BsmFinal_1

3.5     Impact Of Floodway Revegetation And Full Culvert Blockage

A final model run was undertaken for a worst-case scenario involving climate change, completely
blocked culverts within and downstream of the site, and full revegetation of the floodways (to a
Manning’s n of 0.15) through and downstream of the site. The consequent 100 year flood levels on the
site are summarised in Table 5, below, to indicate the minimum required house floor levels:

Table5: Maximum 100 Yr Flood Levels With Climate Change, Revegetation And Fully Blocked Culverts
 Node 100 Year Worst-Case Flood Level

 N44                   91.77
 N45                   91.68
 N46                   91.55
 N47                   91.40
 N48                   91.49
 N49                   91.45
 N50                   91.44
 N51                   91.39
 N52                   91.31
 N53                   91.31
 N54                   91.31
 N58                   92.82
 N59                   91.98
 N60                   91.50
 N61                   91.37
 N62                   91.30


3.6 Depth -Velocity Parameters On Causeways

The critical points for access immunity and safety are the two culverts under the driveway leading to Lots
2 and 3, with driveway sag levels of 91.035 over both culverts. The XPStorm model results indicate a
flood immunity of 15 to 20 year for these crossings, or comfortably more than the 10 year minimum
standard required, and with DxV parameters of 0.07 / 0.08 during a 100 year storm. In the climate change
scenario, these crossings will be overtopped by about 0.03 metre (i.e. 3 centimetres) during a 10 year
storm, with the 100 year DxV parameters increasing to 0.11 / 0.12, easily satisfying the requirements of
QUDM/ARR.

The driveway causeway to Lot 4 will be set at the 100 year flood level and hence will have a DxV of zero
in a 100 year storm.
.




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      Brisbane Stormwater Management Pty Ltd Document File: ChurchSt.Doc