Stormwater Management Plan 12_05_26

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TABLE 7: DRAINS MITIGATED PEAK FLOWS

    Storm Event           Existing Case      Mitigated Case         Difference                 Difference
       (AEP)                  (m3/s)              (m3/s)              (m3/s)                       (%)
        63%                   0.041               0.039                -0.002                      -4.9%
        39%                   0.063               0.053                -0.010                     -15.9%
        18%                   0.092               0.072                -0.020                     -21.7%
        10%                   0.110               0.080                -0.030                     -27.3%
         5%                   0.134               0.094                -0.040                     -29.9%
         2%                   0.154               0.113                -0.041                     -26.6%
         1%                   0.174               0.156                -0.018                     -10.3%
      1% (CC)                 0.218               0.199                -0.019                      -8.7%
                                             Average (mean)            -0.023                     -18.2%

4.5.6 OSD Tank Details
On-Site Detention (OSD) is proposed with flow controls as shown in Table 8.
TABLE 8: DETENTION TANK DETAILS

                Feature                                             Details
 Detention Volume (Total)                                       Minimum 76kL
 Detention Volume                                 Eight 9.5kL underground concrete tanks.
                                                          47.5m2 base x 1.6m high.
 Maximum Water Elevation                                    1.6m (internal height)
 Orifice Flow                                        Stainless steel sheet to wall of tank.
                                                     70mm diameter orifice, at the base.
                                                105mm diameter orifice, 0.5m above the base.
                                                90mm diameter orifice, 1.0m above the base.
 Surcharge                                600mm x 600mm surcharge grate, at driveway surface level

4.5.7 Reuse Tank Details
In addition to OSD storage, a minimum rainwater reuse volume of 3,000L is required for each dwelling,
in accordance with the Sustainable Building Desing Code. This will require a 75kL of reuse storage for
the 25 dwellings.
The reuse tank is proposed to be stored within eight 9.5kL underground tanks with a pump to allow the
stormwater to be utilised, refer to Civil Drawings. Only the roof water runoff will be piped to the reuse
tank with all other sources directly flowing to the OSD tank. Flows from the reuse tank will overflow to
the OSD tank through a piped connection and backflow prevention fitting.




12 May 2026