24572-05 Response to Council information request - Engineering · MCU24/0125

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FRONTAGE WORKS

Item 6 – Kerb and Channel and bike lane.

Response

Frontage works including kerb and channel and a 2.0m wide bike lane are detailed on the
revised drawings.



EARTHWORKS

Item 7 & 8 – spot levels, retaining walls and cross sections.

Response
Additional information for the earthworks has been added to the revised drawings, including
cross sections showing bulk earthworks levels and the interface with neighbouring properties.
Separate plans have been provided to show retaining wall levels and heights (TOW, BOW) and
standard details. Refer plans C020 – C024.



EXTERNAL DRAINAGE WORKS AND NON WORSENING

Item 9 – Provide updated SWMP and drainage design details.

Response

A revised SWMP accompanies this response and addresses the non-worsening issue. A
detention tank has been added to the design to mitigate peak flows. Stormwater long sections
including HGL information have been included in the revised drawings for both the 10% and 1%
AEP events. It should be noted that within the development site we have elected to pipe the 1%
AEP event to the detention tank, however there will be some minor surcharging at the pit
immediately downstream from the detention tank in the 1% AEP (2100) event as the
downstream pipe network is only designed for a 10% AEP (2015) event. Refer also to wording
in the SWMP that explains the rationale for the detention tank design and sizing. With respect to
item 9 d) we consider Council’s position that there shall be no surcharging of the existing
network in the 1% AEP (2100) to be unreasonable and not in consistent with standard
stormwater design principles where the major event is conveyed via the road network or other
overland flow paths.

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INTERNAL DRAINAGE DESIGN

Item 10 & 11 – Provide stormwater drainage calculations and long sections

Response

Stormwater drainage calculations and long sections have been included in the revised drawing
set for the 10% and 1% AEP (2100) events. We have not provided long sections or calculations
for the 0.5EY as this superfluous information given the 10% AEP demonstrates the design
sufficiently.
As noted above we have elected to pipe the 1% AEP event within the development site,
however, we have also provided an overland flow path along the northern boundary as a
contingency. Downstream of the site there will be some minor surcharge of the new drainage pit
immediately downstream of the detention tank (pit FI2/4 approx 95L/s) in the 1% AEP event, to
convert part of the major flow to an overland flow which will be conveyed down the existing
access to Starboard Avenue. Please note that the overland flow down the driveway in the 1%
AEP will actually be less than the predevelopment overland flow – refer SWMP for further
comments/explanation. There will also be some minor surcharge at the existing pit at the bottom
of the driveway in the 10% AEP (2100) event again, due to the fact that the downstream
network is designed to convey the 10% AEP( 2015) flows instead of 10% AEP 2100. As noted
in the SWMP there will be no surcharge in the 10% AEP (2015) event.
The overland flow capacity of the existing driveway is shown in the calculation sheet (613 L/s),
which is substantially more than the proposed surcharge flow.


STORMWATER QUALITY

Item 12 – Provide updated SWMP and MUSIC model to include external catchments.

Response

Please refer to response in the updated SWMP.


We trust the above is satisfactory. Should you have any queries regarding this matter, please
contact the undersigned.

Yours faithfully,




Doug Reynolds, Consultant
07 5449 9600 | [email protected]
TOD consulting engineers