USC FloodStudyUpdate Report - Flipbook - Page 255
3.4. Design Storms
The modelled design AEP storms adopt ARR 2019 methodology (Reference 1). The data used to derive
these storms is provided with the model. The catchment has been split into 3 IFD zones, corresponding to
the 3 models, as outlined in Table 2. The design rainfall depth obtained at the IFD location noted was
applied to all subcatchments within the major creek catchment areas listed in Table 2.
Table 2: IFD Zones Adopted in the XP-RAFTS Model
Zone / Model
IFD Location
Catchments Covered
East
33.9819°S 150.791°E
Bonds Creek, Scalabrini Creek, Kemps Creek, Rileys Creek
Mid
33.9906°S 150.754 °E
South Creek
West
33.9676°S 150.723 °E
Lowes Creek, Thompsons Creek
Three storms were selected for each event to represent the critical duration and mean temporal pattern in
the upper, middle and lower catchment areas. The same storms were selected for each temporal pattern
bin. A summary of the adopted storms is contained in Table 3. The design flood results for a particular
event are an envelope of the three corresponding storms.
Table 3: Design Storm Events Selected
Bin
Frequent
Intermediate
Rare
N/A
Events
Duration (mins)
Temporal Pattern ID
(Ensemble No.)
50% AEP
20% AEP
30
4523 (9)
540
4771 (5)
1440
4879 (6)
60
4568 (6)
360
4591 (1)
1080
4826 (6)
10% AEP
5% AEP
2% AEP
1% AEP
0.5% AEP
0.2% AEP
30
4402 (1)
360
4694 (5)
720
4785 (8)
PMP
60
GSDM
120
GSDM
240
GSDM
Maximum Precipitation (PMP, Reference 2). Spatial distribution of the PMP was undertaken for the Upper
South Creek catchment (including Rileys Creek and Lowes Creek), with Scalabrini, Kemps and Bonds
Creeks being assigned ellipse A in the lower half and ellipse B in the upper half, and smaller tributaries to
Bringelly Road being assigned to ellipse A.
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