Stormwater Management Plan (Quantity)

 

Results

The results of the analysis indicate that the new and reconfigured detention basins and outlet structures
achieve the non-worsening objective. There is now a decrease in peak flows for an 100 Year ARI event
of 5%. Peak flow results are shown in Table 3 below.

Table 3: Existing and Mitigated (Option 3) Peak Flows

 

The Water Surface Levels (WSL’s) for each basin have also been considered (refer to Table 4 below).
Basin B1A, B1C and the Twigrush Basin are consistent with freeboard requirements. Depth of flow
across the overflow weirs are also less than 300mm during the Peak 100 year ARI event.

 

Table 4: Option 3 Basin WSL’s

 
 
   
 

    
  

 

   

 

 

 

 

 

 

 

 

 

 

“Dodonaea Basin —
evious Peak | OPTION3
* WSL =) | Peak WSL |
* (nm. AHD) ~~ | (m.AHD) |
10.81 9.79
5 11.32 10.25
10 11.59 10.47
20 11.90 10.75
50 12.04 10.99
100 12.11 11.21 -0.90 8.89 10.30 14.32
Freeboard to top of Basin (m) 0.81 0.50 0.48

 

 

 

 

 

 

For the Dodonaea Basin results indicate that there is a dectease in peak WSL’s compared to that
specified in the previous report. Results are presented in the Table 4 above. Significant reductions in
the detention volume and the WSL between the previous strategy and Option 3 have been provided.
The resulting changes in volume in the Dodonaea basin are presented in Table 5 below.

Table 5: Dodonaea Basin Ch: in Volume

 

480 50 -430
950 170 -780
1,300 270 -1,030

1,810 430 -1,380
2,070 620 -1,450
100 830 -1,380

The peak 100 year ARI WSL in the Dodonaea Basin (11.21m. AHD) will also ensure the fauna passage
will remain flood free during this event. A reduction in the time for the basin to drain has also been
demonstrated. It takes Dodonaea Basin 30 minutes less to empty during a 100 year ARI event then
previously determined.

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