Appendix D - Flood Assessment

R1593: FLOOD ASSESSMENT – 9A JIRRIMA CRESCENT, COOROIBAH



4.5.             RESULTS – FLOOD MAPPING                                                      5        SUMMARY
Flood maps are provided in Appendix B, representing:                                          The modelling undertaken as part of this assessment demonstrates the proposed
                                                                                              driveway can be constructed without causing adverse flood impacts for neighbouring
       +      Pre-development Peak Water Level – 1 % AEP                                      properties. The proposed driveway also remains trafficable during the critical
                   o Drawing No. D02                                                          duration 1 % AEP storm event, and therefore complies with the requirements of
       +      Pre-development Maximum Depth – 1 % AEP                                         Noosa Council.
                   o Drawing No. D03
       +      Post-development Peak Water Level – 1 % AEP                                     2 x 1200 x 300 mm box culverts are required under the main flowpath, while an
                   o Drawing No. D04                                                          additional 1200 x 300 mm box culvert is proposed to the west to ensure ponding
       +      Post-development Maximum Depth – 1 % AEP                                        does not occur in an existing low point of the site.
                   o Drawing No. D05
       +      Post-development Maximum Depth – 1 % AEP – Depths Greater than 200mm
                   o Drawing No. D06
                                                                                              This report and associate modelling have been prepared by Steven Chamberlain of
       +      Post-development Velocity x Depth – 1 % AEP
                                                                                              Topo (RPEQ 15,545).
                   o Drawing No. D07
       +      Afflux Assessment – 1 % AEP event
                   o Drawing No. D08

The results of this assessment indicate there are no adverse impacts in terms of
flooding for the upstream or downstream properties, and the building envelope for
the proposed lot can be provided outside of the flood extents. An extract of the
afflux assessment plot is included as Figure 7.

4.6.             RESULTS – DRIVEWAY FLOODING

An assessment has been made of the flow regime at the proposed driveway crossing
during the 1 % AEP event to ensure it complies with the requirements of QUDM.
QUDM requires for transverse flow such as over a causeway:

       +      Maximum flow depth, dg ≤ 200 mm
       +      The product of flow depth and velocity shall be limited by the formula d g ,.
              Vave <= 0.3 m²/s (risk to life).

The velocity-depth plots demonstrate the product of flow depth and velocity is less
than the limiting criteria and the depth of flow is less than 200 mm. Therefore the
proposed driveway remains trafficable during the 1 % critical duration storm event.
An extract of the maximum depth plot for depths greater than 200 mm only, and the
velocity-depth product plots are included as Figure 8 and Figure 9 respectively.




Environment. Engineering. Education.                                                                                                                                      PAGE 8