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

        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, hardstand and landscaped areas
infiltrated into the natural sands via a series of Rapid Infiltration Pits (RIPs)
and a consolidated Rapid Infiltration Culvert (RIC) in order to achieve no net
reduction in rainwater infiltration.

Discrete RIPs are to be located along the northern and eastern edges of the site
accepting runoff from relatively minor nearby impervious and landscaped
areas.
 Treatment of runoff prior to infiltration by RIPs will be via small bioretention
basins adjacent individual RIPs with low flows (< 3 month ARI) directed to
the bioretention surface.

Major event surcharge of RIPs would be directed to adjacent roadways (legal
point of discharge) as dispersed overland flow.

Runoff from approximately 7,532m2 (80%) of roofed areas will be piped to the
abovementioned rainwater harvesting tank at the south-western corner of the
site with tank overflow discharging to an adjacent Bioretention Basin and
Rapid Infiltration Culvert (RIC).

A weir and splitter pit arrangement will be employed within the tank such
that flows of 3 month ARI or lower will be directed to the bioretention basin
surface for formal treatment with larger event flows piped directly into the
RIC.

__________________________________________________________________________

A6769/25/SWMP/Rev OpW(A) – Feb 2025
                                                                               Page 6 of 9
SH/PL
                           Brah101 Pty Ltd t/as ALTA PROJECTS