BBNE00529_0002_0001-REP-001-1-73 Eumundi-Noosa Rd SMP

  4.1.4       Existing Detention Basin – ARR Update
An additional assessment was completed of the above assessment of the existing detention basin using the updated IFD values
recommended as part of a recent ARR update. From this the IFD values increased by a factor of between 1.12 to 1.18, depending on the
duration.

A comparison of the existing and mitigated peak flows at the Site outlet is presented in Table 4.7. The results show that a minor increase in
peak flows is expected in 63%, 50%, 20%, 2% and 1% AEP, with reductions in the 10% and 5% AEP events. These results are consistent with
those presented in Table 4.6, with the update to IFD effectively increases the magnitude of e ach event compared to the previous assessment.
As such, it is considered that these minor increases would not result in actionable nuisance, and the outcome remains consistent with the
approved SMP. Further to this, the gap flow from the townhouse site (refer 4.3) is approx. 0.19 m3/s in the 1% AEP, which would report
south downs Starboard Street (away from basin) and improve results further in the 2% and 1% AEP events.

TABLE 4.7: PEAK DISCHARGE COMPARISON – EXISTING VS MITIGATED SCENARIOS


 Scenario               63.2% AEP        50% AEP          20% AEP          10% AEP         5% AEP           2% AEP           1% AEP

 Existing (m3/s)        0.76             0.91             1.40             1.76            2.07             2.43             2.73

 Mitigated (m3/s)       0.81             0.97             1.42             1.69            2.05             2.53             2.87

 Difference (m3/s)      0.05             0.06             0.02             -0.07           -0.03            0.10             0.15




73 EUMUNDI - NOOSA ROAD, NOOSAVILLE I BBNE00529_0002_0001-REP-001-1                                                                       16