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

Three other minor historical events (January 1976, May        Existing climate scenarios are used to inform the disaster




                         T
1985 and June 1985) were used for model verification.         management mapping for the Noosa River. This model




                       F
                                                              continues to utilise the combination of RAFTS hydrological




                     A
The findings of this study and subsequent associated
                                                              modelling and MIKE11 hydraulic modelling that was




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investigations have formed the basis of planning and
                                                              established by JWP in 1995.




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decision making in the River for almost 20 years.

In late 2013, prior to de-amalgamation and as part of a       5.1.2     Emerging Issues and Concerns for the
region-wide flood hazard mapping project, the Sunshine                  Noosa River
Coast Council (SCC) revised and re-ran the design event       5.1.2.1   Foreshore Erosion          and     Flood      Velocity
temporal patterns for all flood models within the Noosa                 Distributions
Council area.
                                                              Several locations along the foreshores of the lower Noosa
The revised design rainfall patterns represent Duration       River and Weyba Creek are currently experiencing shoreline
Independent Storm (DIS) patterns derived from Australian      erosion. In some locations the erosion is threatening
Rainfall and Runoff (AR&R) Intensity Frequency and            infrastructure, reducing accessibility and impacting upon the
Duration (IFD) curves for this region.                        amenity of the shoreline. Council is seeking to understand
                                                              the origin of the erosive forces which are contributing to
For the Noosa River the SCC 2013 update also included
the modifications to cross section depths for the river       the shoreline erosion with the view of developing further
bathymetry near to the river mouth (as applied in the 1995    mitigation plans and works to reduce these forces and where
model) and the inclusion of dynamic tailwater boundary        possible to rehabilitate these sites.
conditions for Laguna Bay.
                                                              Unfortunately, the 1D structure of the original Noosa
The dynamic tide boundary assumed the probability of the      River Flood Study was only suitable for providing a
river flood matched the probability of the storm tide with    broad understanding of the anticipated extents of flood
the peak of the storm tide timed to coincide with the peak    inundation from a variety of flood events and provided
of the rainfall.                                              limited insight into the distribution of flood velocities
                                                              across the river and adjacent floodplains.
The SCC 2013 model updates included model scenarios for
both existing and future climates. Future climate scenarios   Whilst still valid, 1D modelling is rapidly being replaced
were used as the basis for the 2016 amendment to the          by 2D modelling which allows improved representation
Planning Scheme Overlay’s flood hazard area.                  of the terrain surfaces and a more contiguous modelling
                                                              approach. 2D models are typically favoured in locations
                                                              with relatively flat waterway gradients and adjacent flood
                                                              plains, such as in the lower reaches of the Noosa River
                                                              system. Contemporary desktop computing capabilities
                                                              have also increased the useability of 2D models. 2D models
                                                              provide greater insight into the flow paths and associated
                                                              flow velocities of waterways and floodplains. The original
                                                              1D hydraulic flood model was unable to provide any
                                                              reliable flow path or flood velocity information. Hence, to
                                                              address the need to better understand the erosive processes
                                                              associated with flow velocities within the River an upgraded
                                                              2D hydraulic flood model has been commenced.




                                                                                      Noosa Council | Flood Management Plan | Page 16