Narellan Creek Overland Flood Study (Vol 1) - Flipbook - Page 17
Narellan Creek Catchment
Flood Study
River flood level to serve as the downstream boundary conditions, except for the 50% AEP
local catchment flood, which adopted a 50% AEP Nepean River water level.
Although this study was considered to reflect best practice at the time it was prepared, it
now suffers several limitations, namely:
Only major trunk drainage pits and pipes were included in the model
Hydrology was defined using the 1987 version of 8Australian Rainfall and Runoff - A
Guide to Flood Estimation9 (Engineers Australia). This has since been superseded by the
2019 revision.
Parts of the catchment have undergone significant development over the last decade.
As a result, the results no longer provide the best description of contemporary
catchment conditions.
The representation of some components of the various lakes and hydraulic structures
was limited (this is discussed further in Section 2.2.4).
2.2.3
Narellan Creek Flood Study Peer Review Reports (2014)
Three separate peer reviews of the draft 8Narellan Creek Flood Study9 (Worley Parsons,
2014) were commissioned by Camden Council due to some notable differences in the draft
design flood levels relative to the 8Harrington Park Hydrologic and Hydraulic Report9 (SMEC,
2000).
The first peer review report was prepared by WMAwater and is titled 8Peer Review of Draft
Narellan Creek Flood Study9 (2014). This peer review report recommended that the
hydrologic approach be updated by using a dedicated hydrologic model (rather than a direct
rainfall approach with an embedded design burst) as well as modifications to some other
hydraulic model inputs (e.g., bridge loss coefficients, additional survey, 1D structure
instabilities, allowances for structure blockage).
The 8Review of Narellan Creek Flood Study and Peer Review by WMA Water9 (Square Link,
2014) was subsequently completed. This report recommended that the updates
documented by WMAwater (2014) be implemented and the draft 8Narellan Creek Flood
Study9 be updated to reflect these changes before being placed on public exhibition.
The 8Hydrological Modelling of the 1% AEP Flood in the Narellan Creek Catchment9 report
was then completed by Cardno. This study focussed on whether the hydrologic approach
employed as part of the draft flood study is suitable or should be updated based on the
WMAwater recommendation. This study concluded that the primary reason for the design
flood level differences was the hydrologic approach (i.e., embedded design burst) and that
this approach should be modified before adoption of the flood study.
The draft 8Narellan Creek Flood Study9 took account of the recommendations documented in
each peer review, and the associated updates are reflected in the final 8Narellan Creek Flood
Study9 (Worley Parsons, 2015), as discussed above.
2.2.4
Update of Narellan Creek Flood Study (2017)
The 8Update of Narellan Creek Flood Study9 was prepared by Public Works Advisory and
Manly Hydraulics Laboratory for Camden City Council in 2017. The study aimed to update
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