Stormwater Management Plan (Quantity)

New Peak Flow Management Strategy (Option 3)

The Option 3 strategy to mitigated peak flow increase from the development involves incorporating
changes to the configuration of the previously proposed Twigrush and Dodonaca Basins, with two new
Detention Basins designated as Basins B1A and B1C.

Changes to the T'wigrush Basin and provision of two new basins allows for the reconfiguration of the
Dodonaea Basin outlet to incorporate a fauna crossing, with the objective to also reduce peak flood
levels and times of inundation within this basin.

The configuration of all the detention basins within the strategy to achieve the objectives is presented
in Table 1 below. Note that for Option 3 Sub Catchment 2B2 now bypasses the Twigrush Basin. Refer
to Drawing No. B09182.W-SK01B in Attachment 2 for the updated Stormwater Management
Catchment Plan.

 

Table 1: Option 3 Basin Configurations

 

 

 

 

 

 

 

 

 

a
Upstream Catchment BiA BIC C1,,C3, €2 aA, B1B
Storage Volume (m+) 1,080 1,100 1,210
Detention Depth (m) 1.5! 1.8! 2.1! -
chien Ae 9.3! 13! 7.6! 9
Basin Top RL (m. AHD) 10.8 14.8 9.7 12.25
Outlet Structure 1x 225 diaRCP | 1x 225diaRCP | 1x375mmdiaRCP | 1x 450mm dia RCP

 

 

 

 

 

 

1. A depth of 300mm is provided for bio-retention treatment below the detention bottom.

The previous Watershed Bounded Network Model (WBNM) for the site has been updated to
incorporate the Option 3 strategy. Assumptions and methodology are consistent with previous
investigations and analysis for the site. Details of the updated developed sub-catchment areas and
calculated fraction impervious values are presented in Table 2 below. Refer to Drawing
No. B09182.W-SK01 IssueB for the location and delineation of each sub catchment area.

Table 2: Developed Scenario Sub-Catchment Details

 

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