AS PUBLISHED - Information Request - RAL26-0001

•     Changes to peak discharge, frequency and duration of stormwater discharge, and
      velocity of inflows
Information Required
1.    Provide additional detail that demonstrates how the proposed new lot achieves a Legal
      Point of Discharge in accordance with section 3.9.1 of QUDM. The detail must be
      prepared by a suitably qualified person (RPEQ) and address:
      a.    concentration of flows – demonstrate how the concentration of flows from the
            development will not alter the downstream property in a manner that may cause
            substantial damage.
      b.    change to peak discharge – demonstrate that the peak discharge rate at the
            discharge location will not worsen for all events up to, and including, the 1% AEP
            event.
      Note – This item should be read in conjunction with the following Issue.
      c.    Frequency and duration of stormwater discharge – demonstrate that the proposed
            development will not result in a more frequent surface runoff response with an
            increased duration.
      d.    change to velocity of inflows – demonstrate that the location and direction of the
            proposed headwall will not adversely affect the performance of the existing open
            channel. Council recommends investigating alternate outlet configurations to
            address this item.
Issue – Location and Sizing of Detention Tanks
The Stormwater Management Plan makes assumptions about the total impervious area in the
developed scenario (i.e., 180m2 from the future dwelling) when calculating the size of the
detention tank. Additionally, the increase in impervious area from the driveway has not been
considered in this calculation. It is currently unclear how flows from the driveway are being
controlled and released from the site.
Council recognises that it is unreasonable to impose planning controls (i.e., a building
envelope) to control that assumption to ensure the detention tank accurately attenuates the
peak flow.
Council suggests that to ensure the peak discharge in the developed scenario is properly
attenuated, the sizing of the detention tank is calculated on the ‘worst-case’ developed
scenario (i.e., maximum allowable roof/impervious area).
Information Required
2.    Provide a revised Stormwater Management Plan that includes a detention tank sized to
      the ‘worst-case’ developed scenario and considers the increase in impervious area by
      the proposed driveway.
3.    Provide detention to the proposed driveway area.
Note – Council will not support an ‘over-attenuation’ of the driveway through the future dwelling
detention tank(s). Council recommends investigating opportunities to capture flows from the
driveway into the proposed piped system via a pit.
Issue – Stormwater Drainage Infrastructure
Acceptable Outcome AO12.4 of the Reconfiguring a Lot Code seeks that new lots that are
located within a Local plan area are connected to Council’s Stormwater Drainage
Infrastructure. Council recognises that there is no available stormwater infrastructure available
downstream limiting the opportunity to comply with the Acceptable Outcome.
An assessment against the corresponding Performance Outcome has not been provided.




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