Narellan Creek Overland Flood Study (Vol 1) - Flipbook - Page 47
Narellan Creek Catchment
Flood Study
4.3
March 2022 Flood
4.3.1
WBNM Modelling
Rainfall
The March 2022 flood occurred as a result of rain falling over a 1 week period commencing
on 1st March. As shown in Figure 11 and Table 8, total rainfall depths across the catchment
during this event varied between 410 and 430 mm.
Accumulated rainfall totals for each active rain gauge over this 1-week period were used to
prepare the isohyet map shown in Figure 11.
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 Figure E1 in Appendix E and
indicates that the March 2022 event produced rainfall that was between a 20% AEP and 5%
AEP design rainfall event.
Rainfall Losses
An initial loss of 10 mm and a continuing loss rate of 1.48 mm/hour was adopted for
pervious surfaces as per the June 2016 simulation. An initial loss of 1 mm was adopted for
effective impervious surfaces with a continuing loss rate of 0 mm/hour.
Results
The WBNM model was used to simulate rainfall-runoff behaviour for the March 2022 flood
based upon the rainfall and rainfall loss information presented in the preceding sections.
Peak discharges for each WBNM model subcatchment for the March 2022 flood are
included in Appendix F.
The hydrographs generated by the WBNM model were subsequently routed through the
TUFLOW model. Further discussion on the TUFLOW model simulation, are provided below.
4.3.2
TUFLOW Modelling
Boundary Conditions
Discharge hydrographs generated by the WBNM hydrologic model were used to define
inflows to the TUFLOW model.
The downstream boundary condition for the TUFLOW model was defined based on
recorded water levels at the Camden Weir stream gauge for the March 2022 event. This
was incorporated into the TUFLOW model as a time varying water level for the Nepean
River.
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