Reference Document - Stormwater Mangement Report & Letter Repsonse - MCU24 0094 · MCU24/0094

2. 2       Law fu l P oint of D is ch ar ge

Stormwater runoff from the lot is assumed to discharge to the coastal bushland, which interfaces with
the eastern boundary as sheet flow.
The proposed lawful point of discharge for the roof water, driveway, crossover, and impervious ground-
level areas shall be the soakage trenches installed on the lower ground level towards the northeast and
southeast corners of the site. It is proposed that the catchment areas discharging to each soakage
trench be balanced with roof water and runoff from the impervious areas directed to the soakage
trenches via the construction of new on-site drainage. Lower pervious areas of the lot will continue to
discharge to the eastern boundary as sheet flow as per existing site conditions. Refer to Appendix B for
further information regarding the proposed stormwater works for the development.

2. 3       Ups tr e am D r ain ag e C onne ct ion

The development site does not have any upslope properties unable to gravity drain to a lawful point of
discharge.

2. 4       Flood ing

The proposed development site is not impacted by any NC flood mapping and is therefore considered
to be flood free.

3      STO R M WAT E R Q UA N TIT Y M AN AG E ME NT


A detailed stormwater quantity analysis of the existing and developed site conditions has not been
undertaken. The proposal is for a residential dwelling on an existing residential lot, with the final
impervious area fraction generally in line with lumped C10 values for low-density residential lots. It is
also to be noted that the impervious area change as a result of the proposed development will not be
significant, and therefore, no detention is considered to be required.

4      W AT ER Q U AL IT Y M A NAG E M EN T


4. 1       O pe r at io na l Ph a se

The development is not required to meet the Queensland Government’s State Planning Policy (July
2017), although the site does exceed the 2,500m2 minimum site area, as the development is considered
exempt from the stormwater water quality design objectives. 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.


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