Narellan Creek Overland Flood Study (Vol 1) - Flipbook - Page 49
Narellan Creek Catchment
Flood Study
The comparison in Table 10 show that most simulated flood levels agree to the surveyed
flood mark elevations to within 0.2 metres. The average difference between simulated and
surveyed levels is better than 0.1 metres.
As with the 2016 comparisons, more significant differences are predicted at some locations.
These more significant differences coincide with flood marks elevations that are typically
inconsistent with nearby flood marks and may indicate less reliable survey information. This
appears to be most common in heavily vegetated locations where the GPS survey accuracy
can be limited by a lack of satellite coverage (this was also noted in the 8Update of Narellan
Creek Flood Study9).
The comparison in Table G2 also indicates that anecdotal reports of inundation extents and
depths are being well reproduced by the model.
4.4
July 2022 Flood
4.4.1
WBNM Modelling
Rainfall
The July 2022 flood occurred as a result of rain falling over a 5-day period (i.e., from 1st July
to 6th July). As shown in Figure 12 and Table 8, total rainfall depths across the catchment
during this event varied between 195 and 230 mm.
All rainfall gauges that were active during the event were incorporated into the WBNM
model to represent the spatial variation in rainfall event, while the temporal distribution of
rainfall was defined based upon the Camden Golf Course gauge (Gauge #568156). The total
rainfall depth that was applied to each subcatchment as part of the simulations is provided
in Appendix F.
The continuous rainfall information was also analysed relative to design rainfall-intensityduration information. This information is presented in as Figure E1 in Appendix E and
indicates that the July 2022 event produced rainfall that was typically less than a 20% AEP
event. Accordingly, the July 2022 event appears to be the smallest of the three calibration
events.
Rainfall Losses
The rainfall losses adopted for the June 2016 and March 2022 simulations were also
retained as part of the July 2022 simulation.
Results
The WBNM model was used to simulate rainfall-runoff behaviour for the July 2022 flood.
Peak discharges for each WBNM model subcatchment for the July 2022 flood simulation are
included in Appendix F.
A comparison of the peak discharges listed in Appendix F confirms that the July 2022
produced the lowest peak discharges of the three calibration events while the June 2016
event produced the highest.
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