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

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




8         Conclusions

Hydraulic modelling has demonstrated that the proposed development will have minimal impacts on the flood
levels within surrounding areas. Areas where minor impacts are shown are restricted to locations that are
inaccessible to the public and are inundated in current rainfall events.
The majority of the flood level increases resulting from the proposed development are contained within the
development area with the exception of the Eenie Creek Road reserve adjoining the development boundary
and drainage reserves to the south. Areas that show impacts off site are inaccessible to the public, posing
minimal risk to persons, the environment or infrastructure. 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.
To the south at the legal point of discharge, (environmental reserve) there are minor increases in flood levels
during the 39% and 20% AEP events. These increases are caused by improvements to the drainage system
removing water that currently flows along Hofmann Drive and passing it under Hofmann Drive into this area.
The insignificance of these minor flood level increases is demonstrated in Figure 7-8, with the developed flood
level still 1.5 m below the Noosa Civic Carpark.
Flood levels along Hofmann Drive to Rene Street decrease in all events as a results of minor increases on the
development site northern boundary area. Due to the development increasing storage in this natural flood
storage area, reductions in flood depths along a 200 metre section of Hofmann Drive from the site access to
Rene Street are anticipated for all flooding events.
RAFTS and MUSIC modelling has demonstrated that the proposed development can satisfy stormwater
quantity and quality requirements as per the SPP 2017, through the use of WSUD devices and stormwater
detention. On-site stormwater detention is required to ensure that peak discharges from the site are not
worsened. A detention tank with a minimum volume of 1500 m3 is proposed to mitigate flow increases from
the development footprint area.
A severe storm assessment has demonstrated that the development can proceed with no significant risk to
persons. The site remains accessible during the 1% AEP event, with limited access during the PMF event for
a short period of time.
Further detailed modelling of the stormwater quantity, quality requirements and flooding may be necessary
during the Operational Works stage once detailed design is completed.




V190428 | 10 September 2019 | Commercial in Confidence                                                        36