Narellan Creek Overland Flood Study (Vol 1) - Flipbook - Page 42
4
COMPUTER MODEL CALIBRATION
4.1
Overview
Computer flood models are approximations of a very complex process and are generally
developed using parameters that are subject to natural variability. This includes catchment
roughness as well as blockage of hydraulic structures. Accordingly, the model should be
calibrated using rainfall, flow, and flood mark information from historic floods to ensure the
adopted model parameters are producing reliable estimates of flood behaviour.
Calibration is typically completed by routing recorded rainfall from historic floods through
the hydrologic model and comparing simulated flows against recorded flows at stream
gauge locations. Unfortunately, there are no stream gauges located within the catchment.
Therefore, it was not possible to complete a full calibration of the hydrologic model
developed for this study.
However, surveyed flood mark information along with descriptions of flood behaviour were
provided by the community as part of the community consultation for several historic
floods. Moreover, there are several rainfall gauges located within and near to the
catchment. Therefore, it was possible to jointly calibrate the computer models by routing
recorded rainfall from the rain gauges through the hydrologic model. The flows from the
hydrologic model can then be applied to the hydraulic model and simulated floodwater
levels and depths can be validated against surveyed flood levels as well as floodwater
depths and flood photographs provided by the community.
As documented in Chapter 2, the following events provided the most abundant surveyed
flood level and community information and were selected for model calibration:
June 2016
March 2022
July 2022.
Further information on the outcomes of the model calibration is provided in the following
sections.
4.2
June 2016 Flood
4.2.1
WBNM Modelling
Rainfall
The June 2016 flood occurred as a result of rain falling between the 4th and 7th of June. The
rainfall was generated by an East Coast Low that produced significant rainfall along the
coast of NSW. As shown in Plate 10, parts of the NSW coast experienced more than
400 mm of rainfall. However, as shown in Table 8, the Narellan Creek catchment
experienced rainfall totals of between 280 and 310 mm.
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