Appendix B - Amended Biome Consulting Response

Central Bioretention Basin
Critical Section
CROSS SECTION DETAILS                                                                10% AEP                            1% AEP
     POINT       CH                          Z             n                  wA       wP         n x wA        wA        wP      n x wA




                   1           ‐16.2         100.95     0.060
                   2           ‐16.2         100.35     0.060
                   3             ‐15         100.05     0.060             0.04            0.57     0.00        0.05      0.66      0.00
                   4              15         100.05     0.060             4.14            30.00    0.25        4.79      30.00     0.29
                   5            18.6         100.95     0.060             0.04            0.57     0.00        0.05      0.66      0.00




                                                                          wA       wP     n x wA     wA       wP     n x wA
                                                      TOTAL            4.216176 31.13798 0.252971 4.886761 31.31527 0.293206
                               S
                             0.005                                         R                n       Q            R         n        Q
                                                                       0.135403           0.060    1.31       0.15605    0.060     1.67
                                                             Flow                          1.31                           1.67

                                                            WSL                      100.188                            100.210

                       Calculated by Manning's Equation                                   1.31                           1.67
                                               Vel (m/s)                                  0.31                           0.34

                                                                    Basin Section
                                                                101

                                                               100.9

                                                               100.8

                                                               100.7
  Height (m AHD)




                                                               100.6

                                                               100.5

                                                               100.4

                                                               100.3

                                                               100.2

                                                               100.1

                                                                100
      -20              -15             -10            -5                  0               5        10           15         20        25
                                                                              Width (m)

                                                      Existing Sur face             10 % AEP        1% A EP




As indicated in results above velocities are less than 0.5m/s during the minor and major storm
events. This is also within the requirements for the major storm (less than 2m/s). However, scour or
damage of vegetation is unlikely as the results do not take into account the backflow effect caused
by the outlet pit and weir which will reduce velocities through the basin. Therefore the design of the
basin is appropriate to cater for inflow velocity.