Ltr-20190925-IR Response-Noosa Marketplace_FINAL (1)

•      The combined bioretention areas deliver an improved function than the previously proposed
       proprietary devices;
•      The bioretention areas will be designed and constructed in accordance with Healthy Waterways
       Water By Design Guidelines, which is accepted as best practice in Queensland; and
•      The indicative location of 3 rainwater detention tanks is shown on Figure 6-1 of the report.
In regards, the physical drainage infrastructures internal and external to the site the following
information is provided:

•      The lawful point of discharge for the site is the 4 1200 mm x 600 mm RCBCs under Hofmann
       Road, located adjacent to the South East boundary on Lot AB SP222982. Flows leaving the site
       will drain south along the eastern side of the site into these pipes;

•      For the post development scenario, an upgrade to the existing under sized 1200 mm x 300 mm
       RCBC at the site access from Hofmann Drive is required due to the increased flows along the
       eastern boundary of the site. It is proposed to upgrade this culvert to a 2400 mm x 700 mm
       RCBC, reducing the flows currently being diverted onto Hofmann Drive.

•      A 750 mm RCP is proposed to connect to the existing 750 mm RCP entering the site off
       Commerce Court. This pipe conveys flows around the development footprint and discharges
       upstream of the 2400 mm x 600 mm RCBC. This extension of the existing 750 mm RCP is only
       intended to convey flows in events up to the 39% AEP. The complete drainage networks for the
       existing and developed cases are shown in Appendix C.

•      The floodplain to the north of the building footprint retains floodwater and drains via a field inlet
       connected to the 750 mm RCP through the site via a 525 mm RCP. This drainage feature allows
       the area to the north to drain more efficiently after a flood event.

c) As detailed in Appendix B of the IWMP report, the existing and proposed roughness values are
   reconfirmed for roads, buildings, industrial and vegetated areas.

d) In coordination with the contour and detail survey information and RL’s requested in Issue 3, sub-
   item 11 above, a revised plan showing topographic differences between existing and proposed
   scenarios is included in Appendix H.

e) The following blockage assumptions have been applied in the model. As detailed in response to
   sub-item 42 part b above, infrastructure upgrades are proposed as part of the proposed
   development and these can form a reasonable and relevant condition of any future development
   approval.

f)     In coordination with response to Issue 13, sub-item 44 below for extreme flood impacts, a severe
       blockage / severe storm assessment has been completed. Based on the Noosa Council
       Enterprise Mapping system, there are no existing overland flow paths mapped. Nonetheless, it is
       recognised that previous development in Shire Business Centre locality and construction of the
       Hofmann Drive loop road have altered historic overland flow paths and these have been
       addressed in this response.
Overall, we note that the information provided is contextual to the proposed development only as a
response to localised events, and that flood events are not a major issue for the property based on the
intended layout and additional mitigation measures.




     Ltr-20190925-IR Response-Noosa Marketplace_FINAL                                                      79