Further information re Request to Change Approval MCU 132003.221132.8

                                                                                                      BROWN
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            Doonella OPTIONS Analysis OPTIONS 2-4

                                            B09182.W

                           BROWN Consulting: B09182.w, 14/03/2013, MS, IP


Below is a summary of the options investigations as requested by the client. It should be noted that

for Options 2-3, with the incorporation of additional basins, runoff of up to 100 Year ARI from their

corresponding catchments has to be diverted to the respective basins for the water quantity
strategies to be effective. Assumptions in this analysis are carried from Brown Consulting Report
B09182.W-02A dated October 2011.


OPTION 2:Strategy incorporates Basins B1A and Ble and original Twigrush Basin.


As required by Sunshine Coast Council the Dodonaea Basin is to be removed from the strategy. To

mitigate peaks flows, Basins B1A and B1C have been included. They are to mitigate the flow from
their corresponding developed catchment areas.            Twigrush (original configuration) basin has also
been included      0   mitigate the flows from the removal of Dodonaea            Basin. The basin    design
requirements are shown in the Table 1 below; refer to sketches for sizing of basins. It should also be
noted that for this option runoff from Sub Catchment 2B2 bypasses the Twigrush Basin.


                                 Table 1: Original Twigrush Basin Configuration



                                                                                       Twigrush Ba~in
OPTION 2                       Basin B1A                       Basin B1C
                                                                                        (original size)
Upstream
                                  B1A                             B1C                    0,C3,C2
Catchment

Storage Volume
                                 1080                             1100                      1,210
(m3)

Design Depth (m)                  1.2                              1.2                       1.8

Basin Invert RL (m.
                                  8.5                              13                        7.5
AHD)
Basin Top RL (m.
                                   10                             14.5                       9.6
AHD)




As expected with the original sized Twigrush basin and the removal of Dodonaea basin, the strategy

does not meet the requirements of mitigating peak flows (apart for the 2 year ARI). Refer to Table 2

below.


                                            Table 2: OPTION 2 Results



                                Existing WBNM               Developed WBNM         Change (%)from Existing
ARI
                               (Peak Flow m3/s)              (Peak Flow m3/s)              Scenario
2                                    0.89                           0.88                    -0.9%

5                                    1.42                           1.56                    10.1%

10                                   1.75                           1.99                    13.6%
20                                   2.20                           2.51                    14.1%
50                                   2.61                           2.94                    12.6%
100                                  3.07                           3.42                    11.3%




B09182.W_Options_2_3_40N LV _130314.docx                                                              Page 1