Attachment 6 - Stormwater Management Plan and Engineering Response. · MCU23/0078

Civil Response:

The SWMP has been revised to incorporate increased rainfall intensities (a uniform 20% increase) to account for
future predicted storm event intensity and duration increases in the Year 2100, in accordance with the Noosa
City Plan. These increases have been applied both to the flood assessment of the natural drainage channel, and
when sizing the proposed stormwater detention.

The flood study determined that under existing conditions for the 1% AEP flood event in the Year 2100, the water
level at the existing culvert system below Hoffmann Drive (south-west of the site) is above existing roadway
levels. As such, if stormwater run-off from the development site is not detained up to the 1% AEP flood event,
water depths over Hoffmann Drive will increase for the 1% AEP flood event due to the proposed development.
This is not considered an acceptable outcome and thus detention up to the 1% AEP flood event is proposed to
ensure no worsening of downstream flood levels at the Hoffmann Drive culvert crossing.


Issue – Stormwater Quality – Item 40:

Provide a revised SWMP and design drawings which achieve compliance with PO7 of the Water Quality and Drainage
Code and PO3 of the sustainable Building Design Code

Civil Response:

The SWMP has been revised and proposes bio-retention treatment systems only to achieve the required water
quality run-off objectives, in accordance with the Noosa City Plan.

Issue – Stormwater Quality – Item 41:

Provide updated plans and a SWMP which incorporates rainwater/roofwater collection and resuse at the site, sufficient
to supply external non-potable fixtures such as landscape irrigation and bin washdown and internal non-potable fixtures
such as toilet flushing.

Civil Response:

The SWMP and Serviceability Report have both been revised noting proposed locations for roof water harvesting
tanks for water re-use across the development site. Following the conservative methodology that any roof water
harvesting tanks may already be full prior to significant rainfall events, these tanks were not factored into any of
the stormwater quantity run-off calculations and modelling.


Yours faithfully,
BORNHORST & WARD PTY LTD




Per: STEWART GRANT
CIVIL ENGINEER




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