S25-107-Stormwater Report

2.2        Lawful Point of Discharge

Under existing site conditions, roofwater runoff from the existing dwelling appears to discharge to ground surface
areas and continue downslope toward Martin Street and Avocet Parade as sheet flow.
Stormwater drainage for the proposed development shall ensure no adverse impacts on upstream, downstream or
adjoining properties. Runoff from roof and hardstand areas for the proposed duplex is to be collected on site and
discharged to an existing stormwater grate located on the northeastern verge of the lot. Refer to Appendix B for
further information regarding the proposed stormwater works for the development.

2.3        Upstream Drainage Connection

The development site does not have any upslope properties that are unable to achieve a lawful point of discharge,
impacting the proposed development.

2.4        Flooding

The proposed development site is outside of flood and tide inundation extents indicated by NC disaster maps and
therefore is considered to be flood free.

3          STORMWATER QUANTITY MANAGEMENT

A detailed stormwater quantity analysis of the existing and developed site conditions has not been undertaken as the
proposal is for a residential duplex on an existing residential lot without substantial change in site impervious fraction
as a result of the development.

4          STORM WATER QUALITY MANAGEMENT

4.1        Operational Phase

The development is not required to meet the Queensland Government’s State Planning Policy (July 2017) as the site
does not exceed the 2,500m2 minimum site area. However, stormwater quality management must still be undertaken
via the application of best management practices (BMPs) to ensure no adverse impacts to the downstream environment.

Pollutants typically generated during the operational phase of the development include:
      •    Litter/gross pollutants;

      •    Sediment;

      •    Nutrients (N & P);
      •    Hydrocarbons (oils and grease); and

      •    Heavy metals.

Stormwater quality best management practices may be implemented for the development as follows:
      •    First flush diversion system for roof water diverting the roof water for irrigation purposes

      •    Rainwater storage tanks may be used to collect rainwater for landscape irrigation.
Best management practices have been deemed sufficient for the site area and land use. Refer to Appendix C for the
stormwater management drawing.




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