Swmp

65-67 Elanda Street, Sunshine Beach
Site Based Stormwater Management Plan
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3.3 Modelling of Detention Devices
For all the storm events, the mitigation strategy is designed as follows:

Surface runoff from the proposed landscaping and driveway area will become bypass flow
without being mitigated. While the roof water will be captured by a series of roof gutter and
down pipes to the proposed detention tank for mitigation, and be discharged to the proposed
soakage trench, then discharged to the downstream area as sheet flow.

The “no worsening” target is that the sum of the mitigated flows from all the roof areas, and
the un-mitigated by-pass flows from landscaping and driveway area are no more than the
flows discharged from the pre-development scenario. The target flows of mitigation for each
AEP will be the flows from Pre-development scenario, as list in Table 3.5.

Table 3.5 Target flows of mitigation

   Storm event            63%           39%       20%      10%       5%      2%      1%
                          AEP,         AEP,      AEP,      AEP,     AEP,    AEP,    AEP,
                          25min        25min     25min     25min    25min   25min   25min
  Targeted flow           0.017        0.022     0.035     0.046    0.054   0.059   0.069
  after mitigation
       (m3/s)




Through XPSTORM-2016, a hydraulic coupling with hydrological model is developed. Two
7KL roof water detention tank is proposed, each tank is responsible for half of the entire roof
area of the development. Each detention tank has two orifices. Landscaping and driveway
area are modelled as By-pass area. The model layout is presented in Figure 3.2.




                                      Figure 3.2 XP-storm model layout



File Name:            WCD-22936 – 65-67 Elanda_SWMP.docx
Revision:             A                                                                     14