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RFI - updated flood investigation report
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3. HYDROLOGY
Hydrologic modelling of the catchment has been carried out using WBNM software (2019
version) developed jointly by the University of Wollongong, Rienco Consulting and Balance
R&D. Australian Rainfall and Runoff 2019 (ARR2019) methodology was used for this
assessment.
Catchment
The objective of this component of the study was to investigate the peak flows contributing
to the site. The catchment has been delineated based on 2015 LiDAR survey data. The
catchment layout is shown in Appendix B, with a total catchment area of 434 ha being
assessed. The proposed site is located within sub-catchment 1H and 1L, with a contributing
catchment area of 130 ha. A summary of the catchment details is presented below in Table
3-1. The impervious values applied are representative the rural, rural residential and
bushland land-use of the catchment. The existing and proposed impervious values are
noted for catchments 1H and 1L to represent the development.
The default catchment lag parameter within WBNM of 1.6, was applied to the model setup.
Rainfall losses have been applied as per the ARR Data Hub, with an initial loss of 35mm, and
continuing loss of 3.0mm/hr for pervious areas. 0mm was applied for impervious. The median
pre-burst rainfall depth was applied to the model setup.
Table 3-1: Catchment Details
Catchment Downstream Area (ha) Impervious
Name Catchment (%)
1A 1C 29.842 5
1B 1C 14.787 10
1C 1F 18.826 10
1D 1H 19.329 0
1E 1G 24.075 0
1F 1K 4.325 10
1G 1H 13.695 10
1H 1M 6.056 0 / 10
1I 1K 4.445 10
1J 1L 3.637 20
1K 1L 1.461 20
1L 1M 11.036 5 / 20
1M 2F 5.527 10
2A 2C 64.299 0
2B 2C 62.751 2
2C 2D 28.965 2
2D 2E 38.306 5
2E 2F 43.203 10
2F SINK 39.526 10
TOTAL 434.091
21-0288-FS001-V3 | Flood Investigation | 60 Glenridge Drive, Cooroibah |7
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