Response to Information Request Letter 10-6-2025 · OPW25/0042

   Provide a table identifying each property fronting Serenity Close for the section of Serenity
   Close which grades to the sag and provide an explanation of how the direction of drainage for
   each property has been determined (in particular, where it is assumed to not fully drain to
   Serenity Close).

Response
ALTA advise that upon further detailed review it was found that ‘Elandra’ discharges runoff to
internal Rapid Infiltration Pits (RIPs) sized for Q100 events and surcharging northward away from
Serenity Close in the event of failure.

Refer attached amended catchment drawing CA01 with tabulation of contributing external
catchments and explanatory comments now added. Refer also collated set of catchment drawings
for all developments along the northern side of Serenity Close serviced by RIPs. Note also that
RIP infiltration capabilities have been conservatively ignored.

2. Clarify what design blockage values have been adopted for the stormwater inlets in the design
   case in the overland flow assessment.

Response
Engeny advise that blockage applied as per QUDM (field inlets 50%, which is applied to the rating
curve for each pit).

3. Clarify what climate change assumptions have bene adopted in the overland flow assessment.

   It is suggested that SPP2-4.5 and a planning horizon of 2100 be adopted consistent with the
   current methodology of ARR.

Response
Engeny advise that the SPP2-4.5 and a planning horizon of 2100 have been adopted. Current
climate has applied an uplift to the IFD’s as recommended recently by ARR.

4. It is noted that 1% AEP (2100) immunity for the staff facilities building is achieved by the use of
   a levee (block wall).
   It would be preferable if the levee was only used to achieve freeboard rather than 1% AEP
   (2100) immunity.

Response
ALTA advises that immunity to staff facilities will be provided by a concrete pathway adjacent to
the ephemeral stream’ which maintains a minimum height of 1m above the adjacent stream base.
The staff amenities area will have no openings (doors, windows etc) addressing the pathway or
‘ephemeral stream’. By way of better explanation see Section D1 now provided on amended
drawing D03.

5. Provide further contours or sections in the location of RIP 3B and RIP 5 to demonstrate that
   surface levels or an overland flow path (which may be informal) will allow and surcharge flows
   from these devices to flow to a lawful point of discharge without impacting any of the
   development buildings or facilities.