H - Revised Integrated Water Management Plan by Cardno (inc MUSIC file) (13.09.19)

                                                                                                 Integrated Water Management Plan
                                                                                         Noosa Marketplace : 2-20 HOFMANN DRIVE



7.4.4                   Impacts of Development
The impacts to peak flood levels at the reporting points are summarised in Table 7-4. As outlined above, the
proposed development forms a partial blockage of the existing flow path and hence slightly increases the peak
flood levels North of the development area within the Eenie Creek Road reserve during events equal or greater
than a 10% AEP. It is noted that during the existing case 1% AEP, flood depths of up to 1 metre already exist
at this location with the existing topography acting as a detention basin. Minor increases are shown in the
drainage reserve at the legal point of discharge.
To the north of the site, increases in flood levels are generally less than 150 mm during the 1% AEP event.
These increases extend approximately 2 - 4 metres beyond the site boundary (Figure 7-5). Increases are
confined to the road reserve in a bush land area that is inaccessible to the public and result in a minor increase
in flood extent area.
Despite this location being inundated by floodwaters, the maximum 1% AEP water surface level at the northern
boundary is approximately 1.2 metres below the Eenie Creek Road pavement level in the developed case.
Therefore, the proposed development further enhances the existing detention function with no additional risk
to persons, property, environment or infrastructure at this location.
Due to the enhancement of the natural detention basin by the development and site drainage improvements,
reductions in peak flood levels during the 1% AEP event are indicated along a significant section of Hofmann
Drive. (Appendix C)
Figure 7-5 demonstrates the difference in water surface profiles between the existing and developed case 1%
AEP events at P4.

                                                             P4 Surface Profiles

                      10
                                  Property Boundary
                                  Distance = 0
   Elevation (mAHD)




                      9.5



                       9
                                                                         Eenie Creek
                                                                         Road Verge
                      8.5



                       8
                            0             5           10     15     20       25        30          35         40         45
                                                                    Distance (m)

                                       Existing 1% AEP WSE        Developed 1% AEP WSE            Ground Surface


Figure 7-5                      P4 Water Surface Profile




V190428 | 10 September 2019 | Commercial in Confidence                                                                        29