Stormwater Management Plan -OPW (A) · OPW25/0042

6.0     STORMWATER TREATMENT & INFILTRATION

Treatment and disposal of runoff from the subject site will be carried out in
accordance with the approved document Settlers Cove Noosa Residential High
Density (RHD) Environmental Management Plan (EMP 1) by WBM Oceanics
Australia and above Conditions 46-48 & 53 of Council’s decision notice.

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 rainfall 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.

Section 3.1 of the EMP is reproduced below:-

Strategy: To ensure no net reduction of rainwater infiltrating the sand dunes
beneath the site. To ensure adequate treatment of runoff from landscaped and
hardstand areas prior to infiltration.

Responsibility: Consulting Engineer and Landscape Architect.

Management Actions: All design within the Residential High Density areas to comply
with the following guidelines:
        1. All runoff from storms up to 10 year average recurrence interval (ARI) to
        be infiltrated into the sand subgrade without runoff.
        2. Infiltration to be achieved via swales and ephemeral streams and rapid
        infiltration pits (RIP’s)
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A6769/25/SWMP/Rev OpW(A) – Feb 2025
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SH/PL
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