (future
                                                                    climate) scenario form the basis of the 2016 amendment
This model has ultimately been adopted as the basis for             to the Planning Scheme flood hazard area.
the Six Mile Creek flood study upgrade undertaken by
Sunshine Coast Council in 2013. Cross sections in the
lower 15km extension of the model were sourced from 5m
contour plans.


 9
  Six Mile Creek Flood Study Upgrade Final Report By Sunshine Coast Council February 2014
 10
    Noosa Shire Council Lake MacDonald Dam Break Flood Study by John Wilson and Partners June 2001
 11
    Cooroy Flood Study by Water Technology, July 2013




                                                                                       Noosa Council | Flood Management Plan | Page 19