2019-12-16 GC Agenda - Item 5 - Attachment 1 - Noosa Spit Shoreline Erosion Management Plan-Part 1

Noosa Spit SEMP Final Report                                                                            41
Numerical Modelling of Entrance Configurations




3.6     Entrance Configuration Assessment
        The Model has been used to investigate historical and conceptual river entrance configuration and
        the relationship with erosion potential at Dog Beach and lower river water levels under normal tidal
        conditions. In addition to the ‘existing’ (2019) case the following scenarios were considered:

        • 1986/87 ‘east-west’ aligned entrance channel condition, informed by historical aerial imagery.

        • 2010 ‘northeast-southwest’ aligned entrance channel condition, informed by historical aerial
          imagery and bathymetric survey data provided by Council.

        • Dog Beach breakthrough entrance condition, hypothetical breakthrough to Noosa Sound.

        • Post 1 in 100 (1%) Annual Exceedance Probability (AEP) river flood entrance condition, input
          design river flow conditions informed by the Noosa River Flood Study (WMA Water, 2017).

        The model representations of these bathymetric/morphological conditions are shown in

        The testing of each scenario involved the following steps:

        (3)    Update of the model bathymetry using the bathymetric representation of the entrance
               configuration of interest. In the case of the flood event, this involved simulating the
               morphological response to the design river flow with the 2019 bathymetry used to define the
               model ‘initial condition’.

        (4)    One-month simulation of sediment transport and morphology under typical tidal conditions.
               This allows the modelled bed to ‘warm-up’.

        (5)    Simulation of ‘normal’ spring and neap tidal conditions to understand the system response to
               the morphological change.

        The key findings are presented below and have been summarised using maps that illustrate the
        ‘impact’ (or difference) relative to the entrance condition in March/April 2019.




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