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

6.4 GridFlow flood extent estimation                           The absolute flood levels and flood flow velocities




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                                                               determined by the GridFlow analysis are not suitable for




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The GridFlow flood extent estimation project was               setting minimum floor levels or for estimating flood flow




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conducted by the Sunshine Coast Council across all             forces. More detailed, local calculations and observations




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catchments of the Sunshine Coast.                              would be required to inform these values. GridFlow flood
                                                               extents may be a useful trigger for highlighting potentially
The project’s aim was to prepare a preliminary estimate of
                                                               flood sensitive locations that are beyond the limits of
flood inundation extents for a 1% AEP flood event, for all
                                                               existing flood models.
identified water courses.

The analysis process utilised to determine the preliminary
                                                               6.5 Key initiatives – Flood mapping
flood extent was based upon GIS algorithms which
                                                               The implementation plan will include initiatives that aim
determined contributing catchment areas at regular
                                                               to –
increments along a waterway and then estimated flood
discharge for each location using standard Rational            •   Review the flood hazard area mapping for the Ringtail
Method computations.                                               Creek sub-catchment (Cooroibah area) following
                                                                   completion of the Noosa River Flood Study Upgrade.
A flood extent was then estimated at each location by
                                                               •   Update disaster management flood mapping series to
applying the computed flood discharge to the standard
                                                                   reflect flood mitigation works and completion of the
Mannings equation based upon a cross section derived
                                                                   Noosa River Model Upgrade.
from a Digital Elevation Model (DEM). The resulting
flood extent provides a preliminary estimate for flood         •   Prepare and maintain flood mapping layers showing
inundation extents. These estimated flood extents do not           flood levels, flood extents and associated minimum
consider local channel features or structures which may            floor levels for existing and future climate.
influence the actual extents of inundation.                    •   Include 1% AEP flood contour mapping and associated
                                                                   minimum floor levels mapping, 1%AEP flood extents
In the absence of more detailed local flood modelling the
                                                                   and depths to Council’s mapping system for officer
GridFlow flood estimation method is a useful first-pass for
                                                                   assess.
identifying locations that may be subject to potential flood
inundation from a 1% AEP flood event.




                                                                                   Noosa Council | Flood Management Plan | Page 24