080624 2383-01 FINAL Engineering Report for DA.pdf [As Published] · 132008.1128

BLUE CARE SUNRISE BEACH
ENGINEERING REPORT FOR DEVELOPMENT APPLICATION


    within Lot 1, was directed to the Lot 6 basin. The resulting catchment areas for each
    basin were: Lot 1, 3.24ha; Lot 6, road and part of Lot 1, 1.812ha. The proposed
    catchment areas to each basin are shown on Drawing No. 2383-01 SK02.

    Details of the modelled basins are summarised in the Table 2.9.

    Table 2.9, Proposed Detention Basins
                      Basin                                         Lot 1                     Lot 6
      Base Level (mAHD)                                            19.5                       27.0
      Base Area (m2)                                               735                         708
      Top of Walls (m AHD)                                         23.5                       30.0
      Max. Wall Ht above Nat. Surf. (m)                             3.0                        4.0
      Overflow Grate Level (m AHD)                                 19.8                       27.4
      Outlet Pipe Dia. (mm)                                        0.30                       0.15
      Spreader Channel Length (m)                                   60                          40


    2.6.3          System Performance

    The performance of the drainage systems from the developed site, with the above basin
    configurations, is summarised in the Table 2.10.

    Table 2.10, Developed Site – Detention Basin Performance
         Average                      Basin    Basin       Basin               Basin Peak   Undeveloped
        Recurrence                              Max      Max Water             Discharge        Site
         Interval                              Water      Depth                                Peak
                                               Level        m                                Discharge
                                               m AHD                             m3/s
              years                                                                            m3/s

                2                      Lot 1   20.968       1.468                0.173         0.140
                2                      Lot 6   27.792       0.792                0.045         0.033
                10                     Lot 1   21.593       2.093                0.208         0.223
                10                     Lot 6   28.381       1.381                0.047         0.052
               100                     Lot 1   23.160       3.660                0.283         0.385
               100                     Lot 6   28.986       1.986                0.052         0.090

    These results show that, for the 10 year and 100 year ARI events, the proposed basins
    will provide sufficient detention storage to reduce the peak discharges, from the
    developed site, to values which are less than those for the same average recurrence
    intervals from the undeveloped site. For the 2 year ARI event, peak discharges from
    the basins are greater than those for the undeveloped site.

    The model calculations, however, do not consider the flow losses due to infiltration from
    the bio-retention basin filter media into the natural sands underlying the basin or from
    the spreader channels. The adopted water quality treatment flows, through the bio-
    retention basin filter media, are approximately 0.08m3/s for each basin. These flows
    are driven by the head of 0.4m within the extended detention zones of the basins.
    From the data presented above, it can be seen that the water depths, within the basins,
    during significant rainfall events, will, generally, exceed 1 metre. Infiltration through the
    filter media and also into the natural sands underlying the basin will be significantly
    greater than the water quality treatment flows of 0.08m3/s. Infiltration losses into the
    base and batters of the spreader channels will also be significant.



Blue Care Property Development Unit                      Version 1.1                                   24 June 2008
2008 06 24 2383-01 Engineering Report for DA        Commercial in Confidence                                Page 12