RFI - Stormwater Management Plan

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)
        3. All infiltration devices to be located within the “residential high density
        building envelope” as shown on Ken Hicks and Associates drawing 1128
        Master.
        4. Surcharge runoff from storms greater than the capacity of infiltration
        devices to be directed toward ecological restoration areas and roadways as
        dispersed sheet flow rather than concentrated flows.
        5. Stormwater runoff from landscaped and hardstand areas to be pretreated
        prior to infiltration.
        6. Runoff from roadways and landscaped areas to be directed to landscaped
        swales or ephemeral streams for biological treatment including vegetative
        plantings in accordance with the Landscape Master Plan.
        7. Areas of swales and ephemeral streams shall be lined with a soil layer to
        retard infiltration and allow biological treatment of runoff. Soils will be
        remediated by mixing with loams to achieve a hydraulic conductivity of
        100mm/hr.
        8. Swales and ephemeral streams to be planted in accordance with approved
        Landscape Master Plan in order to promote biological treatment of runoff.


Consequently, and in order to counteract the effect of significant impervious
areas being constructed, the design approach will see stormwater runoff from
the proposed development’s roofs and hardstand areas, for events up to 100-
year ARI infiltrated into the natural sands via a series of Rapid Infiltration Pits
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A6769/22/SWMP/RevB – June
2023                                                                           Page 3 of 9
SH/PL
                       Brah101 Pty Ltd t/as ALTA PROJECTS