Stormwater Report

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

Under existing site conditions, roofwater runoff from the existing dwelling appears to discharge to the
Weyba Road kerb and channel with runoff from ground level areas discharging towards Weyba Road
as sheet flow.

The proposed lawful point of discharge for the site shall be the Weyba Road kerb and channel in line
with existing conditions. Roofwater runoff from the proposed development shall be collected on site
and directed to the kerb and channel via the construction of new on site drainage. 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 onn e ct ion

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

2. 4       Flood ing

The proposed development site is impacted by NC flood overlay mapping for both river flooding and
stormtide sources. The proposed development will need to adequately achieve immunity to these flood
events in accordance with the Noosa Council Flood Overlay Code. The Flood Information Certificate
(refer Appendix B) obtained from Council has identified a Defined Flood Level (DFL) of 2.40m AHD and
an applicable immunity level for habitable rooms of 2.70m AHD (300mm freeboard). The proposed
duplex will need to have a minimum floor level of 2.70m AHD to comply with the Flood Overlay Code
requirements. A reduced floor level of 2.60m AHD is proposed for the garages to assist with driveway
grading.

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 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      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) 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.

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