Refernce Documents - RAL25 0001

                     For catchments with 0 % impervious, no runoff would occur for this storm making it
                     impossible to mitigate runoff to pre-development conditions. As such, Council needs
                     to accept that in allowing development, not all storm events and durations can be
                     mitigated to pre-developed discharge rates.


                     This report demonstrates that the storms that produce the critical peaks in discharge
                     (those that create the highest velocities, depth of flow and discharge for an AEP) for
                     the majority of AEP events and storm durations will not cause an actionable nuisance.



                     5.3     Flooding

                     To determine the extent of local flooding in the 1% AEP event a direct rain on grid TUFLOW
                     model was created to model the local catchment for the pre and post developed
                     scenarios. This model utilises the ARR ensemble temporal pattern, pre-burst rainfall and
                     initial and continuing losses for the pervious areas with rainfall applied directly to the
                     model grid. A 2m grid resolution was chosen for this model.


                     The pre developed model uses the Noosa 2015 LIDAR data to generate the existing
                     surface levels with the existing Hoy Road pipe crossing details added. The post developed
                     model includes the preliminary design surface for the internal road, the proposed 5x750
                     RCP’s under the Hoy Road causeway and reflects the causeway being raised by 100mm.


                     After comparison with the XP-Storm results a temporal pattern was chosen that produced
                     a 1% AEP peak discharge downstream of Hoy Road equivalent to the peak mean discharge
                     from the XP-Storm models. The results of this model run were used to generate 1% AEP
                     and 10% AEP (to demonstrate immunity to the causeway following propose works) flood
                     extent maps included in Appendix D. It should be noted that a 50mm cut off depth has
                     been applied to the model results.




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Document Set ID: 23448644
Version: 1, Version Date: 13/01/2025