Attachment 3 - Revised Engineering Report (rec. 7.04.2025) MCU24-0165 & OPW24-0222

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FIGURE 7 - SITE FLOOD HAZARD OVERLAY MAPPING

5.5      Stormwater Quantity Management
5.5.1 General
Due to the increase in impervious area for the development, it is expected that stormwater runoff peak
flow will increase. As such, consideration of the peak flow increase to the surrounding system and
properties is to be considered and managed.
The natural drainage reserve at the rear of the lot which acts as the lawful point of discharge is expected
to be flooded during peak storm events based on flood mapping. This existing drainage channel is sized
such that additional flows received from the subject lot would be accepted by the channel without
resulting in negative impacts to the wider network.
The site is located very close to the receiving waterway, Cooroorah Creek, that experiences significant
flooding all the way along the creek to Six Mile Creek and beyond in major flood events. Providing
detention to this site, particularly for larger rainfall events would likely cause adverse effects due to the
coinciding peak flows.
The transport corridor will not be impacted by runoff from the proposed works of the subject site with
the lawful point of discharge being located at the rear of the lot, and surface grading to the drainage
channel.
Therefore, it is proposed that no stormwater detention is to be provided for the subject site as it would
have a negligible effect on the site and wider catchment.
In accordance with the sustainable building code each unit will be fitted with a 3kL rainwater re-use
tank. Tanks will be located as per architectural design drawing and connected to a minimum of 50% of
roof area. Refer to hydraulic consultant drawings for internal plumbing design.

5.6      Stormwater Quality Management
5.6.1 Construction Phase
The site's management is important in ensuring water quality standards are achieved during the
construction phase. Implementing best practice Erosion and Sediment Control techniques is imperative
to managing the runoff quality affected by construction works.




 15 November 2024                                                                                             Page 9