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

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




7         Hydraulic Analysis

7.1       Introduction
The site is not affected by regional or tidal flooding. The level of Mean High Water Spring Tide (MHWS) in the
nearby Noosa River at Tewantin is RL 0.61 mAHD (Maritime Safety Queensland, 2015). Due to the site being
at a level of approximately RL 9.0 mAHD, only local flows from the surrounding sub-catchments were
considered for this hydraulic investigation.

7.2       Model Setup
To determine the effects of the proposed development on surrounding properties, a TUFLOW model was
developed. The inputs into the model are outlined below;
> Hydrological (flow) information;
> Topography (LiDAR);
> Key drainage infrastructure (1D);
> Land uses;
> Key drainage infrastructure; and
> Model boundary conditions.
Flow information for the TUFLOW model was obtained from the hydrological modelling described earlier in this
report (Section 4).
LIDAR topographical data was obtained from the Department of Natural Resources, Mines and Energy
(DERM), 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 described above. The downstream boundary condition was modelled free flowing due to the
steepness of the topography. A sensitivity analysis of the tail water level was conducted by setting the water
level to RL 5.1 mAHD. This analysis found that by raising the standing tail water level, the maximum flood
levels on the site do not increase. This shows that the flooding behaviour on the site is not sensitive to tail
water conditions and as a result the assumed tail water conditions can be deemed adequate.
Modelling was performed with a cell size of 2 metres. This size was deemed to provide sufficient resolution
while ensuring reasonable run times. Mannings n values are shown in Table 7-1 with layer extents in Appendix
B.
               Mannings ‘n’ Values
 Material ID    Land Use     Manning's Number
 2              Road         0.015
 3              Rural        0.050
 5              Industrial   0.020
 6              Buildings    0.030




V190428 | 10 September 2019 | Commercial in Confidence                                                        23