Swmp

Peak flow rates for the median design storms for the developed site are given in Table 6.4

                                     Table 6.4 – Developed Site Peak Flow Rates (L/s)

   Storm Event          Q1             Q2             Q5            Q10           Q20          Q50       Q100
                       (1EY)         (0.5EY)       (0.2EY)      (10%AEP)       (5%AEP)     (2%AEP)     (1%AEP)

         Cat A         124            156            193            233           270          321        359
  Developed PFR

         Cat B             60          75             93            111           129          149        166
  Developed PFR

(PFR – Peak Flow Rate)



6.1.4      Peak Flow Comparison
Table 6.5 indicates the increased peak flow rates for the developed cases.

                           Table 6.5 – Comparison of Existing Vs Developed Peak Flows (L/s)

     AEP Storm                  Q1      Q2          Q5           Q10           Q20         Q50        Q100
                           (1EY)      (0.5EY)    (0.2EY)     (10%AEP)       (5%AEP) (2%AEP) (1%AEP)

            Cat A               45       37         33            47            52            62       72
        Increase PFR
            Cat B               33       36         41            52            60            66       75
        Increase PFR
   (PFR – Peak Flow Rate )



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.




SCG Consulting Engineers                         Page 18                                SCG Ref: 33132(SWMP).RevB