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

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