SWMP change reps

As shown in Table 6.5 Stormwater peak discharge will increase as a result of the proposed development
due to the increase in impervious area. Therefore, it is proposed to utilise two On Site Detention (OSD)
systems to mitigate the peak stormwater discharge rates from the proposed development prior to
discharging to the lawful point of discharge as discussed in section 4.2.



6.1.5    Peak Flow Mitigation (OSD)
To mitigate the peak flow increase from the developed site, it is proposed to include a mixture of
inground detention tanks located under the proposed driveway and inground open bio retention basins
that include a volume dedicated to on site detention of stormwater runoff.

Catchment A will be detained through the use of a in-ground open detention basin, Bio-Retention Bed
(BR-A) located in the northeast corner of the site to detain all flows from Catchment A

For catchment B it is proposed to utilize a series of underground detention tanks to capture all roof
water from building 5, 6 & 7. Tank overflows & all groundwater runoff will then drain to an in-ground
open bio retention/ detention basin, (BR-B) located at the southern corner of the site on Headland Dr.

We propose for the detention systems to cater for flows up to the Q100 storm event and a limit the peak
flow rates of pre-development levels for all storms up to the Q100 storm event.

For proposed Catchment A, the proposed BR-A will have the following properties: -

         •      Base Area                             =     98m2
         •      Internal Depth                        =     1.0m
         •      Low Flow Orifice                      =     275mm diameter
         •      High Flow Orifice                     =     250mm diameter
         •      Overflow Wier Elevation From Base =         1.0m
         •      Required Volume                       =     100m3
         •      Provided Volume                       =     110m3

For proposed Catchment B, the proposed inground detention tanks, located under the driveway will have
the following properties:

Detention Tank for Building 5 roof water:

         •      Base Area                             =     26m2
         •      Internal Depth                        =     1.1m
         •      Low Flow Orifice                      =     55mm diameter

SCG Consulting Engineers                  Page 19                            SCG Ref: 33132(SWMP).RevC