1909-13367 SRA referral response approved docs

2D Fill Areas

2D fill areas have been used to modify (either lift or lower) certain areas of the 2D mesh to reflect their
levels. An example of this is the development site which was lifted to reflect approximately the finished
surface level of the site.
Elevation Shapes

Similar to fill areas above elevation shapes are used to modify the 2D mesh levels from the underlying
DTM. This model has utilised elevation shapes to model the affect that the proposed creek crossing
would have (for instance the abutments of a bridge) on the flow widths and filling in the existing
floodplain. Elevation shapes vary from fill areas where each individual vertex of the polygon can be set
to a different elevation, where a fill area polygon is limited to a single elevation per polygon.
3.1.10 D ev e lop ed S it e Dr a i nag e

The proposed development consists of two hundred and forty five lots with associated hardstand and a
large central clubhouse. The proposed road access over the existing natural channel shall be designed
to limit the changes to the existing water course to ensure that the access does not cause increases to
the peak water level during the design flood events.

The developed catchments hydrology has been modified to reflect the increase in impervious
percentage of the development and catchment areas directed to each location. The proposed
development area to discharge downstream of the development (through proposed basins 1 and 2)
including the associated stormwater detention has been incorporated for all design storms up to the 1%
AEP event. The developed catchment discharges through a combination of a low level orifice and
overflow weir the location of which reflects the proposed stormwater management solution (see
separate SWMR by Westera Partners). All catchments that have been modified from the existing case
are highlighted in table 7 below. Catchment 1.05 has been split into catchments 1.05a and 1.05b as a
part of the development catchment will directed to the proposed bioretention basin (1.05a) and a portion
will discharge directly to the proposed golf course (1.05b). Basin 1 discharges catchment 1.05a while
basin 2 discharges the developed portion of catchment 5.01.




                                               Flood Study                                              21
S19-007                                 122 & 144 Myall St, Cooroy