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

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



Issue – Flood Modelling
Further details of the flood modelling are required before an assessment of the suitability of the model can be
made.
Information Required
Provide further details of the hydraulic model assumptions and a revised assessment as necessary to address
the following:
a. Clarify model grid size and provide a plan showing location of 1-D elements in existing and proposed
scenarios
b. Provide a plan showing the locations of the proposed drainage upgrades/features described in the post-
development scenario (Section 6.4.3). Is the detention tank proposed to detain only the local site catchment
flows?
c. Provide plans of existing and proposed roughness values
d. Provide a plan showing topographic differences between existing and proposed scenarios
e. Provide further information on what blockage assumptions have been applied in the model consistent with
ARR2016 and QUDM. Particularly since it seems pipe upgrades are a significant component of the impact-
mitigation strategy being employed.
f. Provide a severe blockage/severe storm assessment in addition to the design blockages requested above.
It should be clarified whether the proposed 750mm RCP is completely replacing the existing overland flowpath
and if so, what the consequences are during a severe blockage or severe storm scenario. For clarity, complete
removal of overland flowpaths is not supported and there should be provision made for severe blockage such
that floor levels are not inundated in such an occurrence.
Response
Section 7 of the IWMP has been updated to cover points above with comments below.
    a) TUFLOW model cell size is 2 metres.
    b) Figure 7-3 Section 7.4.3 shows drainage proposed upgrades. Section 5 details that the detention tank
       will only mitigate local site flows.
    c) Existing and proposed roughness values are shown in Appendix B
    d) The topographical differences between the existing and developed case are shown in Appendix B
    e) A blockage factor of 20% has been applied to all pipes and culverts in the drainage network (Section
       7.2)
    f)   Severe storm assessment is contained in Section 7.5. Section 7.4.3 describes the functionality of the
         proposed 750 mm RCP. It is only intended to carry the flows for minor events around the northern
         portion of the site. Flows greater than the 39% AEP will use the flow path describe in Section 7.4.3.


Issue – Local Flood Impacts
The local flood impact maps provided with the IWMP demonstrate that flood depths external to the site are
predicted to increase as a result of the proposal. This is in conflict with Specific Outcome O17 of the Noosaville
Locality Code and Specific Outcome O33 of the Business Uses Code.
Information Required
Provide revised proposed plans and flood impact mapping which demonstrates compliance with Specific
Outcome O17 of the Noosaville Locality Code and Specific Outcome O33 of the Business Uses Code and
specifically demonstrates no flood impacts external to the development site boundary.
Response
The proposed development levels have been adjusted to ensure that impacts do not significantly impact on
neighbouring properties, road reserves or adversely affect safety or use of any land.
There are no anticipated significant adverse effects on the biodiversity, natural vegetation, native wildlife,
habitats, landscape quality, water quality or heritage values, including those related to changes to natural
drainage or disturbance to wetland systems. Areas where impacts are recorded are inundated for all events in
the existing case.

V190428 | 10 September 2019 | Commercial in Confidence                                                           6