16-001014-02A (Ultimate SCMMP)

Bioretention Basin Velocity Checks
Velocity checks were undertaken at the critical section through the Bioretention Basins (i.e. section
with the shortest width). Note that these calculations do not take into account backflow effect and
ponding, since the outflow of the Bioretention Basins is limited by the outlet pit and weir
configuration. These calculations are therefore considered to be conservative.
Northern 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                ‐9   100.1      0.060
               2                ‐9   100.1      0.060
               3                ‐6    99.1      0.060              0.07           0.67        0.00          0.10      0.82     0.01
               4                 6    99.1      0.060              2.54          12.00        0.15          3.10      12.00    0.19
               5                 9   100.1      0.060              0.07           0.67        0.00          0.10      0.82     0.01




                                                                 wA       wP                 n x wA          wA       wP     n x wA
                                              TOTAL           2.678832 13.34081              0.16073      3.295692 13.63174 0.197742
                          S
                        0.005                                        R             n           Q              R          n      Q
                                                                  0.2008         0.060        1.08        0.241766    0.060    1.51
                                                     Flow                         1.08                                 1.51

                                                    WSL                         99.312                               99.358

                    Calculated by Manning's Equation                              1.08                                1.51
                                            Vel (m/s)                             0.40                                0.46

                                                             Basin Section
                                                              100.2


                                                                  100


                                                                  99.8
  Height (m)




                                                                  99.6


                                                                  99.4


                                                                  99.2


                                                                    99
     -10           -8           -6       -4             -2                0              2        4              6       8       10
                                                                   Width (m)

                                              Existing Sur face               10 % AEP          1% A EP




As indicated in the results above, velocity is below 0.5m/s during both the major and minor storm
events. The potential for scour or damage to vegetation is therefore low and below requirements
specified in WSUD Technical Design Guidelines (2006)