Reference Documents RAL21 0035

 FLOOD ASSESSMENT
Flood protection measures are required to ensure the proposed future allotment can be safely accessed in all storm
events up to and including 1% AEP storm event (as discussed below, refer Section 3.1) and be flood immune to the
storm frequency level of Jirrima Crescent at the culvert crossing upstream of the subject site. Noosa Council flood
modelling data has been obtained for Jirrima Crescent which found that immunity is achieved up to the 50% AEP
storm event, while remaining trafficable for both the 10% and 1% AEP storms. Refer to Appendix B Council Flood
Modelling Results.

The project will involve an upgrade to the existing concrete causeway which currently services the rear of the subject
site to a culvert crossing. Modelling of the existing and proposed developed access road has been undertaken to
ensure that the proposed upgrade will not result in impacts that may result in damage to the upstream or
downstream properties and infrastructure.


     3.1. Available Data
The following data has been reviewed and used in preparation of this assessment.

          -     LiDAR Topographic Data – The 1m interval digital elevation model from the aerial LiDAR survey of the
                Noosa-Gympie 2015 project (vertical accuracy +/- 150mm, 1 sigma) used to develop digital terrain
                model.

          -     Aerial Photography – NearMap aerial imagery (2022) to designate surface characteristics to upstream
                catchments.

          -     GIS information – Noosa Council IntraMaps used to identify upstream culverts and piped road crossings.

          -     Noosa Council Flood Model Data – Used to identify the immunity requirements for the driveway access.

          -     Layout – Plan of Proposed Reconfiguration of Lot (21-5581AA) by Max Watterson & Associates

          -     Rainfall data – Bureau of Meteorology IFD data and ARR Data Hub parameters for Northeast Coast region
                (Latitude: -26.3509, Longitude: 153.0001, obtained 14/12/22)


     3.2. Catchment Hydrology

          3.2.1 Areas
In order to assess the peak flows at the existing causeway the upstream contributing catchment was determined
based on contour mapping of the locality. A catchment of approximately 0.65km² is conveyed through the existing
causeway as shown in Figure 2.2 – Existing Site Drainage Characteristics (Queensland Globe Watercourse
Identification Map, 2022).


          3.2.2 Rainfall Data
Rainfall data for the locality was obtained from the Bureau of Meteorology IFD charts, with the temporal distribution
of rainfalls provided using the patterns obtained from the ARR Datahub. The rainfall intensities have been increased
by a factor of 1.2 to allow for climate change impacts projected to 2100 climate conditions.

Models were run for 1%, 10% and 50% AEP storm durations of 30 minutes to 720 minutes for the ensemble of ARR
temporal patterns for each event. The duration of storms was extended by a minimum of 1 hour to ensure the full
impacts of the temporal patterns would be realised at the existing causeway.




Project number 20220089                                                                                  Page 9 of 23
File 20220089 Jirrima Cr SWMP.docx, 2023-05-09 Revision 0


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