A6107 Lot9 Stormwater Management Plan (RevB) June 2022 · OPW22/0166

4.0    STORMWATER TREATMENT & DISPOSAL

Treatment and disposal of runoff will be carried out in accordance with the
approved document Settlers Cove Noosa Residential High Density Environmental
Management Plan (EMP 1) by WBM Oceanics Australia.

Alta Projects engineers (formally TATE) were involved in formulation of the
overarching development approval document and EMP1 produced by WBM
Oceanics.

EMP1 recognises in particular the regimes of stormwater runoff and
infiltration which existed over the broader RHD site pre-development.

Essentially it was recognised that the RHD site lies atop a dune of poorly
graded sand with particularly high rainfall infiltration rates. As such the
natural state sees all rainfall for events up to 10 year ARI infiltrate the dune
close to where it lands and replenish the water table below with little or no
runoff.

The standing water table forms a profile similar to the shape of the dune,
albeit at a depressed scale and emerges as seepage flows adjacent Noosa inlet
at or about RL 5.0m.

The zone between RL 5.0m and the inlet was recognised as having
particularly high ecological values, supporting numerous stands of swamp
mahogany and various species of fauna. Critically it was recognised that
these ecological values were dependant on maintenance of the natural
hydrogeological regime and no nett reduction in rainwater infiltration post-
development.

Consequently, and in order to counteract the effect of significant impervious
areas being constructed, the design approach will see stormwater runoff from
roofs and hardstand areas, up to 100-year ARI infiltrated into the natural
sands via a series of Rapid Infiltration Pits (RIPs) in order to achieve no net
reduction in rainwater infiltration and no net increase in stormwater runoff.

Carpark areas at the top of the vehicular access ramp will be passed through a
Fox BPT600 GPT/oil arrester to remove oils and hydrocarbons prior to
infiltration. The Fox unit will require regular servicing and maintenance by
the building’s body corporate as part of the building’s Community
Management Scheme (Refer drawings at Appendix A and Maintenance plan
at Appendix B). Notably the balance area of driveway ramp totalling 127m2
will be collected via a grate at the base of the ramp and directed untreated to
downstream RIPs for infiltration. Given the transient nature of vehicles on the
ramp and the minor volumes of runoff in play this is not considered to pose
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A6107/L9/SMP/RevB/Jun 2022                                                   Page 3 of 7
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                       Brah101 Pty Ltd t/as ALTA PROJECTS