20220206 48 Elm St OPW RFI Response · OPW24/0043

Response:

The previously submitted stormwater design has been amended. The following key changes have
been made to the previously submitted design:

       The bioretention basin has been deleted from the design. As the site is less than 2,500m2
        in area, water quality objectives are not required to be met under the State Planning Policy
        (2017).
       All downpipes and roofwater will be connected directly to the proposed on site detention
        (OSD) tank. All gutters, downpipes and roofwater pipes are to be designed for the 1%
        Annual Exceedance Probability (AEP) storm event. These will be documented by the
        Hydraulic Consultant for the project.
       A kerb has been added along the eastern side of the proposed carpark. This will grade
        downhill towards the north. A new grated inlet pit will be constructed within the existing
        easement in the north eastern corner of the site over the existing 300mm diameter
        stormwater pipe. The proposed kerb will direct runoff from the carpark area to the new
        grated inlet pit. An upstand kerb is proposed around the grated inlet to ensure runoff ponds
        on field inlet and enters pipe.
       It should be noted that runoff from the proposed carpark will bypass the proposed OSD
        tank. The OSD tank has been designed so that roofwater is attenuated to a level that
        ensures the total peak runoff from the entire developed site is not more than existing
        conditions.

We have updated our previously submitted Stormwater Management Plan to reflect the above
amendments to the design. Attached is a copy of the amended Stormwater Management Plan for
review.

Information Required

2. Provide amended stormwater plans clarifying the direction of stormwater flow between the three
structures A1, A2 & A3.

Response:

As discussed above, the proposed stormwater design has been amended. Please refer to attached
updated drawings and Stormwater Management Plan for further details.

3. Clarify the outlet connection for the bio basin.

Response:

As discussed above, the previously proposed bioretention basin has been removed from the
design.

4. Provide finished surface levels for the drainage easement to clarify the proposed direction of
overland flow along the eastern boundary.

Response:

The attached updated design drawings were amended to include additional details. As discussed
above, a kerb has been added along the eastern edge of the proposed carpark instead of the
previously proposed grass swale. This will ensure the carpark drains to the north eastern corner of
the site and ultimately to Pearl Street.




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