Response to Information Request 10-6-2025 Overland Flow Assessment · OPW25/0042

CONTENTS
1.      Introduction                                                                                                                                                                                              1
        1.1         Site Characteristics                                                                                                                                                                          1
        1.2         Regional Flooding                                                                                                                                                                             2
        1.3         Project Data and Guidelines                                                                                                                                                                   2
        1.4         Performance Criteria                                                                                                                                                                          3

2.      Overland Flow Assessment                                                                                                                                                                                  4
        2.1         Local Hydrology Model                                                                                                                                                                         4
                    2.1.1          Catchments                                                                                                                                                                     4
                    2.1.1          Modelling Parameters                                                                                                                                                           6
                    2.1.2          Summary of Peak Flows                                                                                                                                                          6
        2.2         Local Flood Model                                                                                                                                                                             6
                    2.2.1          Model Setup                                                                                                                                                                    6
                    2.2.1          Results                                                                                                                                                                      10
                    2.2.1          Sensitivity Results                                                                                                                                                          14
        2.3         Lawful Point of Discharge                                                                                                                                                                   16

3.      Conclusion                                                                                                                                                                                              17
4.      Qualifications                                                                                                                                                                                          18
Appendix A: Site Layout                                                                                                                                                                                         19
Appendix B: Engineering Design Plans                                                                                                                                                                            20
Appendix C: Proposed Flood Maps                                                                                                                                                                                 21

Tables
Table 2.1: Existing and Developed Catchment Parameters ................................................................................................................................. 4
Table 2.2: Key modelling parameters - Hydrology ............................................................................................................................................... 6
Table 2.3: Peak Discharge .................................................................................................................................................................................... 6
Table 2.4: Adopted manning’s ‘n’ roughness....................................................................................................................................................... 7
Table 2.5: Summary of Finished Floor Levels and Flood Immunity.................................................................................................................... 11

Figures
Figure 1.1: Site Locality ........................................................................................................................................................................................ 1
Figure 1.2: NSC Flood Hazard Mapping ............................................................................................................................................................... 2
Figure 2.1: Catchment Plan .................................................................................................................................................................................. 5
Figure 2.2: TUFLOW Setup ................................................................................................................................................................................... 8
FIGURE 2.3: MANNING’S ‘N’ VALUE..................................................................................................................................................................... 9
Figure 2.4: Excerpt of Flood Depth and DV Map - 1% (2100) AEP ..................................................................................................................... 10
Figure 2.5: Freeboard Assessment..................................................................................................................................................................... 12
Figure 2.6: Excerpt of Severe Storm depth map - 1% (2100) AEP Fully Blocked ................................................................................................ 13
Figure 2.7: Sensitivity 1 – Increased Flow Path Roughness - 1% (2100) AEP Fully Blocked – Depth and Hazard............................................... 14
Figure 2.8: Sensitivity 2 – Blocked RIP - 1% (2100) AEP Fully Blocked – Depth and Hazard .............................................................................. 15
Figure 2.9: Sensitivity 3 – Partially Blocked RIP - 1% (2100) AEP Fully Blocked – Depth and Hazard................................................................. 16




NOOSA CALILE I BBNE01676-0001-REP-001-1                                                                                                                                                                          iii