Attachment D - Stormwater Management Plan · 132008.175.04

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.

Driveway and carpark areas will be passed through a GPT/oil arrester to
remove oils and hydrocarbons prior to infiltration.

Main roofed areas from both buildings will drain to a Rainwater Harvesting
Tank with captured runoff utilized for landscape irrigation. Tank overflow
will be directed to catchment specific RIPs.




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A6107/L9/SMP/RevA/Aug 2021                                                   Page 3 of 7
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