16-001014-01A (Swmp)

WQCP Design Velocity Check
Since the pond has not been modelled in MUSIC and therefore isn’t ‘required’ for stormwater quality
treatment, the re‐suspension of suspended solids is not critical (i.e. WQOs will still be met for the
site if the amount of total suspended solids pollutant loads discharging into the pond is the same of
that discharging from the pond). The treatment that the pond will contribute to the site has not
been modelled in the stormwater quality management strategy.

Notwithstanding this, velocity checks were undertaken to ensure no scouring of macrophyte plants
and to demonstrate that re‐suspension of TSS is unlikely to occur.

First Assessment Criterion
For Macrophyte Zone Resuspension Protection, Equation 6.3 in WSUD Technical Design Guidelines
(2006) indicates the objective for velocities within typical wetland to ensure that stored pollutants
are not resuspended or remobilised. Figure A indicates Equation 6.3.




                Figure A – Equation 6.3 from WSUD Technical Design Guidelines (2006)

As per the Constructed WQCP Design Calculations Summary provided in this Appendix, velocities
based on this first criterion are 0.001m/s, which is below the minimum requirement and meets the
design objective.

Qmax riser is typically determined by the outlet conditions (i.e. riser pit), which is low due to retention
features of the wetland. This is the frequent flow check resulting from drainage of the extended
detention depth.

Second Assessment Criterion
For events greater than frequent flow ponding, the detention basin will have near zero velocity. We
have undertaken a check based on the total basin ponding. For flows greater than frequent flows we
have adopted Qmax riser using peak inflows derived from XP‐RAFTS, i.e. peak flows entering the basin
without considering backwater effects. This is conservative and will result in higher velocities than
what will actually occur in operation.

Velocities were determined at the critical section of the WQCP as indicated in the Figure A.