RFI - Attachment 3 - Stormwater Management Plan

     2.3. Proposed Development Drainage Patterns

          2.3.1 Stormwater Concept
A drainage system designed to capture and/or convey runoff from minor and major stormwater events will be
provided throughout the development. The “minor” system will consist of field inlet pits, piped drainage, roof water
connections, surface grading and swales to manage runoff. Final sizing of the minor system will be undertaken as
part of the detailed design in accordance with the Queensland Urban Drainage Manual, Table 7.3.1, providing
conveyance for storms up to and including the Q10 (defined as 10% AEP) storm event as required for urban
residential developments with greater than 20 dwelling units/ha.

The “major” drainage system will rely on the natural contours of the land to provide overland surface flow conveyance
to the west of the site towards the existing drainage feature to which the site currently discharges. The internal
driveway through the proposed development will been graded to ensure an overland flow path is available through
convey run-off from the development as the major drainage system flow path to minimise impacts of surface flows
on the proposed cabins.

Internally, stormwater quality will be managed through a combination of rainwater reuse tanks (plumbed for internal
and external reuse), litter basket pit inserts for pits within the driveway and an end of line bioretention area providing
finishing treatment for the majority of run-off from the development. The typically undeveloped area of the site which
is not captured by the drainage system, will be conveyed by swale drains adjacent the driveway to be discharged
from the development towards the watercourse providing for water quality improvement of these areas to minimise
impacts on the downstream environment.

Within the access easement, the road upgrade will convert the existing gravelled surface into a sealed road, reducing
the overall sediment load likely to be generated from the access road. Runoff from the driveways will be conveyed
in roadside swale drains to provide treatment and nutrient removal from the stormwater.

Water quantity impacts have been assessed from both the proposed development site and the upgraded access
road, which have found that due to the significant upstream catchments which are conveyed by the drainage feature
to which the site drains, the overall increase in run-off volumes does not result in a significant increase to the peak
water volumes, therefore attenuation is not required for the proposed development.

The Carpenters Road access will be upgraded to ensure that the development is able to be safely accessed for all
storms up to and including the 1% AEP storm. Flooding analysis has been undertaken using the TUFLOW model to
ensure that the proposed upgrade will not cause impacts to the upstream and downstream environments. The
existing 1200mm diameter piped culvert crossing beneath Carpenters Road will be upgraded to provide an
increased flow capacity to such that overtopping of the access road is limited to a safe velocity depth product for the
1% AEP storm.

The internal stormwater and inter-allotment drainage networks shall be designed to comply with:

     1. Noosa Plan 2020 Schedule 6 – PSP6 Engineering Design Standards;
     2. The Queensland Urban Drainage Manual (QUDM); and

     3. AS/NZS 3500.3:2015 - Plumbing and Drainage Part 3: Stormwater Drainage.

Refer to Appendix A - Proposed Concept Plans for the proposed development concept plans plan illustrating the
stormwater layout described above. Other elements of the proposed stormwater system are described in the
following sections.


          2.3.1 Lawful Point of Discharge
The site typically drains east towards the existing drainage feature within the Carpenters Road access easement,
which continues downstream to the north. The catchments upstream of the development are also conveyed
through this drainage channel. The lawful point of discharge test, as described in Section 3.9.1 of QUDM, requires:


Project number 21020                                                                                    Page 9 of 36
File RECOR Concept Stormwater Management Report - 21020.docx, 2022-09-05
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