MCU21 0146 Stockwell_Information Request Response Letter · MCU21/0146

7. Issue

Further information and / or amendments are required in relation to access and
manoeuvrability

Information Required

7. Provide a widened access driveway to satisfactorily accommodate the swept path of the
design vehicle, with the clearance envelope of the design vehicle remaining within the
driveway and clear of kerb lines.

8. Ensure opposing cars clear of each other moving to/from the driveway and to/from the
top of the basement ramp.

9. Provide modified ramp grading details in accordance with the requirements of AS/NZS
2890.1-2004, including with the grading being measured along the inside of the curve at
the base of the ramp.

10. Provide further clarification If a gate is to be proposed to secure the basement carpark
where will it is satisfactorily located, and how will it be satisfactorily activated?

Response

Refer to attached Traffic Engineer's cover letter and updated report and swept path
drawings.

8. Issue

There are a number of issues with the proposed management of stormwater quantity as noted
below:

¢ The development proposes only 14m? of detention storge to mitigate the impacts,
which is only 4% the size expected for this type of land use change

e The analysis does not consider climate change

¢ The development relies on the extended detention depth within the bioretention basins
for mitigating peak flow impacts. This volume is generally excluded from such analysis
due to the extended time that water is held in this zone (and risk that the volume will
not be available/empty to mitigate peak flows when the design event occurs)

¢ The model results show almost no change between pre-development and developed
(unmitigated) peak flows from the site for the 1%AEP and 2%AEP events, even
though very significant changes in imperviousness occurs

« The sketch designs in Appendix C do not clearly show the detention system referred
to in the report

e Nosections are provided showing the interaction between bioretention and detention
systems/storages

¢ There is no comparison of the pre-development or developed (un-mitigated) model
results to rational method estimates. This would highlight the above discrepancy in
the 1% and 2%AEP model results

¢ The use of ensemble temporal patterns is not discussed and results are provided for
a single duration rather than a range of durations.

¢ Part of the site discharges by kerb adaptor to Hoffman Drive. No analysis is provided
showing that Hoffman Drive has capacity for these flows. The preference would be for
no new kerb adaptors.

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