USC FloodStudyUpdate Report - Flipbook - Page 261
Bridge structures were modelled in the 2D domain. The primary structures are the South West Rail Link
bridges and the Bringelly Road twin bridges over South Creek (under construction). Details of these
structures were obtained from design drawings. Additional structures which were surveyed in the field and
large enough to influence flow behaviour were also included in the model. The bridge soffit and deck levels
are included in the TUFLOW model, with an estimate of the hydraulic obstruction and losses due to the
piers and deck. These loss coefficients were estimated using Reference 6. Most bridge structures were
assigned a blockage factor in line with ARR 2019 (Reference 1) blockage methodology. Some minor bridge
structures (such as footbridges) were assigned a nominal blockage factor of 5%.
Detention basin outlets should also have blockage considered. For basin outlets, all grated pits should have
a blockage factor of 25% and all headwall outlets should have 10% blockage applied.
4.8. Inflows
Inflows into the TUFLOW model are sourced from the XP-RAFTS simulated local runoff hydrographs for
each subcatchment. Where subcatchments drain to urban pits, the flow is applied to 2D cells at the pit inlet.
Elsewhere, the subcatchment flow is applied to a group of 2D cells located at the subcatchment outlet (the
lowest point of the terrain).
For Bonds Creek, which is modelled from Camden Valley Way in the TUFLOW model, the total catchment
flow to this point is applied at the model boundary.
4.9. Downstream Boundary
For the creeks that cross Bringelly Road, a stage-discharge boundary was applied at least 250 m
downstream of Bringelly Road. The stage discharge relationship is automatically calculated by TUFLOW,
given the cross section of each creek or tributary and a channel slope.
There several other small catchments upstream of Camden Valley Way that discharge east into Bonds
Creek. At these locations, a stage-discharge boundary was also applied, or in some circumstances culverts
that flow under Camden Valley Way and out of the model were extended and have a fixed water level
applied at their downstream end.
4.10. Running the Model
The model is to be run with TUFLOW version 2018-03-AE in single precision (iSP) mode. The model
should be run using the HPC engine and typically runs quicker on a graphics card as opposed to multiple
CPU cores.
The model requires events and scenarios to be defined to run as follows:
EP. Valid options for this event variable are [50pc, 20pc, 10pc,
5pc, 2pc, 1pc, 1in200, 1in500 or PMF].
r other design events, this is a four
AEP are summarized in Table 3.
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