Appendix E v 2 - Revised Integrated Water Mangement Plan

                                                                                Callaghan & Toth


6        STORMWATER DETENTION AND FLOODING REPORTS
6.1      Existing Conditions

This site is subject to ponding of floodwaters from the Q100 year ARI flood levels. The habitable
floor areas of the new buildings and new carpark are above the Q100 year ARI flood levels.


6.2      Proposed Drainage System

The carpark surface level is proposed to be drained to an underground drainage system
capable of taking a Q5 flow. The overflow will discharge to the existing storm water drains and
surrounding grass verge.

The habitable minimum floor level for the proposed centre is to be set at RL10.5. The minimum
carpark level is RL8.25, which is approximately at the Q100 flood level.

The proposed biopods filter media level will be 300mm below the carpark level of RL8.25. Final
carpark levels will be determined at detailed design stage.

Allowance has been made to collect the runoff from the proposed new buildings, carparks, and
hard stand areas. The roofwater is collected in above ground rainwater tanks and will be used
for toilet flushing and landscape irrigation. The overflow from roofs will be piped to underground
ECO AID detention cells which will attenuate the flow back to predevelopment levels. Outlets
from the ECO AID cells and field inlet pits in carpark and landscape. Runoff from patio and
landscape garden areas will be directed to the biopods which will then treat the water to remove
pollutants before releasing the stormwater into the existing gully riparian zone.

The Bioretention basin, rainwater tanks and infiltration/ detention basins have been modelled to
act as a detention basin. The storage size is sufficient to reduce the increase in runoff from the
additional hard stand area and buildings back to predevelopment levels as summarised in
preliminary design of stormwater detention volume Appendix C.


6.3      Filling Within the Flood Plain

Q10 and Q100 flood levels based on amended Cardno flood study is shown on Middap
Architectural plan 1717 DA-01 A.

Filling within some edges of the Q10 to Q100 flood levels is required for the purpose of safe
access to all buildings refer to Middap Architectural plan 1717 DA-04A.

These fill areas are to be offset by excavation of similar flood storage heights under the new
buildings. These excavations under buildings are shown on Middap Architectural plans 1717
DA06 – 07 A.

The flood consultant will be required to rerun the flood model incorporating these compensatory
excavated areas and fill areas at the Operational Works stage. Adjustments will be made as
necessary to the compensatory excavation areas to ensure that the flood levels remain at pre-
development levels.


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1714-Cartwrigth Village Extension_IWMP_Version1.doc                           January 2018