16-001014-02A (Ultimate SCMMP)

Design Velocity Check Through Critical Section of WQCP
Filename:         H:\B14\150-199\B14158.W\01 Final Layout Op Works\Checklists\[B14158.W_Riser Calc.xlsx]Crit. Section
Date:             5/09/2016
By:               CM

Critical Section Through WQCP

1 to102.5
     100 Y ARI
WSL (m)                                               100.28                              m3/s
        102

            Basin Water Depth Above Extended Detention Depth (m) Cross Sectional Area (m2)
    101.5 1               0.43                            100.28                           14.25
          2               0.54                            100.50                           19.86
          5               0.66                            100.65                           23.97
     101
         10               0.73                            100.77                           27.42
         20               0.82                            100.90                           31.39
    100.550               0.89                            100.97                           33.50
        100               0.96                            101.03                           35.41

        100
                                                 Extended Detention Depth
     99.5                                                                                        WSL (m)        Design Channel



        99
              0             5           10           15           20          25           30              35             40


                                       Basin Water Depth Above Extended
AEP (%)           Qin at B2 (m3/s)                                      Cross Sectional Area (m2)               Velocity (m/s)
                                       Detention Depth (m)
   63%                    2.58                        0.43                           14.25                                0.18
   39%                    2.97                        0.54                           19.86                                0.15
   18%                    3.52                        0.66                           23.97                                0.15
   10%                    3.96                        0.73                           27.42                                0.14
    5%                    4.30                        0.82                           31.39                                0.14
    2%                    4.64                        0.89                           33.63                                0.14
    1%                    5.07                        0.96                           35.41                                0.14

As indicated in the results, velocities range from 0.14m/s to 0.18m/s at the critical section. This is
only slightly above the velocity re‐suspension objective of 0.05m/s, but is well below the velocity
limits of 0.5m/s and 2.0m/s to protect against vegetation scour, as provided in Section 2.3.5 of the
WSUD Technical Design Guidelines (2006).

The following should also be considered:

           As mentioned the velocity check equation indicated in WSUD Technical Design Guidelines
            (2006) is determined based on outflow conditions. Our calculations have conservatively
            considered basin inflow conditions.
           The velocities determined do not take into account backwater effect caused by the outlet
            that has been designed to restrict flows for detention. This will reduce velocities.
           The velocities do not take into account the coincidence of flows from both that is expected
            to reduce velocities further.

The results above demonstrate that the velocities through the WQCP are appropriate to avoid scour
and are unlikely to cause re‐suspension of stored pollutants.