1909-13367 SRA referral response approved docs

4. 2       Dev elo ped C a se R e s ult s

The developed model results detailed below show the maximum water level at the key locations shown
in figure 7 above. The developed models differ from the existing case through the following ways.
           Filling of development footprint to approximate finished surface levels

           Modification of proposed access servicing development and proposed bridge to match
            proposed finished surface levels
           Modification of hydrology to match increase in impervious area and discharge location (through
            proposed stormwater detention system detailed in separate stormwater management report).
            Stormwater detention proposed in the separate SWMR has been incorporated into developed
            cases for events 50% - 1% AEP.

           Modification of extents of Manning’s Roughness areas due to clearing of vegetation for
            construction of proposed bridge

The peak flows downstream of the development site have been extracted from flow line 10 to show the
effect of the proposed bridge on the existing flow conditions (see figure 5 above for the location of flow
line 10).

The developed catchment characteristics are detailed in table 7 above.


4.2.1 50 % Ae p Re su lt s ( De v elop ed no b loc k ag e)

The peak water level during the above event at reporting point 1 was 105.82m AHD. The peak water
level at point 2 is 104.31m AHD. The above peak water elevations are approximately 0.03m lower than
the peak water elevation during the existing case. This shows that the proposed bridge structure and
development does not create any additional nuisance during this event.

The peak flow at flow line 10 was 18.41m3/s. This shows a decrease of 0.96m3/s compared to the
existing case.


4.2.2 50 % Ae p Re su lt s ( De v elop ed w ith blo c ka g e)

The peak water level during the above event at reporting point 1 was 105.82m AHD. The peak water
level at point 2 is 104.46m AHD. The above peak water levels show no increase at point compared to
the developed case without blockage. Point 2 shows an increase of 0.15m compared to the developed
case without blockage.

The peak flow at flow line 10 was 18.41m3/s as per the above case without blockage.


4.2.3 20 % Ae p Re su lt s ( De v elop ed no b loc k ag e)

The peak water level during the above event at reporting point 1 was 106.09m AHD. The peak water
level at point 2 is 104.62m AHD. The peak water elevation for the developed case at point 1 is 0.03m
lower than the existing case. Point 2 shows a decrease of 0.02m compared to the existing case.

The peak flow at flow line 10 was 26.80m3/s. This is 1.38m3/s less than the existing case.


4.2.4 20 % Ae p Re su lt s ( De v elop ed w ith blo c ka g e)

The peak water level during the above event at reporting point 1 was 106.13m AHD. The peak water
level at point 2 is 104.75m AHD. The peak water elevation has increased at each point compared to




                                                   Flood Study                                         26
S19-007                                     122 & 144 Myall St, Cooroy