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

              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 to sub-item 42:
Additional flood modelling has been provided in Appendix H which includes updated hydraulic
modelling and assumptions refined based on Council’s sub-item 42, parts (a) to (f).
In regards the specifics parts of sub-item 42, the following additional information is provided:
Section 7.2 of the report, notes that a TUFLOW model was developed from the following inputs:

•     Hydrological (flow) information;
•     Topography (LiDAR);
•     Key drainage infrastructure (1D);
•     Land uses;
•     Key drainage infrastructure; and
•     Model boundary conditions.

The LIDAR topographical data was obtained from State Government records and was used as the key
input to represent the existing scenario topography. Minor changes to the existing topography were
made to ensure known flow blockages were included. This LIDAR data was then
modified in the TUFLOW model using ‘2d-z shapes’ to represent the changes as a result of the
development with the building footprint areas and carpark raised above the flood level.

Existing drainage infrastructure details were sourced from Noosa Council’s Enterprise Mapping
System. Upgraded/new drainage infrastructure was sized and input into the developed scenario
hydraulic model. Drainage networks in both the existing and developed case were modelled with a
blockage factor of 20%.

The boundary conditions for the model consisted of ‘local’ inflows from each of the surrounding sub-
catchments as indicated by Council.

In response to the specific items parts (a) to (f) below:



    Ltr-20190925-IR Response-Noosa Marketplace_FINAL                                                   77