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

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



4.2.4         Rational Method Verification
The peak flows determined using RAFTS were compared with peak flows determined using the Rational
Method. Catchments 2 and 3 were chosen for this comparison due to having clearly defined drainage lines
and catchment boundaries. C10 values were sourced using Table 4.5.3 of the Queensland Urban Drainage
Manual 2017. The results of this verification are shown in Table 4-3 below for the 1% AEP event. It was found
that the RAFTS model produced higher peak flows than the Rational Method for Catchments 2 and 3. The
RAFTS flows were therefore considered acceptable.
                 Rational Method Verification
 Parameter                                       Value
                                     Catchment 2      Catchment 3
 C10                                       0.7             0.7
 tc (min)                                10.68           9.07
 I (1yr,10min)                            102            102
 A (ha)                                   0.77             0.6
 Rational Method Flow (m3/s)              0.46           0.38
 RAFTS Peak Flow (m3/s)                   0.58           0.45
 Difference (m3/s)                        0.12           0.07



4.2.5         Results
Peak flows for each of the sub catchments are listed in Table 4-4 for the 1% AEP event. The critical storm
duration for 1%, 2%, 20% and 39% AEP events was determined to be 10 minutes, while, for the 5% and 10%
AEP events, the critical storm duration was 15 minutes. This difference in critical storm duration is considered
to be typical for models run with ARR 2019 rainfall patterns. In addition to the peak flows coming from each
catchment, the peak total flow from the development site was found to be 0.75 m3/s in the 1% AEP event.
                 1% AEP Peak Flows (m3/s)
 Catchment ID        Peak Flow (m3/s)       Catchment ID     Peak Flow (m3/s)

          1                  1.71                12                 0.05

          2                  0.58                13                 0.02

          3                  0.45                14                 0.06

          4                  0.52                15                 0.03

          5                  0.51                16                 0.01

          6                  0.03                17                 0.05

          7                  0.02                18                 0.07

          8                  0.85                19                 0.02

          9                  0.34                20                 0.04

        10                   0.37                21                 1.13

        11                   0.04




V190428 | 10 September 2019 | Commercial in Confidence                                                               12