USC FloodStudyUpdate Report - Flipbook - Page 264
5.3. Design Events to be Modelled
The assessment should demonstrate there are no significant adverse off-site impacts for the 20%, 5% and
1% AEP events, for all three event durations specified in Table 3.
The PMF 60 minute duration should also be modelled, to identify high hazard flood extents in and around
the site for proposed development conditions.
The storm events outlined in Table 3 should be simulated in both the XP-RAFTS model and TUFLOW
model, for both the pre-development and post-development scenarios.
5.4. Reporting Requirements
The following should be provided with the flood impact assessment report:
1. A mapped comparison of peak flood levels from TUFLOW should be provided (mapped
impact grids) for the 20% AEP, 5% AEP and 1% AEP events, including changes in flood
extents. Comparisons should be provided for the following scenarios:
a)
-run
and the results obtained are exactly the same as those provided with the model. This
map should show no change in 1% AEP peak flood levels (i.e. results for the 20% AEP
and 5% AEP is not required).
b) If the base case model has been revised by including detailed survey or nearby
approved development, a grid comparing the impacts of the base case model revision
for the 1% AEP event (i.e. results for the 20% AEP and 5% AEP is not required).
c) Impacts of the updates to the hydrologic model to represent proposed development,
without any landform or structure modifications in TUFLOW (i.e. just the impacts of the
change in hydrologic model parameters from proposed development) (only for the 1%
AEP event).
d) Impacts of the proposed development scenario in TUFLOW (including hydrology
changes plus all land-use, topography and structural changes etc. in the hydraulic
models) compared with the base case or revised base case as relevant (for each of
the three design AEP events).
For each design event the mapped results should be the envelope of the maximum results from
three storm durations simulated. The impact grid should be the difference between the envelope of
durations for the post-development scenario, versus the envelope of the three durations from the
base scenario. This grid should encompass the entire TUFLOW Model extent. Any impacts outside
the range of ±0.01 m should be mapped.
2. Peak flow hydrographs for both pre-development and post-development conditions for each
flow path at the downstream boundary of the site. Flow hydrographs are to be extracted from
TUFLOW, for both pipes and overland flow if relevant. Any downstream locations at junctions
on major creek systems should also be provided (for example, if the development is located
within the Lowes Creek catchment, hydrographs at the Lowes Creek and South Creek
junction should be provided. Flow hydrographs should also be provided just upstream of
Bringelly Road, for the creek to which the development discharges. The critical duration for
each event should be provided at each location.
WMAwater Pty Ltd
118112: 201030_USC_Regional_Model_User_Guide_Final: 30 October 2020
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