Narellan Creek Overland Flood Study (Vol 1) - Flipbook - Page 56
Narellan Creek Catchment
Flood Study
Once the critical duration was determined for each AEP, a representative temporal pattern
was selected for that duration. The temporal pattern that generated the peak discharge
immediately above the median discharge was selected as the most representative temporal
pattern for each subcatchment. The adopted temporal pattern for each subcatchment along
with the peak discharge generated by the representative temporal pattern is also provided
in Appendix I.
The results of the hydrologic analysis also indicate many unique combinations of critical
durations and temporal patterns for each subcatchment. More specifically:
50% AEP: 51 unique critical storms
20% AEP: 45 unique critical storms
10% AEP: 46 unique critical storms
5% AEP: 49 unique critical storms
2% AEP: 47 unique critical storms
1% AEP: 46 unique critical storms
0.5% AEP: 44 unique critical storms
0.2% AEP: 45 unique critical storms.
5.3
Hydraulics
5.3.1
Boundary Conditions
Inflow Boundary
As discussed in the previous section, a WBNM hydrologic model was used to simulate the
transformation of rainfall into runoff and generate discharge hydrographs throughout the
catchment for each design storm. The discharge hydrographs generated by the WBNM
model was used to define inflow boundary conditions for the TUFLOW model.
However, as noted above, many unique critical durations and temporal patterns were
determined as part of the hydrologic analysis (i.e., more than 370 unique combinations of
AEP, duration and temporal patterns). Although the WBNM model runs in a matter of
seconds and can run a large number of storms in a relatively short amount of time, the
hydraulic model takes several hours to run a single storm. Therefore, it was not considered
feasible to run all unique combinations of storm durations and temporal patterns through
the hydraulic model in a timely manner.
Therefore, the WBNM results were reviewed to determine if a reduced number of temporal
patterns and durations could be applied without significantly impacting on the overall
hydrologic outcomes. A total of 4-6 unique storms were targeted for each AEP/design flood
that captured the majority of critical events.
The peak discharges generated by the most commonly
